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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. 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…

  3. Novel methods for preparing EC STM tips

    NASA Astrophysics Data System (ADS)

    Kazinczi, R.; Szõcs, E.; Kálmán, E.; Nagy, P.

    We present a dynamic electrochemical etching technique for preparing scanning tunneling microscope (STM) tips. Current vs. potential measurements have led to the development of a dynamic technique which provides atomic resolution and which is faster and more reliable, reproducible and productive than conventional static methods. Tungsten tips are prepared in a 2M NaOH film while the electrolyte is flowing through the film, keeping concentrations and etching rate constant. In order to apply the STM in liquids, an appropriate tip insulating technique is developed so as to prevent Faradaic current. A molten thermoplastic wax film is used for reproducible insulation. The STM tips and insulated tips were characterized by optical microscopy, scanning electron microscopy, STM, and electrochemical STM. Imaging with atomic resolution was demonstrated on HOPG.

  4. STM-SQUID probe microscope

    NASA Astrophysics Data System (ADS)

    Hayashi, Tadayuki; Tachiki, Minoru; Itozaki, Hideo

    2007-11-01

    We have developed a STM-SQUID probe microscope. A high TC SQUID probe microscope was combined with a scanning tunneling microscope for investigation of samples at room temperature in air. A high permeability probe needle was used as a magnetic flux guide to improve the spatial resolution. The probe with tip radius of less than 100 nm was prepared by microelectropolishing. The probe was also used as a scanning tunneling microscope tip. Topography of the sample surface could be measured by the scanning tunneling microscope with high spatial resolution prior to observation by SQUID microscopy. The SQUID probe microscope image could be observed while keeping the distance from the sample surface to the probe tip constant. We observed a topographic image and a magnetic image of Ni fine pattern and also a magnetically recorded hard disk. Furthermore we have investigated a sample vibration method of the static magnetic field emanating from a sample with the aim of achieving a higher signal-to-noise (S/N) ratio.

  5. TEM-STM for Novel Nanotechnological Experimentation

    NASA Astrophysics Data System (ADS)

    Vaughn, Joel

    2005-03-01

    We present the design and construction of a miniature scanning tunneling microscope (STM) to be used inside a transmission electron microscope (TEM). In our system, the entire STM head is fitted inside the TEM sample holder, which allows for both TEM imaging/diffraction and STM-tip indentation experiments. The positioning of STM-tip over the desired sample locations can be guided through the real time TEM images. In addition to the nano indentation experiments, the STM program also allows the state-of-the-art control of atom/molecule manipulation procedures [1]. This hybrid TEM-STM system can be used for nanoscale manipulation, electrical characterization and mechanical strength examination of various nanomaterials including nanowires, nanotubes and quantum dots. [1]. S.-W. Hla, K.-F. Braun, V. Iancu, A. Deshpande, Nano Lett. 4 (2004) 1997-2001. This work is financially supported by the NSF-NIRT grant no. DMR- 0304314 and the US-DOE grant no. DE-FG02-02ER46012.

  6. Mechanism of high-resolution STM, AFM and IETS-STM imaging with functionalized tips

    NASA Astrophysics Data System (ADS)

    Temirov, R.; Hapala, P.; Tautz, F. S.; Jelinek, P.

    2015-03-01

    High-resolution AFM and STM with functionalized tips is well established, but a detailed understanding of the image mechanism is still missing. Moreover, recently this family of imaging techniques has been complemented by a method based on inelastic electron tunneling spectroscopy. Here we present a comprehensive mechanical and transport simulation model that explains essentially all image features in functionalized tip STM, AFM and IETS-STM. Important aspects of the mechanism are: (i) Images are dominantly determined by Pauli repulsion, (ii) in STM and IETS STM this force signal is transduced into an elastic or inelastic conductance signal, (iii) probe particle relaxation leads to image sharpening, (iv) the apparent imaging of hydrogen bonds can be explained by a relaxation effect, and (v) electrostatic forces may also influence the image contrast.

  7. STM investigation of irradiated carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Osváth, Z.; Vértesy, G.; Pető, G.; Szabó, I.; Gyulai, J.; Maser, W.; Biró, L. P.

    2004-09-01

    Multi-wall and single wall carbon nanotubes (MWCNTs, SWCNTs) dispersed on graphite (HOPG) and gold substrates were irradiated with two different doses of Ar+ ions. The irradiated samples were investigated by scanning tunneling microscopy (STM) and spectroscopy (STS). The investigation of SWCNTs irradiated with low-dose Ar+ ions revealed isolated defects in the nanotube-walls, similar to the hillocks observed earlier on ion irradiated HOPG. These results are in agreement with recent predictions, which attribute the STM features produced by ion irradiation to local modifications of the local electronic structure. The high-dose irradiation of MWCNTs produced numerous defects in the nanotube-walls, and the surface of the nanotubes appeared rugged in the STM images. The rugged surface can be regarded as a summation of the individual hillocks, measured at the defect sites.

  8. STM Properties and Manipulation of Epitaxial Graphene

    NASA Astrophysics Data System (ADS)

    Thibado, Paul

    2014-03-01

    Epitaxial graphene grown on SiC has been identified as one of the most likely avenues to graphene-based electronics. Understanding how morphology affects electronic properties is therefore important. In our work, epitaxial graphene was grown on the polar and non-polar a-, m-, and r-crystallographic oriented surfaces of SiC, and was investigated using scanning tunneling microscopy (STM). Bunched nano-ridges ten times smaller than previously recorded were observed throughout the surface. A new STM technique called electrostatic-manipulation scanning tunneling microscopy (EM-STM) was performed to modify the morphology of the nano-ridges. By modeling the electrostatics involved in the EM-STM measurement, we estimate that a force of 5 nN and energy of 10 eV was required to alter the local interfacial bonding. At the atomic scale, STM images of Moire patterns reveal low-angle, twisted bi-layer graphene, grain boundaries, and an apparent lattice constant dilation. We will show that this dilation is due to the STM tip electrostatically dragging the graphene surface. Collaborators: P. Xu, D. Qi, M.L. Ackerman, S.D. Barber, J.K. Schoelz, and J. Thompson, Department of Physics, University of Arkansas, Fayetteville, AR, 72701, USA; V.D. Wheelr, R.L. Myers-Ward, C.R. Eddy, Jr., and D.K. Gaskill, U.S. Naval Research Laboratory, Washington, DC 20375, USA; and L.O. Nyakiti, Texas A&M University. Department of Physics, University of Arkansas, Fayetteville, AR, 72701, USA.

  9. 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.

  10. 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…

  11. STM tunneling spectroscopy on high Tc superconductors

    SciTech Connect

    Hasegawa, T.; Nantoh, M.; Ogino, M.

    1995-08-01

    STM tunneling spectroscopy has been performed on the bulk single crystals of BiSrCaCuO (BSCCO) and the epitaxial thin films of YBaCuO (YBCO) at cryogenic temperatures. The STM images and tunneling spectra observed on the (001) surfaces can be classified into three cases; (1) Atomic image is visible. However, the tunneling spectrum shows semiconducting or smeared superconducting gap structures, depending on the tip-sample distance. (2) Clear atomic image can be obtained. But, the tunneling spectrum shows flat bottom region with quite low zero bias conductance. (3) Tunneling spectra demonstrate gapless behavior, independent of the tip-sample separation. These observations support the quasi-2D electronic picture in which s-wave like 2D superconducting layers are coupled with each other through the Josephson effect.

  12. STM-assisted manipulation of Ag nanoparticles

    NASA Astrophysics Data System (ADS)

    Radojkovic, P.; Schwartzkopff, M.; Gabriel, T.; Hartmann, E.

    We report scanning tunneling microscope (STM) investigations of inert-gas-evaporated Ag nanoparticles deposited on atomically flat, H-terminated Si(111) surfaces, to which they weakly stick. For the present purpose, nanoparticles having an average size of 3 nm are fabricated and the particle coverage on the substrate fluctuates between one and three monolayers. The weakly coupling particle network can repeatedly be imaged with the STM without inadvertently manipulating the fundamental building blocks. When the STM is operated in the field-emission regime and the tunnel current is kept between 50 pA and 39 μA, the temperature of the nanoparticles rises, thus stimulating local manipulation processes. Depending on the power density dissipated in the particles, we distinguish between a local sintering process leading to the formation of narrow necks to the nearest neighbors, while the original granular nature of the particle layer is maintained, and a complete fusion. In the latter case, stable nanometer-scale structures are fabricated which strongly interconnect with the underlying substrate. In combining nanoparticle-inherent properties with existing theory, we roughly estimate the temperature rise of the nanoparticles and confirm the possibility of particle liquefaction for the highest power densities generated.

  13. Expression of STM4467-encoded arginine deiminase controlled by the STM4463 regulator contributes to Salmonella enterica serovar Typhimurium virulence.

    PubMed

    Choi, Younho; Choi, Jeongjoon; Groisman, Eduardo A; Kang, Dong-Hyun; Shin, Dongwoo; Ryu, Sangryeol

    2012-12-01

    Arginine deiminase (ADI), carbamate kinase (CK), and ornithine transcarbamoylase (OTC) constitute the ADI system. In addition to metabolic functions, the ADI system has been implicated in the virulence of certain pathogens. The pathogenic intracellular bacterium Salmonella enterica serovar Typhimurium possesses the STM4467, STM4466, and STM4465 genes, which are predicted to encode ADI, CK, and OTC, respectively. Here we report that the STM4467 gene encodes an ADI and that ADI activity plays a role in the successful infection of a mammalian host by S. Typhimurium. An STM4467 deletion mutant was defective for replication inside murine macrophages and was attenuated for virulence in mice. We determined that a regulatory protein encoded by the STM4463 gene functions as an activator for STM4467 expression. The expression of the ADI pathway genes was enhanced inside macrophages in a process that required STM4463. Lack of STM4463 impaired the ability of S. Typhimurium to replicate within macrophages. A mutant defective in STM4467-encoded ADI displayed normal production of nitric oxide by macrophages.

  14. Expression of STM4467-Encoded Arginine Deiminase Controlled by the STM4463 Regulator Contributes to Salmonella enterica Serovar Typhimurium Virulence

    PubMed Central

    Choi, Younho; Choi, Jeongjoon; Groisman, Eduardo A.; Kang, Dong-Hyun

    2012-01-01

    Arginine deiminase (ADI), carbamate kinase (CK), and ornithine transcarbamoylase (OTC) constitute the ADI system. In addition to metabolic functions, the ADI system has been implicated in the virulence of certain pathogens. The pathogenic intracellular bacterium Salmonella enterica serovar Typhimurium possesses the STM4467, STM4466, and STM4465 genes, which are predicted to encode ADI, CK, and OTC, respectively. Here we report that the STM4467 gene encodes an ADI and that ADI activity plays a role in the successful infection of a mammalian host by S. Typhimurium. An STM4467 deletion mutant was defective for replication inside murine macrophages and was attenuated for virulence in mice. We determined that a regulatory protein encoded by the STM4463 gene functions as an activator for STM4467 expression. The expression of the ADI pathway genes was enhanced inside macrophages in a process that required STM4463. Lack of STM4463 impaired the ability of S. Typhimurium to replicate within macrophages. A mutant defective in STM4467-encoded ADI displayed normal production of nitric oxide by macrophages. PMID:23006851

  15. Feasibility study of simultaneous capacitance detection during STM of silicon

    NASA Astrophysics Data System (ADS)

    Kim, Hyun; Dwyer, Kevin; Pomeroy, Joshua

    2015-03-01

    We are examining the feasibility of capacitance detection during STM to image buried metal nanostructures in silicon. As the hydrogen STM lithography for quantum information enables us to fabricate the atomically precise devices such as single atom qubits, the accurate alignment of metal contacts such as electrodes to the buried nanostructures on the surface becomes very challenging. Using SCM with STM gives benefits to locate the buried nanostructures and image the surface morphology simultaneously.

  16. In-situ TEM observation on STM tunneling gap

    NASA Astrophysics Data System (ADS)

    Kim, Suhyun; Tanishiro, Yasumasa; Takayanagi, Kunio

    2009-03-01

    Transmission Electron Microscope and Scanning Tunneling Microscope in an ultra high vacuum environment (UHV-TEM-STM) have been combined to simultaneously perform both high resolution TEM and atomically resolved STM experiments. This system was constructed for in-situ investigation of physical property of impurity atoms embedded below semiconductor surface. To image TEM and STM at the same time, crucial requirement is that, the STM image must be acquired under the electron beam irradiation. As a preliminary test, we used HOPG (Highly Oriented Pyrolytic Graphite) sample and tungsten tip as schematically shown in Fig 1(a). Fig 1(b) shows an atomic resolution STM image of HOPG obtained with 300mV sample bias and 3nA tunneling current even in the condition of the electron beam irradiation on the tip. TEM image can be simultaneously acquired by performing In-situ TEM observation on STM tunneling gap formed between the tip and a thin sample. Fig 1(a) Geometry of STM observation on STM tunneling gap Fig 1(b) STM image of HOPG obtained with 300mV sample bias and 3nA tunneling current

  17. STM: Imaging of gasified carbon structures

    SciTech Connect

    Tandon, D.; Hippo, E.J.

    1994-12-31

    The basic mechanisms of carbon gasification are essential to understanding carbon gasification. It has been shown that more carbon can be gasified with the help of a catalyst that increases the efficiency of the gasification process by at least one order of magnitude. Natural graphites are extensively used as the industrial carbon materials, but their studies have received little attention. Imaging of natural graphites will help in identifying the defects, and edge sites prone to gasification. The scanning tunneling microscope (STM) and help in providing a better insight for catalytic carbon gasification. The authors have imaged two samples of natural graphites: (1) Ticonderoga graphite from upper New York state, and (2) Ceylon graphite from Sri Lanka. The natural graphites have oxygen complexes on the edge site surfaces (peroxide groups). Interlayer oxygen complexes have also been observed. These oxygen complexes were confirmed by the bond length measurements in the cross-sectional analysis. The extent of oxidation is very high in some places and is very similar to the HOPG oxidized surface. Basal plane attack is found to be higher than previously thought. In Ceylon graphite the authors have found fullerene type giant molecules. These images are essential to STM study of catalytic gasification.

  18. 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).

  19. 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…

  20. Preparation and characterization of STM tips for electrochemical studies

    NASA Astrophysics Data System (ADS)

    Nagahara, L. A.; Thundat, T.; Lindsay, S. M.

    1989-10-01

    We report on a fabrication technique for scanning tunneling microscopy (STM) tips for in situ electrochemical investigations. Unwanted Faradaic currents were minimized by insulating the STM tips with Apiezon wax. Cyclic voltammetry showed Apiezon wax to be inert in various electrolytes.

  1. 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…

  2. STM CONTROL OF CHEMICAL REACTIONS: Single-Molecule Synthesis

    NASA Astrophysics Data System (ADS)

    Hla, Saw-Wai; Rieder, Karl-Heinz

    2003-10-01

    The fascinating advances in single atom/molecule manipulation with a scanning tunneling microscope (STM) tip allow scientists to fabricate atomic-scale structures or to probe chemical and physical properties of matters at an atomic level. Owing to these advances, it has become possible for the basic chemical reaction steps, such as dissociation, diffusion, adsorption, readsorption, and bond-formation processes, to be performed by using the STM tip. Complete sequences of chemical reactions are able to induce at a single-molecule level. New molecules can be constructed from the basic molecular building blocks on a one-molecule-at-a-time basis by using a variety of STM manipulation schemes in a systematic step-by-step manner. These achievements open up entirely new opportunities in nanochemistry and nanochemical technology. In this review, various STM manipulation techniques useful in the single-molecule reaction process are reviewed, and their impact on the future of nanoscience and technology are discussed.

  3. 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).

  4. Collective Surface Diffusion Measurements with the STM

    NASA Astrophysics Data System (ADS)

    Tringides, Michael C.

    1996-03-01

    Time dependent processes in surface overlayers at finite coverage are described in terms of the collective diffusion coefficient D_c. Dc can be measured from the time dependent correlation function C(t), of an initial concentration fluctuation formed in a probe area A. C(t) follows a characteristic 1/D_ct time dependence at long times. The STM can be easily used^1 to measure C(t) and, therefore, Dc by monitoring the current fluctuations with the tip fixed over a location (i.e, by suspending the scanning process). The probe area A is defined by the tunneling region. Experiments on O/Si(111) at low coverage will be described that show a dramatic increase of the current fluctuations (when compared to the clean surface) with the addition of oxygen. The analysis of the current fluctuations obtained at different temperatures is consistent with the 1/D_ct form of the correlation function. This method of measuring collective surface diffusion has the unique advantage of ultrafast speed (limited only by the electronics) and can be used to test predictions about the statistical mechanics of surface diffusion in an ensemble of particles. * Ames Laboratory is operated for the U. S. Department of Energy under Contract No. W-7405-Eng-82. 1. M. L. Lozano and M. C. Tringides, Europhys. Lett. 30 , 537 (1995).

  5. STM driven modification of bismuth nanostructures

    NASA Astrophysics Data System (ADS)

    Kowalczyk, P. J.; Mahapatra, O.; Brown, S. A.; Bian, G.; Chiang, T.-C.

    2014-03-01

    The tip of a scanning tunneling microscope (STM) gently interacting with the substrate is used to modify (110) bismuth islands deposited on highly oriented pyrolitic graphite (HOPG), and hence to investigate the atomic and electronic structure of the islands. The tip interaction leads to the evolution of metastable 3 ML thick regions into structures of higher thermodynamic stability, which in the case of bismuth on graphite are rods (typically ≥ 5 ML high) and stripes. The formation of trenches that extend along the stripes is observed which is related to the presence of kinks and weak bonds at the 3-5 ML interface. Migration of whole islands along particular substrate directions is evidence for superlubricity due to the misfit between Bi and HOPG unit cells. Perimeter diffusion through atoms and not vacancies is a driving force of all observed modifications. The Bi islands are found to be able to deform and their decay is not governed by Ostwald ripening (which is absent in this system). Instead quantum size effects play a major role in the evolution of the islands, as evidenced by the observation of preferred widths. Density functional theory calculations reveal an oval Fermi surface with de Broglie wavelength corresponding to observed width of islands. These results are all consistent with a thin film Bi allotrope which has both paired atomic layers on the surface and bulk-like chains of bonds vertically through the structure.

  6. STM studies of single molecules: molecular orbital aspects.

    PubMed

    Li, Bin; Li, Zhenyu; Yang, Jinlong; Hou, J G

    2011-03-14

    As a fundamental and frequently referred concept in modern chemistry, the molecular orbital plays a vital role in the science of single molecules, which has become an active field in recent years. For the study of single molecules, scanning tunneling microscopy (STM) has been proven to be a powerful scientific technique. Utilizing specific distribution of the molecular orbitals at spatial, energy, and spin scales, STM can explore many properties of single molecule systems, such as geometrical configuration, electronic structure, magnetic polarization, and so on. Various interactions between the substrate and adsorbed molecules are also understood in terms of the molecular orbitals. Molecular engineering methods, such as mode-selective chemistry based on the molecular orbitals, and resonance tunneling between the molecular orbitals of the molecular sample and STM tip, have stimulated new advances of single molecule science.

  7. 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.

  8. STM fingerprints of point defects in graphene: a theoretical prediction

    SciTech Connect

    Amara, Hakim; Latil, Sylvain; Meunier, Vincent; Lambin, Philippe; Charlier, Jean Christophe

    2007-01-01

    Scanning tunneling microscopy (STM) is one of the most appropriate techniques to investigate the atomic structure of carbon nanomaterials. However, the experimental identification of topological and nontopological modifications of the hexagonal network of sp{sup 2} carbon nanostructures remains a great challenge. The goal of the present theoretical work is to predict the typical electronic features of a few defects that are likely to occur in sp{sup 2} carbon nanostructures, such as atomic vacancy, divacancy, adatom, and Stone-Wales defect. The modifications induced by those defects in the electronic properties of the graphene sheet are investigated using first-principles calculations. In addition, computed constant-current STM images of these defects are calculated within a tight-binding approach in order to facilitate the interpretation of STM images of defected carbon nanostructures.

  9. In situ STM studies of polycrystalline platinum electrodes

    NASA Astrophysics Data System (ADS)

    Szklarczyk, Marek; Bockris, John O'M.

    1991-01-01

    In situ scanning tunneling microscopy (STM) was applied in a 10 -2M NaClO 4 solution to study topographical changes of a platinum electrode surface due to its oxidation and reduction. Surface morphology depends on the electrode potential. There are two stages in surface reduction: the fast electrochemical charge transfer and the slow crystallographic reconstruction. Reconstruction during surface reduction tends to proceed in the direction of the topography obtained during the annealing process. Methods of avoiding Faradaic current flowing through the STM tip are discussed in detail.

  10. Nanoscale Decoration of Electrode Surfaces with an STM

    DTIC Science & Technology

    1999-05-30

    covered Au( 111) surface due to underpotential deposition . E,,,P, = + 10 mV vs. Cu/Cu++, E, = - 30 mV, I, = 2 nA. (b) Same area, but after anodic...Abstract The tip of a scanning tunnelling microscope (STM) has been used to deposit nanometer-sized clusters of copper or silver on bare and thiol...covered gold electrode surfaces at predetermined positions. First, metal is deposited electrochemically onto the STM tip, then the clusters are formed by a

  11. Ion Irradiation of Carbon Nanotubes: a STM Study

    NASA Astrophysics Data System (ADS)

    Osváth, Z.; Vértesy, G.; Horváth, Z. E.; Gyulai, J.; Biró, L. P.

    2009-03-01

    Multi-walled carbon nanotubes irradiated with Ar+ ions of low (5×1011 ions/cm2) and high (1015 ions/cm2) fluences were investigated by STM. Contrary to the case of low fluence irradiation, the defects produced during the high fluence irradiation could not be observed individually, and the surface of nanotubes became rough. Irradiated nanotubes could be easily bent by the STM tip. However, some nanotubes parts could not be moved, which suggest that these parts were bound to the substrate during irradiation.

  12. Cryogenic AFM-STM for mesoscopic physics

    NASA Astrophysics Data System (ADS)

    Le Sueur, H.

    ésolution en énergie inégalée (10 μeV). Cet appareil combine les fonctions de Microscopie par Force Atomique (mode AFM) et de spectroscopie Tunnel locale (mode STM), et fonctionne à 30 mK. Dans le mode AFM, la topographie de l'échantillon est imagée grâce à un diapason en quartz piézoélectrique, ce qui permet de repérer les circuits. La spectroscopie tunnel peut ensuite être faite sur les zones conductrices. Avec ce microscope, nous avons mesuré la DOS locale dans une structure hybride Supraconducteur-métal Normal-Supraconducteur (S-N-S). Dans un tel circuit, les propriétés électroniques de N et de S sont modifiées par l'effet de proximité supraconducteur. Notamment, pour des fils N courts, nous avons pu observer -comme prédit- la présence d'un gap dans sa DOS, indépendant de la position dans la structure : le " minigap ". De plus, en modulant la phase supraconductrice entre les deux S, nous avons mesuré la modification de ce gap, et sa disparition lorsque la différence de phase vaut π. Nos résultats expérimentaux pour la DOS, ainsi que ses dépendances en phase, en position, et en longueur de N sont en accord quantitatif avec les prédictions de la théorie quasiclassique de la supraconductivité. Certaines de ces prédictions sont observées pour la première fois.

  13. Type-specific proactive interference in patients with semantic and phonological STM deficits.

    PubMed

    Harris, Lara; Olson, Andrew; Humphreys, Glyn

    2014-01-01

    Prior neuropsychological evidence suggests that semantic and phonological components of short-term memory (STM) are functionally and neurologically distinct. The current paper examines proactive interference (PI) from semantic and phonological information in two STM-impaired patients, DS (semantic STM deficit) and AK (phonological STM deficit). In Experiment 1 probe recognition tasks with open and closed sets of stimuli were used. Phonological PI was assessed using nonword items, and semantic and phonological PI was assessed using words. In Experiment 2 phonological and semantic PI was elicited by an item recognition probe test with stimuli that bore phonological and semantic relations to the probes. The data suggested heightened phonological PI for the semantic STM patient, and exaggerated effects of semantic PI in the phonological STM case. The findings are consistent with an account of extremely rapid decay of activated type-specific representations in cases of severely impaired phonological and semantic STM.

  14. Mesoscale STM Study of Thermally Annealed Copper Foils

    NASA Astrophysics Data System (ADS)

    Sarajlic, Olesya; Mani, Ramesh

    2012-02-01

    The growth of high quality graphene has become a topic of significance. There have been utilized several methods of material growth including the epitaxial growth on SiC, method of exfoliation of graphite, and chemical vapor deposition (CVD). The CVD approach typically utilizes foils of copper or nickel that are exposed to organic compounds at a high temperature. The purpose of the study is to investigate the role of the metal surface morphology during the growth process, relative grain size before and after thermal treatment, and relative flatness of the substrate after annealing. We investigated the effects of thermal annealing of polycrystalline Cu foil at the mesoscale using an ultrahigh vacuum (UHV) scanning tunneling microscope (STM). Prolonged low-temperature and rapid high-temperature annealing of the samples is being carried out and the resulting surface morphology will be reported. The STM observations reveal that the film quality is limited by grain boundaries.

  15. 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.

  16. STM investigation of carbon nanotubes completely covered with functional groups

    NASA Astrophysics Data System (ADS)

    Koos, Antal A.; Horvath, Zsolt Endre; Osvath, Zoltan; Tapaszto, Levente; Niesz, Krisztián; Konya, Zoltan; Kiricsi, Imre; Grobert, Nicole; Ruehle, Manfred; Biro, Laszlo P.

    2003-04-01

    The functionalization of carbon nanotubes (CNTs) is important both for composite - to improve load transfer between CNTs and matrix - and nanoelectronic applications - to interlink individual nanotubes in a network. Oposite to earlier results, complete coverage of CNT surface with functional groups was achieved. The distribution of functional groups on the nanotube surface was investigated using STM and TEM. The influence of functional groups on the electron density of states of the nanotubes was studied with scanning tunneling spectroscopy (STS).

  17. 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].

  18. Physical Modeling of Contact Processes on the Cutting Tools Surfaces of STM When Turning

    NASA Astrophysics Data System (ADS)

    Belozerov, V. A.; Uteshev, M. H.

    2016-08-01

    This article describes how to create an optimization model of the process of fine turning of superalloys and steel tools from STM on CNC machines, flexible manufacturing units (GPM), machining centers. Creation of the optimization model allows you to link (unite) contact processes simultaneously on the front and back surfaces of the tool from STM to manage contact processes and the dynamic strength of the cutting tool at the top of the STM. Established optimization model of management of the dynamic strength of the incisors of the STM in the process of fine turning is based on a previously developed thermomechanical (physical, heat) model, which allows the system thermomechanical approach to choosing brands STM (domestic and foreign) for cutting tools from STM designed for fine turning of heat resistant alloys and steels.

  19. STM manipulation of a subphthalocyanine double-wheel molecule on Au(111).

    PubMed

    Nickel, Anja; Meyer, Joerg; Ohmann, Robin; Jacquot de Rouville, Henri-Pierre; Rapenne, Gwénaël; Ample, Francisco; Joachim, Christian; Cuniberti, Gianaurelio; Moresco, Francesca

    2012-10-10

    A new class of double-wheel molecules is manipulated on a Au(111) surface by the tip of a scanning tunneling microscope (STM) at low temperature. The double-wheel molecule consists of two subphthalocyanine wheels connected by a central rotation carbon axis. Each of the subphthalocyanine wheels has a nitrogen tag to monitor its intramolecular rolling during an STM manipulation sequence. The position of the tag can be followed by STM, allowing us to distinguish between the different lateral movements of the molecule on the surface when manipulated by the STM tip.

  20. 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.

  1. STM/STS on proximity-coupled superconducting graphene

    NASA Astrophysics Data System (ADS)

    Ovadia, Maoz; Ji, Yu; Hoffman, Jennifer; Wang, Joel I.-Jan; Jarillo-Herrero, Pablo

    2015-03-01

    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.

  2. Extraction and STM Imaging of Spherical Giant Fullernes

    NASA Astrophysics Data System (ADS)

    Lamb, Lowell D.; Huffman, Donald R.; Workman, Richard K.; Howells, Sam; Chen, Ting; Sarid, Dror; Ziolo, Ronald F.

    1992-03-01

    High-temperature, high-pressure extracts of soot produced by the Kratschmer-Huffman technique (KH carbon) were characterized by mass spectrometry and imaging with scanning tunneling microscopes (STMs). The mass spectra of these samples are similar to those of ambient-pressure, high-boiling-point solvent extractions, supporting the idea that solvent temperature and possibly pressure are key parameters in extraction of the giant fullerenes. The STM images show that the giant fullerenes in these samples are roughly spherical in shape and range in diameter from approximately 1 to 2 nanometers, corresponding to fullerenes containing 60 to 330 atoms. No evidence of bucky tubes was found.

  3. Cryomagnetic STM spectroscopy study of multiband pairing in layered superconductors

    NASA Astrophysics Data System (ADS)

    Fridman, Igor; Lukic, Vladimir; Kloc, Christian; Petrovic, Cedomir; Dai, Pengcheng; Wei, J. Y. T.

    2013-03-01

    Cooper pairing in layered superconductors can involve multiple bands and give rise to complex gap structures in momentum space. Using scanning tunneling microscopy (STM) with a magnetic field applied parallel to the ab -plane, we investigate multiband pairing under diamagnetically-induced superfluid momentum. STM spectroscopy and conductance imaging were performed down to 300 mK and up to 9 T, on single-crystals of the Nb-chalcogenide 2 H -NbSe2 and the Fe-pnictides LiFeAs and electron-doped BaFe2As2. Spectroscopy data taken on 2 H -NbSe2 at 300 mK showed a distinctly two-sloped field evolution of the zero-bias conductance, consistent with Doppler-induced depairing on parts of the Fermi surface. Spatial conductance maps revealed stripe patterns that originate from in-plane vortices whose cores are buried in the bulk and which undergo a transition as pairing on one of the bands is suppressed. Our results demonstrate a general method for probing multiband superconductors, especially ones whose band structures host coexisting orders and also play a direct role in the pairing mechanism. Work supported by NSERC, CFI/OIT, CIFAR, U.S. DOE and Brookhaven Science Associates (No. DE-Ac02-98CH10886).

  4. Acetophenone on Si(001) with STM and DFT

    NASA Astrophysics Data System (ADS)

    Schofield, Steven; Rahnejat, Adam; Warschkow, Oliver; Belcher, Daniel; Radny, Marian; Smith, Phillip

    2012-02-01

    Organic molecules are likely to play an important role in future technologies, e.g., in novel devices where individual molecules are incorporated as active elements, and in extending the functionality of existing technologies. A detailed, atomic-scale understanding of the structural and electronic properties of molecules on surfaces is key to the development of these technologies. Here we present scanning tunnelling microscopy (STM) and density functional theory (DFT) data of the surface binding configurations of acetophenone adsorbed to Si(001). Topographic and spectroscopic tunnelling experiments were performed at 77 K and room temperature in the limit of very low coverage. We find in analogy to other similar molecules such as acetaldehyde [1], acetone [2,3] and acetic acid [4], acetophenone molecules covalently bond to the Si(001) surface in a variety of configurations that can be directly manipulated using the STM tip. In its most stable configuration, the adsorbate stands upright on the surface, attached via the C and O atoms of its acetyl group, producing a geometry that is robust and attractive for molecular electronics applications. [1] JCP 131, 104707 (2010), [2] PCCP 11, 2747 (2009), [3] JACS 129, 11402 (2007), [4] PRB 84, 153302 (2011).

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

    NASA Astrophysics Data System (ADS)

    Giordano, Pietro; Raimondo, Giacomo; Messidoro, Piero

    1994-11-01

    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.

  6. 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.

  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. Cryogenic STM/STS observation on oxide superconductors

    SciTech Connect

    Nantoh, M.; Hasegawa, T.; Takagi, A.; Yamaguchi, W.; Ogino, M.; Kitazawa, K. ); Kawasaki, M.; Gong, J.P.; Fujito, K.; Koinuma, H. )

    1994-04-01

    The topographic and electronic properties of the surfaces of (001) and (110) oriented YBa[sub 2]Cu[sub 3]O[sub y] epitaxial films have been probed by atomic resolution STM/STS at 4.2 K. The STM image on the (001) surface clearly revealed the atomic corrugation of the tetragonal lattice with an average spacing of 0.4 nm, while on the (110) surface the orthorhombic atomic lattice, corresponding to the Cu atoms of both CuO[sub 2] and CuO chain planes, was observed. The STS result on the (001) surface indicated the semiconducting nature of the terminating layer. As the tunneling tip came closer to the surface, however, the shape of the tunneling spectrum became more metallic and showed a superconducting energy gap, which seems to arise from the underlying superconducting layer. On the other hand, the tunneling spectra on the (110) surface indicated superconducting gap structures, independent of the tip-sample distance. 11 refs., 5 figs.

  9. Women's Education in Science Technology and Mathematics (STM) Challenges for National Development

    ERIC Educational Resources Information Center

    Aguele, Lawrence I.; Idialu, Ethel E.; Aluede, Oyaziwo

    2008-01-01

    The paper presents Science, Technology and Mathematics (STM) as the bedrock of the development of any nation. It emphasizes the role of women in national development. To achieve meaningful advancement in national development, the paper emphasizes the need to give priority to the education of women in STM. It recommended that deliberate efforts be…

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

    NASA Astrophysics Data System (ADS)

    Perdigão, Luís M. A.; Saywell, Alex

    2011-07-01

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

  11. Manipulation of organic “needles” using an STM operated under SEM control

    NASA Astrophysics Data System (ADS)

    Hänel, K.; Birkner, A.; Müllegger, S.; Winkler, A.; Wöll, Ch.

    2006-06-01

    Nano-sized P4P ( para-quaterphenylene) organic crystallites grown on a gold substrate were removed and redeposited using the tip of an STM. The controlled lift-off of the needle-shaped crystallites was imaged by a simultaneously operated SEM. The forces exerted by the metal STM tip on the nano-crystal during this nano-manipulation process could be determined by monitoring the deflection of the STM tip. After the lift-off process the former contact area was imaged using the STM. These STM micrographs clearly demonstrate that the region between the needles is covered by a P4P layer with a thickness of at least 3 nm.

  12. 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.

  13. Adsorbate Orbital Mediated Tunneling Spectroscopy in an STM

    NASA Astrophysics Data System (ADS)

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

    2001-03-01

    While adsorbate orbital mediated tunneling spectroscopy (OMTS) has been extensively demonstrated in the M-I-A-M' tunnel diode environment, it has only recently been observed in the scanning tunneling microscope (STM). We will present OMTS data for monolayer and sub-monolayer coverage of phthalocyanines and porphyrins adsorbed on Au(111). Features associated with transient oxidation and reduction of the rings, as well as oxidation of the central metal ion are observed. The positions of bands associated with tunneling through occupied porphyrin ring orbitals will be compared to UPS bands seen in similar samples. A simple electrochemical model can be used to estimate the positions of the OMT peaks associated with unoccupied or partially occupied orbitals. These predictions are in reasonable agreement with the observed OMTS peaks. Constant current images with sub-molecular resolution show the relative contributions of metal, nitrogen, and carbon orbitals to the tunneling process.

  14. Evaluation of the STM4-120 kinematic Stirling engine

    NASA Astrophysics Data System (ADS)

    Linker, Kevin L.; Rawlinson, K. Scott; Smith, Greg

    The Department of Energy's (DOE) Solar Thermal Program has identified the Stirling cycle heat engine as the conversion device for dish-electric systems with the most potential for meeting the program's goals. To advance the technology toward commercialization in a dish-electric system, Sandia National Laboratories has acquired a Stirling Thermal Motors, Inc. kinematic Stirling engine, STM4-120, for evaluation. During the past year this engine has been operating at Sandia's Engine Test Facility. The engine's heat input was provided through fossil fuel combustion and sodium heat pipes, while the output power was absorbed with an eddy-current dynamometer. The evaluation of the engine performance during the past year is presented.

  15. 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

  16. 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.

  17. STM measurements of Charge Density Waves in S-doped NbSe2

    NASA Astrophysics Data System (ADS)

    Wurstbauer, Ulrich; Rosenthal, Ethan; Andrade, Erick F.; Arguello, Carlos; Chockalingam, Subbaiah P.; Jia, Shuang; Cava, Robert J.; Pasupathy, Abhay N.

    2012-02-01

    Recent scanning tunneling microscopy (STM) measurements have shown that crystal defects have a profound influence on the nature of the charge density wave (CDW) transition in the transition-metal dichalcogenides (TMD). In order to examine this effect systematically, we employ low temperature STM to visualize the CDW transition in intentionally doped TMD crystals. We use a newly designed homebuilt ultra-low-loss, variable temperature STM to perform measurements on crystal samples of NbSxSe2-x. We describe the effect of the sulphur atoms on both the local and global charge order in this material.

  18. STM and LEED studies of atomically ordered terraced Si(557) surfaces

    SciTech Connect

    Chaika, A. N. Bozhko, S. I.; Ionov, A. M.; Myagkov, A. N.; Abrosimov, N. V.

    2007-04-15

    We report results of LEED, STM, and photoemission studies of the atomic and electronic structure of atomically ordered terraced Si(hhm) surfaces. LEED and STM data demonstrate the possibility of fabricating atomically accurate terraced structures based on Si(557) with different periodicities depending on the thermal treatment procedure. Atomically resolved STM images reveal (7 x 7) terrace ordering and triple step structure. Comparative photoemission studies of the valence band and Si 2p core level electronic structure have been done on clean stepped surfaces with different terrace widths (namely, Si(557), Si(556)) and flat Si(111)-(7 x 7)

  19. STM Images of Atomic-Scale Carbon Nanotube Defects Produced by Ar+ Irradiation

    NASA Astrophysics Data System (ADS)

    Osváth, Z.; Vértesy, G.; Tapasztó, L.; Wéber, F.; Horváth, Z. E.; Gyulai, J.; Biró, L. P.

    2005-09-01

    Multi-wall carbon nanotubes (MWCNTs) dispersed on graphite (HOPG) substrate were irradiated with Ar+ ions of 30 keV, using a low-dose of D = 5×1011 ions/cm2. The irradiated samples were investigated by scanning tunneling microscopy (STM) under ambient conditions. Atomic resolution STM images reveal individual nanotube defects, which appear as hillocks of 1-2 angstroms in height, due to the locally changed electronic structure. After annealing at 450 °C in nitrogen atmosphere, the irradiated MWCNTs were investigated again by STM. The effect of the heat treatment on the irradiation-induced nanotube defects is also discussed.

  20. STM Study of Lead and Bismuth Structures on COPPER(001)

    NASA Astrophysics Data System (ADS)

    Chen, Yun

    This work studies the stable room temperature structures of metal on metal overlayers. The purpose of this study is twofold. First, the advent of the atomic imaging technique of Scanning Tunneling Microscopy (STM) makes it now possible to directly observe complicated surface structures. This was demonstrated by the success of unraveling the (7times7)-Si(111) surface structure that had withstood the storm of investigation for over 20 years. We wanted to apply this technique to the study of metallic overlayer structures, a field known for its large variety of structures. The second purpose was to investigate the feasibility and to hopefully develop a simple intuitive approach to metallic overlayer structure prediction, an approach that incorporates explicitly the extended nature of the metallic electron system. The Pb and Bi systems have large numbers of valence electrons per atom. Therefore, the electronic effects are expected to be prominent. The difference between the numbers of valence electrons of the respective atoms is relatively small but significant. This provides an opportunity to observe a quantitative variation of the effects. This study constitutes the first STM investigation of the ordered Pb and Bi structures on Cu(001). Many structural features observed using this technique disagree with the existing models derived from the electron diffraction and other scattering experiments. The differences between our observation and the current structural models are qualitative ones, thus demanding a rethinking and supplementation of the basic ideas involved in the construction of the structural models. Observation of the great similarities between the adsorbed Pb and Bi systems, lead to the new modeling approach. In our discussion, the metal adsorbate layers are described as a simple quasi-two-dimensional metal weakly coupled to the host substrate. This is consistent with the familiar notion that all metals exhibits similar properties. Our detailed analysis also

  1. Damped harmonic oscillator model for analyzing the dynamic characteristics of STM system

    NASA Astrophysics Data System (ADS)

    Liu, A. P.; Yao, X. X.; Wang, X.; Yang, D. X.; Zhang, X. M.

    2015-09-01

    Recognizing and distinguishing the dynamic characteristics of scanning tunneling microscopy (STM) system is fatal for studying STM image. In this paper, a method for analyzing system’s characteristics by using a damped harmonic oscillator model is presented. The model is driven by random force and all of its properties are described by damping and periodic. For the general solution of such harmonic oscillator’s Langevin equation is deduced and the auto-correlation function (ACF) is obtained for fitting curve. It is shown that damping and periodic property of the two curves have a good agreement by comparing the fitting curve with the auto-correlation curve of time series dates which are acquired by STM. It could be concluded that the damped harmonic oscillator model and auto-correlation method are feasible for analyzing the dynamic characteristics of STM system.

  2. SHI induced surface modification studies of HOPG using STM

    NASA Astrophysics Data System (ADS)

    Tripathi, A.; Khan, S. A.; Kumar, M.; Baranwal, V.; Krishna, R.; Pandey, A. C.

    2006-03-01

    The highly oriented pyrolytic graphite (HOPG) samples (Grade ZYB with grain size ∼1 mm) are irradiated with 150 MeV Au beam with fluences varying from 1 × 1011 ions/cm2 to 2 × 1013 ions/cm2. The surface topography and the I-V characteristics are studied using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) at Nuclear Science Centre, New Delhi. The formation of hillocks is observed for the samples irradiated with fluences of 1 × 1011 ions/cm2, 1 × 1012 ions/cm2 and 1 × 1013 ions/cm2 with typical diameters of 6.2, 2.2 and 1.5 nm, respectively. No hillocks are observed for the sample irradiated with fluence of 2 × 1013 ions/cm2, though the formation of small craters at some places are observed. The formation of hillocks is attributed to nuclear energy loss induced collision cascades near the surface. The reduction in hillocks size and formation of craters at higher fluence is attributed to the electronic sputtering from the surface. The STS studies of I-V characteristics show an increasing ohmic behavior with fluence which is attributed to increasing metallic state for HOPG surface due to irradiation induced increase of carbon bond lengths.

  3. 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).

  4. Self-Assembled Monolayers: a Molecular Resolution STM Study

    NASA Astrophysics Data System (ADS)

    Dhirani, Al-Amin

    Building on studies of self-assembled monolayers (SAMs) based on the (CH_3(CH _2)_{rm n{-}1}SH) + Au(111) prototype, we have designed and constructed a high impedance STM to consider the formation and properties of new SAM systems with molecular resolution. On Au-, Ag-, and Pt-(111), the monolayer structures of n-decanethiol were found to be (1) ordered on gold and silver but not platinum (2) strongly correlated with the structures formed by simpler sulfur components. In addition the potential formation and properties of new molecular classes of ordered SAMs were considered by studying monolayers of H(C _6H_4Cequiv C)_{rm n}C _6H_4SH (n = 0 - 2) (1a - c) on Au(111). An increase in order with chain length as well as the formation of an ordered SAM by 1c were observed. Finally, current-voltage (I-V) measurements of 1 monolayers displayed an increasing nonlinearity with chain length and an asymmetry for 1c. The electrical behavior is consistent with a model based on a semi-classical tunneling formalism using the barrier height and molecular polarizability of 1.

  5. Subkelvin spin polarized STM: measuring magnetization curves of individual adatoms

    NASA Astrophysics Data System (ADS)

    Wiebe, Jens

    2008-03-01

    Magnetic nanostructures consisting of a few atoms on non-magnetic substrates are explored as model systems for miniaturized data storage devices and for the implementation of novel spin-based computation techniques. Since these nanostructures are well defined and controllable on the atomic scale, they are ideally suited to study the fundamentals of magnetic interactions. We used spin polarized scanning tunneling spectroscopy at subkelvin temperatures to image the magnetization of individual adatoms as a function of an external magnetic field. This allows to directly measure their magnetic interactions at very low energy scale. We will present the design of the 300mK STM [1] and then focus on the results. Interestingly, Co atoms on Pt(111) behave paramagnetic even at very low temperatures, 300 times smaller than the previously reported giant barrier between up and down spin [2]. A peculiar variation in the saturation flux density, which is measured for each atom, is found. This is attributed to their mutual indirect exchange via the substrate electrons. Indeed, we observe an interaction between the adatom and a Co monolayer stripe oscillating with distance between ferromagnetic and antiferromagnetic coupling on the scale of the Fermi wavelength. [1] J. Wiebe et al., Rev. Sci. Instrum. 75, 4871 (2004). [2] P. Gambardella et al., Science 300, 1130 (2003).

  6. Ferromagnetic STM tip operating as a Spin-diode

    NASA Astrophysics Data System (ADS)

    Penteado, Poliana H.; Souza, Fabricio M.; Seridonio, Antônio C.; Coutinho, Renato M.; Vernek, Edson; Egues, J. Carlos

    2011-03-01

    We study spin-dependent transport in a system composed of a ferromagnetic STM tip coupled to an adsorbed atom (adatom) and to a host metallic (non-magnetic) surface. Electrons can tunnel directly from the tip to the surface or through the adatom. Our calculation is based on the nonequilibrium Green functions technique (Keldysh formalism). We self-consistently calculate the adatom spin occupation and its magnetization as a function of the tip position. We find that the adatom becomes magnetized when the tip approaches it; this magnetization switches sign as the voltage changes from forward to reverse bias. We also calculate the spin-resolved currents. If the tip is near the adatom, we obtain the spin-diode effect [PRB 75, 165303 (2007)] - i. e., unpolarized current for positive bias and polarized current for reverse bias - when the adatom is singly occupied. We also observe Friedel oscillations in the current as the tip-adatom distance increases [F. M. Souza, P. H. Penteado, et al. - to be submitted]. This work was supported by the funding agencies CNPq, CAPES, FAPEMIG and FAPESP.

  7. Design of wireless video transmission system based on STM32 microcontroller

    NASA Astrophysics Data System (ADS)

    Yang, Fan; Ma, Chunting; Li, Haoyi

    2017-03-01

    The design of a wireless video transmission system based on STM32, the system uses the STM32F103VET6 microprocessor as the core, through the video acquisition module collects video data, video data will be sent to the receiver through the wireless transmitting module, receiving data will be displayed on the LCD screen. The software design process of receiver and transmitter is introduced. The experiment proves that the system realizes wireless video transmission function.

  8. 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

  9. Cryogen-free low temperature STM/AFM based on a closed cycle cryostat

    NASA Astrophysics Data System (ADS)

    Choi, Byoung; Ulrich, Stefen; Murdick, Ryan; RHK Technology, Inc. Team

    2015-03-01

    Closed cycle cryogenic scanning tunneling microscope (CCC-STM) and atomic force microscope (AFM) will be presented. By using He heat exchange gas, thermally linked and mechanically decoupled CCC-STM/AFM enables atomically resolved microscopy and spectroscopy on various surfaces. We will present the noise measurement of the tunneling current and the thermal drift analysis. Temperature as low as 14K on the sample and the tip-sample distance fluctuation as low as 2 picometer have been achieved from 9K cryostat after 8h of cooling time. Low thermal drift in a lateral direction (<0.1nm/hr) enables to get a scanning tunneling spectroscopy grid with more than 64x64 pixels which typically takes over 10 hrs. We will also present the high stability and reproducibility of the CCC-STM/AFM with the atom resolved imaging of Si, Pt, Au and KBr surfaces in STM and AFM mode. These results demonstrate that the developed CCC-STM/AFM is a versatile instrument enabling experiments on a variety of materials and surfaces at picometer resolution without using any liquid cryogen.

  10. STM-Controlled Capillary Based Non-Contact Fluid Deposition Nanolithography

    NASA Astrophysics Data System (ADS)

    Lutfurakhmanov, Artur; Sailer, Rob; Schulz, Doug; Akhatov, Iskander

    2007-11-01

    A new method of fluid deposition based on scanning tunneling microscopy (STM) is presented. STM-Controlled Capillary Based Non-Contact Fluid Deposition Nanolithography consists of a Au-coated glass nanocapillary tip integrated into a commercial STM scanner platform where the tip serves the dual purpose of imaging and deposition. The small diameter hollow fiber (O.D. less than 500 nm) coupled with a conducting coating allows sub-angstrom-level z-resolution imaging using standard STM methodology. For fluid deposition, the tip is first located within 10 nm of the substrate before the nanocapillary is pressurized with a fluid (P = 50-500 KPa) leading to the formation of a small meniscus that then interacts with the underlying surface to give small spot of fluid deposition. Initial results show the ability to form features less than 500 nm in diameter using alpha-terpineol as the model fluid and highly-oriented pyrolytic graphite as the substrate. In addition to non-contact deposition, this technology also allows non-contact imaging using the constant height STM mode thereby eliminating the difficulties associated with finding nanometer-sized features.

  11. Atomic scale contact formation: A combined Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM) study

    NASA Astrophysics Data System (ADS)

    Hagedorn, Till; El Ouali, Mehdi; Miyahara, Yoichi; Grütter, Peter

    2008-03-01

    We are investigating contact formation at the atomic scale, in particular the interplay of forces and conductivity [1]. As it has been shown (e.g. in the case of C60 in between a STM tip and an Au(111) sample [2]), the conductivity in molecular junctions depends strongly on the contact geometry. In order to fully characterize the junction, we use a homebuilt ultra high vacuum (UHV) (p < 10-10 mbar) microscope which runs in simultaneous scanning tunneling microscope (STM) and atomic force microscope (AFM) modes. Additionally we image the STM tip structure with field ion microscopy (FIM) prior to using it in our experiments [3]. In order to realize a controlled contact we use the STM tip as one electrode and the sample as counter electrode. We are investigating bare Au(111) samples and W STM tips as an example of a nano metal-metal contact and one C60 molecule sandwiched between the W-tip and the Au(111) sample as a model for a controlled metal-molecule-metal contact. We will present new measurements of I(z), F(z) and dI/dV (z) curves of the above mentioned systems, where z is the tip-sample separation as well as images of the sample and tip structure. [1] Sun et. al. PRB 71 193407, 2005 [2] De Menech et. al. PRB 73, 155407, 2006 [3] Lucier et. al. PRB 72, 235420, 2005

  12. Giant apparent lattice distortions in STM images of corrugated sp2-hybridised monolayers

    NASA Astrophysics Data System (ADS)

    Dubout, Q.; Calleja, F.; Sclauzero, G.; Etzkorn, M.; Lehnert, A.; Claude, L.; Papagno, M.; Natterer, F. D.; Patthey, F.; Rusponi, S.; Pasquarello, Alfredo; Brune, H.

    2016-10-01

    We report on the strengths and limitations of scanning tunnelling microscopy (STM) when used for characterising atomic-scale features of quasi two-dimensional materials, such as graphene and single layers of hexagonal boron nitride, which may present strong corrugations when grown epitaxially on a substrate with a lattice mismatch. As a paradigmatic test case, we choose single-layer and bilayer graphene on Ru(0001), because their STM images show both a long-range moiré modulation and complex atomic-scale distortions of the graphene lattice. Through high-resolution STM measurements, we first determine with high accuracy the moiré epitaxial relations of the single layer and the bilayer with respect to the metal substrate. In particular, we also provide direct evidence for the existence of AA-stacked bilayer graphene domains on Ru(0001). We then demonstrate that the local strain distribution, as inferred from the same STM images, can be affected by large errors, so that apparent giant strains arise in some regions of the moiré as an imaging artefact. With the aid of density functional theory simulations, we track down the origin of these fictitious distortions in the high directionality of the graphene π-orbital density combined with the large corrugation of the sample. The proposed theoretical model correctly accounts for the observed dependence of the apparent strain on the STM tip-sample separation and on the different degree of curvature of the second graphene layer with respect to the single layer.

  13. First Experiences with Chip Development on the Commercial STM 65 nm Process

    NASA Astrophysics Data System (ADS)

    Syed, M.; Helfers, T.; Baumgarte, V.; Papadas, C.

    2013-08-01

    Currently Astrium GmbH is involved in the High Performance Data Processor (HPDP) development programme targeting the implementation of the commercially available reconfigurable array processor IP (XPP from the company PACT XPP Technologies) in a radiation hardened technology. In the current complementary development phase, it is planned to prototype the HPDP chip in commercial STM 65 nm technology. The idea behind this prototyping approach is not only to verify the functionality of the HPDP chip design, but also to get accustomed to the chip development flow of the future European deep sub-micron process. The prototyping is being carried out within the ESA Greek Industry Incentive Scheme by Integrated Systems Development (ISD). It is estimated that the HPDP prototype chip will be available in Q3 of 2013. As the STM 65nm process is planned to be made available as a radiation hardened process in the near future, the current exercise enables Astrium to gain experience with using this technology, to get accustomed to the STM development flow, to identify and avoid any hurdles in the future planned radiation hardened HPDP chip development. The HPDP chip is foreseen by ESA as a candidate for the first manufacturing run of the radiation hardened STM 65nm process. This exercise also assists in identifying any shortcomings of the proposed design methodology for the STM 65nm process.

  14. Surface Confined Metallosupramolecular Architectures: Formation and STM Characterization

    PubMed Central

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

    2009-01-01

    CONSPECTUS Metallosupramolecular compounds have attracted a great deal of attention over the past two decades largely because of their unique, highly-complex structural characteristics, the fact that they can be prepared with relative ease using coordination-driven self-assembly techniques, and their potential electronic, magnetic, optical, and catalytic properties. In particular, the use of electron-poor square planar Pt(II) transition metals in conjunction with rigid, electron-rich pyridyl donors had enabled the spontaneous self-assembly of a rich library of 2D metallacyclic and 3D metallacage assemblies via the directional-bonding approach. With the tremendous progress that has been made in the preparation and characterization of metallosupramolecules, much attention is now being turned toward fully exploring and developing their materials properties. Assembling metallosupramolecular compounds on solid supports represents a vitally important step toward developing their materials properties. Surfaces provide a means of uniformly aligning and orienting these highly symmetric metallacycles and metallacages, which increases the level of coherence between molecules above that which can be achieved in the solution phase and affords a means of integrating adlayers into a solid-state materials setting. The dynamic nature of kinetically labile Pt(II)-N coordination bonds, however, requires that deposition and imaging conditions be appropriate to retain the assemblies' stability. Toward these aims it is imperative to understand the factors that govern surface self-assembly and the interactions that influence the structure and stability of the resulting adlayer. Such insight can be obtained from Scanning Tunneling Microscopy (STM), which has emerged as a powerful technique for the imaging and characterization of self-assembled adlayers. This account describes the means by which 2D rectangular and square metallacycles and 3D trigonal bipyrimidal and chiral trigonal prism

  15. 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.

  16. STM and HREELS investigation of gas phase silanization on hydroxylated Si(100)

    NASA Astrophysics Data System (ADS)

    Fan, C.; Lopinski, G. P.

    2010-06-01

    The gas phase anhydrous reaction of glycidoxypropyldimethylethoxysilane (GPDMES) with a model hydroxylated surface has been investigated using high-resolution electron energy loss spectroscopy (HREELS) and scanning tunneling microscopy (STM). Water dissociation on the clean reconstructed (2 × 1)-Si(100) surface was used to create an atomically flat surface with ~ 0.5 ML of hydroxyl groups. Exposure of this surface to GPDMES at room temperature under vacuum was found to lead to formation of covalent Si-O-Si bonds although high exposures (6 × 10 8 L) were required for saturation. STM images at the early stages of reaction indicate that the reaction occurs randomly on the surface with no apparent clustering. The STM images together with semi-empirical (AM1) calculations provide evidence for hydrogen bonding interactions between the oxygen atoms in the molecule and surface hydroxyl groups at low coverage.

  17. Principles and simulations of high-resolution STM imaging with a flexible tip apex

    NASA Astrophysics Data System (ADS)

    Krejčí, Ondrej; Hapala, Prokop; Ondráček, Martin; Jelínek, Pavel

    2017-01-01

    We present a robust but still efficient simulation approach for high-resolution scanning tunneling microscopy (STM) with a flexible tip apex showing sharp submolecular features. The approach takes into account the electronic structure of the sample and tip as well as relaxation of the tip apex. We validate our model by achieving good agreement with various experimental images which allows us to explain the origin of several observed features. Namely, we have found that the high-resolution STM mechanism consists of standard STM imaging, convolving electronic states of the sample and the tip apex orbital structure, with the contrast heavily distorted by the relaxation of the flexible apex caused by interaction with the substrate.

  18. First Principles and STM Studies of Cl Adsorption on TiO2 (110) Surfaces

    NASA Astrophysics Data System (ADS)

    Vogtenhuber, D.; Podloucky, R.; Redinger, J.; Hebenstreit, E. L. D.; Hebenstreit, W.; Diebold, U.

    2000-03-01

    Atomic Cl adsorption on reduced and stoichiometric TiO2 (110) surfaces was calculated by applying a Full Potential Linearized Augmented Plane Wave method (FLEUR), and the Tersoff-Hamann model for simulating STM images. The electronic structure results are compared to experimental ISS, STM and XPS data for dissociative adsorption of Cl_2. Adsorption on O-defect sites, which is favored from our results of the adsorption energies, is found experimentally at elevated T (> 200^circ C) only. According to measurements at low T, adsorption in registry with the bridging O seems to be kinetically hindered. Distinct differences between high- and low T adsoption types are found for ISS, STM, \\varphi and Cl-2p bonding energies, in excellent agreement between calculations and experiment.

  19. Atomically resolved STM images of carbon nanotube defects produced by Ar+ irradiation

    NASA Astrophysics Data System (ADS)

    Osváth, Z.; Vértesy, G.; Tapasztó, L.; Wéber, F.; Horváth, Z. E.; Gyulai, J.; Biró, L. P.

    2005-07-01

    Multiwall carbon nanotubes (MWCNTs) dispersed on graphite on highly oriented pyrolytic graphite (HOPG) substrate were irradiated with Ar+ ions of 30keV . The irradiated samples were investigated by scanning tunneling microscopy (STM) and spectroscopy (STS) in air. The irradiation-induced defects appear as hillocklike protrusions on the nanotube walls, similar to the hillocks observed earlier on ion irradiated HOPG. The results are in agreement with recent predictions, which attribute the STM features produced by ion irradiation to local modifications of the electronic structure. “ 3×3R ” type superstructures are also observed near some of the defects. After annealing at 450°C in nitrogen atmosphere, the irradiated MWCNTs were investigated again by STM. The effect of heat treatment on the irradiation-induced nanotube defects is also discussed.

  20. Acoustic Test Prediction and Correlation for the SGEO Satellite Platform STM Model

    NASA Astrophysics Data System (ADS)

    Ruess, Florian; Segelke, Harald; Obst, Andreas; Rubio, Alberto

    2014-06-01

    Spacecraft structural designs have to be designed and verified for a number of mechanical environments, namely:- Quasi-static loads- Sinusoidal vibration- Acoustic Noise- ShockThe environments are present during launch or due to activation of spacecraft equipment.The paper presents the Structural Thermal Model (STM) acoustic test prediction vibration analysis performed in the frame of the SGEO satellite project and the analysis correlation to STM test results.For the analysis the same Finite Element Model (FEM) as for the sinusoidal vibration analysis has been used. Then the FEM has been exposed to an acoustic field using the boundary element method (BEM) based on the program code Rayon, which is included in the vibro- acoustic pre/post processor VA One.Analysis results have been compared with STM test results and a very good correlation as well as confirmation of the baseline assumptions has been found.

  1. 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.

  2. Magnetic field enhanced nano-tip fabrication for four-probe STM studies.

    PubMed

    McKendry, J E; Allen, C S; Critchley, K; Górzny, M L; Walton, A S; Evans, S D

    2008-02-27

    We present an improved method for fabricating tungsten STM tips for measuring nanoscale objects using a multiprobe STM. The tips were prepared by a 'drop-off' technique combined with a magnetic field. For magnetic field strengths above 150 Oe the electrolyte was seen to rotate about the tungsten anode. This rotation reduced the adhesion of bubbles and led to a reduction in the cone angle of the tips produced. This property is advantageous for multiprobe measurements as it allows one to bring multiple tips into close proximity.

  3. Impurity in a d-wave superconductor: Kondo effect and STM spectra.

    PubMed

    Polkovnikov, A; Sachdev, S; Vojta, M

    2001-01-08

    We present a theory for recent STM studies of Zn impurities in the superconductor Bi2Sr2CaCu2O8+delta, using insights from NMR experiments which show that there is a net S = 1/2 moment on the Cu ions near the Zn. We argue that the Kondo spin dynamics of this moment is the origin of the low bias peak in the differential conductance, rather than a resonance in a purely potential scattering model. The spatial and energy dependence of the STM spectra of our model can also fit the experiments.

  4. Using STM to understand diffraction oscillations for Fe growth on Cu(100)

    NASA Astrophysics Data System (ADS)

    Chambliss, David D.; Johnson, Kevin E.

    1994-07-01

    The relationship between diffraction intensity variations and topography measured with the scanning tunneling microscope (STM) is examined quantitatively, for room-temperature growth of Fe on Cu(100). Predictions from STM data based on kinematical formulas yield good agreement with the experimental medium-energy electron diffraction (MEED) results of Thomassen et al. [Surf. Sci. 264 (1992) 406]. The agreement demonstrates the similarity of samples prepared in the different laboratories, the applicability of kinematical analysis to MEED oscillations, and the importance of identifying and understanding the characteristic lengths of the sample and the measurement.

  5. In situ STM studies of electrochemically polished Cd(0001) electrode in aqueous electrolyte solutions

    NASA Astrophysics Data System (ADS)

    Pikma, P.; Grozovski, V.; Kasuk, H.; Lust, E.

    2014-10-01

    The in situ STM studies of electrochemically polished Cd(0001) electrode in the H3PO4 aqueous solution have been performed under negative electrode potentials from - 1.4 to - 0.9 V (versus Ag|AgCl in sat. KCl aqueous solution) in the 0.1 M Na2SO4 + 1 × 10- 5 M H2SO4 aqueous solution. The atomic resolution parameters of Cd(0001) surface have been calculated. The in situ STM data show that there are no surface reconstruction processes and the surface structure of electrochemically polished Cd(0001) is stable within the potential region investigated.

  6. Synthesis and STM imaging of symmetric and dissymmetric ethynyl-bridged dimers of boron-subphthalocyanine bowl-shaped nanowheels.

    PubMed

    Jacquot de Rouville, Henri-Pierre; Garbage, Romain; Ample, Francisco; Nickel, Anja; Meyer, Joerg; Moresco, Francesca; Joachim, Christian; Rapenne, Gwénaël

    2012-07-16

    The future's wheel: A new class of wheels, based on subphthalocyanine fragments, for future incorporation in functional nanovehicles is reported (see figure). The syntheses of a symmetric wheel, a nitrogen-tagged wheel, and their ethynyl-bridged homodimers are presented. Theoretical calculations and STM imaging demonstrate the advantage of a bowl-shaped structure and the efficiency of the tag for STM imaging.

  7. High-quality draft genome sequence of Rhizobium mesoamericanum strain STM6155, a Mimosa pudica microsymbiont from New Caledonia.

    PubMed

    Klonowska, Agnieszka; López-López, Aline; Moulin, Lionel; Ardley, Julie; Gollagher, Margaret; Marinova, Dora; Tian, Rui; Huntemann, Marcel; Reddy, T B K; Varghese, Neha; Woyke, Tanja; Markowitz, Victor; Ivanova, Natalia; Seshadri, Rekha; Baeshen, Mohamed N; Baeshen, Nabih A; Kyrpides, Nikos; Reeve, Wayne

    2017-01-01

    Rhizobium mesoamericanum STM6155 (INSCD = ATYY01000000) is an aerobic, motile, Gram-negative, non-spore-forming rod that can exist as a soil saprophyte or as an effective nitrogen fixing microsymbiont of the legume Mimosa pudica L.. STM6155 was isolated in 2009 from a nodule of the trap host M. pudica grown in nickel-rich soil collected near Mont Dore, New Caledonia. R. mesoamericanum STM6155 was selected as part of the DOE Joint Genome Institute 2010 Genomic Encyclopedia for Bacteria and Archaea-Root Nodule Bacteria (GEBA-RNB) genome sequencing project. Here we describe the symbiotic properties of R. mesoamericanum STM6155, together with its genome sequence information and annotation. The 6,927,906 bp high-quality draft genome is arranged into 147 scaffolds of 152 contigs containing 6855 protein-coding genes and 71 RNA-only encoding genes. Strain STM6155 forms an ANI clique (ID 2435) with the sequenced R. mesoamericanum strain STM3625, and the nodulation genes are highly conserved in these strains and the type strain of Rhizobium grahamii CCGE501(T). Within the STM6155 genome, we have identified a chr chromate efflux gene cluster of six genes arranged into two putative operons and we postulate that this cluster is important for the survival of STM6155 in ultramafic soils containing high concentrations of chromate.

  8. 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…

  9. 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…

  10. High-quality draft genome sequence of Rhizobium mesoamericanum strain STM6155, a Mimosa pudica microsymbiont from New Caledonia

    DOE PAGES

    Klonowska, Agnieszka; López-López, Aline; Moulin, Lionel; ...

    2017-01-17

    Rhizobium mesoamericanum STM6155 (INSCD=ATYY01000000) is an aerobic, motile, Gram-negative, non-spore-forming rod that can exist as a soil saprophyte or as an effective nitrogen fixing microsymbiont of the legume Mimosa pudica L.. STM6155 was isolated in 2009 from a nodule of the trap host M. pudica grown in nickel-rich soil collected near Mont Dore, New Caledonia. R. mesoamericanum STM6155 was selected as part of the DOE Joint Genome Institute 2010 Genomic Encyclopedia for Bacteria and Archaea-Root Nodule Bacteria (GEBA-RNB) genome sequencing project. Here we describe the symbiotic properties of R. mesoamericanum STM6155, together with its genome sequence information and annotation. Themore » 6,927,906bp high-quality draft genome is arranged into 147 scaffolds of 152 contigs containing 6855 protein-coding genes and 71 RNA-only encoding genes. Strain STM6155 forms an ANI clique (ID 2435) with the sequenced R. mesoamericanum strain STM3625, and the nodulation genes are highly conserved in these strains and the type strain of Rhizobium grahamii CCGE501 T . Within the STM6155 genome, we have identified a chr chromate efflux gene cluster of six genes arranged into two putative operons and we postulate that this cluster is important for the survival of STM6155 in ultramafic soils containing high concentrations of chromate.« less

  11. 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…

  12. Majorana STM as a perfect detector of odd-frequency superconductivity

    NASA Astrophysics Data System (ADS)

    Kashuba, Oleksiy; Sothmann, Björn; Burset, Pablo; Trauzettel, Björn

    2017-05-01

    We propose a novel scanning tunneling microscope (STM) device in which the tunneling tip is formed by a Majorana bound state (MBS). This peculiar bound state emerges at the boundary of a one-dimensional topological superconductor. Since the MBS has to be effectively spinless and local, we argue that it is the smallest unit that shows itself the properties of odd-frequency superconducting pairing. Odd-frequency superconductivity is characterized by an anomalous Green's function, which is an odd function of the time arguments of the two electrons building the Cooper pair. Interestingly, our Majorana STM can be used as the perfect detector of odd-frequency superconductivity. The reason is that a supercurrent between the Majorana STM and any other superconductor can only flow if the latter system exhibits itself odd-frequency pairing. To illustrate our general idea, we consider the tunneling problem of the Majorana STM coupled to a quantum dot placed on a surface of a conventional superconductor.

  13. Atomically resolved STM imaging with a diamond tip: simulation and experiment.

    PubMed

    Grushko, V; Lübben, O; Chaika, A N; Novikov, N; Mitskevich, E; Chepugov, A; Lysenko, O; Murphy, B E; Krasnikov, S A; Shvets, I V

    2014-01-17

    The spatial resolution of a scanning tunneling microscope (STM) can be enhanced using light element-terminated probes with spatially localized electron orbitals at the apex atom. Conductive diamond probes can provide carbon atomic orbitals suitable for STM imaging with sub-Ångström lateral resolution and high apex stability crucial for the small tunneling gaps necessary for high-resolution experiments. Here we demonstrate that high spatial resolution can be achieved in STM experiments with single-crystal diamond tips, which are generally only considered for use as probes for atomic force microscopy. The results of STM experiments with a heavily boron-doped, diamond probe on a graphite surface; density functional theory calculations of the tip and surface electronic structure; and first-principles tunneling current calculations demonstrate that the highest spatial resolution can be achieved with diamond tips at tip-sample distances of 3-5 Å when frontier p-orbitals of the tip provide their maximum contribution to the tunneling current. At the same time, atomic resolution is feasible even at extremely small gaps with very high noise in the tunneling current.

  14. 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.

  15. WUS and STM-based reporter genes for studying meristem development in poplar

    USDA-ARS?s Scientific Manuscript database

    We describe the development of a reporter system for monitoring meristem initiation in poplar using promoters of poplar homologs to the meristem-active regulatory genes WUSCHEL (WUS) and SHOOTMERISTEMLESS (STM). When ~3 kb of the 5’ flanking regions of close homologs were used to drive expression o...

  16. 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…

  17. Adsorption of oxygen on Pt{sub 3}Sn(110) studied by STM and LEED

    SciTech Connect

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

    2005-01-15

    The adsorption of oxygen on the Pt{sub 3}Sn(110) alloy surface was studied by means of scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). After exposure to 2300 L O{sub 2} at 750 K LEED shows additional c(2x2) spots with regard to the substrate p(2x1) pattern. This agrees straightforward with STM topographies revealing a thin layer of large protrusions, arranged in a pseudohexagonal lattice. This layer is split into domains separated by distinctive zigzagging boundaries. Post-annealing allowed to partially uncover substrate regions. That way it could be shown that the protrusions are located above Sn locations. Further post-annealing restored the original substrate completely. A model of the adlayer structure consistent with all STM and LEED findings is given. These features observed after high temperature oxygen exposure of the Pt{sub 3}Sn(110) surface resemble to a large extent structures obtained on the Pt{sub 3}Sn(111) surface under similar conditions. The observed structures can be understood in terms of Sn-O entities interacting with each other. However, results from the oxidation of Pt{sub 3}Sn(111) indicate the formation of a Sn layer with chemisorbed oxygen on top, but not of separated SnO{sub x} entities. The protrusion patterns observed with STM on both surfaces are a topographic signature of such Sn-O layers on Pt{sub 3}Sn.

  18. 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…

  19. Low Temperature STM Manipulation and Spectroscopy of Chlorophyll-a Single Molecules from Spinach

    NASA Astrophysics Data System (ADS)

    Benson, Jessica J.; Iancu, Violeta; Deshpande, Aparna; Hla, Saw-Wai

    2004-04-01

    We interrogate single chlorophyll-a, a molecule produced from Spinach, on Cu(111) surface to check its mechanical stability and electronic properties using an ultra-high-vacuum low-temperature scanning-tunneling-microscope (UHV-LT-STM) at liquid helium temperatures. The measured results of isolated single chlorophyll-a molecules are then compared with that of self-assembled molecular layer. The tunneling I/V and dI/dV spectroscopy techniques are used to probe the electronic properties of the chlorophyll-a molecule with atomic precision (1). These spectroscopic investigations elucidate properties of the single molecule such as the band gap and additional molecular orbital states. Mechanical stability of the chlorophyll-a molecule is examined using lateral manipulation techniques with the STM tip (2). In this procedure, the STM tip is placed in close proximity to the molecule (just a few angstrom separation) to increase the tip-molecule interaction. Then the tip is laterally moved across the surface, which results in pulling of the chlorophyll-a molecule to relocate to the specific surface sites. The detailed molecule movement during this manipulation is directly monitored through the corresponding STM-tip height signals. Our results highlight that the Spinach molecule is a promising candidate for environmental friendly nano-electronic device applications. (1) F. Moresco et al, Phy. Rev. Lett. 86, 672-675, (2001) (2) S-W. Hla, K-H. Rieder, Ann. Phy. Chem. 54, 307-330, (2003)

  20. Chemistry at the square nanometer: reactivity at liquid/solid interfaces revealed with an STM.

    PubMed

    Münninghoff, Joris A W; Elemans, Johannes A A W

    2017-02-02

    For more than three decades the scanning tunnelling microscope (STM) has proven to be an indispensable tool to image molecules adsorbed at a surface at the highest detail possible. In addition to simply imaging molecules, STM can also be applied to monitor dynamic surface phenomena, including chemical reactions. By studying reactions at a surface at the single molecule level, unique information about reaction mechanisms can be obtained which remains hidden when conventional ensemble techniques are used. Many STM studies of chemical reactions have been performed in extreme environments like ultrahigh vacuum or high pressure chambers, but these are far removed from conditions in which most chemical and biological processes take place, i.e., in a liquid at ambient atmospheres. This feature paper highlights the developments in the relatively unexplored research area of investigating chemical reactions with an STM at a liquid/solid interface under ambient conditions. Covalent couplings between molecules, light-induced isomerisations, reactions under electrochemical control, and complex multistep processes and catalysis are discussed.

  1. Innovations in Scholarly Electronic Journals: The Challenge from Nontraditional STM Publishers (SIG PUB, SIG STI).

    ERIC Educational Resources Information Center

    Panagopoulos, Beata; Chu, Heting

    2000-01-01

    Presents an abstract of a planned session on costs of STM (scientific, technical and medical) journals and how the Web is providing alternative, nontraditional publishing options. Highlights include the impact on libraries; pricing and licensing; additional services such as selective dissemination of information; and archival, publishing,…

  2. Short-Term Memory (STM) Constraints in Children with Specific Language Impairment (SLI): Are There Differences between Receptive and Expressive SLI?

    ERIC Educational Resources Information Center

    Nickisch, Andreas; von Kries, Rudiger

    2009-01-01

    Purpose: Specific language impairment (SLI) is assumed to be causally related to deficits in auditory short-term memory (STM). Although verbal STM deficits have been consistently found in SLI, the results of visual STM tests are inconsistent. Do these inconsistencies reflect different study populations of expressive SLI (ELI) and…

  3. Short-Term Memory (STM) Constraints in Children with Specific Language Impairment (SLI): Are There Differences between Receptive and Expressive SLI?

    ERIC Educational Resources Information Center

    Nickisch, Andreas; von Kries, Rudiger

    2009-01-01

    Purpose: Specific language impairment (SLI) is assumed to be causally related to deficits in auditory short-term memory (STM). Although verbal STM deficits have been consistently found in SLI, the results of visual STM tests are inconsistent. Do these inconsistencies reflect different study populations of expressive SLI (ELI) and…

  4. 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.

  5. Theory of STM junctions for π-conjugated molecules on thin insulating films

    NASA Astrophysics Data System (ADS)

    Sobczyk, Sandra; Donarini, Andrea; Grifoni, Milena

    2012-05-01

    A microscopic theory of the transport in a scanning tunneling microscope (STM) setup is introduced for π-conjugated molecules on insulating films, based on the density matrix formalism. A key role is played in the theory by the energy dependent tunneling rates which account for the coupling of the molecule to the tip and to the substrate. In particular, we analyze how the geometrical differences between the localized tip and extended substrate are encoded in the tunneling rate and influence the transport characteristics. Finally, using benzene as an example of a planar, rotationally symmetric molecule, we calculate the STM current-voltage characteristics and current maps and analyze them in terms of few relevant angular momentum channels.

  6. Automated extraction of single H atoms with STM: tip state dependency.

    PubMed

    Møller, Morten; Jarvis, Samuel P; Guérinet, Laurent; Sharp, Peter; Woolley, Richard; Rahe, Philipp; Moriarty, Philip

    2017-02-17

    The atomistic structure of the tip apex plays a crucial role in performing reliable atomic-scale surface and adsorbate manipulation using scanning probe techniques. We have developed an automated extraction routine for controlled removal of single hydrogen atoms from the H:Si(100) surface. The set of atomic extraction protocols detect a variety of desorption events during scanning tunneling microscope (STM)-induced modification of the hydrogen-passivated surface. The influence of the tip state on the probability for hydrogen removal was examined by comparing the desorption efficiency for various classifications of STM topographs (rows, dimers, atoms, etc). We find that dimer-row-resolving tip apices extract hydrogen atoms most readily and reliably (and with least spurious desorption), while tip states which provide atomic resolution counter-intuitively have a lower probability for single H atom removal.

  7. 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.

  8. Liquid fueled external heating system for STM4-120 Stirling engine

    NASA Astrophysics Data System (ADS)

    Meijer, R. J.; Ziph, B.; Godett, T. M.

    1985-12-01

    The STM4-120 Stirling engine, currently under development at Stirling Thermal Motors, Inc., is a 40 kW variable stroke engine with indirect heating using a sodium heat pipe. The engine is functionally separated into an application independent Energy Conversion Unit (ECU) consisting of the Stirling cycle and drive heated by condensing sodium and the application dependent External Heating System (EHS), designed to supply the ECU with sodium vapor heated by the particular energy source, connected by tubes with mechanical couplings. This paper describes an External Heating System for the STM4-120 ECU designed for the combustion of liquid fuel, comprised of a recuperative preheater, a combustion chamber, and a heat exchanger/evaporator where heat is transferred from the flue gas to the sodium causing it to evaporate. The design concept and projected performance are described and discussed.

  9. 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.

  10. STM characterization of DNA immobilized via Zr ion glue onto gold thiol SAMs

    NASA Astrophysics Data System (ADS)

    Pourbeyram, S.; Shervedani, R. K.; Sabzyan, H.

    2013-10-01

    In this paper layer-by-layer (LBL) assembly of calf thymus DNA (ct-DNA) onto gold-mercaptopropionic acid self-assembled monolayer via Zr(IV) ion glue, Au-MPA-Zr(IV)-ct-DNA SAM, is monitored by scanning tunneling microscopy (STM) technique. The STM images of Au-MPA-Zr(IV) template show well-organized arrays of rod-like peaks. ct-DNA has been immobilized on the Au-MPA-Zr(IV) surface in hilly forms, implying globular structure for the immobilized ct-DNA. This immobilization strategy offers a simple and fast method to prepare the Au-MPA-Zr(IV)-ct-DNA template with promising applications for immobilization and study of the other compounds.

  11. Automated extraction of single H atoms with STM: tip state dependency

    NASA Astrophysics Data System (ADS)

    Møller, Morten; Jarvis, Samuel P.; Guérinet, Laurent; Sharp, Peter; Woolley, Richard; Rahe, Philipp; Moriarty, Philip

    2017-02-01

    The atomistic structure of the tip apex plays a crucial role in performing reliable atomic-scale surface and adsorbate manipulation using scanning probe techniques. We have developed an automated extraction routine for controlled removal of single hydrogen atoms from the H:Si(100) surface. The set of atomic extraction protocols detect a variety of desorption events during scanning tunneling microscope (STM)-induced modification of the hydrogen-passivated surface. The influence of the tip state on the probability for hydrogen removal was examined by comparing the desorption efficiency for various classifications of STM topographs (rows, dimers, atoms, etc). We find that dimer-row-resolving tip apices extract hydrogen atoms most readily and reliably (and with least spurious desorption), while tip states which provide atomic resolution counter-intuitively have a lower probability for single H atom removal.

  12. 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.

  13. STM and STS investigation of few-wall carbon nanotubes containing non-hexagonal rings

    NASA Astrophysics Data System (ADS)

    Osvath, Zoltan; Fulcheri, Laurent; Mark, Geza I.; Tapaszto, Levente; Gyulai, Jozsef; Biro, Laszlo P.

    2003-04-01

    We performed scanning tunneling microscopy (STM) measurements on few wall carbon nanotubes that exhibited changing diameter. Such change in the diameter may occur if non-hexagonal carbon ring configurations are introduced in the nanotube walls. A few-walled nanotube knee of 4 degrees, with different diameter values on the two sides of the knee was imaged by STM. Theoretical model structures [1] of single-wall carbon nanotubes show that a bend of 4 degrees may occur when a pentagonal and a heptagonal carbon ring is incorporated side by side in the hexagonal nanotube structure. Scanning tunneling spectroscopic (STS) measurements show that additional electronic states are present in the energy gap in the region where the bend occurs. We also performed STS measurements on a single-wall nanotube with conical tip. In agreement with theory, the results show that the energy gap in the tapered end is larger than in the nanotube.

  14. Arc-grown Y-branched carbon nanotubes observed by scanning tunneling microscopy (STM)

    NASA Astrophysics Data System (ADS)

    Osváth, Z.; Koós, A. A.; Horváth, Z. E.; Gyulai, J.; Benito, A. M.; Martínez, M. T.; Maser, W. K.; Biró, L. P.

    2002-10-01

    Scanning tunneling microscopy (STM) observation of Y-branched carbon nanotubes produced by the arc-discharge method is reported. A drilled out graphite rod filled with a nickel/yttrium particle mixture was used as anode in the arc chamber under He atmosphere of 660-mbar pressure. Straight multi-wall nanotubes and asymmetrical Y-branches were found in a sample taken from the cathodic deposit. As measured by STM the Y-junctions have low apparent heights in the range of 1 nm. This may be an indication that these nanotubes have only few walls, or possibly they are single-walled. The asymmetrical Y-branches found in this experiment may be related to the additional use of metals or/and to changed temperature conditions on the cathode side due to the switch-off of the cathode water-cooling.

  15. 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.

  16. Surface sensitivity of four-probe STM resistivity measurements of bulk ZnO correlated to XPS

    NASA Astrophysics Data System (ADS)

    Lord, Alex M.; Evans, Jonathan E.; Barnett, Chris J.; Allen, Martin W.; Barron, Andrew R.; Wilks, Steve P.

    2017-09-01

    Multi-probe instruments based on scanning tunnelling microscopy (STM) are becoming increasingly common for their ability to perform nano- to atomic-scale investigations of nanostructures, surfaces and in situ reactions. A common configuration is the four-probe STM often coupled with in situ scanning electron microscopy (SEM) that allows precise positioning of the probes onto surfaces and nanostructures enabling electrical and scanning experiments to be performed on highly localised regions of the sample. In this paper, we assess the sensitivity of four-probe STM for in-line resistivity measurements of the bulk ZnO surface. The measurements allow comparisons to established models that are used to relate light plasma treatments (O and H) of the surfaces to the resistivity measurements. The results are correlated to x-ray photoelectron spectroscopy (XPS) and show that four-probe STM can detect changes in surface and bulk conduction mechanisms that are beyond conventional monochromatic XPS.

  17. The ethylene pathway contributes to root hair elongation induced by the beneficial bacteria Phyllobacterium brassicacearum STM196.

    PubMed

    Galland, Marc; Gamet, Lydia; Varoquaux, Fabrice; Touraine, Brigitte; Touraine, Bruno; Desbrosses, Guilhem

    2012-07-01

    In Arabidopsis roots, some epidermal cells differentiate into root hair cells. Auxin regulates root hair positioning, while ethylene controls cell elongation. Phyllobacterium brassicacearum STM196, a beneficial strain of plant growth promoting rhizobacteria (PGPR) isolated from the roots of field-grown oilseed rape, stimulates root hair elongation in Arabidopsis thaliana seedlings. We investigated the role of ethylene in the response of root hair cells to STM196 inoculation. While we could not detect a significant increase in ethylene biosynthesis, we could detect a slight activation of the ethylene signalling pathway. Consistent with this, an exhaustive survey of the root hair elongation response of mutants and transgenic lines affected in the ethylene pathway showed contrasting root hair sensitivities to STM196. We propose that local ethylene emission contributes to STM196-induceed root hair elongation.

  18. An in situ STM and DTS study of the extremely pure [EMIM]FAP/Au(111) interface.

    PubMed

    Borisenko, Natalia; Zein El Abedin, Sherif; Endres, Frank

    2012-05-14

    Herein the structure of the interfacial layer between the air- and water-stable ionic liquid 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIM]FAP) and Au(111) is investigated using in situ scanning tunneling microscopy (STM), distance tunneling spectroscopy (DTS) and cyclic voltammetry (CV) measurements. The in situ STM measurements reveal that structured interfacial layers can be probed in both cathodic and anodic regimes at the IL/Au(111) interface. The structure of these layers is dependent on the applied electrode potential, the number of subsequent STM scans and the scan rate. Furthermore, first DTS results show that the tunneling barrier during the 1st STM scan does not seem to change significantly in the cathodic potential regime between the ocp (-0.2 V) and -2.0 V.

  19. Analysis of STM images with pure and CO-functionalized tips: A first-principles and experimental study

    NASA Astrophysics Data System (ADS)

    Gustafsson, Alexander; Okabayashi, Norio; Peronio, Angelo; Giessibl, Franz J.; Paulsson, Magnus

    2017-08-01

    We describe a first-principles method to calculate scanning tunneling microscopy (STM) images, and compare the results to well-characterized experiments combining STM with atomic force microscopy (AFM). The theory is based on density functional theory with a localized basis set, where the wave functions in the vacuum gap are computed by propagating the localized-basis wave functions into the gap using a real-space grid. Constant-height STM images are computed using Bardeen's approximation method, including averaging over the reciprocal space. We consider copper adatoms and single CO molecules adsorbed on Cu(111), scanned with a single-atom copper tip with and without CO functionalization. The calculated images agree with state-of-the-art experiments, where the atomic structure of the tip apex is determined by AFM. The comparison further allows for detailed interpretation of the STM images.

  20. Surface sensitivity of four-probe STM resistivity measurements of bulk ZnO correlated to XPS.

    PubMed

    Lord, Alex M; Evans, Jonathan E; Barnett, Chris J; Allen, Martin W; Barron, Andrew R; Wilks, Steve P

    2017-09-27

    Multi-probe instruments based on scanning tunnelling microscopy (STM) are becoming increasingly common for their ability to perform nano- to atomic-scale investigations of nanostructures, surfaces and in situ reactions. A common configuration is the four-probe STM often coupled with in situ scanning electron microscopy (SEM) that allows precise positioning of the probes onto surfaces and nanostructures enabling electrical and scanning experiments to be performed on highly localised regions of the sample. In this paper, we assess the sensitivity of four-probe STM for in-line resistivity measurements of the bulk ZnO surface. The measurements allow comparisons to established models that are used to relate light plasma treatments (O and H) of the surfaces to the resistivity measurements. The results are correlated to x-ray photoelectron spectroscopy (XPS) and show that four-probe STM can detect changes in surface and bulk conduction mechanisms that are beyond conventional monochromatic XPS.

  1. Electronic structure of Ge(111)c(2×8) : STM, angle-resolved photoemission, and theory

    NASA Astrophysics Data System (ADS)

    Razado-Colambo, I.; He, Jiangping; Zhang, H. M.; Hansson, G. V.; Uhrberg, R. I. G.

    2009-05-01

    The surface electronic structure of Ge(111)c(2×8) was studied by experimental techniques [low-energy electron diffraction, scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES)] and theoretical band-structure calculations. Bias-dependent STM images exhibit two different types of adatoms (AT,AR) and rest atoms (RT,RR) confirming the presence of asymmetries within the c(2×8) cell. The ARPES study resulted in a more detailed picture of the surface electronic structure of the Ge(111)c(2×8) surface compared to earlier studies. The energy dispersion curves showed the presence of seven surface bands labeled A1, A2, A2' , A3, A4, A4' , and A5. The experimental surface bands were compared to the calculated band structure of the full c(2×8) unit cell. The most important results are (i) we have identified a split surface-state band in the photoemission data that matches a split between RT and RR derived rest atom bands in the calculated surface band structure. This allows us to identify the upper A2 band with the RR and the lower A2' band with the RT rest atoms. (ii) The uppermost highly dispersive band (A1) originates from states below the adatom and rest atom layers and should not be confused with rest atom bands A2 and A2' . (iii) The bias-dependent changes in the adatom/rest atom contrast in the experimental STM images were closely reproduced by simulated STM images generated from the calculated electronic structure. (iv) A split was observed in the back-bond derived surface band at higher emission angles (A4 and A4' ).

  2. Electron tunneling using STM/STS on iron-based oxypnictides

    NASA Astrophysics Data System (ADS)

    Kawashima, Yuuki; Ichimura, Koichi; Kurosawa, Toru; Oda, Migaku; Tanda, Satoshi; Takahashi, Hiroki; Okada, Hironari; Kamihara, Yoichi; Hosono, Hideo

    2010-12-01

    We report the electron tunneling study on SmFeAsO1-xFx (x = 0, 0.045, 0.046, 0.069) by using low temperature UHV-STM/STS. The superconducting gap and pseudogap structures are observed on x = 0.045, 0.046, 0.069. We also found similar structures on non-superconducting sample of x = 0. The value of 2Δ/kT decreases as T increases.

  3. Ethylene dissociation on flat and stepped Ni(1 1 1): A combined STM and DFT study

    NASA Astrophysics Data System (ADS)

    Vang, Ronnie T.; Honkala, Karoliina; Dahl, Søren; Vestergaard, Ebbe K.; Schnadt, Joachim; Lægsgaard, Erik; Clausen, Bjerne S.; Nørskov, Jens K.; Besenbacher, Flemming

    2006-01-01

    The dissociative adsorption of ethylene (C 2H 4) on Ni(1 1 1) was studied by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The STM studies reveal that ethylene decomposes exclusively at the step edges at room temperature. However, the step edge sites are poisoned by the reaction products and thus only a small brim of decomposed ethylene is formed. At 500 K decomposition on the (1 1 1) facets leads to a continuous growth of carbidic islands, which nucleate along the step edges. DFT calculations were performed for several intermediate steps in the decomposition of ethylene on both Ni(1 1 1) and the stepped Ni(2 1 1) surface. In general the Ni(2 1 1) surface is found to have a higher reactivity than the Ni(1 1 1) surface. Furthermore, the calculations show that the influence of step edge atoms is very different for the different reaction pathways. In particular the barrier for dissociation is lowered significantly more than the barrier for dehydrogenation, and this is of great importance for the bond-breaking selectivity of Ni surfaces. The influence of step edges was also probed by evaporating Ag onto the Ni(1 1 1) surface. STM shows that the room temperature evaporation leads to a step flow growth of Ag islands, and a subsequent annealing at 800 K causes the Ag atoms to completely wet the step edges of Ni(1 1 1). The blocking of the step edges is shown to prevent all decomposition of ethylene at room temperature, whereas the terrace site decomposition at 500 K is confirmed to be unaffected by the Ag atoms. Finally a high surface area NiAg alloy catalyst supported on MgAl 2O 4 was synthesized and tested in flow reactor measurements. The NiAg catalyst has a much lower activity for ethane hydrogenolysis than a similar Ni catalyst, which can be rationalized by the STM and DFT results.

  4. Enhancement of the spin transfer torque efficiency in magnetic STM junctions

    NASA Astrophysics Data System (ADS)

    Palotás, Krisztián; Mándi, Gábor; Szunyogh, László

    2016-08-01

    We introduce a method for a combined calculation of charge and vector spin transport of elastically tunneling electrons in magnetic scanning tunneling microscopy (STM). The method is based on the three-dimensional Wentzel-Kramers-Brillouin (3D-WKB) approach combined with electronic structure calculations using first-principles density functional theory. As an application, we analyze the STM contrast inversion of the charge current above the Fe/W(110) surface depending on the bias voltage, tip-sample distance, and relative magnetization orientation between the sample and an iron tip. For the spin transfer torque (STT) vector we find that its in-plane component is generally larger than the out-of-plane component, and we identify a longitudinal spin current component, which, however, does not contribute to the torque. Our results suggest that the torque-current relationship in magnetic STM junctions follows the power law rather than a linear function. Consequently, we show that the ratio between the STT and the spin-polarized charge current is not constant, and more importantly, it can be tuned by the bias voltage, tip-sample distance, and magnetization rotation. We find that the STT efficiency can be enhanced by about a factor of seven by selecting a proper bias voltage. Thus, we demonstrate the possible enhancement of the STT efficiency in magnetic STM junctions, which can be exploited in technological applications. We discuss our results in view of the indirect measurement of the STT above the Fe/W(110) surface reported by S. Krause et al. [Phys. Rev. Lett. 107, 186601 (2011), 10.1103/PhysRevLett.107.186601].

  5. The STM bias voltage-dependent polymorphism of a binary supramolecular network.

    PubMed

    Cometto, F; Frank, K; Stel, B; Arisnabarreta, N; Kern, K; Lingenfelder, M

    2017-10-04

    A Scanning Tunneling Microscope (STM) is used to induce a reversible transition between different polymorphs in a binary supramolecular network at the liquid/solid interface. The transition is driven externally by switching the polarity of the sample by positive or negative sample bias potentials. We demonstrate that by mixing bias-sensitive and non-sensitive molecules, we gain access to a variety of binary porous structures that can be prepared and reliably actuated for each relative concentration.

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

    SciTech Connect

    Dunphy, James Christopher

    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(2xl) 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.

  7. Li-intercalated graphene on SiC(0001): An STM study

    NASA Astrophysics Data System (ADS)

    Fiori, Sara; Murata, Yuya; Veronesi, Stefano; Rossi, Antonio; Coletti, Camilla; Heun, Stefan

    2017-09-01

    We present a systematical study via scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) on the effect of the exposure of lithium on graphene on silicon carbide (SiC). We have investigated Li deposition both on epitaxial monolayer graphene and on buffer layer surfaces on the Si face of SiC. At room temperature, Li immediately intercalates at the interface between the SiC substrate and the buffer layer and transforms the buffer layer into a quasi-free-standing graphene. This conclusion is substantiated by LEED and STM evidence. We show that intercalation occurs through the SiC step sites or graphene defects. We obtain good quantitative agreement between the number of Li atoms deposited and the number of available Si bonds at the surface of the SiC crystal. Through STM analysis, we are able to determine the interlayer distance induced by Li intercalation at the interface between the SiC substrate and the buffer layer.

  8. 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.

  9. Design and Characterization of a millikelvin dual-tip Josephson STM

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    We describe the design and characterization of a dual-tip Josephson STM that operates at millikelvin temperatures. We report an effective noise temperature for the STM on the order of 200 mK. In addition to the expected phase diffusive super current in the ultra-small Nb-Nb junction formed by one tip and the sample, our high resolution spectroscopy at mK temperatures reveals resonant coupling between the STM junction and the electromagnetic environment it is embedded in, as predicted by P(E) theory. We have for the first time, observed Shapiro-like steps in this limit by measuring the response of the P(E) supercurrent to microwave radiation as a function of amplitude. Fits to theory indicate that the coupling of an ultra-small Josephson junction to its environment/circuit may be used to a) directly measure dissipation channels associated with circuit resonances and b) calibrate the frequency dependent microwave attenuation in cryogenic circuits as seen by the junction.

  10. Graphene flakes obtained by local electro-exfoliation of graphite with a STM tip.

    PubMed

    Rubio-Verdú, C; Sáenz-Arce, G; Martinez-Asencio, J; Milan, D C; Moaied, M; Palacios, J J; Caturla, M J; Untiedt, C

    2017-03-15

    Graphite surfaces can be manipulated by several methods to create graphene structures of different shapes and sizes. Scanning tunneling microscopy (STM) can be used to create these structures either through mechanical contact between the tip and the surface or through electro-exfoliation. In the latter, the mechanisms involved in the process of exfoliation at an applied voltage are not fully understood. Here, we show how a graphite surface can be locally exfoliated in a systematic manner by applying an electrostatic force with a STM tip at the edge of a terrace, forming triangular flakes several nanometers in length. We demonstrate, through experiments and simulations, how these flakes are created by a two-step process: first a voltage ramp must be applied at the edge of the terrace, and then the tip must be scanned perpendicular to the edge. Ab initio electrostatic calculations reveal that the presence of charges on the graphite surface weakens the interaction between layers allowing for exfoliation at voltages in the same range as those used experimentally. Molecular dynamics simulations show that a force applied locally on the edge of a step produces triangular flakes such as those observed under STM. Our results provide new insights into surface modification that can be extended to other layered materials.

  11. 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.

  12. STM Observation of Molecular Adsorption on Graphene and Nitrogen Doped Graphene

    NASA Astrophysics Data System (ADS)

    Obata, Seiji; Saiki, Koichiro

    2014-03-01

    Carbon alloy catalyst (CAC) shows catalytic activity to oxygen reduction reaction (ORR) and it is expected as a substitution of Pt in fuel cells due to its catalytic property. At present CAC are synthesized by burning organic compounds which contain nitrogen atoms such as phthalocyanine. The catalytic activity of CAC is lower than Pt. Since catalytic sites and oxygen reduction process is still unknown, elucidation of catalytic sites of CAC helps to synthesize high performance CAC. STM is a useful tool to investigate adsorption and reaction at atomic level. However, disordered structure of CAC makes it difficult to use STM for catalytic site observation. To overcome this difficulty, we synthesized nitrogen doped graphene (NG) and and pristine graphene (PG) on Pt (111) and used it as model catalyst to study the catalytic property of CAC. Oxygen adsorption is the first step of oxygen reduction reaction. Therefore we investigated the oxygen adsorption to NG and PG by STM. Oxygen adsorbed at domain boundary (DB) of NG?According to XPS measurement nitrogen atoms exist at edge site preferably. These results indicate that nitrogen atom enhances oxygen adsorption activity. In addition, actual reaction process occurs in H2O. Thus we also investigated H2O adsorption on NG.

  13. 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

    2013-09-04

    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).

  14. Structure Determination of Au on Pt(111) Surface: LEED, STM and DFT Study

    PubMed Central

    Krupski, Katarzyna; Moors, Marco; Jóźwik, Paweł; Kobiela, Tomasz; Krupski, Aleksander

    2015-01-01

    Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations have been used to investigate the atomic and electronic structure of gold deposited (between 0.8 and 1.0 monolayer) on the Pt(111) face in ultrahigh vacuum at room temperature. The analysis of LEED and STM measurements indicates two-dimensional growth of the first Au monolayer. Change of the measured surface lattice constant equal to 2.80 Å after Au adsorption was not observed. Based on DFT, the distance between the nearest atoms in the case of bare Pt(111) and Au/Pt(111) surface is equal to 2.83 Å, which gives 1% difference in comparison with STM values. The first and second interlayer spacing of the clean Pt(111) surface are expanded by +0.87% and contracted by −0.43%, respectively. The adsorption energy of the Au atom on the Pt(111) surface is dependent on the adsorption position, and there is a preference for a hollow fcc site. For the Au/Pt(111) surface, the top interlayer spacing is expanded by +2.16% with respect to the ideal bulk value. Changes in the electronic properties of the Au/Pt(111) system below the Fermi level connected to the interaction of Au atoms with Pt(111) surface are observed.

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

    DOE PAGES

    Yan, Hui; Cummings, Marvin; Camino, Fernando; ...

    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

  16. 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.

  17. Hydrogen adsorption and mass flow on aluminum surfaces: Combined STM-infrared study

    NASA Astrophysics Data System (ADS)

    Go, Eden Parreno

    The influence of chemical adsorbates on surfaces is an important aspect of interface stability and chemical reactivity. This thesis addresses the adsorption properties of H and its effects on the equilibrium and dynamical properties on Al(111) surfaces. Using a combination of scanning tunneling microscopy (STM) and infrared reflection absorption spectroscopy (IRRAS) as probes, I observe dramatic changes in the surface morphology that occur upon hydrogen adsorption. I determine that gaseous H reacts directly with the surface by extracting surface atoms and initiates the formation of mobile ad-Al-H species that undergo a sequence of condensation and etching reactions to form molecular alanes that range from monomer to 30-mers in size. From IRRAS measurements, I establish the aluminum-hydrogen speciation as a function of coverage. Following adsorption, H preferentially occupies atop sites along the step edge, thereby modifying the properties of crystallographic steps. Using STM, I determine the influence of submonolayer coverages of H on the stability and kinetics of steps on Al(111) at room temperature. I determine that H raises the mobility of steps on the surface by lowering the kink and adatom formation energies. To determine the dominant mass transport at the step edge near equilibrium, I quantify the step fluctuation by employing the Langevin formalism. From the statistical analysis of step fluctuations, I deduce that the kink diffusion is the dominant mass transport mechanism at the step edge on the clean surface. Upon the adsorption of H, I determine that H amplifies the fluctuation of steps on Al(111) and propose a mechanism for H-induced step motion. Finally, I show that contrast in the STM images of molecular alanes is dependent on the chemical composition of the STM tip apex. Surface alanes are imaged as protrusions with a metallic W tip, but as depressions with an alane-terminated W tip. I observe that the change in contrast in the STM images is

  18. 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.

  19. Organic superconductors revisited. STM imaging and DFT based simulations of the bc plane of κ-(BEDT-TTF)2Cu(NCS)2

    NASA Astrophysics Data System (ADS)

    Rohr, C.; Büttner, J. M.; Palitschka, F. A.; Kushch, N. D.; Kartsovnik, M. V.; Biberacher, W.; Gross, R.; Hermann, B. A.

    2009-05-01

    The surfaces of a ten years aged crystal and a freshly prepared κ-(BEDT-TTF)2Cu(NCS)2 crystal were compared by scanning tunneling microscopy (STM). The molecularly-resolved STM images of the bc plane of the crystals agree with each other and with the electronic contrast obtained by new density functional theory (DFT) based simulations. Even after ten years STM images of the molecular stacking of BEDT-TTF display a variation in brightness at the positions of different molecules. We attribute this symmetry breaking concerning the brightness in the STM images of the otherwise equivalent BEDT-TTF dimers to the electronic states of a relaxed surface.

  20. 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.

  1. Local chemical reaction of benzene on Cu110 via STM-induced excitation.

    PubMed

    Komeda, T; Kim, Y; Fujita, Y; Sainoo, Y; Kawai, Maki

    2004-03-15

    We have investigated the mechanism of the chemical reaction of the benzene molecule adsorbed on Cu(110) surface induced by the injection of tunneling electrons using scanning tunneling microscopy (STM). With the dosing of tunneling electrons of the energy 2-5 eV from the STM tip to the molecule, we have detected the increase of the height of the benzene molecule by 40% in the STM image and the appearance of the vibration feature of the nu(C-H) mode in the inelastic tunneling spectroscopy (IETS) spectrum. It can be understood with a model in which the dissociation of C-H bonds occurs in a benzene molecule that induces a bonding geometry change from flat-lying to up-right configuration, which follows the story of the report of Lauhon and Ho on the STM-induced change of benzene on the Cu(100) surface. [L. J. Lauhon and W. Ho, J. Phys. Chem. A 104, 2463 (2000)]. The reaction probability shows a sharp rise at the sample bias voltage at 2.4 V, which saturates at 3.0 V, which is followed by another sharp rise at the voltage of 4.3 V. No increase of the reaction yield is observed for the negative sample voltage up to 5 eV. In the case of a fully deuterated benzene molecule, it shows the onset at the same energy of 2.4 eV, but the reaction probability is 10(3) smaller than the case of the normal benzene molecule. We propose a model in which the dehydrogenation of the benzene molecule is induced by the formation of the temporal negative ion due to the trapping of the electrons at the unoccupied resonant states formed by the pi orbitals. The existence of the resonant level close to the Fermi level ( approximately 2.4 eV) and multiple levels in less than approximately 5 eV from the Fermi level, indicates a fairly strong interaction of the Cu-pi(*) state of the benzene molecule. We estimated that the large isotope effect of approximately 10(3) can be accounted for with the Menzel-Gomer-Redhead (MGR) model with an assumption of a shallow potential curve for the excited state. (c

  2. Adaptation of acoustic model experiments of STM via smartphones and tablets

    NASA Astrophysics Data System (ADS)

    Thees, Michael; Hochberg, Katrin; Kuhn, Jochen; Aeschlimann, Martin

    2017-10-01

    The importance of Scanning Tunneling Microscopy (STM) in today's research and industry leads to the question of how to include such a key technology in physics education. Manfred Euler has developed an acoustic model experiment to illustrate the fundamental measuring principles based on an analogy between quantum mechanics and acoustics. Based on earlier work we applied mobile devices such as smartphones and tablets instead of using a computer to record and display the experimental data and thus converted Euler's experimental setup into a low-cost experiment that is easy to build and handle by students themselves.

  3. The homoepitaxial growth of Pt on Pt(111) studied with STM

    NASA Astrophysics Data System (ADS)

    Bott, Michael; Michely, Thomas; Comsa, George

    The homoepitaxial growth of Pt on Pt(111) has been investigated by STM and the results have been compared to recent thermal He scattering (TEAS) data obtained on the same system. Additional information on the growth modes is obtained and the real space aspect of the growing surface, which results in TEAS and RHEED oscillations is evidenced. The three different growth modes, including the reentrant layer-by-layer growth at low temperatures, are confirmed. The limited diffusion along the adatom island edges, which causes their fractal aspect with dendritic structures, appears to play a significant role in the appearance of the low temperature layer-by-layer growth.

  4. Excited states at surfaces: Fano profiles in STM spectroscopy of adsorbates.

    PubMed

    Gadzuk, J W; Plihal, M

    2000-01-01

    The Fano-Anderson model for a discrete state embedded within a continuum is revisited within the context of excitation and decay processes which lead to some manifestations of Fano lineshape profiles. The phenomenon of resonance tunneling between an STM tip and a metal surface upon which there are isolated adsorbed atoms is discussed and the relationship between the spectroscopic signature of such systems and that of the Fano profile is taken up. Recent experimental studies of Kondo systems of magnetic adsorbates such as Co and Ce adsorbed on noble metal (111) surfaces have motivated this work.

  5. [Design of portable pressure-pained-detector based on STM32].

    PubMed

    Chen, Xiaojuan; Huo, Xiaoliang; Zhang, Shu

    2014-09-01

    In accordance with the bulky volume and not easy to carry of pain detection equipment limitations, designs a kind of portable high-precision dolorimeter based on STM32. Using the high precision pressure sensor pressure contact as the main body to make the pressure pain signals. Through the signal preprocess of the amplifying circuit and the filter circuit, to eliminate the system noise effectively. Use the TFT-LCD to display the real-time measured pressure value, and establish a pressure pain threshold of the object. The USB interface transmits the data to PC to store, and it's beneficial to the diagnosis and treatment of subsequent.

  6. Self-organized structure of Alanine on Cu(111) Studied with STM

    NASA Astrophysics Data System (ADS)

    Jia, Jinfeng; Xue, Qukun; Seiberling, Liz

    2002-03-01

    There is an increasing interest in the interaction between organic molecules and metal surfaces. One reason for this is that well-ordered biological layers on metal surfaces have many important technological applications in biocatalysis, bioelectronics, biomaterials and nano-technology. The self-organized surface structure of alanine adsorbed on Cu(111) was studied with scanning tunneling microscopy. Well-ordered alanine islands are observed on the Cu(111) surface and the unit cell is about 20A x 20A. Based on our STM images, a structure model is proposed.

  7. Modal Parameter Identification of ATV STM Using Modal and Base Excitation Approaches

    NASA Astrophysics Data System (ADS)

    Wagner, Mark; Grillenbeck, Anton, , Dr.

    2004-08-01

    In 2002, a modal survey and a dynamic qualification test were performed on the structural-thermal model (STM) of the Automated Transfer Vehicle (ATV). These tests were conducted by the European Test Services (ETS) with support of IABG at the test facilities of ESTEC in Noordwijk by order of EADS ST. In order to minimize test duration and set-up complexity, the dynamic qualification test and a classical modal test were planned to be performed within one combined test campaign. The objectives of these tests were the experimental dynamic characteri- zation of the ATV STM structure and its qualification with respect to the ARIANE 5 flight loads.. The results of this dynamic characterization had to be used to verify, respectively to update the mathematical models. This paper focuses on the modal characterisation aspects of these tests. Considering the excitability of the vibration modes of this large test article and the demand to accomplish the modal survey and qualification test in very short time, it was foreseen to combine the modal and the vibration test in a manner, such that with minimum effort, an optimum of modal characterisation could be achieved. In the first part of the test campaign, with its main objective to determine the modal parameters of the lateral ATV modes, the ATV STM was excited by using locally distributed electrodynamic shakers. The modal parameters were determined by applying tuned sine excitation and in addition by a modal analysis of the measured frequency response functions. In the second test sequence, in which the qualification test was performed, the ATV STM was mounted onto the HYDRA vibration test facility. The modal parameter identification for mainly the longitudinal ATV modes was performed by using modal analysis of the recorded structural responses resulting from the applied longitudinal base excitation. Also, the responses of the lateral vibration tests were available for a modal analysis. This paper describes the test set-ups and

  8. 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.

  9. 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.

  10. 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.

  11. Electronic properties and STM images of vacancy clusters and chains in functionalized silicene and germanene

    NASA Astrophysics Data System (ADS)

    Jamdagni, Pooja; Kumar, Ashok; Sharma, Munish; Thakur, Anil; Ahluwalia, P. K.

    2017-01-01

    Electronic properties and STM topographical images of X (=F, H, O) functionalized silicene and germanene have been investigated by introducing various kind of vacancy clusters and chain patterns in monolayers within density functional theory (DFT) framework. The relative ease of formation of vacancy clusters and chain patterns is found to be energetically most favorable in hydrogenated silicene and germanene. F- and H-functionalized silicene and germanene are direct bandgap semiconducting with bandgap ranging between 0.1-1.9 eV, while O-functionalized monolayers are metallic in nature. By introducing various vacancy clusters and chain patterns in both silicene and germanene, the electronic and magnetic properties get modified in significant manner e.g. F- and H-functionalized silicene and germanene with hexagonal and rectangle vacancy clusters are non-magnetic semiconductors with modified bandgap values while pentagonal and triangle vacancy clusters induce metallicity and magnetic character in monolayers; hexagonal vacancy chain patterns induce direct-to-indirect gap transition while zigzag vacancy chain patterns retain direct bandgap nature of monolayers. Calculated STM topographical images show distinctly different characteristics for various type of vacancy clusters and chain patterns which may be used as electronic fingerprints to identify various vacancy patterns in silicene and germanene created during the process of functionalization.

  12. STM Spectroscopy Probe of Field Depairing and Vortex Lattice Transition in a Multiband Superconductor

    NASA Astrophysics Data System (ADS)

    Fridman, I.; Lukic, V.; Kloc, C.; Petrovic, C.; Wei, J. Y. T.

    2014-03-01

    The Cooper pairing in a variety of superconductors involves carriers from multiple bands, which can optimize the pairing phase space and provide novel pairing interactions. We have developed a novel technique to probe multiband pairing, using a directional diamagnetic supercurrent to perturb the quasiparticle density-of-states spectrum, and measuring the spectral evolution due to pair breaking by finite superfluid momentum. This technique is demonstrated on the layered superconductor 2H-NbSe2, using a scanning tunneling microscope (STM) at 300 mK with an in-plane magnetic field up to 9 T. The STM spectroscopy measurements revealed unambiguous evidence for multiband pairing, as well as a novel reorientation transition of the in-plane vortex lattice. We will discuss the first-order and quantum-critical characteristics of this transition, in terms of the geometric frustration of a distorted hexagonal vortex lattice, and show that this transition is intimately related to the multiband pairing. Work supported by NSERC, CFI/OIT, CIFAR, U.S. DOE and Brookhaven Science Associates (No. DE-Ac02-98CH10886).

  13. 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.

  14. Towards bipolar atomic scale dopant devices defined by STM-lithography

    NASA Astrophysics Data System (ADS)

    Fuhrer, Andreas; Köster, Sigrun; Pascher, Nikola

    2015-03-01

    Dopant device fabrication with hydrogen resist lithography has been demonstrated only for n-type dopants. The reason for this is the ease with which phosphorus can be incorporated and activated after gas phase doping with phosphine. Specifically, incorporation on the silicon (001) surface can be achieved at 350°C while keeping the hydrogen resist intact and thus avoiding surface diffusion of the dopants. Here, we present new results on p-type δ-doping of silicon, towards the fabrication of bipolar dopant devices with hydrogen resist lithography. Using diborane as a gas-phase dopant source, Hall bar devices were fabricated to extract hole densities and mobilities in cryogenic magneto-transport experiments. Furthermore, the dependence of these parameters on diborane dose and dopant activation temperatures is investigated. We find that gas-phase doping with diborane is compatible with hydrogen resist lithography and dopant structures can be patterned using the STM. However, activation of the boron dopants currently still leads to significant diffusion and therefore blurring of the patterned devices. We will discuss the prospects of further optimising this and present a possible path forward towards bipolar atomic scale device fabrication with the STM. Support from EU grants PAMS, SiSpin, SiAM and from Swiss NCCR QSIT is gratefully acknowledged.

  15. 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.

  16. Structure of tetracene films on hydrogen-passivated Si(001) studied via STM, AFM, and NEXAFS

    SciTech Connect

    Tersigni, A.; Shi, J.; Jiang, D. T.; Qin, X. R.

    2006-11-15

    Scanning tunneling microscopy (STM), atomic force microscopy (AFM), and near-edge x-ray absorption fine structure (NEXAFS) have been used to study the structure of tetracene films on hydrogen-passivated Si(001). STM imaging of the films with nominal thickness of three monolayers (3 ML) exhibits the characteristic 'herringbone' molecular packing known from the bulk crystalline tetracene, showing standing molecules on the ab plane. The dimensions and orientation of the herringbone lattice indicate a commensurate structural relationship between the lattice and the crystalline substrate. The corresponding AFM images illustrate that at and above the third layer of the films, the islands are anisotropic, in contrast with the submonolayer fractals, with two preferred growth directions appearing orthogonal to each other. The polarization dependent NEXAFS measurements indicate that the average molecular tilting angle with respect to the surface first increases with the film thickness up to 3 ML, then stabilizes at a value close to the bulk tetracene case afterwards. The combined results indicate a distinct growth morphological change that occurs around a few monolayers of thickness.

  17. Non-magnetic impurity effects in LiFeAs studied by STM/STS

    NASA Astrophysics Data System (ADS)

    Hanaguri, T.; Khim, Seung Hyun; Lee, Bumsung; Kim, Kee Hoon; Kitagawa, K.; Matsubayashi, K.; Mazaki, Y.; Uwatoko, Y.; Takigawa, M.; Takagi, H.

    2012-02-01

    Detecting the possible sign reversal of the superconducting gap in iron-based superconductors is highly non-trivial. Here we use non-magnetic impurity as a sign indicator. If the sign of the superconducting gap is positive everywhere in momentum space, in-gap bound state should not be observed near the impurity site unless it is magnetic. On the other hand, if there is a sign-reversal in the gap, even non-magnetic impurity may create in-gap bound state [1]. We performed STM/STS experiments on self-flux and Sn-flux grown LiFeAs crystals and examined the effects of Sn impurity. In STM images of Sn-flux grown samples, we found a ring-like object which may represent Sn. Tunneling spectrum taken at this defect site exhibits in-gap bound state. Together with flat-bottom superconducting gap observed far from the defects, sign-reversing s-wave gap is the most plausible gap structure in LiFeAs. [1] T. Kariyado and M. Ogata, JPSJ 79, 083704 (2010).

  18. 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].

  19. STM investigation of FeSe/SrTiO3 band structure

    NASA Astrophysics Data System (ADS)

    Webb, Tatiana A.; Huang, Dennis; Song, Can-Li; Chang, Cui-Zu; Moodera, Jagadeesh; Hoffman, Jennifer E.

    2015-03-01

    Growing a single unit cell of FeSe on a SrTiO3 substrate (1 u.c. FeSe/STO) enhances the superconducting transition temperature (Tc) by an order of magnitude. While the dramatic effect of the interface is evident, a mechanism is not. ARPES studies have revealed that the band structure differs significantly from bulk FeSe and the majority of other Fe-based superconductors, most notably in lacking a hole pocket at the Fermi level. ARPES, however, is limited to probing the filled electron states. STM/STS has access to the band structure, both above and below the Fermi level, with spatial resolution, and the data encodes electronic properties including orbital character and interactions. We present an STM/STS study of 1 u.c. FeSe/STO grown by molecular beam epitaxy (MBE), focusing on the empty-state band structure of this new high Tc superconductor. Work supported by the US National Science Foundation grant DMR-0847433, and STC Center for Integrated Quantum Materials under NSF grant DMR-1231319.

  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. STM study of the Ga thin films grown on Si(111) surface

    NASA Astrophysics Data System (ADS)

    Tao, Min-Long; Tu, Yu-Bing; Sun, Kai; Ye, Juan; Hao, Shao-Jie; Xiao, Hua-Fang; Wang, Ya-Li; Xie, Zheng-Bo; Wang, Jun-Zhong

    2017-09-01

    Structural evolution of Ga thin films grown on the Si(111)-√{ 3 } × √{ 3 } -Ga template have been investigated with a low-temperature scanning tunneling microscopy (STM). The first Ga layer exhibits a stripe structure along the base vectors of Si(111) lattices. Individual Ga dimers have been directly visualized from the high-resolution STM images of the first Ga layer. The second Ga layer reveals a pseudo 1×1 structure with respect to the Si(111). A new 5×5 phase has been found in the second Ga layer when annealing the sample to 120 ℃. Further annealing to 150 ℃ leads to the formation of 6.3×6.3 phase, which is more stable than the 5×5 phase. The existences of a variety of superstructures of Ga films demonstrates the delicate balance between the interactions of Si(111)-Ga and Ga-Ga. These results shed important light on the epitaxial growth mechanism of Ga films on semiconductor surfaces.

  2. Morphology and Magnetism of Atomically Thin Layers of Chromia -- An STM Investigation

    NASA Astrophysics Data System (ADS)

    Chen, Xumin; Kenkel, Donna; Rojas, Geoffrey; He, Xi; Binek, Christian; Enders, Axel

    2012-02-01

    A low temperature scanning tunneling microscopy (LT-STM) study of ultrathin chromium oxide films on Cu(111) is presented. The (0001) surface of Cr2O3 (chromia) exhibits long-range antiferromagnetic ordering, and its usefulness for electric field control of exchange bias has been recently established [Xi He, Ch. Binek, et al., Natuer Materials 9, 579 -- 585 (2010)]. We deposited ultrathin chromium layers on Cu(111), followed by post-annealing in oxygen partial pressures to promote oxidation of the chromium films. We find that chromium grows on Cu(111) in the Volmer-Weber mode, resulting in small 3D islands. During annealing, the small islands coalesce to form large, flat terraces and the most stable oxide of chromium, Cr2O3, is formed at 630 C. Spin-polarized scanning tunneling microscopy has been performed to image the layer-wise antiferromagnetism in different structural layers of the chromia films. Thin layers of cobalt have been deposited on the chromia so that the magnetism of the Co couples to that of the chromia. Imaging the magnetism of the Co islands on the Cr2O3 terraces with spin-polarized STM helped us distinguishing between magnetic and electronic contrast in the complex dI/dV maps of the chromia surface.

  3. 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.

  4. SmallGEO Structural-Thermal Model (STM) Mechanical Test Campaign

    NASA Astrophysics Data System (ADS)

    Di Carlo, A.; Ruess, F.; Obst, A.; Segelke, H.; Rubio Blanes, A.

    2014-06-01

    SmallGEO is a general-purpose small geostationary satellite platform developed by an industrial team managed by OHB System AG. The consortium includes OHB subsidiaries LuxSpace and OHB Sweden, and RUAG Space. SmallGEO's first use is for Hispasat Advanced Generation 1 (AG1) satellite.RUAG Space was responsible for the development, qualification, production and assembly of the Structure Sub-system as well as the thermal control system.A Structural-Thermal Model (STM) was developed and assembled at RUAG Space premises in Zurich, in parallel with the Protoflight Model (PFM), to qualify the structure and the thermal control system.Between August and December 2012, the STM was subject to testing at European Test Services ETS in Noordwjik to qualify the platform versus all the specified mechanical and thermal environmental loads. Objective of the paper is to describe the phases of the mechanical test campaign, with special focus on the sine burst test, used to substitute the traditional static load tests in qualifying the structure versus the quasi-static launch environment.The challenge was to apply the right accelerations (at least 2.6g lateral and 7.5g axial) to a 3500 kg S/C with a sine vibration at a frequency close enough to resonance to generate the desired amplification and far enough to consider the load application still quasi-static.

  5. The electronic structure of hematite (001) surfaces: Applications to the interpretation of STM images and heterogeneous surface reactions

    SciTech Connect

    Becker, U.; Hochella, M.F. Jr.; Apra, E.

    1996-11-01

    Scanning tunneling microscope (STM) images and scanning tunneling spectroscopy (STS) spectra of hematite ({alpha}-Fe{sub 2}O{sub 3}) surfaces were calculated using ab-initio methods, not only to interpret experimentally collected STM data, but also to gain insight into atomic level changes in electronic structure that are associated with heterogeneous surface reactions. The electronic structure and wave functions inside the studied crystal were obtained as a periodic solution of the Schroedinger equation by using the program Crystal92. STM images and STS spectra were calculated by applying a technique similar to the Tersoff and Hamann (1985) method. Experimental STM images of the upper valence band of hematite (001) surfaces, cleaved in air, show a periodic array of bright spots that differs slightly from the O-O separation in the bulk. However, our calculations show that these spots are located at the Fe positions of the surface Fe atoms and above the Fe atoms between the first and second hexagonally close-packed O layers. The calculated STS spectra for tip positions above the three non-equivalent Fe positions show significant differences, in particular because the contribution of O 2p-like and Fe 3d-like states changes with the distance between the tip and the respective Fe atom underneath. Hematite crystals that were used to obtain STM images experimentally in previous studies were cleaved in air, and the presence of adsorbed H{sub 2}O and O{sub 2} was considered in this study. Calculations that optimize the surface atomic arrangement with respect to total energy of the slab indicate that H{sub 2}O and O{sub 2} adsorbed to the surface have binding energies too low to withstand the dragging force and the electric potential applied during the scanning process. In addition, only calculations of STM images of fresh hematite surfaces exactly mimic the periodicity of high electronic density spots, as observed in experiments.

  6. Tracking Invisible Transformations of Physisorbed Monolayers: LDI-TOF and MALDI-TOF Mass Spectrometry as Complements to STM Imaging.

    PubMed

    He, Jian; Fang, Chen; Shelp, Russell A; Zimmt, Matthew B

    2017-01-17

    Triphenyleneethynylene (TPEE) derivatives bearing one long aliphatic chain on each terminal aryl ring and two short aliphatic chains on the central aryl ring (core chains) self-assemble single component and 1-D patterned, two-component, crystalline monolayers at the solution-graphite interface. The monolayer morphology directs the core chains off the graphite, making them accessible for chemical reactions but invisible to imaging by scanning tunneling microscopy (STM). This precludes using STM to monitor transformations of the core chains, either by reaction or solution-monolayer exchange of TPEE molecules. Laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF MS) successfully identifies TPEE compounds within physisorbed monolayers. The LDI-TOF spectra of TPEE monolayer-graphite samples exhibit strong molecular ion peaks and minimal fragmentation or background. LDI-TOF and STM techniques are combined to evaluate monolayer composition and morphology, track solution-monolayer exchange, to identify reaction products and to measure kinetics of chemical reactions at the solution-monolayer interface. LDI-TOF MS provides rapid qualitative evaluation of monolayer composition across a graphite substrate. Challenges to quantitative composition evaluation by LDI-TOF include compound-specific light absorption, surface desorption/ionization and fragmentation characteristics. For some, but not all, compounds, applying matrix onto a self-assembled monolayer increases molecular ion intensities and affords more accurate assessment of monolayer composition via matrix assisted laser desorption/ionization (MALDI) MS. Matrix addition precludes subsequent chemical or STM studies of the monolayer, whereas reactions and STM may be performed at nonirradiated regions following LDI-TOF measurements. LDI- and MALDI-TOF MS are useful complements to STM and are easily implemented tools for study of physisorbed monolayers.

  7. Ultrathin TiO(x) films on Pt(111): a LEED, XPS, and STM investigation.

    PubMed

    Sedona, Francesco; Rizzi, Gian Andrea; Agnoli, Stefano; Llabrés i Xamena, Francesc X; Papageorgiou, Anthoula; Ostermann, Dieter; Sambi, Mauro; Finetti, Paola; Schierbaum, Klaus; Granozzi, Gaetano

    2005-12-29

    Ultrathin ordered titanium oxide films on Pt(111) surface are prepared by reactive evaporation of Ti in oxygen. By varying the Ti dose and the annealing conditions (i.e., temperature and oxygen pressure), six different long-range ordered phases are obtained. They are characterized by means of low-energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS), and scanning tunneling microscopy (STM). By careful optimization of the preparative parameters, we find conditions where predominantly single phases of TiO(x), revealing distinct LEED pattern and STM images, are produced. XPS binding energy and photoelectron diffraction (XPD) data indicate that all the phases, except one (the stoichiometric rect-TiO2), are one monolayer thick and composed of a Ti-O bilayer with interfacial Ti. Atomically resolved STM images confirm that these TiO(x) phases wet the Pt surface, in contrast to rect-TiO2. This indicates their interface stabilization. At a low Ti dose (0.4 monolayer equivalents, MLE), an incommensurate kagomé-like low-density phase (k-TiO(x) phase) is observed where hexagons are sharing their vertexes. At a higher Ti dose (0.8 MLE), two denser phases are found, both characterized by a zigzag motif (z- and z'-TiO(x) phases), but with distinct rectangular unit cells. Among them, z'-TiO(x), which is obtained by annealing in ultrahigh vacuum (UHV), shows a larger unit cell. When the postannealing of the 0.8 MLE deposit is carried out at high temperatures and high oxygen partial pressures, the incommensurate nonwetting, fully oxidized rect-TiO2 is found The symmetry and lattice dimensions are almost identical with rect-VO2, observed in the system VO(x)/Pd(111). At a higher coverage (1.2 MLE), two commensurate hexagonal phases are formed, namely the w- [(square root(43) x square root(43)) R 7.6 degrees] and w'-TiO(x) phase [(7 x 7) R 21.8 degrees]. They show wagon-wheel-like structures and have slightly different lattice dimensions. Larger Ti deposits

  8. Computational simulation of subatomic-resolution AFM and STM images for graphene/hexagonal boron nitride heterostructures with intercalated defects

    NASA Astrophysics Data System (ADS)

    Lee, Junsu; Kim, Minjung; Chelikowsky, James R.; Kim, Gunn

    2016-07-01

    Using ab initio density functional calculations, we predict subatomic-resolution atomic force microscopy (AFM) and scanning tunneling microscopy (STM) images of vertical heterostructures of graphene/hexagonal boron nitride (h-BN) with an intercalated metal atom (Li, K, Cr, Mn, Co, or Cu), and study the effects of the extrinsic metal defect on the interfacial coupling. We find that the structural deformation of the graphene/h-BN layer caused by the metal defect strongly affects the AFM images, whereas orbital hybridization between the metal defect and the graphene/h-BN layer characterizes the STM images.

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

    NASA Astrophysics Data System (ADS)

    Pong, Wing-Tat; Durkan, Colm

    2005-11-01

    Since its invention in 1981, scanning tunnelling microscopy (STM) is well-known for its supreme imaging resolution enabling one to observe atomic-scale structures, which has led to the flourishing of nanoscience. As successful as it is, there still remain phenomena which are observed using STM but are beyond our understanding. Graphite is one of the surfaces which have been most extensively studied using STM. However, there are a number of unusual properties of graphite surfaces. First reported in the 1980s, superlattices on graphite have since been observed many times and by many groups, but as yet our understanding of this phenomenon is quite limited. Most of the observed superlattice phenomena are widely believed to be the result of a Moiré rotation pattern, arising from the misorientation between two graphite layers, as verified experimentally. A Moiré pattern is a lattice with larger periodicity resulting from the overlap of two lattices with smaller periodicities. As graphite layers are composed of hexagonal lattices with a periodicity of 0.246 nm, as observed using STM, when there are misoriented graphite layers overlapping each other, a Moiré pattern with larger periodicity, depending on the misorientation angle, will be produced and appear as a superperiodic hexagonal structure on top of the graphite atomic lattice of the topmost surface layer. It is important to study graphite superlattices because, firstly, knowledge of this phenomenon will enable us to properly interpret STM images; secondly, it helps us to understand the correlation between electronic structures and atomic-structure rearrangement of graphite which is of tremendous aid for engineering material properties; thirdly, and perhaps most importantly, the observation of the phenomenon exhibits the capability of STM to produce images indicating the nature of internal defects which are below the surface. Over recent years, experimental and modelling techniques have been developed to study this

  10. STM study of surface structures formed by metal adsorption on semiconductor surfaces

    NASA Astrophysics Data System (ADS)

    Yoon, Myonggeun

    By utilizing a variety of the metal-induced superstructures and growth of metal adsorbates on semiconductor surfaces, we have studied how both the arrangements of atoms in topmost surfaces and the bonding mechanism actually affect both the atomic structures and electronic properties of the surface. This work describes the results of experimental studies of the metal adsorbates on two semiconductor surfaces, Si(111) and Ge(111), using scanning tunneling microscopy (STM), large modulation-amplitude local-barrier-height (LM-LBH) imaging as primary tools for structural analysis, and scanning tunneling spectroscopy (STS) as a tool for electronic analysis. Firstly, we have obtained new real-space images of the filled dangling-bond states of the alkali-metal induced 3x1 reconstruction of the Si(111) surface associated with a recently proposed Si=Si double-bond stabilized surface structure. Our new experimental evidence reveals significant subtle differences between this local bonding on Na/Si(111)-(3x1) and Na/Ge(111)-(3x1) which argues a strong case for a previously proposed "Honeycomb-chain-channel model" but with a relaxation of a strict double-bond requirement, particularly on the Ge surface. Secondly, the adsorption mechanism and the origin of the In, Al & Sn-induced surface electronic states on the Si(111)-(7x7) surface have been studied using bias-dependent scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Our experimental evidence suggests that all these metal atoms are covalently bonding with Si topmost atoms on Si(111)-(7x7) surface while In and Al atoms possibly substitute for Si adatoms in the 7x7 unit cell during room temperature adsorption. Both mechanisms remove intrinsic metallic surface states caused by partially occupied Si adatom dangling bonds, opening a bandgap at the surface and producing a metal-insulator transition. Finally, we report on the self-assembly of a superlattice of nanodots of different elements (Sn, In) on a

  11. 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.

  12. STM studies of spin-spin interactions between Mn acceptors in p-type GaAs

    NASA Astrophysics Data System (ADS)

    Lee, Donghun; Daughton, David R.; Gupta, Jay A.

    2008-03-01

    We use a custom STM operating in a cryogenic, ultrahigh vacuum environment to study spin-spin interactions in semiconductors at the single-impurity level. By applying a voltage pulse with the STM tip, single magnetic impurities (e.g. Mn) can be substituted for Ga atoms in the first layer of the GaAs(110) surface. It was previously found that pairs of Mn acceptors exhibit an exchange splitting which depends on their separation and crystal orientation [2]. We are developing a capability for spin-polarized STM to better study long range magnetic ordering between pairs and larger clusters of Mn acceptors. To characterize the magnetic orientation of our STM tips, we have prepared samples such as Co/Cu(111) which exhibits out-of-plane magnetization, and Cr(001), which is an antiferromagnet with in-plane magnetic contrast between alternating terraces. http://www.physics.ohio-state.edu/˜jgupta [2] D. Kitchen et al., Nature 442, 436-439 (2006)

  13. Single-layer ZnS supported on Au(111): A combined XPS, LEED, STM and DFT study

    SciTech Connect

    Deng, Xingyi; Sorescu, Dan C.; Lee, Junseok

    2016-12-31

    Single-layer of ZnS, consisting of one atomic layer of ZnS(111) plane, has been grown on Au(111) and characterized using X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). While the LEED measurement indicates a coincidence structure of ZnS-(3×3)/Au(111)-(4×4), high resolution STM images reveal hexagonal unit cells of 6.7×6.7 Å2 and 11.6×11.6 Å2, corresponding to √3 and 3 times the unit cell of the ideal zincblende ZnS-(1×1), respectively, depending on the tunneling conditions. Calculations based on density functional theory (DFT) indicate a significantly reconstructed non-planar structure of ZnS single-layer on Au(111) with 2/3 of the S anions being located nearly in the plane of the Zn cations and the rest 1/3 of the S anions protruding above the Zn plane. In conclusion, the calculated STM image shows similar characteristics to those of the experimental STM image. Additionally, the DFT calculations reveal the different bonding nature of the S anions in ZnS single-layer supported on Au(111).

  14. 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

    ... COMMISSION In the Matter of Appiant Technologies, Inc., Cobalis Corp., FutureLink Corp., STM Wireless, Inc., Supermail International, Inc. (n/ k/a PBHG, Inc.), and Women First Healthcare, Inc.; Order of Suspension of... current and accurate information concerning the securities of Appiant Technologies, Inc. because it...

  15. Single-layer ZnS supported on Au(111): A combined XPS, LEED, STM and DFT study

    DOE PAGES

    Deng, Xingyi; Sorescu, Dan C.; Lee, Junseok

    2016-12-31

    Single-layer of ZnS, consisting of one atomic layer of ZnS(111) plane, has been grown on Au(111) and characterized using X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). While the LEED measurement indicates a coincidence structure of ZnS-(3×3)/Au(111)-(4×4), high resolution STM images reveal hexagonal unit cells of 6.7×6.7 Å2 and 11.6×11.6 Å2, corresponding to √3 and 3 times the unit cell of the ideal zincblende ZnS-(1×1), respectively, depending on the tunneling conditions. Calculations based on density functional theory (DFT) indicate a significantly reconstructed non-planar structure of ZnS single-layer on Au(111) with 2/3 of the Smore » anions being located nearly in the plane of the Zn cations and the rest 1/3 of the S anions protruding above the Zn plane. In conclusion, the calculated STM image shows similar characteristics to those of the experimental STM image. Additionally, the DFT calculations reveal the different bonding nature of the S anions in ZnS single-layer supported on Au(111).« less

  16. Single-layer ZnS supported on Au(111): A combined XPS, LEED, STM and DFT study

    NASA Astrophysics Data System (ADS)

    Deng, Xingyi; Sorescu, Dan C.; Lee, Junseok

    2017-04-01

    Single-layer of ZnS, consisting of one atomic layer of ZnS(111) plane, has been grown on Au(111) and characterized using X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). While the LEED measurement indicates a coincidence structure of ZnS-(3×3)/Au(111)-(4×4), high resolution STM images reveal hexagonal unit cells of 6.7×6.7 Å2 and 11.6×11.6 Å2, corresponding to √3 and 3 times the unit cell of the ideal zincblende ZnS-(1×1), respectively, depending on the tunneling conditions. Calculations based on density functional theory (DFT) indicate a significantly reconstructed non-planar structure of ZnS single-layer on Au(111) with 2/3 of the S anions being located nearly in the plane of the Zn cations and the rest 1/3 of the S anions protruding above the Zn plane. The calculated STM image shows similar characteristics to those of the experimental STM image. Additionally, the DFT calculations reveal the different bonding nature of the S anions in ZnS single-layer supported on Au(111).

  17. STM Studies of Near-Optimal Doped Bi_2Sr_2CaCu_2O_8 delta

    SciTech Connect

    Kapitulnik, Aharon

    2010-04-05

    In this paper we summarize our STM studies of the density of electronic states in nearly optimally doped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8 + {delta}} in zero field. We report on the inhomogeneity of the gap structure, density of states modulations with four-lattice constant period, and coherence peak modulation.

  18. STM Observations at the Atomic Scale of a Tilt Grain Sub-Boundary on Highly Oriented Pyrolytic Graphite

    NASA Astrophysics Data System (ADS)

    Daulan, C.; Derré, A.; Flandrois, S.; Roux, J. C.; Saadaoui, H.

    1995-09-01

    We report here the first observations at the atomic scale of a symmetrical tilt grain sub-boundary with a STM. The edge dislocations observed at the atomic scale along the boundary line can be understood in the frame of geometrical models. These STM images also reveal a local modification of the charge density near the Fermi level in the junction area. Des observations à l'échelle atomique d'un sous-joint de grains de flexion ont été réalisées pour la première fois par microscopie à effet tunnel (STM). Des modèles géométriques ont permis d'interpréter le réseau de dislocations mis en évidence sur la ligne de jonction. Ces images STM révèlent également la modification locale de la densité volumique de charge près du niveau de Fermi dans la zone de jonction.

  19. Multiband Superconductivity in 2 H - NbSe2 Probed by Cryomagnetic STM Spectroscopy

    NASA Astrophysics Data System (ADS)

    Fridman, Igor; Wei, J. Y. T.; Kloc, C.; Lukic, V.; Hu, Rongwei; Petrovic, C.

    2011-03-01

    Using a novel magnetic field geometry, we study multiband pairing in single crystals of superconducting 2 H - NbSe 2 under finite superfluid momentum. Spectroscopy and conductance imaging were performed with a scanning tunneling microscope (STM) at 300 mK and in a field of up to 9 T, applied in the ab -plane. We observed multiple spectral features that evolve systematically with field, and a two-sloped zero-bias conductance that dips anomalously at 0.7 T. Our analysis yields distinct evidence for multiple gaps coming from the various Fermi-surface sheets, and has possible implications on the origin of the coexisting charge density wave order. Work supported by NSERC, CFI/OIT, CIFAR, U.S. DOE and Brookhaven Science Associates (No. DE-Ac02-98CH10886).

  20. STM/STS studies on vortex and electronic state in YBa 2Cu 3O y

    NASA Astrophysics Data System (ADS)

    Nishizaki, Terukazu; Shibata, Kenji; Maki, Makoto; Kobayashi, Norio

    2006-05-01

    Low temperature scanning tunneling microscopy (LT-STM) studies have been performed on the LT-cleaved and the chemically etched surface of YBa2Cu3Oy single crystals. We find that the vortex structure can be observed on the chemically etched surface of YBa2Cu3Oy as a function of temperature and magnetic field. At low magnetic fields, we observed a slightly distorted triangular lattice, which is attributed to the Bragg-glass phase. The triangular lattice transforms into a disordered structure in high magnetic fields above the order-disorder transition H∗(T). We observed that the disordered vortices form small clusters comprising 5- and 7-fold coordination pairs. These microscopically determined vortex structures are in good agreement with the vortex matter phase diagram derived from the macroscopic measurements, thus providing the evidence of the field-driven transition in the vortex solid phase of YBa2Cu3Oy.

  1. The synthesis and STM/AFM imaging of 'olympicene' benzo[cd]pyrenes.

    PubMed

    Mistry, Anish; Moreton, Ben; Schuler, Bruno; Mohn, Fabian; Meyer, Gerhard; Gross, Leo; Williams, Antony; Scott, Peter; Costantini, Giovanni; Fox, David J

    2015-01-26

    H-Benzo[cd]pyrene ('Olympicene') is a polyaromatic hydrocarbon and non-Kekulé fragment of graphene. A new synthetic method has been developed for the formation of 6H-benzo[cd]pyrene and related ketones including the first time isolation of the unstable alcohol 6H-benzo[cd]pyren-6-ol. Molecular imaging of the reaction products with scanning tunnelling microscopy (STM) and non-contact atomic force microscopy (NC-AFM) characterised the 6H-benzo[cd]pyrene as well as the previously intangible and significantly less stable 5H-benzo[cd]pyrene, the fully conjugated benzo[cd]pyrenyl radical and the ketones as oxidation products.

  2. New Pt/Alumina model catalysts for STM and in situ XPS studies

    NASA Astrophysics Data System (ADS)

    Nartova, Anna V.; Gharachorlou, Amir; Bukhtiyarov, Andrey V.; Kvon, Ren I.; Bukhtiyarov, Valerii I.

    2017-04-01

    The new Pt/alumina model catalysts for STM and in situ XPS studies based on thin alumina film formed over the conductive substrate are proposed. Procedure of platinum deposition developed for porous alumina was adapted for the model alumina support. The set of Pt/AlOx-film samples with the different mean platinum particle size was prepared. Capabilities of in situ XPS investigations of the proposed catalysts were demonstrated in study of NO decomposition on platinum nanoparticles. It is shown that proposed model catalysts behave similarly to Pt/γ-Al2O3 and provide the new opportunities for the instrumental studies of platinum catalysts due to resolving several issues (charging, heating, screening) that are typical for the investigation of the porous oxide supported catalysts.

  3. 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.

  4. 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

  5. Surface induced selective deposition of Dysprosium Polyoxometalate on HOPG surface studied by STM and STS

    NASA Astrophysics Data System (ADS)

    Costa Milan, David; Pinilla Cienfuegos, Elena; Cardona Serra, Salvador; Coronado Miralles, Eugenio; Untiedt Lecuona, Carlos

    2013-03-01

    Scanning Tunneling Microscope (STM) and scanning Tunnelling spectroscopy (STS) techniques have been used to study the Preyssler type Polyoxometalate K12[DyP5W30O110] molecules deposited on Highly Oriented Pyrolytic Graphite surface (HOPG). Chainlike arrangements of clusters containing two or three molecules, as well as different cluster sizes are observed. As many structural artifacts are present on the graphite surface, like Moiré patterns, that could look like the molecular deposits, we have studied their STS and size to ensure the presence of the POM molecules on the surface. This article shows the possibility of addressing POMs on a flat surface to obtain their electronic properties through STS.

  6. [Research on the High Efficiency Data Communication Repeater Based on STM32F103].

    PubMed

    Zhang, Yahui; Li, Zheng; Chen, Guangfei

    2015-11-01

    To improve the radio frequency (RF) transmission distance of the wireless terminal of the medical internet of things (LOT), to realize the real-time and efficient data communication, the intelligent relay system based on STM32F103 single chip microcomputer (SCM) is proposed. The system used nRF905 chip to achieve the collection, of medical and health information of patients in the 433 MHz band, used SCM to control the serial port to Wi-Fi module to transmit information from 433 MHz to 2.4 GHz wireless Wi-Fi band, and used table look-up algorithm of ready list to improve the efficiency of data communications. The design can realize real-time and efficient data communication. The relay which is easy to use with high practical value can extend the distance and mode of data transmission and achieve real-time transmission of data.

  7. Ambient STM study of sequentially adsorbed octanethiol and biphenylthiol monolayers on Au(111)

    NASA Astrophysics Data System (ADS)

    Fitzgerald, Danielle M.; Krisanda, Emily K.; Szypko, Colleen G.; Gaby Avila-Bront, L.

    2017-08-01

    The mixed monolayers of biphenyl-4-thiol (BPT) and octanethiol (OT) are studied at the molecular level using scanning tunneling microscopy (STM) in ambient conditions and X-ray photoelectron spectroscopy (XPS) on Au(111). The effect of both the sequence of deposition, and the concentration of the BPT solution used is investigated. We observe signs of coexisting domains in the form of disordered patches surrounding flat patches when a 100 μM solution of BPT is used. This observation holds for both OT being deposited first, and BPT being deposited first. The most clear formation of coexisting domains occurs when an OT monolayer is immersed in a 100 μM solution of BPT. The XP spectra reveal a shift in the C 1s signal of the monolayers that is unique to what films are deposited on the surface. These data demonstrate the importance characterizing mixed self-assembled monolayers that form final monolayer structures unique to each mixture.

  8. On the superconducting gap structure of high-temperature superconductors by STM/STS

    NASA Astrophysics Data System (ADS)

    Kitazawa, K.; Sugawara, H.; Hasegawa, T.

    1996-05-01

    The tunneling spectra observed by STM on the HTSC's have been converging in terms of the superconducting gap energy values: 2 Δ/ kBTc=6 to 9. There are, however, still disagreements between the details of various results. Both d- and s-wave-like features have been claimed for the superconducting gap structure. Furthermore, both flat and V-shaped structures have been observed in the background conductance curve outside the superconducting gap. The major differences among various reports seem to be attributable to the difference in the top layer and in the carrier density of the sample. It is noted that those who observe on the BiO topmost plane in a Bi2212 crystal or on the CuO-chain plane of YBCO seem to be claiming the d-wave, and those who observe on different top planes the s-wave symmetry.

  9. s +i s superconductivity with incipient bands: Doping dependence and STM signatures

    NASA Astrophysics Data System (ADS)

    Böker, Jakob; Volkov, Pavel A.; Efetov, Konstantin B.; Eremin, Ilya

    2017-07-01

    Motivated by the recent observations of small Fermi energies and comparatively large superconducting gaps, present also on bands not crossing the Fermi energy (incipient bands) in iron-based superconductors, we analyze the doping evolution of superconductivity in a four-band model across the Lifshitz transition including BCS-BEC crossover effects on the shallow bands. Similar to the BCS case, we find that with hole doping the phase difference between superconducting order parameters of the hole bands change from 0 to π through an intermediate s +i s state, breaking time-reversal symmetry (TRS). The transition, however, occurs in the region where electron bands are incipient and chemical potential renormalization in the superconducting state leads to a significant broadening of the s +i s region. We further present the qualitative features of the s +i s state that can be observed in scanning tunneling microscopy (STM) experiments, also taking incipient bands into account.

  10. Germanium adsorption on Ag(111): an AES-LEED and STM study.

    PubMed

    Oughaddou, H; Mayne, A; Aufray, B; Bibérian, J P; Le Lay, G; Ealet, B; Dujardin, G; Kara, A

    2007-09-01

    The adsorption of germanium on Ag(111) has been investigated using Scanning Tunneling Microscopy, Auger Electron Spectroscopy and Low Energy Electron Diffraction. From the shape of the Auger peak-to-peak versus time curves, we deduce that at room temperature the growth mode is nearly layer-by-layer at least for the first two layers. In the sub-monolayer range, the growth starts by the formation of a (mean square root of 3 x mean square root of 3)R30 degrees surface superstructure which is complete at 1/3 monolayer coverage. Beyond this coverage a rectangular c(mean square root of 3 x 7) superstructure is observed. STM images reveal that this last reconstruction is formed by an ordered arrangement of self-assembled Ge tetramers giving rise to a surprising undulation of the surface.

  11. Defects in Thin-Film FeSe/SrTiO3: STM and DFT Investigations

    NASA Astrophysics Data System (ADS)

    Huang, Dennis; Webb, Tatiana A.; Song, Can-Li; Chang, Cui-Zu; Moodera, Jagadeesh S.; Kaxiras, Efthimios; Hoffman, Jennifer E.

    A single-layer of FeSe deposited on SrTiO3 exhibits an order-of-magnitude enhancement of its superconducting transition temperature compared to bulk FeSe. This dramatic effect is curiously absent in a second layer of FeSe deposited on the heterostructure, leading to many questions concerning the role of the interface structure, electron doping and phonon coupling. Here, we approach these questions by using STM to characterize and compare native defects that appear in multi-layer and single-layer FeSe/SrTiO3 grown by MBE under excess Se flux. We use DFT to explore candidate defect configurations, formation energies and diffusion barriers, in order to gain atomic-scale insights into the growth and structure of these film heterostructures. Work supported by NSF DMR-1231319 (STC CIQM) and Moore Foundation EPiQS GBMF4536. Computations run on Harvard RC Odyssey.

  12. 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

  13. HRLEED and STM study of misoriented Si(100) with and without a Te overlayer

    SciTech Connect

    Yala, S.; Montano, P.A. |

    1996-12-01

    The growth of high quality Te on misoriented Si(100) is important as an intermediate phase for epitaxial growth of CdTe. The misorientation angle plays a key role in the growth quality of CdTe/Si(100); this incited the curiosity to investigate the effect of the misorientation angle on the topography of the surface structure of Si(100). The main goal is to show the relation between the misorientation angle, the terrace width and the step height distributions. HRLEED (High Resolution Low Energy Electron Diffraction) provides information in reciprocal space while STM gives real space topographic images of the surface structure. STM and HRLEED measurements were performed on Si(100) with misorientation angle {var_theta} = 0.5{degree}, 1.5{degree} and 8{degree} towards the [110] direction and {var_theta} = 4{degree} towards the [130] direction. Except for the 8{degree} misorientation in which case a regular step array with diatomic step height was observed, for the other misorientations the terrace width was variable. The average terrace width decreased with increasing misorientation angle. A mixture of diatomic and monatomic step heights was observed on the 0.5{degree} and 1.5{degree} misoriented Si(100) samples. It proves that one can not assume purely monatomic step height for low misorientation angles. The results do not agree with the belief that at low miscut angle A and B terraces are equal and that as the misorientation angle increases the B terrace tends to be wider than the A terrace. In fact, pairing of terraces was not observed at all. Te was deposited at a substrate temperature of 200 C. The authors observed a significant reduction in the terrace widths for all miscut angles.

  14. STM imaging ortho- and para-fluorothiophenol self-assembled monolayers on Au(111).

    PubMed

    Jiang, Peng; Deng, Ke; Fichou, Denis; Xie, Si-Shen; Nion, Aymeric; Wang, Chen

    2009-05-05

    Self-assembled monolayers (SAMs) of para- and ortho-fluorothiophenol (p- and o-FTP) spontaneously formed on Au(111) substrate have been contrasted through investigation by a scanning tunneling microscope (STM) at room temperature. High-resolution STM imaging reveals that p-FTP adopts a 6 x radical3R30 degrees molecule arrangement containing six molecules. Two different kinds of p-FTP molecule dimer line structures have been formed on Au(111) by intermolecular pi-pi stacking along 112 substrate directions, besides a single p-FTP molecule line. In contrast, o-FTP molecules self-assemble into a much looser wave-like SAM, which can be described as a 5 x 3 radical3R30 degrees structure containing two molecules. Periodic density functional theory (DFT) calculations for the two systems suggest that these kinds of FTP molecules preferentially take the asymmetrical positions between 3-fold face-centered cubic (fcc) hollow and bridge sites on Au(111), tilting from the substrate surface. Theoretical simulation gives apparent average tilted angles of 58 degrees and 68 degrees for p-FTP and o-FTP with respect to the surface normal, respectively. This simulation shows that o-FTP is more inclined to lie down toward the Au(111) surface compared to p-FTP. The difference between p-FTP and o-FTP SAM structures can be qualitatively understood in terms of the variation of intermolecular dipole-dipole orientation. This suggests that, besides well-known Au-S and pi-pi interactions, electrostatic interactions including dipole-dipole, quadrupole-quadrupole, and dipole-quadrupole interactions might also play an important role in influencing the SAM structures formed by aromatic thiols with a permanent dipole moment.

  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.

  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. Electronic Structure of the Cuprate Superconducting and Pseudogap Phases from Spectroscopic Imaging STM

    SciTech Connect

    Davis, J.C.; Schmidt, A.R.; Fujita, K.; Kim, E.-A.; Lawler, M.J.; Eisaki, H.; Uchida, S.; Lee, D.-H.

    2011-06-21

    We survey the use of spectroscopic imaging scanning tunneling microscopy (SI-STM) to probe the electronic structure of underdoped cuprates. Two distinct classes of electronic states are observed in both the d-wave superconducting (dSC) and the pseudogap (PG) phases. The first class consists of the dispersive Bogoliubov quasiparticle excitations of a homogeneous d-wave superconductor, existing below a lower energy scale E = {Delta}{sub 0}. We find that the Bogoliubov quasiparticle interference (QPI) signatures of delocalized Cooper pairing are restricted to a k-space arc, which terminates near the lines connecting k = {+-}({pi}/a{sub 0},0) to k = {+-}(0,{pi}/a{sub 0}). This arc shrinks continuously with decreasing hole density such that Luttinger's theorem could be satisfied if it represents the front side of a hole-pocket that is bounded behind by the lines between k = {+-}({pi}/a{sub 0},0) and k = {+-}(0,{pi}/a{sub 0}). In both phases, the only broken symmetries detected for the |E| < {Delta}{sub 0} states are those of a d-wave superconductor. The second class of states occurs proximate to the PG energy scale E = {Delta}{sub 1}. Here the non-dispersive electronic structure breaks the expected 90{sup o}-rotational symmetry of electronic structure within each unit cell, at least down to 180{sup o}-rotational symmetry. This electronic symmetry breaking was first detected as an electronic inequivalence at the two oxygen sites within each unit cell by using a measure of nematic (C{sub 2}) symmetry. Incommensurate non-dispersive conductance modulations, locally breaking both rotational and translational symmetries, coexist with this intra-unit-cell electronic symmetry breaking at E = {Delta}{sub 1}. Their characteristic wavevector Q is determined by the k-space points where Bogoliubov QPI terminates and therefore changes continuously with doping. The distinct broken electronic symmetry states (intra-unit-cell and finite Q) coexisting at E {approx} {Delta}{sub 1} are

  18. Formation of dense nitroxide radical layers on the Au(1 1 1) substrate for ESN-STM measurement

    NASA Astrophysics Data System (ADS)

    Krukowski, P.; Kozlowski, W.; Olejniczak, W.; Klusek, Z.; Puchalski, M.; Dabrowski, P.; Kowalczyk, P. J.; Gwozdzinski, K.; Grabowski, G.

    2008-12-01

    Ultra high vacuum scanning tunnelling microscopy and electron paramagnetic resonance spectroscopy were used to investigate ISL and TEMPOL piperidine nitroxides molecules deposited on the Au(1 1 1) substrate by the drop-cast method. The STM results suggest that both compounds form dense layers on Au(1 1 1) with high molecular mobility observed during imaging process. High resolution STM topographies of both compounds suggest a well-defined molecular order which can be ascribed to the presence of self-assembly mechanism during layers formation. The EPR results indicated that both compounds deposited on the Au(1 1 1) substrate were not reduced retaining their paramagnetic properties. The significance of the results obtained in the field of single spin detection is briefly outlined.

  19. Monolayer-by-monolayer compositional analysis of InAs/InAsSb superlattices with cross-sectional STM

    SciTech Connect

    Wood, M. R.; Kanedy, K.; Lopez, F.; Weimer, M.; Klem, J. F.; Hawkins, S. D.; Shaner, E. A.; Kim, J. K.

    2015-02-23

    In this paper, we use cross-sectional scanning tunneling microscopy (STM) to reconstruct the monolayer-by-monolayer composition profile across a representative subset of MBE-grown InAs/InAsSb superlattice layers and find that antimony segregation frustrates the intended compositional discontinuities across both antimonide-on-arsenide and arsenide-on-antimonide heterojunctions. Graded, rather than abrupt, interfaces are formed in either case. We likewise find that the incorporated antimony per superlattice period varies measurably from beginning to end of the multilayer stack. Finally, although the intended antimony discontinuities predict significant discrepancies with respect to the experimentally observed high-resolution x-ray diffraction spectrum, dynamical simulations based on the STM-derived profiles provide an excellent quantitative match to all important aspects of the x-ray data.

  20. Electrosynthesis of poly(para)phenylene in an ionic liquid: cyclic voltammetry and in situ STM/tunnelling spectroscopy studies.

    PubMed

    Carstens, T; El Abedin, S Zein; Endres, F

    2008-02-22

    The electropolymerization of benzene in the air and water-stable ionic liquid 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate (HMIm)FAP is investigated. The study comprises cyclic voltammetry, IR and in situ STM/tunnelling spectroscopy measurements. The IR results indicate that poly(para)phenylene is the end product of the electropolymerization of benzene in the employed ionic liquid. The resulting conjugation lengths of the product fall between 19 and 21. A polymer reference electrode is used successfully for the electrochemical polymerization of benzene. The first in situ STM results show that the electropolymerization of benzene in the ionic liquid can be probed on the nanoscale and the band gap of the prepared polymer can be determined. The electrodeposited polymer film obtained at a constant potential of 1.0 V vs PPP (polyparaphenylene) exhibits a band gap of 2.9+/-0.2 eV.

  1. Monolayer-by-monolayer compositional analysis of InAs/InAsSb superlattices with cross-sectional STM

    DOE PAGES

    Wood, M. R.; Kanedy, K.; Lopez, F.; ...

    2015-02-23

    In this paper, we use cross-sectional scanning tunneling microscopy (STM) to reconstruct the monolayer-by-monolayer composition profile across a representative subset of MBE-grown InAs/InAsSb superlattice layers and find that antimony segregation frustrates the intended compositional discontinuities across both antimonide-on-arsenide and arsenide-on-antimonide heterojunctions. Graded, rather than abrupt, interfaces are formed in either case. We likewise find that the incorporated antimony per superlattice period varies measurably from beginning to end of the multilayer stack. Finally, although the intended antimony discontinuities predict significant discrepancies with respect to the experimentally observed high-resolution x-ray diffraction spectrum, dynamical simulations based on the STM-derived profiles provide an excellentmore » quantitative match to all important aspects of the x-ray data.« less

  2. Adlayer of hydroquinone on Pt(111) in solution and in a vacuum studied by STM and LEED.

    PubMed

    Inukai, Junji; Wakisaka, Mitsuru; Yamagishi, Masaoki; Itaya, Kingo

    2004-08-31

    Hydroquinone (HQ) adlayers were formed on Pt(111) in HF solution and in a vacuum. By using scanning tunneling microscopy (STM) in solution, it was revealed that HQ formed an ordered structure on Pt(111) with a strong attractive interaction between two adjacent hydroxyl groups in neighboring HQ molecules. After the sample was transferred into a vacuum, low-energy electron diffraction (LEED) measurement was performed, which showed that the (2.56 x 2.56)R16 degrees incommensurate structure of the HQ adlayer was formed in solution. The HQ adlayer on Pt(111) was formed also by vapor deposition, and the identical (2.56 x 2.56)R16 degrees adlayer structure was found by LEED and STM in a vacuum.

  3. 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.

  4. 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

  5. Dy uniform film morphologies on graphene studied with SPA-LEED and STM

    SciTech Connect

    McDougall, D.; Hattab, H.; Hershberger, M. T.; Hupalo, M.; Horn von Hoegen, M.; Thiel, P. A.; Tringides, M. C.

    2016-07-01

    The use of graphene for microelectronics and spintronic applications requires strategies for metals to wet graphene and to grow layer-by-layer. This is especially important when metals will be used as electrical contacts or as spin filters. Extensive work in the literature so far has shown that this is very challenging, since practically all metals grow 3D, with multi-height islands forming easily. Reasons for the 3D morphology are the much weaker metal carbon bond when compared to the metal cohesive energy and the role of Coulomb repulsion of the poorly screened charges at the metal graphene interface. We employed the complementary techniques of SPA-LEED and STM to study the growth of Dy on graphene. It was found that under kinetic limitations it is possible to fully cover graphene with a bilayer Dy film, by growing well below room temperature in stepwise deposition experiments. Lastly, the Dy film, however, is amorphous but ways to crystallize it within the 2D morphology are possible, since long range order improves at higher growth temperature.

  6. 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.

  7. 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.

  8. 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.

  9. Landau theory of Anderson localization and STM spectra in Ga1-x Mnx As

    NASA Astrophysics Data System (ADS)

    Mahmoudian, S.; Dobrosavljevic, V.; Miranda, E.

    2014-03-01

    The recently developed Typical Medium Theory provides the conceptually simplest order parameter description of Anderson localization by self-consistently calculating the geometrically-averaged (typical) local density of states (LDOS). Here we show how spatial correlations can also be captured within such a self-consistent theory, by utilizing the standard Landau method of allowing for (slow) spatial fluctuations of the order parameter, and performing an appropriate gradient expansion. Our theoretical results provide insight into recent STM experiments, which were used to visualize the spatially-fluctuating electronic wave functions near the metal insulator transition in Ga1 - xMnx As . We show that, within our theory, all features of the experiment can be accounted for by considering a model of disorder renormalized by long-range Coulomb interactions. This includes the pseudogap formation, the C (R) ~ 1 / R form of the LDOS autocorrelations function, and the ξ ~ 1 / E energy dependence of the correlation length at criticality. V. Dobrosavljević, Int. J. Mod. Phys. B 24, 1680 (2010).

  10. 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.

  11. STM imaging, spectroscopy and manipulation of a self-assembled PTCDI monolayer on epitaxial graphene.

    PubMed

    Yang, H; Mayne, A J; Comtet, G; Dujardin, G; Kuk, Y; Sonnet, Ph; Stauffer, L; Nagarajan, S; Gourdon, A

    2013-04-14

    Scanning Tunneling Microscopy (STM), Scanning Tunneling Spectroscopy (STS), and manipulation studies were performed on an ordered self-assembled monolayer (SAM) of N,N'-bis(1-hexylheptyl)perylene-3,4:9,10-bis(dicarboximide) molecules on epitaxial graphene on hexagonal silicon carbide - SiC(0001). Four novel aspects of the molecular SAM on graphene are presented. Molecules adsorb in both armchair and zig-zag configurations, giving rise to six orientations of the molecular layer with respect to the underlying substrate. The interaction between the molecules and the graphene surface shifts the LUMO towards the Fermi level, inducing a charge transfer and the opening of a band gap in the graphene, with the LUMO inside. This decouples the LUMO from the surface rendering it invisible in the dI/dV spectroscopy. The HOMO only becomes visible at short tip-surface distances, as its energy lies within the band gap of the SiC substrate. Finally, the observed molecular defects are very particular, being composed exclusively of molecular dimers. These molecular dimers have a stronger interaction with the graphene than other molecules.

  12. Dy uniform film morphologies on graphene studied with SPA-LEED and STM

    SciTech Connect

    McDougall, D.; Hattab, H.; Hershberger, M. T.; Hupalo, M.; Horn von Hoegen, M.; Thiel, P. A.; Tringides, M. C.

    2016-07-01

    The use of graphene for microelectronics and spintronic applications requires strategies for metals to wet graphene and to grow layer-by-layer. This is especially important when metals will be used as electrical contacts or as spin filters. Extensive work in the literature so far has shown that this is very challenging, since practically all metals grow 3D, with multi-height islands forming easily. Reasons for the 3D morphology are the much weaker metal carbon bond when compared to the metal cohesive energy and the role of Coulomb repulsion of the poorly screened charges at the metal graphene interface. We employed the complementary techniques of SPA-LEED and STM to study the growth of Dy on graphene. It was found that under kinetic limitations it is possible to fully cover graphene with a bilayer Dy film, by growing well below room temperature in stepwise deposition experiments. Lastly, the Dy film, however, is amorphous but ways to crystallize it within the 2D morphology are possible, since long range order improves at higher growth temperature.

  13. The origin of EL2 family evidenced by STM direct observations of individual photoquenching behaviors

    NASA Astrophysics Data System (ADS)

    Hida, Akira; Mera, Yutaka; Maeda, Koji

    2003-12-01

    Abundant point defects in low-temperature grown (LT-) GaAs, presumably As antisite defects, exhibit a photo-induced transformation at low temperatures with an excitation spectrum very close to that obtained for the macroscopic photoquenching effect of EL2 centers. Some of the defects do not exhibit the photo-induced transformation, disfavoring the hypothesis of variants of EL2-like centers differing in the atomic structures. The unquenchable EL2 centers are commonly located near the interface between the LT-GaAs epi-layer and the n-GaAs substrate. Separate macroscopic photoluminescence experiments showed that the photoquenching efficiency is strongly decreased by external compressive stress, which suggests that the absence of the phototransformation behavior in some centers was due to a local stress field induced by the lattice mismatch between the epi-layer and the substrate. This is shown by STM-electric field modulation spectroscopy that the epi-layer was locally strained to a different degree depending on the position from the interface. Therefore, we conclude that the EL2 variants are the result of the spatial variation of the internal stress environment that is felt by the EL2 centers in an identical atomic structure.

  14. STM observation of a box-shaped graphene nanostructure appeared after mechanical cleavage of pyrolytic graphite

    NASA Astrophysics Data System (ADS)

    Lapshin, Rostislav V.

    2016-01-01

    A description is given of a three-dimensional box-shaped graphene (BSG) nanostructure formed/uncovered by mechanical cleavage of highly oriented pyrolytic graphite (HOPG). The discovered nanostructure is a multilayer system of parallel hollow channels located along the surface and having quadrangular cross-section. The thickness of the channel walls/facets is approximately equal to 1 nm. The typical width of channel facets makes about 25 nm, the channel length is 390 nm and more. The investigation of the found nanostructure by means of a scanning tunneling microscope (STM) allows us to draw a conclusion that it is possible to make spatial constructions of graphene similar to the discovered one by mechanical compression, bending, splitting, and shifting graphite surface layers. The distinctive features of such constructions are the following: simplicity of the preparation method, small contact area between graphene planes and a substrate, large surface area, nanometer cross-sectional sizes of the channels, large aspect ratio. Potential fields of application include: ultra-sensitive detectors, high-performance catalytic cells, nanochannels for DNA manipulation, nanomechanical resonators, electron multiplication channels, high-capacity sorbents for hydrogen storage.

  15. Underpotential deposition of Cd on Ag(1 1 1): an in situ STM study

    NASA Astrophysics Data System (ADS)

    García, S. G.; Salinas, D. R.; Staikov, G.

    2005-02-01

    The kinetics and mechanism of Cd underpotential deposition (UPD) and involved surface alloy formation processes in the system Ag(1 1 1)/Cd 2+, SO42-, are studied by means of combined electrochemical measurements and in situ scanning tunneling microscopy (STM). The results show that the UPD process starts with a formation of an expanded (diluted) adlayer with a superlattice structure Ag(1 1 1)- (√{3}×√{19})R23.4°. In the underpotential range 50 mV < Δ E < 80 mV this adlayer transforms to a condensed close packed Cd monolayer via a first order phase transition. At long polarization times the condensed monolayer undergoes structural changes involving place exchange processes between Cd atoms and surface Ag atoms. A formation of a second Cd monolayer and a significant Ag-Cd surface alloying take place at lower underpotentials (Δ E < 50 mV). The kinetics of surface alloying are analyzed on the basis of a recently proposed diffusion model including a relatively fast initial formation of a very thin surface alloy film and a subsequent slow alloy growth controlled by solid state diffusion. The anodic dealloying results in an appearance of monatomically deep pits, which disappear quickly at relatively high underpotentials (Δ E > 550 mV) indicating a high mobility of surface Ag atoms.

  16. Electrolyte gating in redox-active tunneling junctions--an electrochemical STM approach.

    PubMed

    Pobelov, Ilya V; Li, Zhihai; Wandlowski, Thomas

    2008-11-26

    We report on the construction of an asymmetric tunneling junction between a Au STM tip and a Au(111)-(1 x 1) substrate electrode modified with the redox-active molecule N-hexyl-N'-(6-thiohexyl)-4,4'-bipyridinium bromide (HS6V6) in an electrochemical environment. The experiments focused on the reversible one-electron transfer reaction between the viologen dication V(2+) and the radical cation V(+*). Employing the concept of "electrolyte gating" we demonstrate transistor- and diodelike behavior based on in situ scanning tunneling spectroscopy at constant or variable bias voltages. We derived criteria and verified that the experimental data could be represented quantitatively by a model assuming a two-step electron transfer with partial vibrational relaxation. The analysis illustrates that the magnitude of the tunneling enhancement depends on the initial redox state of HS6V6 (V(2+) or V(+*)). Characteristic parameters, such as reorganization energy, potential drop, and overpotential across the tunneling gap were estimated and discussed. We present a clear discrimination between the redox-mediated enhanced and the off-resonance tunneling currents I(enh) respective I(T) and distinguish between electron transfer in symmetric and asymmetric Au | redox-molecule | Au configurations.

  17. Comparing the Effects of 10-Hz Repetitive TMS on Tasks of Visual STM and Attention

    PubMed Central

    Emrich, Stephen M.; Johnson, Jeffrey S.; Sutterer, David W.; Postle, Bradley R.

    2016-01-01

    Numerous studies have demonstrated that visual STM (VSTM) and attention are tightly linked processes that share a number of neuroanatomical substrates. Here, we used repetitive TMS (rTMS) along with simultaneous EEG to examine the causal relationship between intraparietal sulcus functioning and performance on tasks of attention and VSTM. Participants performed two tasks in which they were required to attend to or remember colored items over a brief interval, with 10-Hz rTMS applied on some of the trials. Although no overall behavioral changes were observed across either task, rTMS did affect individual performance on both the attention and VSTM tasks in a manner that was predicted by individual differences in baseline performance. Furthermore, rTMS also affected ongoing oscillations in the alpha and beta bands, and these changes were related to the observed change in behavioral performance. The results reveal a causal relationship between intraparietal sulcus activity and tasks measuring both visual attention and VSTM. PMID:27626224

  18. Anisotropic superconductivity in β-(BDA-TTP)2SbF6: STM spectroscopy

    NASA Astrophysics Data System (ADS)

    Nomura, K.; Muraoka, R.; Matsunaga, N.; Ichimura, K.; Yamada, J.

    2009-03-01

    We have investigated the gap symmetry in the superconducting phase of β-(BDA-TTP)2SbF6 with use of the scanning tunneling microscope (STM). The tunneling spectra obtained on the conducting surface show a clear superconducting gap structure. Its functional form is of V-shaped similarly to κ-(BEDT-TTF)2X and suggests the anisotropic superconducting gap with line nodes. For lateral surfaces the shape of tunneling spectra varies from the U-shape with relatively large gap to the V-shape with small gap depending on the tunneling direction alternately twice between directional angle 0 and π. From the analysis of conductance curve taking the k dependence of the tunneling probability into account, it is found that the gap has maximum near the a* and c* axes and the nodes appear along near a*+c* and the a-c* directions. These indicate that the d like superconducting pair is formed in this system as the case of κ-(BEDT-TTF)2X. This node direction is consistent with the theoretical prediction based on the spin fluctuation mechanism. However, the zero-bias conductance peak has not been observed yet.

  19. Self-assembly of trimetallic nitride template fullerenes on surfaces studied by STM

    NASA Astrophysics Data System (ADS)

    Leigh, D. F.; Nörenberg, C.; Cattaneo, D.; Owen, J. H. G.; Porfyrakis, K.; Li Bassi, A.; Ardavan, A.; Briggs, G. A. D.

    2007-07-01

    Trimetallic nitride template fullerenes have been deposited onto a variety of substrates in order to elucidate the substrate-fullerene interactions. We have investigated self-assembled island formation and molecular detail of Er 3N@C 80 and Sc 3N@C 80 on Ag/Si(1 1 1), Au(1 1 1)/mica, Si(1 1 1), and Si(0 0 1) using variable temperature scanning tunnelling microscopy (STM). At room temperature, the fullerenes self-assemble into monolayer-high hexagonal close-packed islands on Ag-passivated Si(1 1 1) whereas annealing at elevated temperatures (250-300 °C) is necessary for the self-assembly of close-packed islands on Au(1 1 1). Intra-molecular resolution of the fullerenes has been achieved at liquid nitrogen temperature on Ag/Si(1 1 1) and already at room temperature on Si(0 0 1), when the rotation of the fullerenes is frozen. Whereas the bonding between the fullerenes and Si surfaces is mainly covalent, it appears to be mainly van-der-Waals on the other surfaces.

  20. 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.

  1. Recoding between two types of STM representation revealed by the dynamics of memory search.

    PubMed

    Leszczyński, Marcin; Myers, Nicholas E; Akyürek, Elkan G; Schubö, Anna

    2012-03-01

    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 electrophysiological markers of attention in a memory search task with varying intervals between VSTM encoding and recall, and so we were able to track recoding of representations in memory. Results confirmed the involvement of attention in VSTM recall. However, the amplitude of the N2pc and N3rs components, which mark orienting of attention and search within VSTM, decreased as a function of delay. Conversely, the amplitude of the P3 and sustained posterior contralateral negativity components increased as a function of delay, effectively the opposite of the N2pc and N3rs modulations. These effects were only observed when verbal memory was not taxed. Thus, the results suggested that gradual recoding from visuospatial orienting of attention into verbal recall mechanisms takes place from short to long retention intervals. Interestingly, recall at longer delays was faster than at short delays, indicating that verbal representation is coupled with faster responses. These results extend the orienting-of-attention hypothesis by including an account of representational recoding during short-term consolidation and its consequences for recall from VSTM.

  2. Dy uniform film morphologies on graphene studied with SPA-LEED and STM

    DOE PAGES

    McDougall, D.; Hattab, H.; Hershberger, M. T.; ...

    2016-07-01

    The use of graphene for microelectronics and spintronic applications requires strategies for metals to wet graphene and to grow layer-by-layer. This is especially important when metals will be used as electrical contacts or as spin filters. Extensive work in the literature so far has shown that this is very challenging, since practically all metals grow 3D, with multi-height islands forming easily. Reasons for the 3D morphology are the much weaker metal carbon bond when compared to the metal cohesive energy and the role of Coulomb repulsion of the poorly screened charges at the metal graphene interface. We employed the complementarymore » techniques of SPA-LEED and STM to study the growth of Dy on graphene. It was found that under kinetic limitations it is possible to fully cover graphene with a bilayer Dy film, by growing well below room temperature in stepwise deposition experiments. Lastly, the Dy film, however, is amorphous but ways to crystallize it within the 2D morphology are possible, since long range order improves at higher growth temperature.« less

  3. 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

  4. STM/AFM studies of the evolution of morphology of electroplated Ni/W alloys

    NASA Astrophysics Data System (ADS)

    Zhu, L.; Younes, O.; Ashkenasy, N.; Shacham-Diamand, Y.; Gileadi, E.

    2002-11-01

    The surface morphology evolution of Ni/W alloys was studied, as a function of the alloy composition. Using the modified plating baths developed in our laboratory recently, electroplated Ni/W alloys with different W content, in the range of 7-67 atom percent (a/o), can be obtained. This was found to lead to different structures, ranging from polycrystalline fcc-Ni type structure to amorphous, followed by orthorhombic with increasing W content in the alloy. Powder XRD was studied to determine the crystal structures. Ex situ STM, AFM and SEM were used to study in detail the surface morphologies of the different alloys, and their evolution with increasing W content. The important findings are that a mixture of two crystalline forms can give rise to an amorphous structure. Hillocks that are usually a characteristic of epitaxial growth can also exist in the amorphous alloys. Oriented scratches caused by stress can also be formed. Up to 20 a/o of W is deposited in the alloys in crystalline form, with the fcc-Ni type structure. Between 20 and about 40 a/o an amorphous structure is observed, and above that an orthorhombic crystal structure is seen, which is characteristic of the NiW binary alloy. Careful choice of the composition of the plating bath allowed us to deposit an alloy containing 67 a/o W, which corresponds to the composition NiW 2.

  5. Photon-assisted transport through a 1D-dot-graphene similar to STM model device

    NASA Astrophysics Data System (ADS)

    Zhao, Zhiyun; Min, Yi; Zhou, Pengxia; Huang, Yanyan; Zhong, Chonggui

    2017-08-01

    By using the nonequilibrium Green function method, the photon-assisted electron transport through a graphene-based device similar to STM model is studied theoretically and numerically. The device is composed of a single central site (quantum dot) modulated by an oscillating electric field, a one-dimensional quantum wire and a two-dimensional graphene sheet. Some interesting results on transmission probability and current-voltage (I-V) characteristics of the device are given in this paper. In the presence of an oscillating electric field, we find that besides the central two transmission peaks caused by graphene part, there appear photon-assisted peaks which are distributed on both sides of the Fermi level. The positions of the photon-assisted peaks are linear to the frequency of the oscillating electric field, and the widths of the photon-assisted peaks are relevant to the amplitude of the oscillating electric field. It is found that the current-voltage graphs exhibit step growth due to the existence of photon-assisted tunneling. We hope these results may have guidance meaning for the fabrication of optoelectronic devices.

  6. Quantitative and high-resolution magnetic images obtained by STM-SQUID microscope with distance modulation technique

    NASA Astrophysics Data System (ADS)

    Yokocho, T.; Akaba, H. S.; Miyato, Y.

    2017-07-01

    We have developed an STM-SQUID microscope, in which a scanning tunnelling microscope (STM) is combined with an rf-SQUID. The issue in our STM-SQUID microscope was that the obtained magnetic image was not the same as the sample’s ideal magnetic field distribution. This was because the magnetic image could be affected not only by the sample’s local magnetic field distribution, but also by the magnetic field distribution above the sample, namely “background field”. In this work, we applied the distance modulation technique to our microscope. In this technique, the change of the SQUID output signal was detected while the distance between the sample and the probe tip was modulated in a constant amplitude. As a result, the influence of the background field was cancelled out, and the magnetic information near the sample surface was largely extracted. We successfully obtained the quantitative magnetic images in ~100 nm spatial resolution by using the distance modulation technique.

  7. SIESTA study of c-GaN(001)-4x1 surface reconstruction: Tetramers andtheir STM images.

    NASA Astrophysics Data System (ADS)

    Sandler, Nancy; Ordejon, Pablo

    2005-03-01

    Recent STM, STS and RHEED studies [1] on cubic GaN(001), grown using rf MBE under Ga-rich conditions, have revealed a surface structure consistent with predicted tetramer formation [2,3]. STM images reveal a surface consisting of rows aligned along the [110] direction with a periodicity along the [110] direction of about 12.8 å. STS measurements indicate the semiconducting nature of the surface and RHEED patterns of the surface provide further evidence of a periodicity consistent with tetramer formation. We report on a first principle study of this particular surface reconstruction using the SIESTA code [4], a self-consistent density functional method using standard norm-conserving pseudo-potentials and a flexible numerical linear combination of atomic orbitals basis set. Band structure calculations are in good agreement with previously reported results and the STM images obtained reproduce experimental observations. [1] H. Al-Brithen, M. Haider, A. Smith, N. Sandler and P. Ordejon. Submitted to PRL. [2] Neugebauer et al. Phys. Rev. Lett. 80, 3097 (1998) [3] Feuillet et al. Appl. Phys. Lett. 70, 24 (1997) [4] D. Sanchez-Portal, P. Ordejon, E. Artacho, and J. M. Soler, Int. Journ. of Quant. Chem. 65, 453 (1999).

  8. Comparative investigation of underpotential deposition of Ag from aqueous and ionic electrolytes: An electrochemical and in situ STM study.

    PubMed

    Borissov, D; Aravinda, C L; Freyland, W

    2005-06-16

    Underpotential deposition (UPD) of Ag on Au(111) has been studied with two different electrolytes: aqueous 0.1 M H2SO4 solution in comparison with the ionic liquid 1-butyl-3-methylimidazolium chloride BMICl + AlCl3. Of particular interest is the distinct behavior of 2D phase formation at both interfaces, which has been investigated by cyclic and linear sweep voltammetry in combination with in situ electrochemical scanning tunneling microscopy (STM). It is found that one monolayer (ML) of Ag is formed in the UPD region in both electrolytes. In aqueous solution, atomically resolved STM images at 500 mV versus Ag/Ag+ show a (3 x 3) adlayer of Ag, whereas after sweeping the potential just before the commencement of the bulk Ag deposition, a transition from expanded (3 x 3) to pseudomorphic ML of Ag on Au(111) occurs. In BMICl-AlCl3, the first UPD process of Ag exhibits two peaks at 410 and 230 mV indicating that two distinct processes on the surface take place. For the first time, STM images with atomic resolution reveal a transition from an inhomogeneous to an ordered phase with a (square root of 3 x square root of 3)R30 degrees structure and an adsorption of AlCl4- anions having a superlattice of (1.65 x square root of 3)R30 degrees preceding the deposition of Ag.

  9. Classical electricity analysis of the coupling mechanisms between admolecule vibrations and localized surface plasmons in STM for vibration detectability

    NASA Astrophysics Data System (ADS)

    Inaoka, Takeshi; Uehara, Yoich

    2017-08-01

    The presence of a dynamic dipole moment in the gap between the tip of a scanning tunneling microscope (STM) and a substrate, both of which are made of metal, produces a large dynamic dipole moment via the creation of localized surface plasmons (LSPLs). With regard to the vibration-induced structures that have been experimentally observed in STM light emission spectra, we have incorporated the effect of the phonon vibrations of an admolecule below the STM tip into the local response theory, and we have evaluated the enhancement of the dynamic dipole involving phonon vibrations. Our analysis shows how effectively this vibration becomes coupled with the LSPLs. This was shown using three mechanisms that considered the vibrations of a dipole-active molecule and the vibrations of a charged molecule emitting and receiving tunneling electrons. In each of the mechanisms, phonon vibrations with angular frequency ωp shifted each LSPL resonance by ℏωp or by a multiple of ℏωp . The phonon effect was negligibly small when the position of the dipole-active molecule vibrated with ωp, but it was largest and most detectable when the point charge corresponding to the admolecule at the surface of the tip vibrated with ωp. It was found that a series of LSPL resonances with or without phonon-energy shifts can be characterized by a few dominant orders of multipole excitations, and these orders become higher as the resonance energy increases.

  10. A Role for the EAL-Like Protein STM1344 in Regulation of CsgD Expression and Motility in Salmonella enterica Serovar Typhimurium▿

    PubMed Central

    Simm, Roger; Remminghorst, Uwe; Ahmad, Irfan; Zakikhany, Katherina; Römling, Ute

    2009-01-01

    The bacterial second messenger cyclic di-GMP (c-di-GMP) regulates the transition between sessility and motility. In Salmonella enterica serovar Typhimurium, the expression of CsgD, the regulator of multicellular rdar morphotype behavior, is a major target of c-di-GMP signaling. CsgD expression is positively regulated by at least two diguanylate cyclases, GGDEF domain proteins, and negatively regulated by at least four phosphodiesterases, EAL domain proteins. Here, we show that in contrast to EAL domain proteins acting as phosphodiesterases, the EAL-like protein STM1344 regulated CsgD expression positively and motility negatively. STM1344, however, did not have a role in c-di-GMP turnover and also did not bind the nucleotide. STM1344 acted upstream of the phosphodiesterases STM1703 and STM3611, previously identified to participate in CsgD downregulation, where it repressed their expression. Consequently, although STM1344 has not retained a direct role in c-di-GMP metabolism, it still participates in the regulation of c-di-GMP turnover and has a role in the transition between sessility and motility. PMID:19376870

  11. 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

  12. 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

  13. 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

  14. Sulfur-induced corrosion of Au(111) studied by real-time STM

    SciTech Connect

    Biener, M; Biener, J; Friend, C

    2004-11-02

    The interaction of sulfur with gold surfaces has attracted considerable interest due to numerous technological applications such as the formation of self-assembled monolayers (SAMs), use as a corrosion inhibitor, and as a chemical sensor. In this work, the interaction of sulfur with Au(111) at two different temperatures (300 K and 420 K) was studied by real-time scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). In the low coverage regime (< 0.1 monolayer), S modifies the surface stress leading to a lateral expansion of the Au surface layer. An ordered ({radical}3 x {radical}3)R30{sup o} sulfur adlayer develops as the coverage reaches {approx}0.3 ML. With further increasing S coverage the Au(111) surface undergoes a dynamic rearrangement while forming a two-dimensional AuS phase: gold surface atoms are removed from regular terrace sites and incorporated into the growing gold sulfide phase resulting in the appearance of pits and irregularly shaped AuS islands. Gold sulfide prepared at room temperature exhibits short-range order; an incommensurate, long-range ordered AuS phase develops upon annealing at 450-525 K. Higher temperatures lead to decomposition of the AuS corrosion film. Formation of an ordered AuS phase via rapid step retraction rather than etch pit formation is observed during S-interaction with Au(111) surfaces at 420 K. Our results shed new light on the S-Au(111) interaction.

  15. Synthesis, electrochemistry, STM investigation of oligothiophene self-assemblies with superior structural order and electronic properties

    NASA Astrophysics Data System (ADS)

    Kuo, Cheng-Yu; Liu, Yinghao; Yarotski, Dmitry; Li, Hao; Xu, Ping; Yen, Hung-Ju; Tretiak, Sergei; Wang, Hsing-Lin

    2016-12-01

    Three oligothiophene (terthiophene, tetrathiophene and pentathiophene) derivatives are synthesized and their monolayer self-assemblies on gold (Au) are prepared via Au-S covalent bond. Our UV-Vis experimental characterization of solution reveals the dependence of the optical properties on the conjugation length of the oligothiophenes, which compares well with Time-Dependent Density Functional Theory (TDDFT) simulations of spectra of individual chromophores. Photoluminescent spectra of thin films show pronounced red shifts compared to that of solutions, suggesting strong inter-oligomer interactions. The comparative studies of cyclic voltammograms of tetrathiophene from solution, cast film and self-assembled monolayer (SAM) indicate presence of one, two, and three oxidized species in these samples, respectively, suggesting a very strong electronic coupling between tetrathiophene molecules in the SAM. Scanning tunneling microscopy (STM) imaging of SAMs of the tetrathiophene on an atomically flat Au surface exhibits formation of monolayer assemblies with molecular order, and the molecular packing appears to show an overlay of oligothiophene molecules on top of another one. In contrast, the trimer and pentamer images show only aggregated species lacking long-range order on the molecular level. Such trends in going from disordered-ordered-disordered monolayer assemblies are mainly due to a delicate balance between inter-chromophore π-π couplings, hydrophobic interaction and the propensity to form Au-S covalent bond. Such hypothesis has been validated by our computational results suggesting different interaction patterns of oligothiophenes with odd numbered and even numbered thiophene repeat units placed in a dimer configuration. Observed correlations between oligomer geometry and structural order of monolayer assembly elucidate important structure-property relationships and have implications for these molecular structures in organic optoelectronic devices and energy

  16. 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.

  17. 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.

  18. Two separate pathways including SlCLV1, SlSTM and SlCUC that control carpel development in a bisexual mutant of Silene latifolia.

    PubMed

    Koizumi, Ayako; Yamanaka, Kahori; Nishihara, Kiyoshi; Kazama, Yusuke; Abe, Tomoko; Kawano, Shigeyuki

    2010-02-01

    Carpel suppression is a trigger for sexual dimorphism in the dioecious plant Silene latifolia. To clarify what kind of genes are involved in carpel suppression in this species, we generated a bisexual mutant, R025, by C-ion beam irradiation. R025 produces bisexual flowers with a mature gynoecium and mature stamens. Genetic analysis of R025 attributed the bisexual trait to mutations on the Y chromosome. Scanning electron microscopy (SEM) analysis of early floral development revealed that the carpel size of R025 was different from that of wild-type males in spite of the male background in R025. We also identified an S. latifolia CLAVATA1-like gene (SlCLV1) as a candidate of the CLAVATA-WUSCHEL (CLV-WUS) pathway. Two separate pathways, the CLV-WUS pathway and the CUP-SHAPED COTYLEDON (CUC)-SHOOT MERISTEMLESS (STM) pathway, contribute to carpel development in the Arabidopsis floral meristem. SlSTM1 and SlSTM2 (orthologs of STM) and SlCUC (an ortholog of CUC1 and CUC2) have already been identified in S. latifolia. We therefore examined the expression patterns of SlCLV1, SlSTM (SlSTM1 and SlSTM2) and SlCUC in young flowers of R025 and wild-type males and females. The expression patterns of the three genes in the two pathways differ between the wild-type male and the bisexual mutant, and the differences in expression patterns of the three genes occur at the same stage. These results suggest that in addition to SlSTM1, SlSTM2 and SlCUC, SlCLV1 is also involved in carpel suppression in S. latifolia. They also suggest that a gynoecium-suppressing factor (GSF), which is lost in the R025 Y chromosome, acts on an upstream gene that is common to the two pathways, triggering sexual dimorphism in S. latifolia.

  19. 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.

  20. 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.

  1. STM observation of thia[1 1]heterohelicene on gold( 1 1 1 ) and gold(1 1 0) surface

    NASA Astrophysics Data System (ADS)

    Taniguchi, Masahiro; Nakagawa, Hiroko; Yamagishi, Akihiko; Yamada, Kohichi

    2002-06-01

    Monolayers of helically shaped aromatic compound, hexathia[1 1]heterohelicene ([1 1]TH), which consists of five benzene rings and six thiophene rings were prepared on gold(1 1 1) and gold(1 1 0) surface under UHV condition. LEED and STM were used for the structural study focused on the molecular chirality. [1 1]TH monolayer on gold(1 1 1) substrate showed the same structure as on (1 1 1) analogue of polycrystalline surface. [1 1]TH evaporated on gold(1 1 0) showed loosely packed molecular chains. The results were compared with the results on gold polycrystalline surface and the bulk structural analysis.

  2. Pb deposition on I-coated Au(111). UHV-EC and EC-STM studies.

    PubMed

    Kim, Youn-Geun; Kim, Jay Yu; Thambidurai, Chandru; Stickney, John L

    2007-02-27

    This article concerns the growth of an atomic layer of Pb on the Au(111)( radical3 x radical3)R30 degrees -I structure. The importance of this study lies in the use of Pb underpotential deposition (UPD) as a sacrificial layer in surface-limited redox replacement (SLRR). SLRR reactions are being applied in the formation of metal nanofilms via electrochemical atomic layer deposition (ALD). Pb UPD is a surface-limited reaction, and if it is placed in a solution of ions of a more noble metal, redox replacement can occur, but limited by the amount of Pb present. Pb UPD is a candidate for use as a sacrificial layer for replacement by any more noble element. It has been used by this group for both Cu and Pt nanofilm formation using electrochemical ALD. The I atom layer was intended to facilitate electrochemical annealing during nanofilm growth. Two distinctly different Pb atomic layer structures are reported, studied using in situ scanning tunneling microscopy (STM) with an electrochemical flow cell and ultrahigh vacuum surface analysis combined directly with electrochemical reactions (UHV-EC). Starting with the initial Au(111)( radical3 x radical3)R30 degrees -I, 1/3 monolayer of I on the Au(111) surface, Pb deposition began at approximately 0.1 V. The first Pb UPD structure was observed just below -0.2 V and displayed a (2 x radical3)-rect unit cell, for a structure composed of 1/4 monolayer each of Pb and I. The I atoms fit in Pb 4-fold sites, on the Au(111) surface. The structure was present in domains rotated by 120 degrees. Deposition to -0.4 V resulted in complete loss of the I atoms and formation of a Pb monolayer on the Au(111), which produced a Moiré pattern, due to the Pb and Au lattice mismatch. These structures represent two well-defined starting points for the growth of nanofilms of other more noble elements. It is apparent from these studies that the adsorption of I- on Pb is weak, and it will rinse away. If Pb is used as a sacrificial metal in an

  3. Atomic surface structures on multi-layered cuprate superconductor Ba 2Ca 4Cu 5O 10(O 1-xF x) 2 observed by STM

    NASA Astrophysics Data System (ADS)

    Sugimoto, A.; Ukita, R.; Ekino, T.; Harada, Y.; Furukawa, T.; Itagaki, K.; Tokiwa, K.

    2011-11-01

    We investigate the scanning tunneling microscopy (STM) on the multi-layered cuprate superconductor Ba2Ca4Cu5O10(O1-xFx)2 (F0245, Tc = 79 K, x = 0.72). The STM images show clear atomic lattice structures and large random spot structures. Among the regular square-lattice atomic corrugation with the period of the lattice constant a ∼ 0.38 nm, another kind of atomic spots arranged into the fourfold cross shaped clusters is clearly observed along the diagonal direction with the period of 0.26 nm. These clusters are being distributed inhomogeneously, which are due to the charge imbalance associated with the apical O/F rate. The apical O and F sites are also identified from the positions of such clusters in the STM topographic images.

  4. Initial stages of Lutetium growth on Si (111)-7 × 7 probed by STM and core-level photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Smykalla, Lars; Shukrynau, Pavel; Hietschold, Michael

    2017-09-01

    The interaction of small amounts of Lutetium with the Si (111)-7 × 7 reconstructed surface was investigated in detail using a combination of Scanning Tunneling Microscopy (STM) and Photoelectron Spectroscopy (XPS and UPS). Various immobile and also fastly moving atoms and nanocluster were found in the initial growth of the Lu/Si interface. Density functional theory calculations and photoelectron spectroscopy results suggest that the most attractive adsorption sites for the Lu atoms are basins around Si rest-atoms and there is no strong interaction between Lu and Si at the initial steps of film growth. However Lu nanocluster could also be found on other adsorption sites which results in a different voltage dependence in STM. Coverage-dependent STM images reveal the growth of a closed Lu metal overlayer by joining of the clusters. The existence of a stoichiometric Lu silicide compound was not detected on the surface in the initial growth for deposition at room temperature.

  5. Adlayers of C60-C60 and C60-C70 fullerene dimers formed on au(111) in benzene solutions studied by STM and LEED.

    PubMed

    Matsumoto, Masashi; Inukai, Junji; Tsutsumi, Eishi; Yoshimoto, Soichiro; Itaya, Kingo; Ito, Osamu; Fujiwara, Koichi; Murata, Michihisa; Murata, Yasujiro; Komatsu, Koichi

    2004-02-17

    Scanning tunneling microscopy (STM) and low-energy electron diffraction were used to reveal the structures of ordered adlayers of [2+2]-type C60-C60 fullerene dimer (C120) and C60-C70 cross-dimer (C130) formed on Au(111) by immersingit in abenzene solution containing C120 or C130 molecules. High-resolution STM images clearly showed the packing arrangements and the electronic structures of C120 and C130 on the Au(111) surface in ultrahigh vacuum. The (2 square root3 x 4square root3)R30 degrees, (2square root3 x 5square root3)R30 degrees, and (7 x 7) structures were found for the C120 adlayer on the Au(111) surface, whereas C130 molecules were closely packed on the surface. Each C60 or C70 monomer cage was discerned in the STM image of a C130 molecule.

  6. 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

  7. 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.

  8. Current oscillations in ultra-small superconducting Nb-Nb junctions formed by STM at mK temperatures

    NASA Astrophysics Data System (ADS)

    Dreyer, Michael; Roychowdhury, Anita; Dana, Rami

    2014-03-01

    Using etched Nb STM tips we formed ultra-small tunnel junctions on a Nb crystal at an effective temperature of ~ 200 mK using an Oxford dilution refrigerator. The Nb crystal was prepared in UHV and then transferred into the mK STM. The resulting superconductor-insulator-superconductor (SIS) junction displayed several sub-gap features from multiple Andreev reflections to a zero bias conductance peak. The latter showed features of a Josephson junction in the phase diffusion limit with side structures due to the electrical environment. Upon microwave irradiation the peak split into multiple peaks in accordance with theory, verifying Josephson tunneling. In addition we observed bias dependent oscillations of the tunneling current. The oscillations where recorded at a rate of 10 kS/s while acquiring conventional dI/dV or I(V) spectroscopic curves. Histograms of the current for each bias voltage step then reveal the nature of the oscillation. It ranges from multiple states in certain bias regions through pure oscillations to supercurrent-normal switching. Fourier transform of the current show in some cases a bias dependence of the main frequencies. Possible causes will be discussed.

  9. An STM study of C 60 adsorption on Si(100)-(2 × 1) surfaces: from physisorption to chemisorption

    NASA Astrophysics Data System (ADS)

    Chen, Dong; Sarid, Dror

    1995-05-01

    The adsorption of C 60 molecules on Si(100)-(2 × 1) surfaces before and after annealing has been studied using scanning tunneling microscopy (STM). For room temperature deposition, the STM images reveal that the C 60 molecules adsorb predominantly at the four-dimer sites in the troughs between dimer rows. C 60 molecules bonded to two-dimer sites are also observed in small molecular clusters forming even at a low coverage. The nature of the interaction between the adsorbates and the Si(100)-(2 × 1) surface is explained in terms of a dipole-induced dipole interaction. Subsequent annealing of the samples to 600°C changes the adsorption characteristics of the C 60 molecules. First, the annealing causes a strong covalent bonding between the carbon atoms of the C 60 molecules and the silicon atoms of the substrate, and modifies the bonding sites of the adsorbates from locations in the troughs to locations on the dimer rows. Second, the annealing causes some initial surface diffusion and clustering of the C 60 molecules, which now tend to stick to the ends, rather than the sides, of the dimer rows. Furthermore, after the annealing process, it is observed that small silicon islands form on the substrate terraces along with isolated and clustered adsorbates.

  10. 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.

  11. 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).

  12. FTIR spectroscopic analysis and STM studies of electroluminescent Eu(DBM) 3 bath thin films vacuum deposited onto Au surface

    NASA Astrophysics Data System (ADS)

    Dovbeshko, G.; Fesenko, O.; Fedorovich, R.; Gavrilko, T.; Marchenko, A.; Puchkovska, G.; Viduta, L.; Naumovets, A.; Chubich, D.; Vitukhnovskii, A.; Fichou, D.

    2006-07-01

    Molecular organization and morphology of vacuum deposited (VD) thin films of the europium complex of europium(dibenzoylmethanato) 3(bathophenanthroline) (Eu(DBM) 3 bath) from metal-organic planar light-emitting nanocomposites consisting of gold island films and VD Eu(DBM) 3 bath film were investigated by FTIR spectroscopy and scanning tunneling microscopy (STM). It has been found that thermal evaporation in vacuum does not cause chemical decomposition of Eu(DBM) 3 bath, and that the obtained films are essentially amorphous. Reflection-absorption IR spectra show no predominant orientation of Eu(DBM) 3 bath molecules in the films with respect to the substrate. With the STM method, the morphology and structure of the near-surface layers of Eu(DBM) 3 bath films were characterized, and it was found that they consist of self-assembled molecular dimers closely packed along the Au [110] steps on the Au(111) terrace. With increase of the Eu(DBM) 3 bath film thickness, the ordered structure is lost.

  13. UHV-STM of single-walled carbon nanotubes in registration with the atomic lattices of silicon surfaces

    NASA Astrophysics Data System (ADS)

    Albrecht, Peter

    2005-03-01

    A room-temperature UHV-STM is used to elucidate the registration dependence of the electronic and mechanical properties of single-walled carbon nanotubes (SWCNTs) adsorbed onto silicon surfaces. The SWCNTs are deposited onto the Si surface in situ using a dry contact transfer (DCT) technique [1], with the resultant pristine SWCNT-Si interface enabling a joint atomic-resolution topographic and spectroscopic study of individual SWCNTs on both clean and H-passivated Si(100)-2x1 surfaces. Pronounced variations in the I-V and dI/dV-V spectra acquired along an isolated SWCNT were found to correlate with a transition from parallel to perpendicular alignment of the tube with respect to the dimer rows of the clean Si surface. Recent theoretical work [2] suggests that SWCNT-Si alignment is indeed energetically favorable and may give rise to novel nanotube-surface interactions unobserved in previous STM studies of SWCNTs in contact with a metallic substrate. [1] P.M. Albrecht and J.W. Lyding, APL 83, 5029 (2003). [2] W. Orellana, R.H. Miwa, and A. Fazzio, PRL 91, 166802 (2003).

  14. 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

  15. STM observations of organometallic complexes on the TiO 2(1 1 0) and Si(1 1 1) surfaces

    NASA Astrophysics Data System (ADS)

    Maeda, Y.; Okumura, M.; Daté, M.; Tsubota, S.; Haruta, M.

    2002-08-01

    Gas-phase grafting of organometallic complexes is a relatively new technique for preparing supported metal catalysts. In order to understand the initial stage in this method, we have performed scanning tunneling microscopy (STM) observations of organo-gold and -iridium complexes adsorbed on TiO 2(1 1 0) and Si(1 1 1) surfaces before and after annealing in an ultra-high vacuum. The STM observations revealed that the surface structure was strongly dependent on the interaction between the surface and individual molecules, and the presence of oxygen atoms on the surface.

  16. STM/STS investigations of fullerene C(60), endohedral metallofullerenes M C(82) and carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Lin, Nian

    , ..., and crystalline islands, while Dy@Csb{82} molecules still aggregate as 3-D clusters. The intermolecular interaction is believed to be dominated by a dipole-dipole interaction. After experiencing a strong electric field applied by an STM tip, the Nd@Csb{82} molecules will undergo a structural transformation from the close-packing to ring like configurations. The rings are well-shaped (as a hexagonal polygon), well-numbered (consisting of six or multiples of six molecules) and stable. The mechanism of the tip-driven transformation are discussed. We suggest that molecules within these rings are bonded covalently. As a byproduct, we found a new path to generate carbon nanotubes. After the overlaying mixture of Csb{60} and M@Csb{82} on an HOPG surface has been irradiated with KeV electrons, carbon nanotubes are observed laying on the surface. They are straight, clean and have diameters in the range of 2-50 nm and length up to 3 mum. The detailed atomic images of the tube walls show helical arrangements of the honeycomb structure of a graphite (0001) surface. The formation mechanism of these tubes also is discussed. Future research directions are identified. The systematic study of Lanthanide's endohedral fullerenes would uncover the roles of the metal atoms. More detailed understanding of the formation of the rings and the nanotubes from endohedral metallofullerenes could lead to finding methods for their mass production and novel applications.* ftn*Originally published in DAI Vol. 58, No. 11. Reprinted here with corrected author name.

  17. Draft Genome Sequence of Rhizobium mesoamericanum STM3625, a Nitrogen-Fixing Symbiont of Mimosa pudica Isolated in French Guiana (South America).

    PubMed

    Moulin, Lionel; Mornico, Damien; Melkonian, Rémy; Klonowska, Agnieszka

    2013-01-01

    Rhizobium mesoamericanum STM3625 is a Mimosa pudica symbiont isolated in French Guiana. This strain serves as a model bacterium for comparison of adaptation to mutualism (symbiotic traits, bacterial genetic programs for plant infection) between alpha and beta rhizobial symbionts of Mimosa pudica.

  18. Draft Genome Sequence of Rhizobium mesoamericanum STM3625, a Nitrogen-Fixing Symbiont of Mimosa pudica Isolated in French Guiana (South America)

    PubMed Central

    Mornico, Damien; Melkonian, Rémy; Klonowska, Agnieszka

    2013-01-01

    Rhizobium mesoamericanum STM3625 is a Mimosa pudica symbiont isolated in French Guiana. This strain serves as a model bacterium for comparison of adaptation to mutualism (symbiotic traits, bacterial genetic programs for plant infection) between alpha and beta rhizobial symbionts of Mimosa pudica. PMID:23405314

  19. Thermomyces lanuginosus STm: a source of thermostable hydrolytic enzymes for novel application in extraction of high-quality natural rubber from Taraxacum kok-saghyz (rubber dandelion)

    USDA-ARS?s Scientific Manuscript database

    Hydrolytic enzymes from a newly isolated strain of the thermophilic fungus Thermomyces lanuginosus were used to extract rubber from Taraxacum kok-saghyz commonly known as rubber (or Russian or Kazak(h)) dandelion. The fungus was isolated from garden soil and identified as Thermomyces lanuginosus STm...

  20. 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.

  1. Ordering of Zn-centered porphyrin and phthalocyanine on TiO2(011): STM studies

    PubMed Central

    Godlewski, Szymon; Such, Bartosz; Pawlak, Rémy; Hinaut, Antoine; Jöhr, Res; Glatzel, Thilo; Meyer, Ernst; Szymonski, Marek

    2017-01-01

    Zn(II)phthalocyanine molecules (ZnPc) were thermally deposited on a rutile TiO2(011) surface and on Zn(II)meso-tetraphenylporphyrin (ZnTPP) wetting layers at room temperature and after elevated temperature thermal processing. The molecular homo- and heterostructures were characterized by high-resolution scanning tunneling microscopy (STM) at room temperature and their geometrical arrangement and degree of ordering are compared with the previously studied copper phthalocyanine (CuPc) and ZnTPP heterostructures. It was found that the central metal atom may play some role in ordering and growth of phthalocyanine/ZnTPP heterostructures, causing differences in stability of upright standing ZnPc versus CuPc molecular chains at given thermal annealing conditions. PMID:28144569

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Ordering of Zn-centered porphyrin and phthalocyanine on TiO2(011): STM studies.

    PubMed

    Olszowski, Piotr; Zajac, Lukasz; Godlewski, Szymon; Such, Bartosz; Pawlak, Rémy; Hinaut, Antoine; Jöhr, Res; Glatzel, Thilo; Meyer, Ernst; Szymonski, Marek

    2017-01-01

    Zn(II)phthalocyanine molecules (ZnPc) were thermally deposited on a rutile TiO2(011) surface and on Zn(II)meso-tetraphenylporphyrin (ZnTPP) wetting layers at room temperature and after elevated temperature thermal processing. The molecular homo- and heterostructures were characterized by high-resolution scanning tunneling microscopy (STM) at room temperature and their geometrical arrangement and degree of ordering are compared with the previously studied copper phthalocyanine (CuPc) and ZnTPP heterostructures. It was found that the central metal atom may play some role in ordering and growth of phthalocyanine/ZnTPP heterostructures, causing differences in stability of upright standing ZnPc versus CuPc molecular chains at given thermal annealing conditions.

  4. Electronic structure and properties of highly ordered C60 nano arrays on Au (111): STM & DFT study

    NASA Astrophysics Data System (ADS)

    Win, Zaw-Myo; HUANG, Chao; ZHANG, Rui-Qin

    2017-06-01

    Template assisted assembly of molecular nano arrays is one of the key steps towards molecular electronics and fullerene is one of the potential structural building blocks in fabrication of identical molecular nano arrays for miniature devices such as photovoltaic devices and single-molecule transistors. In this report, the reconstructed Au (111) with defect areas (steps) has been used as a template to assemble the highly ordered C60 nano array at low coverage studied with scanning tunnelling microscopy (STM) in conjunction with density functional theory (DFT). The interaction between the substrate and C60 nano arrays is strong enough to change the geometrical shape of C60. As a result of strong interaction, the C60 molecule appears to be deformed into ellipsoidal shape which causes the reduction of C60 nano arrays on step sites of Au (111).

  5. Development of an automatic measuring device for total sugar content in chlortetracycline fermenter based on STM32

    NASA Astrophysics Data System (ADS)

    Liu, Ruochen; Chen, Xiangguang; Yao, Minpu; Huang, Suyi; Ma, Deshou; Zhou, Biao

    2017-01-01

    Because fermented liquid in chlortetracycline fermenter has high viscosity and complex composition, conventional instruments can't directly measure its total sugar content of fermented liquid. At present, offline artificial sampling measurement is usually the way to measuring total sugar content in chlortetracycline Fermenter. it will take too much time and manpower to finish the measurement., and the results will bring the lag of control process. To realize automatic measurement of total sugar content in chlortetracycline fermenter, we developed an automatic measuring device for total sugar content based on STM32 microcomputer. It can not only realize the function of automatic sampling, filtering, measuring of fermented liquid and automatic washing of the device, but also can make the measuring results display in the field and finish data communication. The experiment results show that the automatic measuring device of total sugar content in chlortetracycline fermenter can meet the demand of practical application.

  6. Preform rod feeding module of the optical fiber drawing tower and its algorithm design based on STM32

    NASA Astrophysics Data System (ADS)

    Zhang, Tao; Fan, Zhaocheng; Liu, Guanyu; Geng, Tao; Li, Xin

    2012-10-01

    Preform rod feeding module is pre-stage module in the system of Optical Fiber Drawing Tower, its stability directly affects the wire diameter precision of the fiber. For meeting the demand of scientific research to special optical fiber, we design a new kind of preform rod feeding system, using STM32 as development platform, high-performance actuating motor as executive device and high precision grating ruler as measurement device. In order to improve the stability of the system, we adopt the algorithm design of PID closed-loop control. Finally, real-time monitoring and fast response control of preform rod operation state is realized. The results show that the system runs steadily, and can meet production requirement of special optical fiber.

  7. 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.

  8. Assembly dynamics and detailed structure of 1-propanethiol monolayers on Au(111) surfaces observed real time by in situ STM.

    PubMed

    Zhang, Jingdong; Chi, Qijin; Ulstrup, Jens

    2006-07-04

    1-Propanethiol is chosen as a model alkanethiol to probe detailed mechanisms of the self-assembled monolayer (SAM) formation at aqueous/Au(111) interfaces. The assembly processes, including initial physi- and chemisorption, pit formation, and domain growth, were recorded into movies in real-time with high resolution by in situ scanning tunneling microscopy (STM) under potential control. Two major adsorption steps were disclosed in the propanethiol SAM formation. The first step involves weak interactions accompanied by the lift of the Au(111) surface reconstruction, which depends reversibly on the electrochemical potentials. The second step is chemisorption to form a dense monolayer, accompanied by formation of pits as well as structural changes in the terrace edges. Pits emerged at the stage of the reconstruction lift and increased to a maximum surface coverage of 4.0 +/- 0.4% at the completion of the SAM formation. Well-defined triangular pits in the SAM were found on the large terraces (more than 300 nm wide), whereas few and small pinholes appeared at the terrace edge areas. Smooth edges were converted into saw-like structural features during the SAM formation, primarily along the Au(111) atomic rows. These observations suggest that shrinking and rearrangement of gold atoms are responsible for both formation of the pits and the shape changes of the terrace edges. STM images disclose a (2 square root 3 x 3)R30 degrees periodic lattice within the ordered domains. Along with electrochemical measurements, each lattice unit is assigned to contain four propanethiol molecules exhibiting different electronic contrasts, which might originate in different surface orientations of the adsorbed molecules.

  9. Whey protein isolate improves acid and bile tolerances of Streptococcus thermophilus ST-M5 and Lactobacillus delbrueckii ssp. bulgaricus LB-12.

    PubMed

    Vargas, Luis A; Olson, Douglas W; Aryana, Kayanush J

    2015-04-01

    Acid tolerance and bile tolerance are important probiotic characteristics. Whey proteins contain branched-chain amino acids, which play a role in muscle building and are popular among athletes. Increasing emphasis is being placed on diets containing less carbohydrate, less fat, and more protein. The effect of incremental additions of whey protein isolate (WPI) on probiotic characteristics of pure cultures is not known. The objective of this study was to determine the influence of added WPI on acid tolerance and bile tolerance of pure cultures of Streptococcus thermophilus ST-M5 and Lactobacillus bulgaricus LB-12. The WPI was used at 0 (control), 1, 2 and 3% (wt/vol). Assessment of acid tolerance was conducted on pure cultures at 30-min intervals for 2h of acid exposure and bile tolerance at 1-h intervals for 5h of bile exposure. Use of 1, 2, and 3% WPI improved acid tolerance of Strep. thermophilus ST-M5 and Lb. bulgaricus LB-12. The highest counts for acid tolerance of Strep. thermophilus ST-M5 and Lb. bulgaricus LB-12 were obtained when 3% WPI was used. Use of 2 and 3% WPI improved bile tolerance of Strep. thermophilus ST-M5 and Lb. bulgaricus LB-12 over 5h of bile exposure. The use of WPI is recommended to improve acid and bile tolerance of the yogurt culture bacteria Strep. thermophilus ST-M5 and Lb. bulgaricus LB-12. Copyright © 2015 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

  10. 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.

  11. 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.

  12. 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.

  13. STM/STS study of the superconducting gap in SmFeAsO1-xFx

    NASA Astrophysics Data System (ADS)

    Kawashima, Yuki; Ichimura, Koichi; Katono, Kazuhiro; Kurosawa, Tohru; Oda, Migaku; Tanda, Satoshi; Kamihara, Yoichi; Hosono, Hideo

    2015-02-01

    We report an electron tunneling study of SmFeAsO1-xFx in the low doping region (x=0, 0.045, 0.046, 0.069) by low temperature UHV-STM/STS. Superconducting gaps are observed for each superconducting sample x=0.045 (Tc=12.9 K), x=0.046 (Tc=32.9 K) and x=0.069 (Tc=46.9 K). We obtained corresponding superconducting gap size of ΔSC = 9.5 ± 0.5 meV, 9.75±0.25 meV and 11±1 meV. While Tc increases, ΔSC is kept the same. This suggests that the effective attractive interaction is the same and that there is some mechanism that suppresses the superconductivity in the low doping region. On the other hand, similar gap structures were found in a non-superconducting sample with x=0 at 7.8 K. The obtained gap size was ΔN = 8.5 ± 1.5 meV, which is almost the same as the superconducting gap in the superconducting samples (x=0.045, 0.046, 0.069).

  14. STM Studies of Spin-­Orbit Coupled Phases in Real-­ and Momentum-­Space

    SciTech Connect

    Madhavan, Vidya

    2016-10-17

    The recently discovered class of spin-orbit coupled materials with interesting topological character are fascinating both from fundamental as well as application point of view. Two striking examples are 3D topological insulators (TIs) and topological crystalline insulators (TCIs). These materials host linearly dispersing (Dirac like) surface states with an odd number of Dirac nodes and are predicted to carry a quantized half-integer value of the axion field. The non-trivial topological properties of TIs and TCIs arise from strong spin-orbit coupling leading to an inverted band structure; which also leads to the chiral spin texture in momentum space. In this project we used low temperature scanning tunneling microscopy (STM) and spectroscopy (STS) to study materials with topological phases in real- and momentum-space. We studied both single crystals and thin films of topological materials which are susceptible to being tuned by doping, strain or gating, allowing us to explore their physical properties in the most interesting regimes and set the stage for future technological applications. .

  15. Bandgap opening in graphene templates on Ru(0001) from subsurface hydrogen effects studied by STM, LEED, and DFT

    NASA Astrophysics Data System (ADS)

    Grady, Maxwell; Diaconescu, Bogdan; Valovcin, Darren; Hagelberg, Frank; Pohl, Karsten

    2013-03-01

    Graphene has aroused tremendous interest due to its remarkable electronic and mechanical properties. Graphene's optical properties, conductance, and the fact that it can be transferred to many substrates make it an ideal candidate for use in nanoelectronic devices and organic photoelectric devices. The lack of a bandgap, however, causes a serious challenge for implementing graphene as a material for electrical switches and therefore creative ways of inducing this bandgap are needed. We will present a STM/LEED/DFT study of the single layer graphene on Ru(0001) system in the presence of hydrogen. Structural studies show arrays of moiré superlattices with sizes ranging from 0.9 to 3.0 nm in the presence of hydrogen on the compact surface of ruthenium. First principle calculations help explain the appearance of these arrays of graphene reconstructions driven by the H presence at the Ru(0001) interface, and furthermore, predict the appearance of a bandgap with values correlated with the moiré superstructure sizes in the presence of hydrogen. Control over moiré superstructure size can aid in future work using graphene as a nanotemplate for self assembled growth of nanoelectronic devices an organic photovoltaics. This work was supported by the Nanoscale Science and Engineering Center for High-rate Nanomanufacturing (NSF NSEC-425826) and NSF DMR-1006863

  16. 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.

  17. Sulfidation of a Cu submonolayer at the Au(1 1 1)/electrolyte interface An in situ STM study

    NASA Astrophysics Data System (ADS)

    Friebel, Daniel; Schlaup, Christian; Broekmann, Peter; Wandelt, Klaus

    2006-07-01

    We describe the electrochemical preparation of an ultrathin copper sulfide film on Au(1 1 1) and its structural characterization by in situ STM. The first step, underpotential deposition of a Cu submonolayer from CuSO 4/H 2SO 4 solution, is followed by two electrolyte exchanges for (i) Cu-free (blank) H 2SO 4 solution and (ii) NaOH/Na 2S solution. The well-known (√3 × √3) R30° structure of the upd Cu layer is stable in the blank electrolyte for at least 2 h. After exposure to bisulfide, the Cu layer contracts and forms two-dimensional islands of two distinct ordered surface phases, i.e. a rectangular and, at higher potentials, a hexagonal phase, with Cu-free Au(1 1 1) regions between them, the latter exhibiting the characteristic (√3 × √3) R30°-S adlayer structure. Potential changes lead to a complex phase behaviour including HS - ⇆ S x oxidation/reduction and, at strongly anodic potentials, dissolution of the Cu adlayer.

  18. Features of Superconducting Gaps Revealed by STM/STS in Iron Based Superconductors With and Without Hole Pockets

    NASA Astrophysics Data System (ADS)

    Wen, Hai-Hu; Hai-Hu Wen Team

    The pairing mechanism and gap structure in iron based superconductors (IBS) remains unresolved. We have conducted extensive STM/STS study on the Na(Fe1-xTx) As (T =Co, Cu, Mn), Ba1-xKxFe2As2KFe2As2, and Li1-xFexOHFeSe single crystals. We found the clear evidence of the in-gap quasi-particle states induced by the non-magnetic Cu impurities in Na(Fe0.97- x Co0.03Cux) As, giving strong evidence of the S+/- pairing. Furthermore, we show the presence of the bosonic mode with the energy identical to that of the neutron resonance and a simple linear relation Ω/kBTc ~ 4.3, being explained a consequence of the S+/-pairing. The STS spectrum in Li1-x FexOHFeSe clearly indicates the presence of double superconducting gaps with Δ1 ~ 14.3 meV and Δ2 ~ 8.6 meV. Further analysis based on QPI allows us to assign the larger (smaller) gap to the outer (inner) hybridized electron pockets. The huge value 2Δ1/kBTc = 8.7 discovered here undoubtedly proves the strong coupling mechanism. This work was supported by the Ministry of Science and Technology of China, National Natural Science Foundation of China.

  19. 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.

  20. Visualizing Donor-Acceptor-Bond Chemistry at Semiconductor Surfaces with STM: NH3 on GaAs(110)

    NASA Astrophysics Data System (ADS)

    Brown, G.; Steinshnider, J.; Weimer, M.

    1997-03-01

    We have previously used STM to examine the room-temperature chemisorption of submonolayer amounts of ammonia on GaAs(110). Atomic-resolution topographs demonstrate this reaction is non-dissociative and that bond formation occurs through the donation of lone-pair electrons from the free molecule to cation dangling bonds at the surface(G. Brown and M. Weimer, J. Vac. Sci. Technol. B 13), 1679-1683 (1995). Reaction sites on both p- and n-type substrates are uncharged so that the screening of individual donor-acceptor-bond dipoles by substrate electrons is observed. We have recently studied the interactions between adsorbed molecules through the distribution of reaction sites as a function of separation vector in the surface plane. The pair correlation function reveals a strong, short-ranged repulsion along the GaAs(110) surface chains that completely excludes bonding at adjacent cation sublattice sites, but the observed anisotropy of the pair potential is inconsistent with the expected dipole-dipole forces between adsorbates. STS indicates ammonia chemisorption significantly disrupts the GaAs(110) surface states at saturation coverages less than 0.1 ML, and that observation, together with the anisotropic short-range nature of the pair potential, suggests the predominant lateral interaction in this system is substrate mediated.

  1. Spectroscopic Ellipsometry, Auger and STM Characterization of Epitaxial Graphene grown on 6H-SiC (0001)

    NASA Astrophysics Data System (ADS)

    Nelson, Florence; Diebold, Alain C.; Sandin, Andreas; Dougherty, Dan; Aspnes, Dave; Rowe, Jack

    2012-02-01

    Graphene grown by the thermal decomposition of SiC has become of interest to the semiconductor industry due to its unique, high-mobility electronic structure. The growth is of a more scalable nature when compared to exfoliated flakes produced from the ``scotch tape'' method. The resulting film rests on a ``buffer layer'' separating the graphene from the underlying substrate, which is thought to consist of a mixture of sp^2 and non-sp^2 bonding due to the sp^3 bonding of the SiC substrate. The mobilities of the graphene layer have previously been shown to differ from that of the interface layer. We investigate the difference in the optical response of the two layers using Spectroscopic Ellipsometry and find a red-shift of the ˜4.5 eV absorbance found in graphene due to the exciton-domianted transition at the M point of the Brilloun Zone. The structural characterization of the films are performed through Auger and STM on substrates which were cleaned by CMP and chemical etching methods prior to the epitaxial growth in UHV.

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. Acquisition and diversification of tendrilled leaves in Bignonieae (Bignoniaceae) involved changes in expression patterns of SHOOTMERISTEMLESS (STM), LEAFY/FLORICAULA (LFY/FLO), and PHANTASTICA (PHAN).

    PubMed

    Sousa-Baena, Mariane Silveira; Lohmann, Lúcia G; Rossi, Magdalena; Sinha, Neelima R

    2014-02-01

    Leaves have undergone structural modifications over evolutionary time, and presently exist in many forms. For instance, in Fabaceae and Bignoniaceae, leaf parts can be modified into tendrils. Currently, no data are available on genic control of tendrilled leaf development outside Fabaceae. Here, we conducted a detailed study of three representatives of Bignonieae: Amphilophium buccinatorium, Dolichandra unguis-cati, and Bignonia callistegioides, bearing multifid, trifid, and simple-tendrilled leaves, respectively. We investigated the structure of their petioles, petiolules, leaflets, and tendrils through histological analyses. Additionally, the expression of SHOOTMERISTEMLESS (STM), PHANTASTICA (PHAN), and LEAFY/FLORICAULA (LFY/FLO) during leaf development was analyzed by in situ hybridizations. Tendrils share some anatomical similarities with leaflets, but not with other leaf parts. Transcripts of both STM and LFY/FLO were detected in leaf primordia, associated with regions from which leaflets and tendril branches originate. PHAN expression was found to be polarized in branched tendrils, but not in simple tendrils. In Bignonieae, tendrils are modified leaflets that, as a result of premature completion of development, become bladeless organs. Bignonieae leaves develop differently from those of peas, as both LFY/FLO and STM are expressed in developing leaves of Bignonieae. Moreover, PHAN is probably involved in tendril diversification in Bignonieae, as it has distinct expression patterns in different leaf types.

  8. Structure of the GaP(001)-4×2-In surface investigated with LEED, STM, photoelectron spectroscopy, and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Shimomura, M.; Ichikawa, D.; Srivastava, G. P.; Liu, K. Z.; Fukuda, Y.

    2008-09-01

    Surface structures at the initial stage of indium adsorption on GaP(001) are studied by low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), photoelectron spectroscopy (PES), and ab initio calculations. After indium deposition on the P -rich GaP(001)-2×1 surface followed by annealing at 400-450°C , ×4 LEED spots were observed along the [110] direction. STM images obtained after 400°C annealing show a 4×2-In reconstruction with row and hump structures. PES result for the 4×2-In surface shows existence of In atoms in two different chemical environments; one with In-In bonding and the other with In surrounded by phosphorus atoms at the surface. These LEED, STM, and PES results are consistent with the ζ structure, which was proposed for cation-rich clean surfaces of III-V semiconductors containing arsenic or antimony. Several plausible models derived from the original ζ model are examined by first-principles calculations for the GaP(001)-4×2-In surface.

  9. Probing the buried Pb/Si(111) interface with SPA LEED and STM on Si(111)-Pbα√3×√3.

    PubMed

    Yakes, M; Tringides, M C

    2011-06-30

    High resolution spot profile analysis low energy electron diffraction (SPA-LEED) and variable temperature scanning tunneling microscopy (STM) have been used to observe the growth of Pb on the Pb/Si(111)-α√3×√3 phase, which is driven by quantum size effects (QSE). A change in the rotation of the Pb grown islands with respect to the Si substrate has been observed with increasing coverage θ. At lower coverage, separated two-step islands are grown and are aligned with the [110] axis of the substrate. With increasing coverage above 1.5 ML, of the islands coalesce and form a bilayer, with additional islands grown on top. The preferred Pb island orientation changes to 5.6° with respect to the [110] direction. These changes at the metal/semiconductor buried interface are obtained both with SPA LEED and STM as changes to the period of the Moire pattern. The method of analysis of the corrugation period and rotation angle of the Moire pattern measured with diffraction and STM can be applied to obtain the structure of buried metal/substrate interfaces in other epitaxial systems.

  10. Expression patterns of STM-like KNOX and Histone H4 genes in shoot development of the dissected-leaved basal eudicot plants Chelidonium majus and Eschscholzia californica (Papaveraceae).

    PubMed

    Groot, Edwin P; Sinha, Neelima; Gleissberg, Stefan

    2005-06-01

    Knotted-like homeobox (KNOX) genes encode important regulators of shoot development in flowering plants. In Arabidopsis, class I KNOX genes are part of a regulatory system that contributes to indeterminacy of shoot development, delimitation of leaf primordia and internode development. In other species, class I KNOX genes have also been recruited in the control of marginal blastozone fractionation during dissected leaf development. Here we report the isolation of class I KNOX genes from two species of the basal eudicot family Papaveraceae, Chelidonium majus and Eschscholzia californica. Sequence comparisons and expression patterns indicate that these genes are orthologs of SHOOTMERISTEMLESS (STM), a class I KNOX gene from Arabidopsis. Both genes are expressed in the center of vegetative and floral shoot apical meristems (SAM), but downregulated at leaf or floral organ initiating sites. While Eschscholzia californica STM (EcSTM) is again upregulated during acropetal pinna formation, in situ hybridization could not detect Chelidonium majus STM (CmSTM) transcripts at any stage of basipetal leaf development, indicating divergent evolution of STM gene function in leaves within Papaveraceae. Immunolocalization of KNOX proteins indicate that other gene family members may control leaf dissection in both species. The contrasting direction of pinna initiation in the two species was also investigated using Histone H4 expression. Leaves at early stages of development did not reveal notable differences in cell division activity of the elongating leaf axis, suggesting that differential meristematic growth may not play a role in determining the observed dissection patterns.

  11. Structure and dynamics of oxy-overlayer on Cu(1 1 1) electrode surfaces in alkaline aqueous solution revealed by electrochemical STM and quartz crystal microbalance measurement

    NASA Astrophysics Data System (ADS)

    Matsuoka, Osamu; Sugiyama Ono, Shoko; Nozoye, Hisakazu; Yamamoto, Sadaaki

    2003-11-01

    The redox reactivity of copper in aqueous solution has attracted much attention due to practical applications such as catalysis, electrodeposition, microelectronic device fabrication. In this work, the structure and dynamic behavior of Cu(1 1 1) electrodes were investigated in 0.01 M NaOH aqueous solution in the potential range where copper electrode shows redox reactivity for aldehyde oxidation by using electrochemical scanning tunneling microscopy (EC-STM), cyclic voltammetry, and electrochemical quartz crystal microbalance (EQCM). EC-STM observations revealed that the Cu(1 1 1) electrode surface was covered with an oxy-overlayer (layer of adsorbates containing oxygen), which formed a terrace-step structure with a monoatomic step height. Two kinds of ordered structures on the terrace were observed at the potential negative-side of the cathodic peak at -0.85 V vs. Ag/AgCl: hexagonal lattice with a unit vector of 0.70 ± 0.03 nm (structure A), and rhombic lattice with a unit vector of 1.40 ± 0.03 nm (structure B). Species with these structures seem responsible for aldehyde oxidation, based on the good agreement between the cyclic voltammogram (CV) for these species and that previously reported for Cu electrodes active for aldehyde oxidation. EC-STM revealed the deposition and dissolution of the oxy-overlayer on Cu(1 1 1) electrode surfaces. Combining the EQCM measurement with EC-STM images suggests that a cluster of water molecules had adsorbed on a species that had ordered structure A at the potential of -0.65 V in an anodic scan. This hydration probably transforms the species into a soluble species, such as Cu(OH) 2-, which induces the partial dissolution of a terrace from a step edge. In addition, dependence of the position of the anodic peak at -0.65 V on a cathode limit was observed for the first time. EC-STM observation revealed that this electrochemical behavior of the anodic peak correlated with the surface structure of the oxy-overlayer, namely

  12. Design and construction of low-temperature ultrahigh vacuum STM/AFM and the effect of dosing pressure on coverage and ordered structure of oxygen on tungsten(110)

    NASA Astrophysics Data System (ADS)

    Muzzall, David Ernest

    A variable temperature (18--400K), ultrahigh vacuum Atomic Force Microscope and Scanning Tunneling Microscope (AFM/STM) has been designed and constructed for the study of atomically resolved surface chemistry, the observation of low temperature and pressure related phase transitions of surface structures, and the measurement of inter-molecular forces. The instrument design supports in situ replacement of STM tips, AFM cantilevers, and samples, thereby enabling one to obtain electronic topography and spectroscopy from STM, as well as normal and frictional force topographs from AFM, in a single dosing experiment. A liquid helium dewar cools samples down to 18 K. A temperature controller, with a silicon-diode thermometer and a resistive heater, enables one to image surfaces 18 to 400 K. An adjacent surface analysis system with Auger electron spectroscopy and low energy electron diffraction (LEED) analysis supports the preparation and study of many types of surface phenomena. This state-of-the-art system was used to study the system of oxygen adsorbed onto W(110), an archetype in the understanding of the oxidation and corrosion of metal surfaces. The three known adsorbate structures of (2 x 1), (2 x 2), and (1 x 1) were observed. In addition, a new fourth structure was discovered characterized using both LEED and STM. The effects of dosing pressure on structure type and total surface coverage have also been observed for low dosing pressures. In most prior surface science studies, it has been assumed that total exposure, rather than both pressure and time as independent variables, controls the types of adsorption structures formed. In this study, STM was used to explore the adsorbate structures and the coverage dependence of oxygen on W(110) as a function of the deposition pressure and for room temperature exposures. For the same total adsorbate exposure in Langmuirs (L), our study shows that changes in deposition pressure of as little as a factor of 3 cause significant

  13. 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.

  14. 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.

  15. In situ STM study of Cu(111) surface structure and corrosion in pure and benzotriazole-containing sulfuric acid solution

    SciTech Connect

    Polewska, W.; Vogt, M.R.; Magnussen, O.M.; Behm, R.J.

    1999-11-25

    The authors present results of an in situ STM study on the surface structure and anodic dissolution of Cu(111) electrodes in pure 0.01 M H{sub 2}SO{sub 4} solution and in solution containing the corrosion inhibitor benzotriazole (BTAH), which is aimed at an atomistic understanding of the dissolution process and the inhibitor effects. The initial stages of Cu dissolution as well as the adsorption of BTAH are pronouncedly influenced by the presence of the ordered sulfate adlayer, which forms in the double layer potential regime and induces a reconstruction of the underlying Cu surface layer, together with a reorientation of the steps along the close-packed lattice directions. Cu dissolution in pure H{sub 2}SO{sub 4} solution proceeds by a step flow mechanism. The onset of dissolution is critically affected by the relative orientation of the sulfate adlayer on the lower terrace side, with the stability being highest for steps running perpendicular to the close-packed sulfate rows. The retracting steps often expose apparently disordered areas, which are attributed to a disordered sulfate adlayer on a Cu surface where, because of kinetic limitations, a well-ordered reconstruction has not yet reformed. BTAH adsorption is only observed in the potential regime of the ordered sulfate adlayer. The BTAH adlayer is highly defective, which is attributed to the removal of the reconstruction due to sulfate adlayer displacement. Islands with poorly ordered 1D chain structures are surrounded by areas with no resolved structure. Cu dissolution inhibition is manifested by an anodic shift in the onset of dissolution as well as by the blocking of the step flow etch mechanism, reflecting a stabilization of the Cu steps by adsorbed BTAH. Dissolution at higher potentials proceeds predominantly via formation of monolayer etch pits. When the potential is reversed back into the double layer regime, smoothening of the surface is observed with a rate that increases strongly with decreasing

  16. 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

  17. 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

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

    PubMed

    Cowles, Kimberly N; Willis, David K; Engel, Tyler N; Jones, Jeffrey B; Barak, Jeri D

    2015-12-11

    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. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

  19. Cannabidiol-2',6'-dimethyl ether stimulates body weight gain in apolipoprotein E-deficient BALB/c. KOR/Stm Slc-Apoe(shl) mice.

    PubMed

    Takeda, Shuso; Hirota, Rena; Teradaira, Sari; Takeda-Imoto, Masumi; Watanabe, Kazuhito; Toda, Akihisa; Aramaki, Hironori

    2015-12-01

    The biological activities of cannabidiol (CBD), a major non-psychotropic constituent of the fiber-type cannabis plant, have been examined in detail (e.g., CBD modulation of body weight in mice and rats). However, few studies have investigated the biological activities of cannabidiol-2',6'-dimethyl ether (CBDD), a dimethyl ether derivative of the parent CBD. We herein focused on the effects of CBDD on body weight changes in mice, and demonstrated that it stimulated body weight gain in apolipoprotein E (ApoE)-deficient BALB/c. KOR/Stm Slc-Apoe(shl) mice, especially between 10 and 20 weeks of age.

  20. STM studies of the electronic structure of vortex cores in Bi(2)Sr(2)CaCu(2)O(8+delta)

    PubMed

    Pan; Hudson; Gupta; Ng; Eisaki; Uchida; Davis

    2000-08-14

    We report on low temperature scanning tunneling microscopy (STM) studies of the electronic structure of vortex cores in Bi 2Sr 2CaCu 2O (8+delta). At the vortex core center, an enhanced density of states is observed at energies near Omega = +/-7 meV. Spectroscopic imaging at these energies reveals an exponential decay of these "core states" with a decay length of 22+/-3 A. The fourfold symmetry sometimes predicted for d-wave vortices is not seen in spectroscopic vortex images. A locally nodeless order parameter induced by the magnetic field may be consistent with these measurements.

  1. Synthesis, magnetic properties, and STM spectroscopy of cobalt(II) Cubanes [Co(II) (4)(Cl)(4)(HL)(4)].

    PubMed

    Scheurer, Andreas; Ako, Ayuk M; Saalfrank, Rolf W; Heinemann, Frank W; Hampel, Frank; Petukhov, Konstantin; Gieb, Klaus; Stocker, Michael; Müller, Paul

    2010-04-26

    Reaction of cobalt(II) chloride hexahydrate with N-substituted diethanolamines H(2)L(2-4) (3) in the presence of LiH in anhydrous THF leads under anaerobic conditions to the formation of three isostructural tetranuclear cobalt(II) complexes [Co(II) (4)(Cl)(4)(HL(2-4))(4)] (4) with a [Co(4)(mu(3)-O)(4)](4+) cubane core. According to X-ray structural analyses, the complexes 4 a,c crystallize in the tetragonal space group I4(1)/a, whereas for complex 4 b the tetragonal space group P$\\bar 4$ was found. In the solid state the orientation of the cubane cores and the formation of a 3D framework were controlled by the ligand substituents of the cobalt(II) cubanes 4. This also allowed detailed magnetic investigations on single crystals. The analysis of the SQUID magnetic susceptibility data for 4 a gave intramolecular ferromagnetic couplings of the cobalt(II) ions (J(1) approximately 20.4 K, J(2) approximately 7.6 K), resulting in an S=6 ground-state multiplet. The anisotropy was found to be of the easy-axis type (D=-1.55 K) with a resulting anisotropy barrier of Delta approximately 55.8 K. Two-dimensional electron-gas (2DEG) Hall magnetization measurements revealed that complex 4 a is a single-molecule magnet and shows hysteretic magnetization characteristics with typical temperature and sweep-rate dependencies below a blocking temperature of about 4.4 K. The hysteresis loops collapse at zero field owing to fast quantum tunneling of the magnetization (QTM). The structural and electronic properties of cobalt(II) cubane 4 a, deposited on a highly oriented pyrolytic graphite (HOPG) surface, were investigated by means of STM and current imaging tunneling spectroscopy (CITS) at RT and standard atmospheric pressure. In CITS measurements the rather large contrast found at the expected locations of the metal centers of the molecules indicated the presence of a strongly localized LUMO.

  2. First-principles investigation for M(CO)n/Ag(110) (M=Fe, Co, Ni, Cu, Zn, and Ag; n=1, 2) systems: Geometries, STM images, and vibrational frequencies

    NASA Astrophysics Data System (ADS)

    Yuan, Lan-Feng; Yang, Jinlong; Li, Qunxiang; Zhu, Qing-Shi

    2002-01-01

    Fe, Cu atoms and CO molecules were manipulated with a scanning tunneling microscope (STM) on a Ag(110) surface, and one or two CO can transfer from the surface and bond with a metal atom through the STM tip [H. J. Lee and W. Ho, Science 286, 1719 (1999); Phys. Rev. B 61, R16347 (2000)]. We perform a density-functional cluster model investigation for the systems. The experimental geometries are validated and understood using the frontier orbital theory. The STM topographic images are reproduced. The vibrational frequencies of the adsorbate systems are obtained by diagonalizing the second-derivative matrices and are in excellent agreement with the experimental measurements. The geometries and C-O stretch frequencies are predicted for systems with the adsorbate metal atom being Co, Ni, Zn, and Ag. These systems can be divided to two classes, and each class exhibits a different set of properties.

  3. Epitaxial deposition of silver ultra-fine nano-clusters on defect-free surfaces of HOPG-derived few-layer graphene in a UHV multi-chamber by in situ STM, ex situ XPS, and ab initio calculations

    PubMed Central

    2012-01-01

    The growth of three-dimensional ultra-fine spherical nano-particles of silver on few layers of graphene derived from highly oriented pyrolytic graphite in ultra-high vacuum were characterized using in situ scanning tunneling microscopy (STM) in conjunction with X-ray photoelectron spectroscopy. The energetics of the Ag clusters was determined by DFT simulations. The Ag clusters appeared spherical with size distribution averaging approximately 2 nm in diameter. STM revealed the preferred site for the position of the Ag atom in the C-benzene ring of graphene. Of the three sites, the C-C bridge, the C-hexagon hollow, and the direct top of the C atom, Ag prefers to stay on top of the C atom, contrary to expectation of the hexagon-close packing. Ab initio calculations confirm the lowest potential energy between Ag and the graphene structure to be at the exact site determined from STM imaging. PMID:22395057

  4. Epitaxial deposition of silver ultra-fine nano-clusters on defect-free surfaces of HOPG-derived few-layer graphene in a UHV multi-chamber by in situ STM, ex situ XPS, and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Ndlovu, Gebhu F.; Roos, Wiets D.; Wang, Zhiming M.; Asante, Joseph KO; Mashapa, Matete G.; Jafta, Charl J.; Mwakikunga, Bonex W.; Hillie, Kenneth T.

    2012-03-01

    The growth of three-dimensional ultra-fine spherical nano-particles of silver on few layers of graphene derived from highly oriented pyrolytic graphite in ultra-high vacuum were characterized using in situ scanning tunneling microscopy (STM) in conjunction with X-ray photoelectron spectroscopy. The energetics of the Ag clusters was determined by DFT simulations. The Ag clusters appeared spherical with size distribution averaging approximately 2 nm in diameter. STM revealed the preferred site for the position of the Ag atom in the C-benzene ring of graphene. Of the three sites, the C-C bridge, the C-hexagon hollow, and the direct top of the C atom, Ag prefers to stay on top of the C atom, contrary to expectation of the hexagon-close packing. Ab initio calculations confirm the lowest potential energy between Ag and the graphene structure to be at the exact site determined from STM imaging.

  5. Epitaxial deposition of silver ultra-fine nano-clusters on defect-free surfaces of HOPG-derived few-layer graphene in a UHV multi-chamber by in situ STM, ex situ XPS, and ab initio calculations.

    PubMed

    Ndlovu, Gebhu F; Roos, Wiets D; Wang, Zhiming M; Asante, Joseph Ko; Mashapa, Matete G; Jafta, Charl J; Mwakikunga, Bonex W; Hillie, Kenneth T

    2012-03-06

    The growth of three-dimensional ultra-fine spherical nano-particles of silver on few layers of graphene derived from highly oriented pyrolytic graphite in ultra-high vacuum were characterized using in situ scanning tunneling microscopy (STM) in conjunction with X-ray photoelectron spectroscopy. The energetics of the Ag clusters was determined by DFT simulations. The Ag clusters appeared spherical with size distribution averaging approximately 2 nm in diameter. STM revealed the preferred site for the position of the Ag atom in the C-benzene ring of graphene. Of the three sites, the C-C bridge, the C-hexagon hollow, and the direct top of the C atom, Ag prefers to stay on top of the C atom, contrary to expectation of the hexagon-close packing. Ab initio calculations confirm the lowest potential energy between Ag and the graphene structure to be at the exact site determined from STM imaging.

  6. Observation of the Gap Distribution on Multi-layered Cuprate Superconductor Ba2Ca4Cu5O10(O1-x, Fx)2 by STM/STS

    NASA Astrophysics Data System (ADS)

    Sugimoto, Akira; Ekino, Toshikazu; Tanaka, Katsuhiro; Mineta, Kyohei; Tanabe, Kenji; Tokiwa, Kazuyasu

    The nano-scale spatial gap distributions on apical-fluorine multi-layered cuprate superconductors Ba2Ca4Cu5O10(O1-x, Fx) (F0245, Tc = 70 K) are investigated by scanning tunneling microscopy/spectroscopy (STM/STS). The STM image shows randomly-distributed bright spot structures, which are assigned to the non-replaced apical oxygen. The dI/dV tunnel spectra show the coexistence of two kinds of the gap structures. The magnitudes of these gaps at 4.9 K are about ΔS ∼25 meV and ΔL ∼78 meV, respectively. The ΔL map shows the inhomogeneous distribution with the characteristic length of ∼1 nm. The smaller ΔL gap regions tend to locate at the bright-spot positions, indicating that the apical oxygen causes reduction of ΔL. These results are consistent with the well known relation between the carrier doping level and macroscopically observed gap size.

  7. 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

  8. 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).

  9. 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.

  10. Work function measurements via STM and TS on clean fresh cleaved HOPG and Gold thin films on HOPG under ambient conditions

    NASA Astrophysics Data System (ADS)

    Marijczuk, Roman; Morean, Casey; Senevirathne, Indrajith

    Stability and homogeneity of HOPG has enabled it to be used as a platform for various applications in understanding many physical and chemical phenomena. Novel emergence of graphene as a derivative of graphite also makes HOPG an interesting system to study. This is an ambient investigation of HOPG and Au thin films (ranging about 20nm) surfaces 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 same systems were then investigated via TS by tunneling current (I) vs. height (z) curves. These spectroscopic data were then used to assess the localized work function measurements and surface variation of the work function. The discussion will attempt to assess the surface electronic environment of these systems in relation to the Au deposition and variation of Au thickness on HOPG. Ambient measurements will inherently complicate these measurements and the complexities will also be discussed. Lock Haven University Nanotechnology Program.

  11. 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.

  12. 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

  13. 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

  14. 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.

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

    PubMed

    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

    2014-06-15

    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 815(T), 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).

  16. 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

  17. STM and DFT study of the Gd wetting layer reconstructions on the Si(0 0 1)-2 × 1 surface

    NASA Astrophysics Data System (ADS)

    Harrison, B. C.; Ryan, Peter; Boland, John J.

    2005-05-01

    This paper presents a structural study of the 2 × 8 and 2 × 7 wetting layer reconstructions that occur on the Si(1 0 0) surface following Gadolinium deposition at elevated temperatures. Scanning tunneling microscopy and density functional theory calculations were used to analyze the detailed structure of the wetting layer. The maxima observed in STM images are consistent with the location of metal atoms determined by geometry optimized DFT calculations. In the 2 × 8 reconstruction metal atoms occupy the dimer positions but with a modulation in height that serves to lower the stress along the dimer row direction. The 2 × 7 reconstruction is formed by the redistribution of metal atoms of the 2 × 8 reconstruction, where the metal can occupy either the dimer position or a bridging site between two silicon atoms.

  18. 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).

  19. In situ STM investigation of spinodal decomposition and surface alloying during underpotential deposition of Cd on Au(111) from an ionic liquid.

    PubMed

    Pan, Ge-Bo; Freyland, Werner

    2007-07-07

    The electrodeposition and anodic dissolution of Cd on Au(111) in an acidic chloroaluminate ionic liquid (MBIC-AlCl(3), 42 : 58 mol%) have been investigated by cyclic voltammetry and in situ STM. In the Cd underpotential deposition region, various nanostructures can be distinguished. At a potential of 0.95 V vs. Al/Al(iii), a transformation from a well ordered AlCl(4)(-) adlayer to a ( radical3 x radical19) superstructure, presumably due to Cd-AlCl(4)(-) coadsorption, is observed. Reducing the potential to 0.45 V, surface alloying of Cd and Au occurs, which is evidenced for the first time by typical spinodal structures occurring both during deposition and dissolution of the surface alloy layer having a hexagonal structure. At still lower potentials below 0.21 V, a layer-by-layer growth of bulk Cd sets in.

  20. A general model of metal underpotential deposition in the presence of thiol-based additives based on an in situ STM study.

    PubMed

    Yanson, Yuriy; Frenken, Joost W M; Rost, Marcel J

    2011-09-21

    Bis(3-sulfopropyl)disulfide (SPS) is a common additive in commercial copper electroplating baths. We have studied the influence of SPS on Cu underpotential deposition (UPD) on a Au(111) single crystal surface by means of cyclic voltammetry (CV) and electrochemical scanning tunneling microscopy (EC-STM). By combining our results with the results from the literature we propose a model that describes different stages of Cu UPD in the presence of SPS. Further analysis shows that our model is also applicable to a more general case of UPD of different metals, e.g. Cu and Ag, on a thiol-modified single-crystal surface, where the bond between the substrate and the thiol is adatom mediated. In addition, we have verified our model by in situ observation of the lifting of the Herringbone reconstruction on the Au(111) surface by Cu UPD.

  1. Modeling STM tips by single absorbed atoms on W(100) films: 3d, 4d and 5d transition metal atoms

    NASA Astrophysics Data System (ADS)

    Hofer, Werner; Redinger, Josef; Kresse, Georg; Podloucky, Raimund

    2000-03-01

    In order to provide comprehensive data on the electronic structure of realistic STM-tips we have calculated W(100) films with single 3d, 4d and 5d transition metal apex atoms by first principles molecular dynamics and full potential methods. Molecular dynamics using ultrasoft pseudopotentials (VASP) has been used to determine the relaxation of the surface layers. The electronic structure of the relaxed film has been calculated by a first principles full potential method with two-dimensional boundary conditions (FLEUR), which seems most suitable to reproduce subtle surface effects. The results suggest that the chemical nature of the tip apex determines to a high degree achievable corrugations and that correct results for the current and corrugation values in a perturbation approach can only be obtained by including the full electronic structure of the tip.

  2. STM study on nonionic fluorosurfactant zonyl FSN Self-Assembly on Au(100): [array: see text] molecular lattice, corrugations, and adsorbate-enhanced mobility.

    PubMed

    Yan, Jiawei; Tang, Yongan; Sun, Chunfeng; Su, Yuzhuan; Mao, Bingwei

    2010-03-16

    Nonionic fluorosurfactant zonyl FSN self-assembly on Au(100) is investigated by using scanning tunneling microscopy under ambient conditions. High-resolution STM images reveal that a [array: see text] arrangement of the FSN SAMs is formed on Au(100). Different from the uniform structure of FSN SAMs on Au(111), the adsorption sites of FSN molecules on Au(100) change gradually and form a kind of corrugated structure. The change in the adsorption sites probably originates from the repulsive force among FSN molecules because the nearest-neighbor distance of FSN molecules is 0.41 nm, which is smaller than 0.50 nm on Au(111). The mobility of surface atoms on the Au substrate is enhanced by the interaction between FSN molecules and the Au substrate; therefore, no Au island is observed on the FSN-SAM-covered Au(100).

  3. An STM study on nonionic fluorosurfactant zonyl FSN self-assembly on Au(111): large domains, few defects, and good stability.

    PubMed

    Tang, Yongan; Yan, Jiawei; Zhou, Xiaoshun; Fu, Yongchun; Mao, Bingwei

    2008-12-02

    Nonionic Fluorosurfactant Zonyl FSN self-assembly on Au(111) is investigated with scanning tunneling microscopy under ambient conditions. STM reveals that the FSN forms SAMs on Au(l11) with very large domain size and almost no defects. A (mean square root of 3 x mean square root of 3)R3 degree arrangement of the FSN SAM on Au(111) is observed. The SAMs show excellent chemical stability and last for at least a month in atmospheric conditions. The structure and stability of the FSN SAMs are compared with those of alkanethiols SAMs. It is expected that FSN may serve as a new kind of molecule to form SAMs for surface modification, which would benefit wider applications for various purposes.

  4. Transient Charge Transfer Processes at Surfaces: From Ion Scattering to Laser-, Tunnel-junction-, and STM- Initiated Hot-Electron Femtochemistry

    NASA Astrophysics Data System (ADS)

    Gadzuk, J. W.

    2000-03-01

    Transient charge transfer (CT) between solid surfaces and external atoms, molecules, or clusters can give rise to time-dependent forces that drive a broad class of processes involving energy transfer between excited electronic states and the nuclear motion(translational, vibrational, and/or rotational arrow TVR) of the external entity. Realizations of such CT processes occur in ion-surface scattering, resonant electron spectroscopy, surface femtochemistry (initiated by hot electrons produced both by ultrafast pulsed lasers and by solid state devices such as a tunnel junction, STM, or photo-excited thin film structure), and in STM atom-manipulation and switching.(J. W. Gadzuk, Phys. Rev. Letters, 76), 4234 (1996); J. Elec. Spect. 98-99, 321 (1999). Ion scattering, as practiced by Barbara Cooper and coworkers, involves mainly T-to-electronic energy flow whereas the hot-electron processes depend upon the time-reversed excited electron-to-TVR direction of energy flow. Viewed from this perspective, it is apparent that a single, unified theoretical framework, which will be presented here, can/should be used to most effectively organize our understanding and to guide us in chosing future directions of experimental inquiry. The crucial role of multiple CT events in such processes has recently been under study. New theoretical insights into this important aspect of the many-faceted family of dynamic CT processes at surfaces will also be discussed, particularly with respect to femtosecond-laser-initiated events.(Special Issue of Chem. Phys. on "Electron Dynamics in Metals" (in press).) note

  5. 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

  6. In situ STM imaging of bis-3-sodiumsulfopropyl-disulfide molecules adsorbed on copper film electrodeposited on Pt(111) single crystal electrode.

    PubMed

    Tu, HsinLing; Yen, PoYu; Chen, Sihzih; Yau, ShuehLin; Dow, Wei-Ping; Lee, Yuh-Lang

    2011-06-07

    The adsorption of bis-3-sodiumsulfopropyldi-sulfide (SPS) on metal electrodes in chloride-containing media has been intensively studied to unveil its accelerating effect on Cu electrodeposition. Molecular resolution scanning tunneling microscopy (STM) imaging technique was used in this study to explore the adsorption and decomposition of SPS molecules concurring with the electrodeposition of copper on an ordered Pt(111) electrode in 0.1 M HClO(4) + 1 mM Cu(ClO(4))(2) + 1 mM KCl. Depending on the potential of Pt(111), SPS molecules could react, adsorb, and decompose at chloride-capped Cu films. A submonolayer of Cu adatoms classified as the underpotential deposition (UPD) layer at 0.4 V (vs Ag/AgCl) was completely displaced by SPS molecules, possibly occurring via RSSR (SPS) + Cl-Cu-Pt → RS(-)-Pt(+) + RS(-) (MPS) + Cu(2+) + Cl(-), where MPS is 3-mercaptopropanesulfonate. By contrast, at 0.2 V, where a full monolayer of Cu was presumed to be deposited, SPS molecules were adsorbed in local (4 × 4) structures at the lower ends of step ledges. Bulk Cu deposition driven by a small overpotential (η < 50 mV) proceeded slowly to yield an atomically smooth Cu deposit at the very beginning (<5 layers). On a bilayer Cu deposit, the chloride adlayer was still adsorbed to afford SPS admolecules arranged in a unique 1D striped phase. SPS molecules could decompose into MPS upon further Cu deposition, as a (2 × 2)-MPS structure was observed with prolonged in situ STM imaging. It was possible to visualize either SPS admolecules in the upper plane or chloride adlayer sitting underneath upon switching the imaging conditions. Overall, this study established a MPS molecular film adsorbed to the chloride adlayer sitting atop the Cu deposit.

  7. Efficient method for the simulation of STM images. II. Application to clean Rh(111) and Rh(111)+c(4{times}2)-2S

    SciTech Connect

    Cerda, J.; Yoon, A. |; Van Hove, M.A.; Sautet, P. |; Salmeron, M.; Somorjai, G.A. |

    1997-12-01

    We apply our recently developed Green-function formalism for the simulation of scanning tunneling microscopy (STM) images to the clean Rh(111) and the Rh(111)+c(4{times}2)-2S systems. The former represents a test case in order to study the adequacy of the extended H{umlt u}ckel theory (EHT) as an approximation to the Hamiltonian matrix elements of the entire system. It is shown that, via a suitable parametrization of the atomic-orbital basis set, the EHT provides a reasonable description of the electronic structure of the sample and the tip, together with the interactions at the STM interface. When the same parametrization scheme is applied to the Rh(111)+c(4{times}2)-2S system, we find a good agreement with the experimental images by considering a Pt tip with its apex terminated in a Pt or S atom. More specifically, the two inequivalent maxima per unit cell that appear in the images are unambiguously assigned to a S atom adsorbed at the hcp site (brightest maximum) and to another S atom at the fcc site. Furthermore, the simulations for each tip termination can be associated to two different types of experimental images which could be acquired in a reproducible way. At the same time, and after a detailed study on the relevance of most of the parameters involved in the calculation, some general criteria for the estimation of their value, prior to the STM calculation, are established. Finally, an analysis of the tunneling current on the Rh(111) system allows us to identify the Rh-d{sub z{sup 2}} orbitals at the surface as the main states responsible for the atomic resolution. It is also found that the most relevant probing orbitals at the tip apex are those with axial symmetry along the surface normal; for the S ended tip, it is the S-p{sub z} orbital which dominates by far the current, whereas, for the Pt-ended tip, first the Pt-s and next the {minus}d{sub z{sup 2}} provide the major contributions. The better resolution obtained with the former tip is a consequence

  8. 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.

  9. Electrodeposition of copper on a Pt(111) electrode in sulfuric acid containing poly(ethylene glycol) and chloride ions as probed by in situ STM.

    PubMed

    Fu, YunLin; Pao, Te; Chen, Sih-Zih; Yau, ShuehLin; Dow, Wei-Ping; Lee, Yuh-Lang

    2012-07-03

    This study employed real-time in situ STM imaging to examine the adsorption of PEG molecules on Pt(111) modified by a monolayer of copper adatoms and the subsequent bulk Cu deposition in 1 M H(2)SO(4) + 1 mM CuSO(4)+ 1 mM KCl + 88 μM PEG. At the end of Cu underpotential deposition (~0.35 V vs Ag/AgCl), a highly ordered Pt(111)-(√3 × √7)-Cu + HSO(4)(-) structure was observed in 1 M H(2)SO(4) + 1 mM CuSO(4). This adlattice restructured upon the introduction of poly(ethylene glycol) (PEG, molecular weight 200) and chloride anions. At the onset potential for bulk Cu deposition (~0 V), a Pt(111)-(√3 × √3)R30°-Cu + Cl(-) structure was imaged with a tunneling current of 0.5 nA and a bias voltage of 100 mV. Lowering the tunneling current to 0.2 nA yielded a (4 × 4) structure, presumably because of adsorbed PEG200 molecules. The subsequent nucleation and deposition processes of Cu in solution containing PEG and Cl(-) were examined, revealing the nucleation of 2- to 3-nm-wide CuCl clusters on an atomically smooth Pt(111) surface at overpotentials of less than 50 mV. With larger overpotential (η > 150 mV), Cu deposition seemed to bypass the production of CuCl species, leading to layered Cu deposition, starting preferentially at step defects, followed by lateral growth to cover the entire Pt electrode surface. These processes were observed with both PEG200 and 4000, although the former tended to produce more CuCl nanoclusters. Raising [H(2)SO(4)] to 1 M substantiates the suppressing effect of PEG on Cu deposition. This STM study provided atomic- or molecular-level insight into the effect of PEG additives on the deposition of Cu.

  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. Isolation of Salmonella enterica subspecies enterica serovar Paratyphi B dT+, or Salmonella Java, from Indonesia and alteration of the d-tartrate fermentation phenotype by disrupting the ORF STM 3356.

    PubMed

    Han, Kyung Ho; Choi, Seon Young; Lee, Je Hee; Lee, Hyejon; Shin, Eun Hee; Agtini, Magdarina D; von Seidlein, Lorenz; Ochiai, R Leon; Clemens, John D; Wain, John; Hahn, Ji-Sook; Lee, Bok Kwon; Song, Manki; Chun, Jongsik; Kim, Dong Wook

    2006-12-01

    Salmonella enterica subspecies enterica serovar Paratyphi B [O1,4,(5),12 : Hb : 1,2] can cause either an enteric fever (paratyphoid fever) or self-limiting gastroenteritis in humans. The d-tartrate non-fermenting variant S. enterica subsp. enterica serovar Paratyphi B dT- (S. Paratyphi B) is the causative agent of paratyphoid fever, and the d-tartrate fermenting variant S. enterica subsp. enterica serovar Paratyphi B dT+ (S. Paratyphi B dT+; formerly called Salmonella Java) causes gastroenteritis. S. Java is currently recognized as an emerging problem worldwide. Twelve dT+ S. Java isolates were collected in Indonesia between 2000 and 2002. One-third of them contained Salmonella genomic island 1 (SGI1), which gives the multidrug-resistant phenotype to the bacteria. In this study, a PCR-based method to detect a single nucleotide difference responsible for the inability to ferment d-tartrate, reported elsewhere, was validated. The d-tartrate fermenting phenotype of S. Java was converted to the non-fermenting phenotype by the disruption of the ORF STM 3356, and the d-tartrate non-fermenting phenotype of the ORF STM 3356-disrupted strain and the dT- reference strain was changed to the dT+ phenotype by complementing ORF STM 3356 in trans. The results show that the dT+ phenotype requires a functional product encoded by STM 3356, and support the use of the PCR-based discrimination method for S. Paratyphi B and S. Java as the standard differentiation method.

  12. Direct evidence of molecular aggregation and degradation mechanism of organic light-emitting diodes under joule heating: an STM and photoluminescence study.

    PubMed

    Gong, Jian-Ru; Wan, Li-Jun; Lei, Sheng-Bin; Bai, Chun-Li; Zhang, Xiao-Hong; Lee, Shuit-Tong

    2005-02-10

    The Joule heating effect on electroluminescent efficiency is important in the degradation origin of organic light-emitting diodes (OLED). Scanning tunneling microscopy (STM) and photoluminescence (PL) measurements were performed on the guest molecule BT (1,4-bis(benzothiazole-vinyl) benzene), host molecule TPBI (2, 2',2' '-(1,3,5-phenylene)tris-[1-phenyl-1H-benzimidazole]), and their mixture deposited on an HOPG surface to study the OLED degradation mechanism due to thermal heating. At room temperature, BT and TPBI in the mixed layer show good compatibility and high PL intensity, but at higher temperatures, they show phase separation and aggregation into their own domains and a concomitant decrease in PL intensity. The PL intensity loss suggests ineffective energy transfer from TPBI to BT due to phase separation, which may cause OLED degradation. Scanning tunneling spectroscopy (STS) results show that the band gaps of TPBI and BT remain unchanged with the annealing temperature, suggesting that the heat-induced decay of OLED is related to the interfacial structural change rather than the respective molecular band gap. The results provide direct evidence showing how the molecular structures of the mixed layer vary and affect the PL intensity due to temperature.

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

    DOE PAGES

    Hattab, H.; Hupalo, M.; Hershberger, M. T.; ...

    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

  14. 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.

  15. 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.

  16. Pump–probe STM light emission spectroscopy for detection of photo-induced semiconductor–metal phase transition of VO2

    NASA Astrophysics Data System (ADS)

    Sakai, Joe; Katano, Satoshi; Kuwahara, Masashi; Uehara, Yoichi

    2017-10-01

    We attempted to observe pump–probe scanning tunneling microscopy (STM)-light emission (LE) from a VO2 thin film grown on a rutile TiO2(0 0 1) substrate, with an Ag tip fixed over a semiconducting domain. Laser pulses from a Ti:sapphire laser (wavelength 920 nm pulse width less than 1.5 ps) irradiated the tip–sample gap as pump and probe light sources. With a photon energy of 2.7 eV, suggesting phase transition from semiconducting monoclinic (M) to metallic rutile (R) phases in relation to the electronic band structure, faint LE was observed roughly 30 ps after the irradiation of the pump pulse, followed by retention for roughly 20 ps. The incident energy fluence of the pump pulse at the gap was five orders of magnitude lower than the threshold value for reported photo-induced M–R phase transition. The mechanism that makes it possible to reduce the threshold fluence is discussed.

  17. In situ STM studies of zinc in aqueous solutions containing PEG DiAcid inhibitor: Correlation with electrochemical performances of zinc-air fuel cells

    NASA Astrophysics Data System (ADS)

    Cohen-Hyams, Tzipi; Ziengerman, Yuli; Ein-Eli, Yair

    Electrochemical performance of prismatic zinc-air fuel cells comprising zinc anode gel containing poly(ethylene glycol) (PEG 600) and poly(ethylene glycol) bis(carboxymethyl) ether (PEG DiAcid 600) as corrosion inhibitor were studied. It was found that in addition to the low zinc corrosion rates obtained from cells utilizing PEG DiAcid 600 as corrosion inhibitor, both analog and global mobile system (GSM) discharge capacities and potential plateaus, in a wide range of temperatures were higher once PEG DiAcid was added to the zinc gel mixtures. The results obtained from in situ scanning tunneling microscopy (STM) studies of zinc substrates immersed in deionized (DI) water containing inhibitors reveal that the film produced on the zinc metal in the presence of PEG DiAcid is by far thinner than the film produced by other inhibitors such as PEG 600 and polyoxyethylene alkyl phosphate ester acid (GAFAC RA 600). These studies also reveal that the addition of PEG DiAcid forms an adherent and a complete protective coverage, while the addition of PEG 600 and GAFAC RA 600 resulted in an incomplete coverage with the appearance of pits and terraces, indicating on a restricted inhibition performance of these two polymers compared with PEG DiAcid. These studies suggest a low interface resistivity of zinc immersed in alkaline solution containing PEG DiAcid, which is expressed in a higher working potential and increased cell capacity in different temperatures at two discharge modes of analog and GSM.

  18. 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.

  19. 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.

  20. Adsorption of the ionic liquid [BMP][TFSA] on Au(111) and Ag(111): substrate effects on the structure formation investigated by STM

    PubMed Central

    Alwast, Dorothea; Wagner, Nadja

    2013-01-01

    Summary In order to resolve substrate effects on the adlayer structure and structure formation and on the substrate–adsorbate and adsorbate–adsorbate interactions, we investigated the adsorption of thin films of the ionic liquid (IL) 1-butyl-1-methylpyrrolidinium-bis(trifluoromethylsulfonyl)imide [BMP][TFSA] on the close-packed Ag(111) and Au(111) surfaces by scanning tunneling microscopy, under ultra high vacuum (UHV) conditions in the temperature range between about 100 K and 293 K. At room temperature, highly mobile 2D liquid adsorbate phases were observed on both surfaces. At low temperatures, around 100 K, different adsorbed IL phases were found to coexist on these surfaces, both on silver and gold: a long-range ordered (‘2D crystalline’) phase and a short-range ordered (‘2D glass’) phase. Both phases exhibit different characteristics on the two surfaces. On Au(111), the surface reconstruction plays a major role in the structure formation of the 2D crystalline phase. In combination with recent density functional theory calculations, the sub-molecularly resolved STM images allow to clearly discriminate between the [BMP]+ cation and [TFSA]− anion. PMID:24367760

  1. Halogen bonding versus hydrogen bonding induced 2D self-assembled nanostructures at the liquid-solid interface revealed by STM.

    PubMed

    Wu, Yican; Li, Jinxing; Yuan, Yinlun; Dong, Meiqiu; Zha, Bao; Miao, Xinrui; Hu, Yi; Deng, Wenli

    2017-01-25

    We design a bifunctional molecule (5-bromo-2-hexadecyloxy-benzoic acid, 5-BHBA) with a bromine atom and a carboxyl group and its two-dimensional self-assembly is experimentally and theoretically investigated by using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The supramolecular self-organization of 5-BHBA in two different solvents (1-octanoic acid and n-hexadecane) at the liquid-solid interface at different solution concentrations is obviously different due to the cooperative and competitive intermolecular halogen and hydrogen bonds. Three kinds of nanoarchitectures composed of dimers, trimers and tetramers are formed at the 1-octanoic acid/graphite interface based on -COOHHOOC-, triangular C[double bond, length as m-dash]OBrH-C, -BrO(H), BrBr, and OH interactions. Furthermore, by using n-hexadecane as the solvent, two kinds of self-assembled linear patterns can be observed due to the coadsorption, in which the dimers are formed by intermolecular -COOHHOOC- hydrogen bonds. The molecule-solvent and solvent-solvent van der Waals force and intermolecular hydrogen bonds dominate the formation of coadsorbed patterns. We propose that the cooperative and competitive halogen and hydrogen bonds are related to the polarity of the solvent and the type of molecule-solvent interaction. The intermolecular binding energy of different dimers and their stability are supported by theoretical calculations. The result provides a new and innovative insight to induce the 2D self-assembled nanostructures by halogen and hydrogen bonds at the liquid-solid interface.

  2. Electrodeposition of Al in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ionic liquids: in situ STM and EQCM studies.

    PubMed

    Moustafa, E M; El Abedin, S Zein; Shkurankov, A; Zschippang, E; Saad, A Y; Bund, A; Endres, F

    2007-05-10

    In the present paper, the electrodeposition of Al on flame-annealed Au(111) and polycrystalline Au substrates in two air- and water-stable ionic liquids namely, 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py(1,4)]Tf(2)N, and 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide, [EMIm]Tf(2)N, has been investigated by in situ scanning tunneling microscopy (STM), electrochemical quartz crystal microbalance (EQCM), and cyclic voltammetry. The cyclic voltammogram of aluminum deposition and stripping on Au(111) in the upper phase of the biphasic mixture of AlCl(3)/[EMIm]Tf(2)N at room temperature (25 degrees C) shows that the electrodeposition process is completely reversible as also evidenced by in situ STM and EQCM studies. Additionally, a cathodic peak at an electrode potential of about 0.55 V vs Al/Al(III) is correlated to the aluminum UPD process that was evidenced by in situ STM. A surface alloying of Al with Au at the early stage of deposition occurs. It has been found that the Au(111) surface is subject to a restructuring/reconstruction in the upper phase of the biphasic mixture of AlCl(3)/[Py(1,4)]Tf(2)N at room temperature (25 degrees C) and that the deposition is not fully reversible. Furthermore, the underpotential deposition of Al in [Py(1,4)]Tf(2)N is not as clear as in [EMIm]Tf(2)N. The frequency shift in the EQCM experiments in [Py(1,4)]Tf(2)N shows a surprising result as an increase in frequency and a decrease in damping with bulk aluminum deposition at potentials more negative than -1.8 V was observed at room temperature. However, at 100 degrees C there is a frequency decrease with ongoing Al deposition. At -2.0 V vs Al/Al(III), a bulk aluminum deposition sets in.

  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. Exploring Nanophotovoltaic Molecules using STM

    NASA Astrophysics Data System (ADS)

    Tao, Chenggang; Sun, Jibin; Zhang, Xiaowei; Yamachika, R.; Wegner, D.; Bahri, Y.; Samsonidze, G.; Louie, S.; Tilly, T.; Segalman, R.; Crommie, M.

    2009-03-01

    Composite molecular solar cells are a promising and exciting alternative to traditional silicon or gallium arsenide solar cells, but the power conversion efficiency remains low. In order to further increase this efficiency, a deeper understanding of the microscopic mechanisms at work in organic solar cells is needed. Using scanning tunneling microscopy and spectroscopy we have investigated nanophotovoltaic molecules that combine both donor and acceptor elements. Submolecular spectral resolution reveals the energy level alignment within these composite molecular structures. This information should be useful for understanding the energy conversion pathways within molecular solar cells, and for developing higher efficiency solar cell materials.

  5. The dense α-√3 × √3Pb/Si(1 1 1) phase: A comprehensive STM and SPA-LEED study of ordering, phase transitions and interactions

    NASA Astrophysics Data System (ADS)

    Stepanovsky, S.; Yakes, M.; Yeh, V.; Hupalo, M.; Tringides, M. C.

    2006-04-01

    The T- θ phase diagram for the system Pb/Si(1 1 1) was determined in the coverage range 6/5 ML < θ < 4/3 ML from complementary STM and SPA-LEED experiments. This coverage is within the range where a "Devil's Staircase" (DS) has been realized. The numerous DS phases answer conflicting information in the Pb/Si(1 1 1) literature and update the previously published phase diagram. The measurements reveal the thermal stability of the different linear DS phases with the transition temperature found to be a function of phase period. Because of additional complexity in the experimental system (i.e. two-dimensionality and 3-fold symmetry) the linear DS phases transform at higher temperature into commensurate phases of 3-fold symmetry HIC (historically named "hexagonal incommensurate phase"). Different types of HIC phases have been discovered differing in the size of the supercell built out of √3 × √3 domains separated by domain walls of the √7 × √3 phase. The detailed structures of these HIC phases (coverage, binding site, twist angle, etc.) have been deduced from the comparison of STM images and diffraction patterns. After heating the system to even higher temperature the HIC phase transforms into the disordered phase. For sufficiently high coverage a SIC ("striped incommensurate phase" which is also built from √3 × √3 domains but meandering √7 × √3 domain walls) is observed which also disorders at high temperatures.

  6. gcpA (stm1987) is critical for cellulose production and biofilm formation on polystyrene surface by Salmonella enterica serovar Weltevreden in both high and low nutrient medium.

    PubMed

    Bhowmick, Patit Paban; Devegowda, Devananda; Ruwandeepika, H A Darshanee; Fuchs, Thilo M; Srikumar, Shabarinath; Karunasagar, Iddya; Karunasagar, Indrani

    2011-02-01

    Biofilm formation by Salmonella is a serious concern in the food-processing industry and the persistence of the organism in biofilms becomes a constant source of contamination. Since there is zero tolerance for Salmonella in foods, it is important to understand the mechanism of biofilm formation and to prevent the formation. Therefore, this study aimed at investigating the biofilm-forming ability of seafood isolates of Salmonella enterica serovar Weltevreden (S. Weltevreden) under two different nutrient conditions (normal strength trypticase soy broth (TSB) and 1:100 diluted TSB). The role of cellulose production in biofilm formation and in the expression of multicellular behavior (rough, dark, red morphotype: rdar) was investigated. Fourteen isolates of seafood associated S. Weltevreden were studied for biofilm production in polystyrene microtitre plates. Only one (SW49) of 14 was a strong biofilm former on polystyrene template and was able to produce biofilm in both undiluted TSB and 1:100 diluted TSB at 24h. All others produced moderate or weak biofilms which was higher in 1:100 diluted TSB compared to undiluted medium. All the isolates except one were positive by PCR for the three genes, gcpA (stm1987), adrA (yaiC) and csgD. Gene expression of gcpA, adrA and csgD was studied by real-time PCR with the one strong (SW49) and one representative weak (SW30) biofilm former. In SW49 at 24h of incubation, the expression of gcpA from biofilm cells was 33 and 36 times higher than from planktonic cells grown in TSB and diluted TSB respectively and at 72h the expression from biofilm cells was 57 and 61 times higher than that from planktonic cells. Quantification of gene expression did not reveal any significant difference in the expression of csgD and adrA gene. Deletion of gcpA in SW49 resulted in its inability to produce cellulose and consequent inability to bind calcoflour, inability to form rdar colony on Congo Red-agar plates and failure to produce biofilm on

  7. Atomic-scale spot structures and gap distributions on apical-fluorine cuprate superconductor Ba2Ca5Cu6O12 (O1-x, Fx)2 observed by STM/STS

    NASA Astrophysics Data System (ADS)

    Sugimoto, A.; Shohara, K.; Ekino, T.; Watanabe, Y.; Harada, Y.; Mikusu, S.; Tokiwa, K.; Watanabe, T.

    2010-12-01

    The atomic-scale surface electronic states on the multi-layered apical-fluorine cuprate superconductor Ba2Ca5Cu6O12 (O1-x, Fx)2(TC≃70K) are investigated by using low temperature scanning tunneling microscopy/spectroscopy (STM/STS). The spatial gap distributions show the patch scale of ˜0.5nm, which is quite shorter than the superconducting coherence length ˜2-3 nm of other cuprate superconducters of a few nm. The high-bias (˜1V) conductance map contains some characteristic spots with contrasts reverse to those at low bias, which are considered to be due to the charge unbalance of apical atoms such as O2- and F-.

  8. In situ STM investigation of the lithium underpotential deposition on Au(111) in the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide.

    PubMed

    Gasparotto, L H S; Borisenko, N; Bocchi, N; El Abedin, S Zein; Endres, F

    2009-12-21

    In the present paper the underpotential deposition (UPD) of lithium on Au(111) from 0.5 mol L(-1) LiTFSA in the air- and water stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py(1,4)]TFSA, has been investigated by cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM). The pure [Py(1,4)]TFSA was found to be inert in the potential regime investigated. The results show that the lithium UPD on Au(111) in [Py(1,4)]TFSA begins at potentials considerably positive to the electrode potential of bulk deposition and follows a layer-by-layer mechanism with the formation of at least two monolayers. A large number of monoatomically deep pits appear when the potential reaches positive values, which is an indication that a Li-Au alloy was formed.

  9. Stress and Structure Evolution during Copper/Gold(111) - (22 multiply the square root of 3) Heteroepitaxy: An In-Situ Study with UHV-STM (Ultra High Vacuum Scanning Tunneling Microscopy)

    NASA Astrophysics Data System (ADS)

    Nah, Jungwoo

    This research focuses on the stress and structure evolution observed in-situ during the earliest stages of thin film growth in Cu on Au(111)-reconstruction. For the research, an ultra high vacuum-scanning tunneling microscopy (UHV-STM) system was modified to have the additional capabilities of in-situ deposition and in-situ stress evolution monitoring. The design and fabrication processes for the modifications are explained in detail. The deposition source enabled imaging during the deposition of Cu thin films, while also being columnar enough to avoid negatively impacting the function of the microscope. It was found that the stress-induced changes in piezo voltage occurred over a substantially longer time scale and larger piezo scale than used during imaging, allowing for the deconvolution of the two sources of piezo voltage change. The intrinsic stress evolution observed at the onset of Cu growth was tensile in character and reached a maximum of 0.19 N/m at approximately 0.8ML, with an average tensile slope of 1.0GPa. As the film thickness increased beyond 0.8 ML, the stress became less tensile as the observation of disordered stripe and trigon patterns of misfit dislocations began to appear. The transport of atoms from the surface of enlarged Cu islands into the strained layer played an important role in this stage, because they effectively reduce the activation barrier for the formation of the observed surface structures. A rich array of structures were observed in the work presented here including stripe, disordered stripe and trigon patterns co-existing in a single Cu layer. Heteroepitaxial systems in existing literature showed a uniform structure in the single layer. The non-uniform structures in the single layer of this work may be attributed to the room temperature Cu growth, which can kinetically limit uniform pattern formation. The development of the UHV-STM system with additional capabilities for this work is expected to contribute to research for the

  10. Structural and electronic properties of ultrathin FeSe films grown on Bi2Se3(0 0 0 1) studied by STM/STS.

    PubMed

    Singh, Udai Raj; Warmuth, Jonas; Markmann, Verena; Wiebe, Jens; Wiesendanger, Roland

    2017-01-18

    We report scanning tunnelling microscopy and spectroscopy (STM/STS) studies on one and two unit cell (UC) high FeSe thin films grown on Bi2Se3(0 0 0 1). In our thin films, we find the tetragonal phase of FeSe and dumb-bell shaped defects oriented along Se-Se bond directions. In addition, we observe striped moiré patterns with a periodicity of (7.3  ±  0.1) nm generated by the mismatch between the FeSe lattice and the Bi2Se3 lattice. We could not find any signature of a superconducting gap in the tunneling spectra measured on the surface of one and two UC thick islands of FeSe down to 6.5 K. The spectra rather show an asymmetric behavior across and a finite density of states at the Fermi level (E F) resembling those taken in the normal state of bulk FeSe.

  11. Structural and electronic properties of ultrathin FeSe films grown on Bi2Se3(0 0 0 1) studied by STM/STS

    NASA Astrophysics Data System (ADS)

    Singh, Udai Raj; Warmuth, Jonas; Markmann, Verena; Wiebe, Jens; Wiesendanger, Roland

    2017-01-01

    We report scanning tunnelling microscopy and spectroscopy (STM/STS) studies on one and two unit cell (UC) high FeSe thin films grown on Bi2Se3(0 0 0 1). In our thin films, we find the tetragonal phase of FeSe and dumb-bell shaped defects oriented along Se-Se bond directions. In addition, we observe striped moiré patterns with a periodicity of (7.3  ±  0.1) nm generated by the mismatch between the FeSe lattice and the Bi2Se3 lattice. We could not find any signature of a superconducting gap in the tunneling spectra measured on the surface of one and two UC thick islands of FeSe down to 6.5 K. The spectra rather show an asymmetric behavior across and a finite density of states at the Fermi level (E F) resembling those taken in the normal state of bulk FeSe.

  12. LEED, STM, and TDS studies of ordered thin films of the rhombus-shaped polycondensed aromatic hydrocarbon C54H22, on MoS2, GeS, and graphite.

    PubMed

    Günther, Christian; Karl, Norbert; Pflaum, Jens; Strohmaier, Rainer; Gompf, Bruno; Eisenmenger, Wolfgang; Müller, Markus; Müllen, Klaus

    2005-01-18

    Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and thermal desorption spectroscopy (TDS) are used to study vacuum vapor-deposited molecular thin films of the rhombus-shaped polycondensed aromatic hydrocarbon "rhombus-C54", C54H22, on MoS2 and graphite (0001) and on GeS (010) substrates. It is found that this compound forms well-ordered incommensurate superstructures of the closest packed flat-lying molecules in well-defined azimuthal orientations to the substrate. These films are thermally remarkably stable. By TDS, a monolayer binding energy on graphite of 2.3 eV was derived, whereas the molecules in the second layer were found to be less strongly bound (1.9 eV). This difference allows the preparation of monolayers by desorbing multilayers at the appropriate temperature. Apparently, this molecule is a promising candidate for further studies aiming at applications in organic electronics such as organic field effect transistors or light emitting displays.

  13. 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

  14. Postscript: Through TCM, STM Shines Bright

    ERIC Educational Resources Information Center

    Davelaar, Eddy J.; Usher, Marius; Haarmann, Henk J.; Goshen-Gottstein, Yonatan

    2008-01-01

    We find the reply by Kahana, Sederberg, and Howard helpful in clarifying the temporal-context model (TCM) function, in particular with regard to the elimination of the recency effect by a difficult distractor under parameters that still enable long-term contiguity effects to emerge. We agree with Kahana et al. that what matters most to the…

  15. Reversible on-surface wiring of resistive circuits† †Electronic supplementary information (ESI) available: Additional experimental details and STM-BJ data, synthetic procedures, X-ray photoelectron and NMR spectra. Raw data used in figure plots is available at http://zenodo.org (10.5281/zenodo.496177). See DOI: 10.1039/c7sc00599g Click here for additional data file.

    PubMed Central

    Leroux, Yann R.; Hapiot, Philippe; Campos, Luis M.

    2017-01-01

    Whilst most studies in single-molecule electronics involve components first synthesized ex situ, there is also great potential in exploiting chemical transformations to prepare devices in situ. Here, as a first step towards this goal, we conduct reversible reactions on monolayers to make and break covalent bonds between alkanes of different lengths, then measure the conductance of these molecules connected between electrodes using the scanning tunneling microscopy-based break junction (STM-BJ) method. In doing so, we develop the critical methodology required for assembling and disassembling surface-bound single-molecule circuits. We identify effective reaction conditions for surface-bound reagents, and importantly demonstrate that the electronic characteristics of wires created in situ agree with those created ex situ. Finally, we show that the STM-BJ technique is unique in its ability to definitively probe surface reaction yields both on a local (∼50 nm2) and pseudo-global (≥10 mm2) level. This investigation thus highlights a route to the construction and integration of more complex, and ultimately functional, surface-based single-molecule circuitry, as well as advancing a methodology that facilitates studies beyond the reach of traditional ex situ synthetic approaches. PMID:28660061

  16. Spectroscopic STM studies of single gold(III) porphyrin molecules.

    PubMed

    Müllegger, Stefan; Schöfberger, Wolfgang; Rashidi, Mohammad; Reith, Lorenz M; Koch, Reinhold

    2009-12-16

    Low-temperature scanning tunneling microscopy, a well-established technique for single-molecule investigations in an ultrahigh vacuum environment, has been used to study the electronic properties of Au(III) 5,10,15,20-tetraphenylporphyrin (AuTPP) molecules on Au(111) at the submolecular scale. AuTPP serves as a model system for chemotherapeutically relevant Au(III) porphyrins. For the first time, real-space images and local scanning tunneling spectroscopy data of the frontier molecular orbitals of AuTPP are presented. A comparison with results from density functional theory reveals significant deviations from gas-phase behavior due to a non-negligible molecule/substrate interaction. We identify the oxidation state of the central metal ion in the adsorbed AuTPP as Au(3+).

  17. STM tip-mediated mass transport on Cu surfaces

    NASA Astrophysics Data System (ADS)

    Sun, Y. S. N.; Huang, R. Z.; Gao, T. F.; Zhang, R. J.; Wang, Y. M.

    2015-02-01

    Atomic-scale simulations are performed to study atomic motion on Cu surfaces to illustrate the effect of the scanning tunneling microscopy tip on mass transport (MT) in the surfaces and on top of the Co island in heteroepitaxial Co/Cu(0 0 1) and Co/Cu(1 1 1) systems. First we investigate tip-induced atomic motion of Co atoms embedded in the Cu(0 0 1) surface at zero bias voltage. With the help of the tip, the Co atom in the surface can freely diffuse toward its nearby vacancy site. So-called vacancy mechanism is used to interpret this phenomenon. Then tip-mediated atomic motion of Co adatoms on the Co islands supported by a Cu(1 1 1) surface is studied. It is revealed that the tip has a significant effect on the diffusion of adatoms on the islands and interlayer mass transport at the island edge. Interlayer mass transport at the island edge is found to depend strongly on the tip height and the lateral distance from the tip. By calculating the diffusion barriers, it is found that the jumping diffusion barrier on the island can be zero by the tip vertical manipulation while the Ehrlich-Schwoebel diffusion barrier at the island edge can be reduced by the tip lateral manipulation. Thus, the quality of thin films can be improved by controlling MT in and/or on the surface.

  18. 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.

  19. STM Images of Cytokeratin and Binding IgG Antibody

    NASA Astrophysics Data System (ADS)

    Vernetti, L. A.; Sarid, D.; Gandolfi, A. J.; Cress, A. E.; Nagle, R. B.; McCuskey, R.; Hameroff, S. R.

    1991-12-01

    In this paper we present scanning tunneling microscopy images of cytokeratin proteins and a monoclonal anti-cytokeratin IgG antibody bound to their carboxyl terminal end. The images are consistent with current models of cytokeratin assembly inferred from biochemical analysis, electron microscopy evaluation of disintegrating cytokeratin filaments, and chemical cross-linking of coiled-coils.

  20. Nano-patterning and single electron tunnelling using STM

    NASA Astrophysics Data System (ADS)

    Hu, Xiaoming; Sarid, D.; von Blanckenhagen, P.

    1999-06-01

    A scanning tunnelling microscope with a gold tip was used to create clusters and form nano-dots, lines and corrals on a clean stepped Si(111) surface by applying a series of bias pulses to the tip-sample tunnelling junction. Nano-dots with diameters as small as a few nm can be realized. By decreasing the distances between nano-dots, it is possible to create continuous nano-lines of a few nm wide and over a few hundred nm long, which can be used as connections between micro- and nano-electronic components. A nano-corral of about 40 nm in diameter formed by many Au dots of a few nm in diameter each was also created on the Si(111) surface. Single electron tunnelling effects through nano-dots were studied and it was found that `Coulomb staircases' can be observed in the I-V (current-voltage) curve at room temperature through an Au tip-Au cluster-Si substrate double junction system.

  1. Combination STM/AFM and AFM Images of Magnetic Domains

    NASA Astrophysics Data System (ADS)

    Yi, L.; Gallagher, M.; Howells, S.; Chen, T.; Sarid, D.

    1991-12-01

    By employing a cantilevered tip in a scanning tunneling microscope, one obtains images that show an enhancement of features associated with forces whose derivatives vary along the direction of scanning. The theory of this process is described together with experimental results showing magnetic domains on a gold coated floppy disk. Also shown are atomic force microscopy images of a ferrofluid-developed magnetic tape.

  2. STM imaging of vortex cores states in superconducting graphene

    NASA Astrophysics Data System (ADS)

    Ji, Yu; Ovadia, Maoz; Hoffman, Jennifer; Lee, Gil-Ho; Philip Kim Collaboration; Wenjing Fang Collaboration

    Graphene becomes superconducting via the proximity effect when it comes in good contact with a superconductor. In the presence of a magnetic field, superconducting vortices will form and will each contain Andreev bound states. If the normal electrons in the vortices have a Dirac dispersion and they are surface bound states, the zero modes of the Dirac dispersion are then Majorana fermions. We investigate the electronic properties of graphene on superconducting NbN and search for these vortex bound states using our home built low temperature scanning tunneling microscope. Harvard University.

  3. Friedel oscillations and quasiparticle interference: Complementary STM and REXS approach

    NASA Astrophysics Data System (ADS)

    Aynajian, Pegor; Gyenis, András; da Silva Neto, Eduardo; He, Feizhou; Sutarto, Ronny; Schierle, Enrico; Weschke, Eugen; Kavai, Mariam; Baumbach, Ryan; Thompson, Joe; Bauer, Eric; Fisk, Zachary; Damascelli, Andrea; Yazdani, Ali

    The origin of a competing charge ordering in the high-temperature superconducting cuprates has recently been subject to intense experimental and theoretical debates. Dalla Torre et al theoretically proposed that Friedel oscillations can reproduce the experimentally observed scattering peak in the resonant elastic x-ray scattering (REXS) of cuprates [NJP, 17 022001 2015]. Using complementary spectroscopic imaging with the scanning tunneling microscope and REXS on the heavy fermion compound CeMIn5 (M =Co, Rh) we observe a scattering peak in REXS, similar, yet broader than that found in cuprates. Through temperature and doping dependent experiments, we demonstrate this enhanced peak to originate from the scattering of hybridized heavy f-electrons. We discuss the origin of this phenomenon and its relation to Friedel oscillations and charge ordering.

  4. STM characterization of a graphitized SiC(0001)surface

    NASA Astrophysics Data System (ADS)

    Brar, Victor; Zhang, Yuanbo; Yayon, Yossi; Ohta, Taisuke; McChesney, Jessica; Rotenberg, Eli; Crommie, Mike

    2007-03-01

    The two-dimensional electron gas in a single graphene sheet exhibits unique properties due the cone-shaped electron band structure near the Fermi energy. Recently the growth of a single layer of graphene on SiC(0001) has been demonstrated, opening new possibilities for fabricating large scale graphene-based devices. We have performed scanning tunneling microscopy and spectroscopy of single and bi-layer graphene films on SiC(0001). Atomically resolved topographs and dI/dV maps show clear differences between the single and bi-layer surfaces at different length scales. We have characterized the energy dependence and spatial distribution of the electron local density of states in these single and bi-layer films.

  5. STM Study of Al CVD Precursors on Si(100)

    NASA Astrophysics Data System (ADS)

    Mitsui, Toshiyuki; Hill, Eric; Curtis, Robert; Ganz, Eric

    1998-03-01

    Dimethylethylamine alane (DMEAA) and dimethyaluminum hydride (DMAH) have been used for chemical vapor deposition aluminum film growth on semiconductor substrates. We investigate the properties of these Al precursors on the Si(100) surface in ultra high vacuum. We use high speed scanning tunneling microscopy to characterize the precursor molecules and fragments of the molecules on the Si(100) surface over a wide range of substrate temperatures. We have observed DMEAA molecules and fragments after dosing the Si(100) surface at temperatures up to 300^0C. Al deposition at low coverages is not observed until temperatures above 300^0C. We will also discuss the initial stages of growth resulting from DMAH deposition and fragmentation on the Si(100) surface.

  6. 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.

  7. Donor wave functions in Si gauged by STM images

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    The triumph of effective mass theory in describing the energy spectrum of dopants does not guarantee that the model wave functions will withstand an experimental test. Such wave functions have recently been probed by scanning tunneling spectroscopy, revealing localized patterns of resonantly enhanced tunneling currents. We show that the shape of the conducting splotches resembles a cut through Kohn-Luttinger (KL) hydrogenic envelopes, which modulate the interfering Bloch states of conduction electrons. All the nonmonotonic features of the current profile are consistent with the charge density fluctuations observed between successive {001 } atomic planes, including a counterintuitive 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 wave vector to k0=(0.82 ±0.03 ) (2 π /aSi) . Unlike prior measurements, averaged over a sizable 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 . We demonstrate that the central-cell-corrected estimates for this ratio are encouragingly accurate, leading to the conclusion that the KL theory is a valid model not only for energies but for wave functions as well.

  8. 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.

  9. Variable temperature STM study of Co deposition on a dodecanethiol self assembled monolayer

    NASA Astrophysics Data System (ADS)

    Breitwieser, Romain; Campiglio, Paolo; Chacon, Cyril; Repain, Vincent; Nemausat, Ruidy; Girard, Yann; Lagoute, Jérôme; Rousset, Sylvie

    2012-02-01

    The present scanning tunneling microscopy study reports on the growth processes of Co vapor-deposited on a dodecanethiol (DDT) self-assembled monolayer (SAM)/Au(111). We observe strongly modified surface and depth diffusions of Co adatoms depending on the growth temperature. Co deposited at 300 K shows an extremely incomplete regime of condensation on the organic layer. Besides, Co penetrates the DDT monolayer and resides at the DDT/Au(111) interface as 2D clusters. This phenomenon takes place through defects in the SAM which are transient channels. In contrast, Co deposited at 50 K shows a complete condensation and nucleates on defects of the SAM layer as 3D islands sitting most likely on top of the DDTs. These results are of interest in the growing field of organic spintronics where the quality of the organic/ferromagnetic interface is a key issue.

  10. 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.

  11. Bending and buckling of narrow armchair graphene nanoribbons via STM manipulation

    NASA Astrophysics Data System (ADS)

    van der Lit, Joost; Jacobse, Peter H.; Vanmaekelbergh, Daniel; Swart, Ingmar

    2015-05-01

    Semiconducting graphene nanoribbons (GNRs) are envisioned to play an important role in future electronics. This requires the GNRs to be placed on a surface where they may become strained. Theory predicts that axial strain, i.e. in-plane bending of the GNR, will cause a change in the band gap of the GNR. This may negatively affect device performance. Using the tip of a scanning tunneling microscope we controllably bent and buckled atomically well-defined narrow armchair GNR and subsequently probed the changes in the local density of states. These experiments show that the band gap of 7-ac-GNR is very robust to in-plane bending and out-of-plane buckling.

  12. Theory of Fano Resonances in Graphene: The Kondo effect probed by STM

    SciTech Connect

    Wehling, T.O.

    2010-06-02

    We consider the theory of Kondo effect and Fano factor energy dependence for magnetic impurity (Co) on graphene. We have performed a first principles calculation and find that the two dimensional E{sub 1} representation made of d{sub xz}, d{sub yz} orbitals is likely to be responsible for the hybridization and ultimately Kondo screening for cobalt on graphene. There are few high symmetry sites where magnetic impurity atom can be adsorbed. For the case of Co atom in the middle of hexagon of carbon lattice we find anomalously large Fano q-factor, q {approx} 80 and strongly suppressed coupling to conduction band. This anomaly is a striking example of quantum mechanical interference related to the Berry phase inherent to graphene band structure.

  13. 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.

  14. Accessing topological superconductivity via a combined STM and renormalization group analysis.

    PubMed

    Elster, Lars; Platt, Christian; Thomale, Ronny; Hanke, Werner; Hankiewicz, Ewelina M

    2015-09-08

    The search for topological superconductors has recently become a key issue in condensed matter physics, because of their possible relevance to provide a platform for Majorana bound states, non-Abelian statistics, and quantum computing. Here we propose a new scheme which links as directly as possible the experimental search to a material-based microscopic theory for topological superconductivity. For this, the analysis of scanning tunnelling microscopy, which typically uses a phenomenological ansatz for the superconductor gap functions, is elevated to a theory, where a multi-orbital functional renormalization group analysis allows for an unbiased microscopic determination of the material-dependent pairing potentials. The combined approach is highlighted for paradigmatic hexagonal systems, such as doped graphene and water-intercalated sodium cobaltates, where lattice symmetry and electronic correlations yield a propensity for a chiral singlet topological superconductor. We demonstrate that our microscopic material-oriented procedure is necessary to uniquely resolve a topological superconductor state.

  15. Se adlattices formed on Au(100), studies by LEED, AES, STM and electrochemistry

    NASA Astrophysics Data System (ADS)

    Huang, Baoming M.; Lister, Tedd E.; Stickney, John L.

    1997-12-01

    Ordered selenium atomic layers have been formed electrochemically on Au(100) at a series of coverages. Cyclic voltammetry and coulometry were used to study the deposition process, and to determine the corresponding coverages of a number of Se structures. Structures, with Se coverages of 0.25, 0.33, 0.5, and 0.89 monolayers, were identified using ultra high vacuum — electrochemical techniques as well as scanning tunneling microscopy. The corresponding unit cells of those structures were: p(2 × 2), (2 × √10), c(2 × 2), and a mostly (3 × √10), composed of close-packed Se 8 rings. Pit formation, associated with the formation of the densely packed Se 8 ring structure, was observed. They are reminiscent of pits observed in self-assembled monolayers of alkane thiols on Au surfaces. The pits disappeared as the structure, composed of Se rings, was converted to lower coverage structures, such as the 0.25 monolayer p(2 × 2), via anodic stripping. Se atomic layers were formed electrochemically in three ways: direct reduction from a HSeO -3 solution; anodic stripping of previously formed bulk Se; or cathodic stripping of previously formed bulk Se. All three methods resulted in equivalent atomic layer structures on the Au(100) surface, but with some variation in the homogeneity and distribution of particular structures.

  16. High-Resolution Molecular Orbital Imaging Using a p-Wave STM Tip

    NASA Astrophysics Data System (ADS)

    Gross, Leo; Moll, Nikolaj; Mohn, Fabian; Curioni, Alessandro; Meyer, Gerhard; Hanke, Felix; Persson, Mats

    2011-08-01

    Individual pentacene and naphthalocyanine molecules adsorbed on a bilayer of NaCl grown on Cu(111) were investigated by means of scanning tunneling microscopy using CO-functionalized tips. The images of the frontier molecular orbitals show an increased lateral resolution compared with those of the bare tip and reflect the modulus squared of the lateral gradient of the wave functions. The contrast is explained by tunneling through the p-wave orbitals of the CO molecule. Comparison with calculations using a Tersoff-Hamann approach, including s- and p-wave tip states, demonstrates the significant contribution of p-wave tip states.

  17. 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.

  18. Electronic properties of epitaxial silicene: a LT-STM/STS study

    NASA Astrophysics Data System (ADS)

    Fleurence, Antoine; Lee, Chi-Cheng; Ozaki, Taisuke; Yamada-Takamura, Yukiko; Yoshida, Yasuo; Hasegawa, Yukio

    2013-03-01

    The astonishing properties of silicene, the Si-counterpart of graphene, together with pioneering experimental observations, triggered in the very recent years, an exponentially increasing interest for this atom-thick material, both at fundamental level and for applications in high-speed electronic devices. We demonstrated, that the spontaneous segregation of silicon on (0001) surface of zirconium diboride (ZrB2) thin films epitaxied on Si(111) wafers gives rise to a wide-scale uniform two-dimensional silicene sheet. The silicene nature of the honeycomb structure imaged by scanning tunneling microscopy is evidenced by the observation of gap-opened π-electronic bands. The band gap opening is primarily due the specifically imprinted buckling. Here, we present the results of a low-temperature scanning tunneling spectroscopy investigation, which evidences the n-doped nature of silicene. The mapping of the local density of states, together with density functional theory give precious insights into the microscopic origin of the electronic bands of silicene. In particular, it shows the correlation between the degree of sp2 hybridization of different Si atoms in the internal structure and the character of the electronic bands.

  19. Phillips with probe-and-cone docking mechanism (StM) in the Zvezda module

    NASA Image and Video Library

    2005-06-19

    ISS011-E-09205 (19 June 2005) --- Astronaut John L. Phillips, Expedition 11 NASA ISS science officer and flight engineer, works on the dismantled probe-and-cone docking mechanism from the Progress 18 spacecraft in the Zvezda Service Module of the International Space Station (ISS). The Progress docked to the aft port of the Service Module at 7:42 p.m. (CDT) as the two spacecraft flew approximately 225 statute miles, above a point near Beijing, China.

  20. Krikalev with probe-and-cone docking mechanism (StM) in the Zvezda module

    NASA Image and Video Library

    2005-06-19

    ISS011-E-09210 (19 June 2005) --- Cosmonaut Sergei K. Krikalev, Expedition 11 commander representing Russia's Federal Space Agency, holds the dismantled probe-and-cone docking mechanism from the Progress 18 spacecraft in the Zvezda Service Module of the International Space Station (ISS). The Progress docked to the aft port of the Service Module at 7:42 p.m. (CDT) as the two spacecraft flew approximately 225 statute miles, above a point near Beijing, China.

  1. Electric Field Induced Reconstructions in STM Experiments on Au(111) Surfaces

    DTIC Science & Technology

    1992-02-27

    COUNT Technical IFROM L/PlTOLO/ 3 1 / 9 1 Fewrr 25. Irr~a’ 1 4 ae 16. SUPPLEMENTARY NOTATION ___ ___ 1pae submitted to the Journal of Chemical Physics . November...the 4[ x22 strctuse are mobile and anneal into a stable surface strucr on the time-scale of tens of seconds Submitted to the Journal of Chemical Physics , November

  2. Theoretical and STM Studies of the Electronic Structure of Metal/Semiconductor/Hydrogen Systems

    DTIC Science & Technology

    1992-11-19

    P. Blaha and K. Schwartz, 1. Phys. F 17, 899 (1987). [9] M.Y. Chou. P. K. Lam, and M. L. Cohen, Phys. Rev. B 28, 4179 (1983). (10] T. L. Loucks and...and H. Partridge, private communication. 22. G. Pichler, A.M. Lyyra, P.D. Kleiber, W.C. Stwalley, R. Hammer, K.M. Sando and H.H. Michels , Chem. Phys

  3. Intramolecular features of individual C 60 molecules on Si(100) observed by STM

    NASA Astrophysics Data System (ADS)

    Yao, Xiaowei; Ruskell, Todd G.; Workman, Richard K.; Sarid, Dror; Chen, Dong

    1996-12-01

    Intramolecular features (IMF) of a variety of individual C 60 molecules adsorbed on an Si(100)-(2 × 1) surface have been imaged by scanning tunneling microscopy under ultrahigh vacuum conditions. Features of individual C 60 molecules clearly show the local density of states superimposed on their cage structure. Both physisorbed (pre-annealed) and chemisorbed (post-annealed) species have been imaged on the same surface, exhibiting characteristics that depend on their bonding nature. Intramolecular features of a physisorbed C 60 molecule and of two chemisorbed molecules are presented.

  4. 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

  5. Self-assembled Ge, Sb and Al nanostructures on graphite: comparative STM studies

    NASA Astrophysics Data System (ADS)

    Kushvaha, S. S.; Yan, Z.; Xiao, W.; Xu, M.-J.; Xue, Q.-K.; Wang, X.-S.

    2007-04-01

    The growth of Ge, Sb and Al nanostructures on highly oriented pyrolytic graphite (HOPG) have been studied comparatively using scanning tunnelling microscopy in ultra-high vacuum. Clusters and crystallites of these elements were grown along HOPG steps in the initial stage. But the nanoparticles of these three elements show quite different size distributions and morphological evolution in later growth stages. Using different deposition flux and amount, Ge clusters with self-limiting height, cluster chains and double-layer ramified cluster islands were obtained on HOPG at room temperature (RT). Compact crystalline Ge islands with high-index facets were observed after annealing at 600 K following RT deposition. Three-dimensional (3D) spherical islands, 2D thin films and 1D nanorods of Sb have been synthesized using different fluxes on HOPG at RT. With higher flux and a substrate temperature of 375 K, only crystalline 2D and 1D structures of Sb were obtained. When Al was deposited on HOPG at RT, the growth and coalescence of clusters formed initially result in flat Al crystallites with (111) top facet. After more deposition, craters were observed on top of the flattened Al islands resulting from a few smaller islands merging together. The mobile Al islands on HOPG can be pinned by Sb. The morphology difference of observed nanostructures reflects unique energetic and kinetic properties of atoms and clusters of each element.

  6. Adsorption and Dissociation of Disilane on Si(001) Studied by STM

    DTIC Science & Technology

    1993-05-01

    Avenue Madison, Wi 53706 Abstract The surface-adsorbed fragments resulting from the room- temperature adsorbtion and dissociation of disilane (Si 2 H 6...on the dissociation process. By heating disilane-dosed silicon surfaces, we 3 can also observe directly the epitaxial growth of silicon from these...controlling electronics, have been described previously [13, 14]. All experiments are carried out at room temperature in an ion- pumped UHV stainless

  7. 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.

  8. 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

  9. 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.

  10. The STM32 microcontroller based pulse intensity registration system for the neutron monitor

    NASA Astrophysics Data System (ADS)

    Shepetov, Alexander; Chubenko, Alexander; Kryakunova, Olga; Nikolayevsky, Nikolay; Salikhov, Nazyf; Yanke, Victor

    2017-06-01

    We present the outlines of a new microcontroller based data acquisition system which is aimed for reliable operation in a typical cosmic ray particle registration experiment. The system supports connection of up to 16 input signals and ensures the following operation functionality: (1) stable monitoring of the intensity of a digital pulse signal, or digitization of a continuous potential level with a low time resolution (typically, about 1 s-100 s); (2) registration of uninterruptable high-resolution (up to 5-10 μs) time series of the input signal intensity; (3) synchronization of registered time series with both external (physical) or local (program-based) trigger signal; (4) possibility of an on-the-fly change of the whole configuration of informational system (both the combination and type of input signals, time resolution and sum duration of the time series measurements, trigger logic, etc.) immediately in operation time through convenient communication by plain text messages in dialog mode. In particular, the considered system is applied now for a long-term, high precision measurement of the counting rate of neutron signals at the NM64 type neutron supermonitor of the Tien Shan mountain cosmic ray station, with a real-time representation of the whole collected dataset in a WWW database.

  11. A RHEED/MBE-STM investigation of the static and dynamic InAs(001) surface

    NASA Astrophysics Data System (ADS)

    Bomphrey, J. J.; Ashwin, M. J.; Jones, T. S.

    2017-02-01

    We report here the temperature-dependent incorporation kinetics of dimeric arsenic in InAs(001) homoepitaxy, using reflection high-energy electron diffraction (RHEED). Surface reconstructions, in combination with the RHEED investigation have provided insight into the growth of InAs(001), developing an accurate method of controlling the V:III ratio, which has been utilised to probe the low temperature epitaxial growth of indium arsenide epitaxial layers.

  12. 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...!

  13. Using a chemical concept for reactivity for the interpretation of STM images of physisorbed molecules

    NASA Astrophysics Data System (ADS)

    Gawronski, Heiko; Henzl, Jörg; Simic-Milosevic, Violeta; Morgenstern, Karina

    2007-09-01

    The electrostatic potential mapped on the electron density contour of gas phase molecules is used to identify several molecules physisorbed on transition metals imaged by scanning tunnelling microscopy within the molecular HOMO-LUMO gap. It is rationalized that the inverted of this potential, representing the potential energy felt by a negative test charge, is a good concept to interpret changes in the dielectricity constant through the influence of physisorbed molecules and thus to understand their submolecular resolution images. The validity of the concept is demonstrated on dichlorobenzene, chloronitrobenzene, and two azobenzene derivates on the surfaces of Au(111), Ag(111), and Cu(111).

  14. A detailed study on the thermal endurance of Kapton HNTM and Upilex STM

    NASA Astrophysics Data System (ADS)

    Heltzel, S.; Semprimoschnig, C. O. A.

    2003-09-01

    Assessing the thermal endurance by isothermal testing in a Thermogravimetric Analyser (TGA) is a time consuming method. A quicker method is to perform kinetic modelling on several decomposition curves. Four temperature scans at different heating rates were recorded with the TGA for two thermal control foils, Kapton HN and Upilex S. Two methods of kinetic modelling were used to calculate the activation energy, i.e. the ASTM E 1641 and the approach of Model Free Kinetics (MFK). The first assumes a constant value for the activation energy whereas the latter calculates it as a function of the conversion. With the activation energy it is possible to make a lifetime prediction that indicates the mass loss that occurs at a certain temperature for a certain duration. The lifetime predictions are used to compare the two materials and also the two modelling methods. The modelling is verified by comparing the results to isothermal TGA tests and thermal ageing of samples in high vacuum chambers at 350°C for durations up to half a year and in combination with UV irradiation screening tests. All the performed experiments indicate that Upilex S has a better thermal endurance than Kapton HN. The results of the kinetic modelling are in good agreement with the isothermal experiments in the TGA and in the vacuum facilities. The MFK approach for kinetic modelling was found to be more adequate than the ASTM method.

  15. Systematic STM and LEED investigation of the Si/Ag(110) surface.

    PubMed

    Colonna, S; Serrano, G; Gori, P; Cricenti, A; Ronci, F

    2013-08-07

    Interest in the Si/Ag(110) system, which forms highly ordered linear nanostructures coined 'silicon nanoribbons', was recently boosted by the claim that such nanoribbons may be formed by silicon atoms arranged in a 2D honeycomb structure as in graphene, i.e. silicene. Despite such a revived interest, many discrepancies still exist in the recently reported results. This paper reports on a systematic investigation by scanning tunneling microscopy and low-energy electron diffraction of the Si/Ag(110) system as a function of the amount of deposited silicon and the deposition temperature. This reveals a complex interplay between these two factors, resulting in a rich array of possible self-assembled nanostructures and surface reconstructions. Several novel findings and clarification of the contradictory results reported in the literature are discussed in this work. In particular, the deposition temperature is demonstrated to be a key parameter to control the width of the Si nanoribbons produced. Recently, massive linear nanostructures were reported to be 'multilayer silicene', forming once the deposited silicon amount exceeds full coverage. However, we show that such nanostructures are also observed at low silicon coverage, demonstrating that their formation is exclusively determined by a deposition temperature higher than 460 K. On the other hand, for Si amounts higher than one monolayer the surface presents a novel c(8 × 4) reconstruction, which is responsible for the ×4 periodicity detected by LEED measurements, previously attributed to the 1.6 nm-wide nanoribbons overlayer or to 'multilayer silicene'. Finally, the large collection of acquired data also allowed us to single out image artifacts that may explain the contradictory results appearing in previous papers.

  16. Epitaxial growth of diindenoperylene ultrathin films on Ag(111) investigated by LT-STM and LEED.

    PubMed

    Huang, Han; Sun, Jia-Tao; Feng, Yuan Ping; Chen, Wei; Wee, Andrew Thye Shen

    2011-12-21

    The epitaxial growth of the 1st and 2nd monolayer (ML) diindenoperylene (DIP) on Ag(111) has been systematically investigated using low temperature scanning tunneling microscopy, low energy electron diffraction and first-principles calculations. At one ML regime, DIP molecules commensurately arrange in either herringbone or brick-wall superstructures, depending on the deposition rate. Tip-induced structural transformation from herringbone to brick-wall is observed. Calculations based on density functional theory reveal that the top site of Ag(111) is energetically favorable for both superstructures. The 2nd ML DIP aggregate in either herringbone or brick-wall superstructures depending on the arrangements of the 1st ML DIP, indicating that the structural properties of DIP thin films on Ag(111) are sensitive to growth conditions. The observed variation in DIP ultrathin film structure may result in different electronic properties and have implications for DIP-based organic electronic devices, such as organic field-effect transistors or organic photovoltaic cells.

  17. STM studies of GeSi thin layers epitaxially grown on Si(111)

    NASA Astrophysics Data System (ADS)

    Motta, N.; Sgarlata, A.; De Crescenzi, M.; Derrien, J.

    1996-08-01

    Ge/Si alloys were prepared in UHV by solid phase epitaxy on Si(111) substrates. The alloy formation, as a function of the evaporation rate and the Ge layer thickness has been followed in situ by RHEED and scanning tunneling microscopy. The 5 × 5 surface reconstruction appeared after annealing at 450°C Ge layers (up to 10 Å thick), obtained from a low rate Knudsen cell evaporator. In this case a nearly flat and uniform layer of reconstructed alloy was observed. When using an e-gun high rate evaporator we needed to anneal the Ge layer up to 780°C to obtain a 5 × 5 reconstruction. The grown layer was not flat, with many steps and Ge clusters; at high coverages (10 Å and more) large Ge islands appeared. Moreover, we then succeeded in visualizing at atomic resolution the top of some of these Ge islands which displayed a 2 × 1 reconstruction, probably induced from the high compressive strain due to the lattice mismatch with the substrate. We suggest that this unusual behavior could be connected to the high evaporation rate, which helped the direct formation of Ge microcrystals on the Si substrate during the deposition process.

  18. Low-temperature STM studies of electronic properties of microbial nanowires

    NASA Astrophysics Data System (ADS)

    Walsh, Kathy; Lampa-Pastirk, Sanela; Veazey, Joshua; Reguera, Gemma; Tessmer, Stuart

    2013-03-01

    Geobacter sulfurreducens expresses pili that act as electrically conductive nanowires. These microbial nanowires transport metabolically generated electrons outside the cell body to electron acceptors in the organism's environment. We have performed scanning tunneling microscopy and spectroscopy on these pili in an endeavor to elucidate the mechanism of conductivity. In particular, we will discuss spectroscopy curves acquired at a temperature of 77 K. This work supported by the NSF-MCB Grant No. 1021948 and a Strategic Partnership Grant from the Michigan State University Foundation. K.W. acknowledges support from a U.S. Department of Education GAANN fellowship.

  19. 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.

  20. Large molecules on surfaces: deposition and intramolecular STM manipulation by directional forces

    NASA Astrophysics Data System (ADS)

    Grill, Leonhard

    2010-03-01

    Intramolecular manipulation of single molecules on a surface with a scanning tunnelling microscope enables the controlled modification of their structure and, consequently, their physical and chemical properties. This review presents examples of intramolecular manipulation experiments with rather large molecules, driven by directional, i.e. chemical or electrostatic, forces between tip and molecule. It is shown how various regimes of forces can be explored and characterized with one and the same manipulation of a single molecule by changing the tip-surface distance. Furthermore, different deposition techniques under ultrahigh vacuum conditions are discussed because the increasing functionality of such molecules can lead to fragmentation during the heating step, making their clean deposition difficult.

  1. Stabilizing forces acting on ZnO polar surfaces: STM, LEED, and DFT

    NASA Astrophysics Data System (ADS)

    Xu, H.; Dong, L.; Shi, X. Q.; Van Hove, M. A.; Ho, W. K.; Lin, N.; Wu, H. S.; Tong, S. Y.

    2014-06-01

    New understanding has been reached on competing forces acting to stabilize the polar surfaces of intrinsic ZnO. To compensate an accumulating dipole moment normal to ionic planes, the Madelung electrostatic force and the bonding ability of undercoordinated Zn ions compete to deplete more Zn atoms from the (0001) face and more O atoms from the (0001¯) face. In this competition, the former mechanism wins because it provides very low energy binding sites for O ions at face-centered-cubic registries on both surfaces. On the Zn-face, a distorted tetrahedral structure is formed, while on the O-face, a vertical Y structure is formed. In both structures, O ions form the topmost atomic plane. The reconstructed polar surfaces containing these novel structures have cleavage energy of 2.36 J/m2, comparable to that of nonpolar surfaces and in agreement with experimental observation. An earlier structure found on the Zn-face annealed at below 1000 K is stabilized mainly by the Madelung electrostatic force and is a metastable structure of that surface.

  2. Superconducting-Tip STM on Cobaltates as a Platform for Exploring Topological Superconductivity

    NASA Astrophysics Data System (ADS)

    Contryman, Alex W.; Niestemski, Francis; Chen, Yulin; Hesjedal, Thorsten; Parra, Carolina; Chung, Suk Bum; Zhang, Hai-Jun; Shen, Z. X.; Zhang, Shou-Cheng; Manoharan, Hari C.

    2013-03-01

    In recent years, NaxCoO2 has attracted much attention for its unconventional superconductivity and antiferromagnetic phases. More recently it has been proposed that inducing superconductivity into the stoichiometric compound through the proximity effect could lead to topological superconductivity where Majorana physics might be accessed. We first explore this surface state with standard scanning tunneling spectroscopy and tuning fork-based atomic force microscopy, and then investigate the proximity effect scenario by introducing a superconducting tip to probe the superconductor-vacuum-topological junction. Supported by DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under contract DE-AC02-76SF00515. Alex W. Contryman is supported by a Dr. Robert N. Noyce Stanford Graduate Fellowship.

  3. 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.

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

    DOE PAGES

    Liu, H. W.; Fujikawa, Y.; Sadowski, J. 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.

  5. Transport characteristics of a single multiwall carbon nanotube by bending in SEM and STM

    NASA Astrophysics Data System (ADS)

    Kim, Suenne; Kim, Jeehoon; Berg, Morgann; de Lozanne, Alex

    2007-03-01

    Multiwall carbon nanotubes(MWCNTs) were grown on a W wire by chemical vapor deposition(CVD). Two homebuilt xyz-walkers were employed to manipulate individual CNTs in our scanning electron microscope (SEM). To improve the electrical and mechanical contact to a second electrode, we welded the CNT by delivering gas to the welding point while focusing the SEM beam on the same spot. The bending dependent I-V characteristics were observed in situ in the SEM at room temperature. We will measure the transport properties by bending the same MWCNT (already measured in SEM) inside our ultrahigh vacuum low temperature scanning tunneling microscope (UHV-LTSTM). We will also compare the bending properties of MWCNTs at different temperatures.

  6. 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.

  7. 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.

  8. "Oh yes, oh yes, these are the atoms!" A personal recollection from the times of the invention of the STM.

    PubMed

    Rieder, Karl-Heinz

    2012-01-01

    The scanning tunneling microscope, invented and developed in the 1980s in the IBM research laboratory in Rüschlikon, has become the dominent scientific tool in surface science and together with its younger brother the atomic force microscope, is widely used also in many other modern research areas. This account contains very personal anecdotal memories from a colleague who worked in a neighboring lab in Rüschlikon describing some events at the periphery of the development of this ingenious instrument.

  9. 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.

  10. 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.

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

    SciTech Connect

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

    2016-07-15

    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.

  12. STM observation of the chemical reaction of atomic hydrogen on the N-adsorbed Cu(001) surface

    NASA Astrophysics Data System (ADS)

    Hattori, Takuma; Yamada, Masamichi; Komori, Fumio

    2017-01-01

    Chemical reaction of atomic hydrogen with the N-adsorbed Cu(001) surfaces was investigated at room temperature by scanning tunnel microscopy. At the low exposure of atomic hydrogen, it reacted with the N atoms and turned to be the NH species on the surface. The reaction rate is proportional to the amount of the unreacted N atoms. By increasing the exposure of atomic hydrogen from this condition, the amount of nitrogen species on the surface decreased. This is attributed to the formation of ammonia and its desorption from the surface. The NH species on the surface turn to NH3 through the surface NH2 species by atomic hydrogen. Coexistence of the clean Cu surface enhances the rate of ammonia formation owing to atomic hydrogen migrating on the clean surface.

  13. 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.

  14. Sulfur-induced mobilization of Au surface atoms on Au(1 1 1) studied by real-time STM

    NASA Astrophysics Data System (ADS)

    Biener, Monika M.; Biener, Juergen; Friend, Cynthia M.

    2007-04-01

    The interaction of sulfur with gold surfaces has attracted considerable interest due to numerous technological applications such as the formation of self-assembled monolayers and as a chemical sensor. Here, we report on the interaction of sulfur with Au(1 1 1) at two different temperatures (300 K and 420 K) studied by real-time scanning tunnelling microscopy, low energy electron diffraction and Auger electron spectroscopy. In the low coverage regime (<0.1 ML), S adsorption lifts the herringbone reconstruction of the clean Au(1 1 1) surface indicating a lateral expansion of the surface layer. An ordered (√3 × √3) R30° sulfur adlayer develops as the coverage reaches ˜0.3 ML. At higher S coverages (>0.3 ML) gold surface atoms are removed from regular terrace sites and incorporated into a growing gold sulfide phase. At 300 K this process leads to the formation of a rough pit and mound surface morphology. This gold sulfide exhibits short-range order and an incommensurate, long-range ordered AuS phase develops upon annealing at 450-525 K. In contrast, formation of an ordered AuS phase via rapid step-retraction rather than etch pit formation is observed during S-interaction with Au(1 1 1) surfaces at 420 K. Our results shed new light on the S-Au(1 1 1) interaction.

  15. 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

  16. 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.

  17. Krikalev dismantles probe-and-cone docking mechanism (StM) in the Progress M-53 (18P)

    NASA Image and Video Library

    2005-06-19

    ISS011-E-09204 (19 June 2005) --- Cosmonaut Sergei K. Krikalev, Expedition 11 commander representing Russia's Federal Space Agency, dismantles the probe-and-cone docking mechanism in the Progress 18 spacecraft. The Progress docked to the aft port of the Zvezda Service Module of the International Space Station (ISS) at 7:42 p.m. (CDT) as the Station flew approximately 225 statute miles, above a point near Beijing, China.

  18. 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.

  19. Different growth mechanisms of Ge by Stranski-Krastanow on Si (111) and (001) surfaces: An STM study

    NASA Astrophysics Data System (ADS)

    Teys, S. A.

    2017-01-01

    Structural and morphological features of the wetting layer formation and the transition to the three-dimensional Ge growth on (111) and (100) Si surfaces under quasi-equilibrium growth conditions were studied by means of scanning tunneling microscopy. The mechanism of the transition from the wetting layer to the three-dimensional Ge growth on Si was demonstrated. The principal differences and general trends of the atomic processes involved in the wetting layers formation on substrates with different orientations were demonstrated. The Ge growth is accompanied by the Ge atom redistribution and partial strain relaxation due to the formation of new surfaces, vacancies and surface structures of a decreased density. The analysis of three-dimensional Ge islands sites nucleation of after the wetting layer formation was carried out on the (111) surface. The transition to the three-dimensional growth at the Si(100) surface begins with single {105} facets nucleation on the rough Ge(100) surface.

  20. CO adsorption on the “29” CuxO/Cu(111) surface: An integrated DFT, STM, and TPD study

    DOE PAGES

    Hensley, Alyssa J. R.; Therrien, Andrew J.; Zhang, Renqin; ...

    2016-10-04

    The elucidation of an accurate atomistic model of surface structures is crucial for the design and understanding of effective catalysts, a process requiring a close collaboration between experimental observations and theoretical models. Any developed surface theoretical model must agree with experimental results for the surface when both clean and adsorbate covered. Here, we present a detailed study of the adsorption of CO on the “29” CuxO/ Cu(111) surface, which is important in the understanding of ubiquitous Cubased catalysis. This study uses scanning tunneling microscopy, temperatureprogrammed desorption, and density functional theory to analyze CO adsorption on the “29” CuxO/Cu(111) surface. Frommore » the experimental scanning tunneling microscopy images, CO was found to form six different ordered structures on the “29” CuxO/Cu(111) surface depending on the surface CO coverage. By modeling the adsorption of CO on our atomistic model of the “29” CuxO/Cu(111) surface at different coverages, we were able to match the experimentally observed CO ordered structures to specific combinations of sites on the “29” CuxO/Cu(111) surface. Lastly, the high degree of agreement seen here between experiment and theory for the adsorption of CO on the “29” CuxO/Cu(111) surface at various CO coverages provides further support that our atomistic model of the “29” CuxO/Cu(111) surface is experimentally accurate.« less

  1. WUS and STM homologs are linked to the expression of lateral dominance in the acaulescent Streptocarpus rexii (Gesneriaceae).

    PubMed

    Mantegazza, Raffaella; Tononi, Paola; Möller, Michael; Spada, Alberto

    2009-08-01

    Acaulescent species of Streptocarpus Lindl. show unusual patterns of growth, characterized by anisocotyly (i.e. the unequal growth of cotyledons after germination) and lack of a conventional embryonic shoot apical meristem (SAM). A SAM-like structure appears during post-embryonic development on the axis of the continuously growing cotyledon. Since we have shown previously that KNOX genes are involved in this unusual morphology of Streptocarpus rexii, here we investigated the expression pattern of WUSCHEL (WUS), which is also required for the indeterminacy of the SAM, but is expressed independently from KNOX in Arabidopsis thaliana. In A. thaliana WUSCHEL is involved in the maintenance of the stem cell fate in the organizing centre. The expression pattern of the WUS ortholog in S. rexii (SrWUS) strongly deviates from that of the model plant, suggesting a fundamentally different spatial and temporal regulation of signalling involved in meristem initiation and maintenance. In S. rexii, exogenous application of growth regulators, i.e. gibberellin (GA(3)), cytokinin (CK) and a gibberellin biosynthesis inhibitor (PAC), prevents anisocotyly and relocates meristematic cells to a position of conventional SAMs; this coincides with a re-localization of the two main pathways controlling meristem formation, the SrWUS and the KNOX pathways. Our results suggest that the establishment of a hormone imbalance in the seedlings is the basis of anisocotyly, causing a lateral dominance of the macrocotyledon over the microcotyledon. The peculiar morphogenetic program in S. rexii is linked to this delicate hormone balance and is the result of crosstalk between endogenous hormones and regulatory genes.

  2. In-situ STM studies of thallium underpotential deposition on Au(111) single-crystal electrode in acid solution

    NASA Astrophysics Data System (ADS)

    Polewska, Wanda; Adzic, Radoslav

    1999-04-01

    The structure of electrodeposited Tl adlayers on Au(111) in 0.1 M. HClO4 has been investigated using in-situ scanning tunneling microscopy method. Incommensurate, rotated hexagonal (RHCP) Tl adlayer was found, within a wide potential window, between Tl bulk deposition at -0.7 V and -0.4 V. This adlayer is closely packed with Tl interatomic distance of 3.4 +/- 0.2 angstroms, its rotation from the gold substrate axis is 60 +/- 10 and its coverage is 0.74. At slightly more positive potentials, between -0.45 V and -0.37 V, low coverage 2 X 2 phase of Tl was found, coexisting together with RHCP monolayer. At the potential region between -0.35 V and 0.8 V both ordered Tl phases disappeared and instead the formation of considerable amount of pits at the surface has been observed.

  3. An STM Observation of Adsorption of CuPc on the Si(100) Surface with Bi-LINE Structures

    NASA Astrophysics Data System (ADS)

    Nakamura, S.; Kashirajima, S.; Johdai, Y.; Yoshiiwa, Y.; Naitoh, M.; Nishigaki, S.; Shimizu, Y.; Ikari, T.; Shoji, F.

    We report the reaction dynamics of the Bi-line structure (BLS) with copper-phthalocyanine (CuPc)molecules as well as hydrogen and Ag atoms on Si(100) surfaces observed by scanning tunneling microscopy. Co-adsorption of hydrogen and Ag on the Si(100) surface with BLSs brought about agglomeration of Ag atoms on the Si terrace. When CuPc molecules were deposited on the Si(100) surface with BLSs at room temperature, domains with c(4 × 4) periodicity appeared in the terraces near the BLS. When the surface was annealed at 200°C-400°C, the area of the c(4 × 4) domain was increased. The CuPc molecules, adsorbed on BLS, were possibly dissociated by catalytic reaction of Bi atoms.

  4. Narrow Au(111) terraces decorated by self-organized Co nanowires: a low-temperature STM/STS investigation.

    PubMed

    Schouteden, K; Van Haesendonck, C

    2010-06-30

    Deposition of Co atoms on Au(111) surfaces leads to the formation of self-organized bilayer Co nanowires at the step edges between adjacent narrow Au(111) terraces. Scanning tunneling microscopy and spectroscopy at low temperatures is used to probe the influence of the finite dimensions on the local density of states for both the Co wires and the narrow Au terraces. Confinement of Au surface state electrons to narrow Au terraces causes a shift of the Au surface state onset energy to higher energies. For the Co nanowires discrete energy levels are observed. Moreover, standing wave patterns occur at the surface of both the Au and the Co. The patterns increase in complexity with increasing energy. All Co nanowires formed at the edges of narrow Au terraces reveal a characteristic maximum in the local density of states at a significantly different energy when compared to the Co islands that are formed on large Au terraces. The experimental results can be interpreted in terms of a simple particle-in-a-box model.

  5. Nano-scale characterization of binary self-assembled monolayers under an ambient condition with STM and TERS.

    PubMed

    Horimoto, Noriko N; Tomizawa, Shigeru; Fujita, Yasuhiko; Kajimoto, Shinji; Fukumura, Hiroshi

    2014-09-07

    Gold surfaces were modified by benzyl-mercaptan (BM) and then partly replaced with benzenethiol (BT), which formed binary self-assembled monolayers (SAM). Initially BT randomly replaced BM in the monolayer, but at long exchange times >15 nm radius domains were observed with specific relative composition of BT and BM.

  6. Kinetic and thermodynamic processes of organic species at the solution-solid interface: the view through an STM.

    PubMed

    Mazur, Ursula; Hipps, K W

    2015-03-21

    A focused review is presented on the evolution of our understanding of the kinetic and thermodynamic factors that play a critical role in the formation of well ordered organic adlayers at the solution-solid interface. While the current state of knowledge is in the very early stages, it is now clear that assumptions of kinetic or thermodynamic control are dangerous and require careful confirmation. Equilibrium processes at the solution-solid interface are being described by evolving thermodynamic models that utilize concepts from the thermodynamics of micelles. A surface adsorption version of the Born-Haber cycle is helping to extract the thermodynamic functions of state associated with equilibrium structures, but only a very few systems have been so analyzed. The kinetics of surface phase transformation, especially for polymorphic phases is in an early qualitative stage. Adsorption and desorption kinetics are just starting to be measured. The study of kinetics and thermodynamics for organic self-assembly at the solution-solid interface is experiencing very exciting and rapid growth.

  7. Dynamics of 2D adislands formed by sulfur adsorption on an O/Cu(110) nanotemplate: an STM study

    NASA Astrophysics Data System (ADS)

    Budinská, Zuzana; Wiame, Frédéric; Maurice, Vincent; Marcus, Philippe

    2017-01-01

    We report on the stability of large sulfur islands, formed by exposing the nanostructured O/Cu(110) surface to H2S. We have found that these islands, composed of several hundreds of atoms, show a dynamic behavior at room temperature and undergo both Smoluchowski and Ostwald ripening. An additional decay mechanism has been observed at sub-saturation sulfur coverages. The island decay can be described by a classical power law. However, oscillatory deviations from the model have been observed and possible reasons for their occurrence are discussed. At saturation sulfur coverage, the islands are still mobile and undergo ripening, but no decay is observed. In these conditions, a new nanostructured S/Cu(110) surface is formed.

  8. Determination of metal atoms incorporated in molecular intermediates: an STM study of acetylide on Ag(1 1 0)

    NASA Astrophysics Data System (ADS)

    Guo, X.-C.; Madix, R. J.

    2004-08-01

    Many inorganic molecular intermediates, such as imide, nitrate, and sulfite, incorporate a stoichiometric number of added metal atoms into their structures on Ag(1 1 0) or Cu(1 1 0). In this paper an example of such general behavior is illustrated with an organic molecular intermediate--acetylide (C 2) on Ag(1 1 0). Acetylide is produced by reacting acetylene with oxygen atoms on the Ag(1 1 0)- p(2 × 1)-O surface. Acetylides form row structures along the <1 1¯ 0> axis, which, as coverage increases, are compressed along the <0 0 1> axis to form nominal " p(2 × 2)", " p(2 × 3)", " p(2 × 1)", and " p(14 × 1)" structures. The final acetylide structure incorporates 0.55 ML silver atoms, which may be released upon titration with acetic acid. A buckled structure is proposed where acetylide bonds to two added silver atoms in a linear configuration in the trough along the <1 1¯ 0> axis with seven equally spaced silver atoms in a p(13 × 1) unit cell.

  9. 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.

  10. 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.

  11. Adatom Extraction from Pristine Metal Terraces by Dissociative Oxygen Adsorption: Combined STM and Density Functional Theory Investigation of O/Ag(110).

    PubMed

    Pal, Jagriti; Rawal, Takat B; Smerieri, Marco; Hong, Sampyo; Alatalo, Matti; Savio, Letizia; Vattuone, Luca; Rahman, Talat S; Rocca, Mario

    2017-06-02

    The reconstruction and modification of metal surfaces upon O_{2} adsorption plays an important role in oxidation processes and in gauging their catalytic activity. Here, we show by employing scanning tunneling microscopy and the ab initio density functional theory that Ag atoms are extracted from pristine (110) terraces upon O_{2} dissociation, resulting in vacancies and in Ag-O complexes. The substrate roughening generates undercoordinated atoms and opens pathways to the Ag subsurface layer. With increasing O coverage, multiple vacancies give rise to remarkable structures. The mechanism is expected to be very general depending on the delicate interplay of energy and entropy, so that it may be active for other materials at different temperatures.

  12. 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

    2016-06-06

    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.

  13. 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.

  14. In Situ STM and Vibrational Study of Nanometer-Scale Reorganization of a Phospholipid Monolayer Accompanied by Potential-Driven Headgroup Digestion.

    PubMed

    Matsunaga, Soichiro; Shimizu, Hiroaki; Yamada, Taro; Kobayashi, Toshihide; Kawai, Maki

    2017-08-11

    In situ dynamic observation of model biological cell membranes, formed on a water/gold substrate interface, has been performed by the combination of electrochemical scanning tunneling microscopy and reflection infrared absorption vibrational spectroscopy. Monolayers of 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) were formed on alkanethiol-modified gold surfaces in a buffer solution, and the microscopic phase transitions driven by electrochemical potential control were observed more in detail than our previous study on the same system [Electrochem. Commun. 2007, 9, 645-650]. This time the transitions were associated with the chemistry of DHPC by the aid of vibrational spectroscopy and the utilization of deuterium-labeled DHPC molecules. A negative potential shift solidifies the fluidic lipid layers into static striped or grainy features without notable chemical reactions. The first positive potential shift over the virginal DHPC monolayer breaks DHPC into choline and the corresponding phosphatidic acid (DHPA). This is the first case of a phospholipid electrochemical reaction microscopically detected at the solid surface.

  15. Coexistence of Two Electronic Nano-Phases on a CH3NH3PbI3-xClx Surface Observed in STM Measurements.

    PubMed

    Yost, Andrew J; Pimachev, Artem; Ho, Chun-Chih; Darling, Seth B; Wang, Leeyih; Su, Wei-Fang; Dahnovsky, Yuri; Chien, TeYu

    2016-10-10

    Scanning tunneling microscopy is utilized to investigate the local density of states of a CH3NH3PbI3-xClx perovskite in cross-sectional geometry. Two electronic phases, 10-20 nm in size, with different electronic properties inside the CH3NH3PbI3-xClx perovskite layer are observed by the dI/dV mapping and point spectra. A power law dependence of the dI/dV point spectra is revealed. In addition, the distinct electronic phases are found to have preferential orientations close to the normal direction of the film surface. Density functional theory calculations indicate that the observed electronic phases are associated with local deviation of I/Cl ratio, rather than different orientations of the electric dipole moments in the ferroelectric phases. By comparing the calculated results with experimental data we conclude that phase A (lower contrast in dI/dV mapping at -2.0 V bias) contains a lower I/Cl ratio than that in phase B (higher contrast in dI/dV).

  16. Adatom Extraction from Pristine Metal Terraces by Dissociative Oxygen Adsorption: Combined STM and Density Functional Theory Investigation of O /Ag (110 )

    NASA Astrophysics Data System (ADS)

    Pal, Jagriti; Rawal, Takat B.; Smerieri, Marco; Hong, Sampyo; Alatalo, Matti; Savio, Letizia; Vattuone, Luca; Rahman, Talat S.; Rocca, Mario

    2017-06-01

    The reconstruction and modification of metal surfaces upon O2 adsorption plays an important role in oxidation processes and in gauging their catalytic activity. Here, we show by employing scanning tunneling microscopy and the ab initio density functional theory that Ag atoms are extracted from pristine (110) terraces upon O2 dissociation, resulting in vacancies and in Ag-O complexes. The substrate roughening generates undercoordinated atoms and opens pathways to the Ag subsurface layer. With increasing O coverage, multiple vacancies give rise to remarkable structures. The mechanism is expected to be very general depending on the delicate interplay of energy and entropy, so that it may be active for other materials at different temperatures.

  17. Controlled impurity study and observation of a bosonic mode in iron based superconductors by STM measurements: implications for the pairing symmetry and mechanism

    NASA Astrophysics Data System (ADS)

    Wen, Hai-Hu

    2014-03-01

    The pairing mechanism in the iron pnictides remains unresolved yet. The pairing model based on the magnetic origin predicts a sign reversal gap on the electron and hole Fermi pockets, leading to the S+/- pairing, however, a more conventional S++ pairing gap was suggested based on the orbital fluctuation mediated pairing. Here we show the clear evidence of the in-gap quasi-particle states induced by the non- or very weak magnetic Cu impurities in Na(Fe0 . 97 - xCo0.03Cux) As by measuring the scanning tunneling spectroscopy, giving strong evidence of the S+/- pairing. Furthermore, we show the presence of the bosonic mode with the energy identical to that of the neutron resonance with a simple linear relation Ω/kBTc ~ 4.3 in several systems. This mode can also be explained very well as the consequence of the S+/- pairing. These observations strongly suggest that the antiferromagnetic spin fluctuation is the key factor for superconductivity. In collaboration with: Huan Yang, Zhenyu Wang, Delong Fang, Lei Shan, Qiangua Wang, Chenglin Zhang, and Pengcheng Dai, et al.

  18. Adsorption of 1,13-tetradecadiene on Si(111)7×7 studied by STM: possible electrostatic interactions between the aliphatic chain and the surface

    NASA Astrophysics Data System (ADS)

    Shachal, D.; Manassen, Y.

    Non-covalent intermolecular forces play an important role in the reactions of complicated chemical systems. In this paper we show how such forces affect the reaction between 1,13-tetradecadiene and Si(111)7×7. Previous work has shown that one double bond reacts with the faulted half of the Si(111)7×7 and the other with the unfaulted half. However, since each half contains six adatoms, there is an additional degree of freedom in which the aliphatic chain can reside mostly above either half. We found a preference of the aliphatic chain to reside above the unfaulted half. This can be explained only as a result of different non-covalent intermolecular forces between the chain and each of the two halves. According to our calculations the difference in energy between the two halves on which an aliphatic chain is physi-sorbed is 30 kcal/molecule.

  19. 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.

  20. 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.

  1. Handling L2 Input in Phonological STM: The Effect of Non-L1 Phonetic Segments and Non-L1 Phonotactics on Nonword Repetition

    ERIC Educational Resources Information Center

    Kovacs, Gabor; Racsmany, Mihaly

    2008-01-01

    This article reports on an experiment comparing the effects of three discrete types of deviance from native language (L1) phonetics and phonology on verbal short-term memory performance. A nonword repetition task was used to measure the recall of four stimulus types: (a) high-probability L1-sounding nonwords, (b) low-probability L1-sounding…

  2. GaAs Deposition on the (100) and (110) Planes of Gold by Electrochemical Atomic Layer Epitaxy (ECALE). A LEED, AES and STM Study

    DTIC Science & Technology

    1992-05-26

    ECALE is based on the alternated underpotential deposition (UPD) of atomic layers of different elements to form a compound. Oxidative UPD of As and...based on the alternated underpotential deposition (UPD) of atomic layers of different elements to form a compound. Oxidative UPD of As and reductive UPD...potential control. Stoichiometric coverages of Ga and As were obtained on the (100) and (110) surfaces when Ga was underpotentially deposited on the As

  3. Identifying magnetic anisotropy of the topological surface state of Cr(0.05)Sb(1.95)Te(3) with spin-polarized STM.

    PubMed

    Yang, Fang; Song, Y R; Li, H; Zhang, K F; Yao, X; Liu, Canhua; Qian, Dong; Gao, C L; Jia, Jin-Feng

    2013-10-25

    The surface magnetic property plays a key role in determining magnetic related quantum phenomena of magnetic topological insulators. Using spin-polarized scanning tunneling microscopy, we investigate the surface magnetism and anisotropy of a Cr doped topological insulator: Cr(0.05)Sb(1.95)Te(3). It is found that the topological surface state of Cr(0.05)Sb(1.95)Te(3) is spin polarized in the surface plane while the bulk shows a ferromagnetism with an out-of-plane easy axis. The upper and lower branch of the helical Dirac cone harbors the opposite spin polarization and the polarization at the Dirac point is zero. Our results show the complexity of surface magnetism of magnetic doped topological insulators.

  4. Sharp organic interface of molecular C60 chains and a pentacene derivative SAM on Au(788): A combined STM & DFT study

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Tang, Jian-Ming; Larson, Amanda M.; Miller, Glen P.; Pohl, Karsten

    2013-12-01

    Controlling the molecular structure of the donor-acceptor interface is essential to overcoming the efficiency bottleneck in organic photovoltaics. We present a study of self-assembled fullerene (C60) molecular chains on perfectly ordered 6,13-dichloropentacene (DCP) monolayers forming on a vicinal Au(788) surface using scanning tunneling microscopy in conjunction with density functional theory calculations. DCP is a novel pentacene derivative optimized for photovoltaic applications. The molecules form a brick-wall patterned centered rectangular lattice with the long axis parallel to the monatomic steps that separate the 3.9 nm wide Au(111) terraces. The strong interaction between the C60 molecules and the gold substrate is well screened by the DCP monolayer. At submonolayer C60 coverage, the fullerene molecules form long parallel chains, 1.1 nm apart, with a rectangular arrangement instead of the expected close-packed configuration along the upper step edges. The perfectly ordered DCP structure is unaffected by the C60 chain formation. The controlled sharp highly-ordered organic interface has the potential to improve the conversion efficiency in organic photovoltaics.

  5. Handling L2 Input in Phonological STM: The Effect of Non-L1 Phonetic Segments and Non-L1 Phonotactics on Nonword Repetition

    ERIC Educational Resources Information Center

    Kovacs, Gabor; Racsmany, Mihaly

    2008-01-01

    This article reports on an experiment comparing the effects of three discrete types of deviance from native language (L1) phonetics and phonology on verbal short-term memory performance. A nonword repetition task was used to measure the recall of four stimulus types: (a) high-probability L1-sounding nonwords, (b) low-probability L1-sounding…

  6. 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.

  7. 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.

  8. 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.

  9. Coexistence of two electronic nano-phases on a CH3NH3PbI3–xClx surface observed in STM measurements

    DOE PAGES

    Yost, Andrew J.; Pimachev, Artem; Ho, Chun -Chih; ...

    2016-10-10

    Scanning tunneling microscopy is utilized to investigate the local density of states of a CH3NH3PbI3-xClx perovskite in cross-sectional geometry. Two electronic phases, 10-20 nm in size, with different electronic properties inside the CH3NH3PbI3-xClx perovskite layer are observed by the dI/ dV mapping and point spectra. A power law dependence of the dI/dV point spectra is revealed. In addition, the distinct electronic phases are found to have preferential orientations close to the normal direction of the film surface. Density functional theory calculations indicate that the observed electronic phases are associated with local deviation of I/Cl ratio, rather than different orientations ofmore » the electric dipole moments in the ferroelectric phases. Furthermore, by comparing the calculated results with experimental data we conclude that phase A (lower contrast in dI/dV mapping at -2.0 V bias) contains a lower I/Cl ratio than that in phase B (higher contrast in dI/dV).« less

  10. 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…

  11. Explaining Semantic Short-Term Memory Deficits: Evidence for the Critical Role of Semantic Control

    ERIC Educational Resources Information Center

    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…

  12. 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…

  13. Explaining Semantic Short-Term Memory Deficits: Evidence for the Critical Role of Semantic Control

    ERIC Educational Resources Information Center

    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…

  14. 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.

  15. Intrinsically disordered and pliable Starmaker-like protein from medaka (Oryzias latipes) controls the formation of calcium carbonate crystals.

    PubMed

    Różycka, Mirosława; Wojtas, Magdalena; Jakób, Michał; Stigloher, Christian; Grzeszkowiak, Mikołaj; Mazur, Maciej; Ożyhar, Andrzej

    2014-01-01

    Fish otoliths, biominerals composed of calcium carbonate with a small amount of organic matrix, are involved in the functioning of the inner ear. Starmaker (Stm) from zebrafish (Danio rerio) was the first protein found to be capable of controlling the formation of otoliths. Recently, a gene was identified encoding the Starmaker-like (Stm-l) protein from medaka (Oryzias latipes), a putative homologue of Stm and human dentine sialophosphoprotein. Although there is no sequence similarity between Stm-l and Stm, Stm-l was suggested to be involved in the biomineralization of otoliths, as had been observed for Stm even before. The molecular properties and functioning of Stm-l as a putative regulatory protein in otolith formation have not been characterized yet. A comprehensive biochemical and biophysical analysis of recombinant Stm-l, along with in silico examinations, indicated that Stm-l exhibits properties of a coil-like intrinsically disordered protein. Stm-l possesses an elongated and pliable structure that is able to adopt a more ordered and rigid conformation under the influence of different factors. An in vitro assay of the biomineralization activity of Stm-l indicated that Stm-l affected the size, shape and number of calcium carbonate crystals. The functional significance of intrinsically disordered properties of Stm-l and the possible role of this protein in controlling the formation of calcium carbonate crystals is discussed.

  16. Intrinsically Disordered and Pliable Starmaker-Like Protein from Medaka (Oryzias latipes) Controls the Formation of Calcium Carbonate Crystals

    PubMed Central

    Różycka, Mirosława; Wojtas, Magdalena; Jakób, Michał; Stigloher, Christian; Grzeszkowiak, Mikołaj; Mazur, Maciej; Ożyhar, Andrzej

    2014-01-01

    Fish otoliths, biominerals composed of calcium carbonate with a small amount of organic matrix, are involved in the functioning of the inner ear. Starmaker (Stm) from zebrafish (Danio rerio) was the first protein found to be capable of controlling the formation of otoliths. Recently, a gene was identified encoding the Starmaker-like (Stm-l) protein from medaka (Oryzias latipes), a putative homologue of Stm and human dentine sialophosphoprotein. Although there is no sequence similarity between Stm-l and Stm, Stm-l was suggested to be involved in the biomineralization of otoliths, as had been observed for Stm even before. The molecular properties and functioning of Stm-l as a putative regulatory protein in otolith formation have not been characterized yet. A comprehensive biochemical and biophysical analysis of recombinant Stm-l, along with in silico examinations, indicated that Stm-l exhibits properties of a coil-like intrinsically disordered protein. Stm-l possesses an elongated and pliable structure that is able to adopt a more ordered and rigid conformation under the influence of different factors. An in vitro assay of the biomineralization activity of Stm-l indicated that Stm-l affected the size, shape and number of calcium carbonate crystals. The functional significance of intrinsically disordered properties of Stm-l and the possible role of this protein in controlling the formation of calcium carbonate crystals is discussed. PMID:25490041

  17. Energy threshold and ion yield for H - ions ejected from Si( 1 1 1 ):H(1×1) during low energy electron collisions: study of ESD process in relation with atom manipulation in STM

    NASA Astrophysics Data System (ADS)

    Bernheim, Marc

    2001-11-01

    This paper deals with an experimental study of H - ions desorption out of a well organised silicon crystal surface Si(1 1 1):H(1×1). It mainly concerns the resonant desorption process attributed to a dissociative electron attachment below 12 eV. In situ access to the work function provides an accurate reference of the incident electron energy. The resonant peak for desorption is centred at 8 eV with a corresponding threshold of about 6 eV. For the resonance energy, a probability 2.0×10 -6 ion H - per electron is deduced from both the incident electron density and the spectrometer calibration. Variation in desorption yield with electron dose suggest that hydrogen leaves the surface as neutral also with a probability about 1.1×10 -3 atom per electron. Evaluation of the image charge influence provides a distance 1.2 Å between external silicon atoms and hydrogen. This determination was based on the measured-desorption threshold and the H - ion kinetic energy, as well as on the hydrogen electron affinity and the SiH binding energy deduced from data tables. This distance fairly agrees with ab initio simulations once the jellium extension is included. Comparing most ESD features for H - ions desorption with hydrogen atom manipulation in scanning tunnel microscopy out of the same substrate, we assume that similar energy threshold and yields strongly suggest a common initial electron excitation process. Projected ESD experiments might enlighten the understanding of such surface atom manipulation.

  18. 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.

  19. Visuospatial and Verbal Short-Term Memory Correlates of Vocabulary Ability in Preschool Children.

    PubMed

    Stokes, Stephanie F; Klee, Thomas; Kornisch, Myriam; Furlong, Lisa

    2017-08-16

    Recent studies indicate that school-age children's patterns of performance on measures of verbal and visuospatial short-term memory (STM) and working memory (WM) differ across types of neurodevelopmental disorders. Because these disorders are often characterized by early language delay, administering STM and WM tests to toddlers could improve prediction of neurodevelopmental outcomes. Toddler-appropriate verbal, but not visuospatial, STM and WM tasks are available. A toddler-appropriate visuospatial STM test is introduced. Tests of verbal STM, visuospatial STM, expressive vocabulary, and receptive vocabulary were administered to 92 English-speaking children aged 2-5 years. Mean test scores did not differ for boys and girls. Visuospatial and verbal STM scores were not significantly correlated when age was partialed out. Age, visuospatial STM scores, and verbal STM scores accounted for unique variance in expressive (51%, 3%, and 4%, respectively) and receptive vocabulary scores (53%, 5%, and 2%, respectively) in multiple regression analyses. Replication studies, a fuller test battery comprising visuospatial and verbal STM and WM tests, and a general intelligence test are required before exploring the usefulness of these STM tests for predicting longitudinal outcomes. The lack of an association between the STM tests suggests that the instruments have face validity and test independent STM skills.

  20. 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.

  1. 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…

  2. Virtual Machine-level Software Transactional Memory: Principles, Techniques, and Implementation

    DTIC Science & Technology

    2015-08-13

    current STM frameworks are inferior and heavily influenced by infrastructure resource management (e.g., operating system scheduling, garbage collection...enables direct memory accesses, ByteSTM avoids Java garbage collection overhead by manually managing memory for transactional metadata, and provides... garbage collection overhead by manually managing memory for transactional meta- data, and provides pluggable support for implementing different STM

  3. Interactive Mental Imagery and Short-Term Memory Search Rates for Words and Pictures. Report from the Project on Children's Learning and Development. Technical Report No. 317.

    ERIC Educational Resources Information Center

    Kerst, Stephen Marshall

    The purposes of this study were to determine if test stimulus was a member of the memory set and if items in an interactive image held in short term memory (STM) could be scanned simultaneously. In experiment one, 50 university subjects compared a test word with a set of one to three words held in STM. The rate of STM search was obtained by…

  4. 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

  5. SHOOT MERISTEMLESS trafficking controls axillary meristem formation, meristem size and organ boundaries in Arabidopsis.

    PubMed

    Balkunde, Rachappa; Kitagawa, Munenori; Xu, Xianfeng Morgan; Wang, Jing; Jackson, David

    2017-05-01

    The shoot stem cell niche, contained within the shoot apical meristem (SAM) is maintained in Arabidopsis by the homeodomain protein SHOOT MERISTEMLESS (STM). STM is a mobile protein that traffics cell-to-cell, presumably through plasmodesmata. In maize, the STM homolog KNOTTED1 shows clear differences between mRNA and protein localization domains in the SAM. However, the STM mRNA and protein localization domains are not obviously different in Arabidopsis, and the functional relevance of STM mobility is unknown. Using a non-mobile version of STM (2xNLS-YFP-STM), we show that STM mobility is required to suppress axillary meristem formation during embryogenesis, to maintain meristem size, and to precisely specify organ boundaries throughout development. STM and organ boundary genes CUP SHAPED COTYLEDON1 (CUC1), CUC2 and CUC3 regulate each other during embryogenesis to establish the embryonic SAM and to specify cotyledon boundaries, and STM controls CUC expression post-embryonically at organ boundary domains. We show that organ boundary specification by correct spatial expression of CUC genes requires STM mobility in the meristem. Our data suggest that STM mobility is critical for its normal function in shoot stem cell control. © 2017 The Authors The Plant Journal © 2017 John Wiley & Sons Ltd.

  6. The Importance of Memory Span and Training in Reasoning Ability. Final Report.

    ERIC Educational Resources Information Center

    Whimbey, Arthur

    Five studies were conducted to investigate the relationship between short term memory (STM) and long term memory (LTM), and the relationship between STM and problem solving. In study I, the necessity of postulating separate learning processes for tasks which are traditionally classified as STM tasks as opposed to LTM tasks was investigated.…

  7. 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…

  8. 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

  9. Integrated micro-scanning tunneling microscope

    NASA Astrophysics Data System (ADS)

    Xu, Y.; MacDonald, N. C.; Miller, S. A.

    1995-10-01

    Two versions of micro-scanning tunneling microscopes (micro-STMs) have been fabricated. The integrated micro-STMs are fabricated from single crystal silicon using the high-aspect-ratio SCREAM process. Each micro-STM includes integrated xy comb drive actuators and a torsional z actuator with integrated cantilever and tip. One micro-STM measures approximately 200 μm on-a-side and is an example of a STM element for a STM array architecture. Another, larger micro-STM/atomic force microscope measures 2 mm on-a-side including a 1 mm long cantilever with a 20 nm diam tip. We demonstrate the operation of this larger STM by obtaining a STM image of a 200 nm metal conductor on a silicon chip.

  10. Scanning tunneling microscope assembly, reactor, and system

    SciTech Connect

    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.

  11. 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.

  12. 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.

  13. "I know your name, but not your number"--Patients with verbal short-term memory deficits are impaired in learning sequences of digits.

    PubMed

    Bormann, Tobias; Seyboth, Margret; Umarova, Roza; Weiller, Cornelius

    2015-06-01

    Studies on verbal learning in patients with impaired verbal short-term memory (vSTM) have revealed dissociations among types of verbal information. Patients with impaired vSTM are able to learn lists of known words but fail to acquire new word forms. This suggests that vSTM is involved in new word learning. The present study assessed both new word learning and the learning of digit sequences in two patients with impaired vSTM. In two experiments, participants were required to learn people's names, ages and professions, or their four digit 'phone numbers'. The STM patients were impaired on learning unknown family names and phone numbers, but managed to acquire other verbal information. In contrast, a patient with a severe verbal episodic memory impairment was impaired across information types. These results indicate verbal STM involvement in the learning of digit sequences. Copyright © 2015 Elsevier Ltd. All rights reserved.

  14. Plant growth and resistance promoted by Streptomyces spp. in tomato.

    PubMed

    Dias, Maila P; Bastos, Matheus S; Xavier, Vanessa B; Cassel, Eduardo; Astarita, Leandro V; Santarém, Eliane R

    2017-09-01

    Plant Growth Promoting Rhizobacteria (PGPR) represent an alternative to improve plant growth and yield as well as to act as agents of biocontrol. This study characterized isolates of Streptomyces spp. (Stm) as PGPR, determined the antagonism of these isolates against Pectobacterium carotovorum subsp. brasiliensis (Pcb), evaluated the ability of Stm on promoting growth and modulating the defense-related metabolism of tomato plants, and the potential of Stm isolates on reducing soft rot disease in this species. The VOC profile of Stm was also verified. Promotion of plant growth was assessed indirectly through VOC emission and by direct interaction with Stm isolates in the roots. Evaluation of soft rot disease was performed in vitro on plants treated with Stm and challenged with Pcb. Enzymes related to plant defense were then analyzed in plants treated with three selected isolates of Stm, and PM1 was chosen for further Pcb-challenging experiment. Streptomyces spp. isolates displayed characteristics of PGPR. PM3 was the isolate with efficient antagonism against Pcb by dual-culture. Most of the isolates promoted growth of root and shoot of tomato plants by VOC, and PM5 was the isolate that most promoted growth by direct interaction with Stm. Soft rot disease and mortality of plants were significantly reduced when plants were treated with StmPM1. Modulation of secondary metabolism was observed with Stm treatment, and fast response of polyphenoloxidases was detected in plants pretreated with StmPM1 and challenged with Pcb. Peroxidase was significantly activated three days after infection with Pcb in plants pretreated with StmPM1. Results suggest that Streptomyces sp. PM1 and PM5 have the potential to act as PGPR. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

  15. 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.

  16. Atom world based on nano-forces: 25 years of atomic force microscopy.

    PubMed

    Morita, Seizo

    2011-01-01

    Scanning tunneling microscopy (STM) has opened up the new nanoworlds of scanning probe microscopy. STM is the first-generation atomic tool that can image, evaluate and manipulate individual atoms and consequently can create nanostructures by true bottom-up methods based on atom-by-atom manipulation. Atomic force microscopy is a second-generation atomic tool that has followed the footsteps of STM, and which is now opening doors to a new atom world based on using nanoscale forces.

  17. 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

  18. 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.

  19. Scanning Tunneling Microscopy Studies of Quasicrystals

    NASA Astrophysics Data System (ADS)

    Becker, Russell S.; Kortan, A. Refik

    The following sections are included: * INTRODUCTION * EXPERIMENTAL * X-RAY DIFFRACTION * SCANNING TUNNELING MICROSCOPY * STRUCTURE MODELLING BASED ON STM * COMPARISON WITH MODELS BASED ON BULK STUDIES * CONCLUSION * REFERENCES

  20. Studies on the topology of the renal type II NaPi-cotransporter.

    PubMed

    Lambert, G; Traebert, M; Hernando, N; Biber, J; Murer, H

    1999-05-01

    The rat type II sodium/phosphate cotransporter (NaPi-2) is a 85- to 90-kDa glycosylated protein located at the proximal tubular brush border membrane. Hydropathy predictions suggest eight transmembrane domains (sTM) with a large glycosylated loop between sTM 3 and sTM 4. We have studied the membrane topology of NaPi-2 expressed in oocytes. A 33-amino-acid fragment containing the FLAG epitope was inserted into seven loops connecting the sTMs and into the NH2- and COOH-ends of the protein. FLAG-antibody binding suggested that the loops connecting sTM 1 and sTM 2 as well as sTM 3 and sTM 4 are located extracellularly. Based on the lack of FLAG-antibody binding we suggest intracellular locations for the NH2- and COOH-termini and the region connecting sTM 4 and sTM 5. Immunoprecipitation studies of in vitro translated protein also suggest that the NH2-terminus is sited extracellularly. In immunohistochemical studies with NaPi-2-transfected MDCK cells, an interaction with NH2- and COOH- terminal antipeptide antibodies could only be obtained after membrane permeabilization. The presented data are an experimental documentation of the intracellular location of the NH2- and COOH-termini, and of the extracellular location of extracellular loops 1 and 2.

  1. Atomic resolution noncontact atomic force and scanning tunneling microscopy of TiO2(110)-(1 x 1) and - (1 x 2): simultaneous imaging of surface structures and electronic states.

    PubMed

    Ashino, M; Sugawara, Y; Morita, S; Ishikawa, M

    2001-05-07

    We present simultaneous imaging of TiO2(110)-(1 x 1) and - (1 x 2) using noncontact atomic force microscopy (NC-AFM) and scanning tunneling microscopy (STM). The surface topography was imaged under NC-AFM feedback, while the surface electronic states were imaged by STM. The image contrasts of NC-AFM and STM were antiphase in (1 x 1) and in phase in (1 x 2). The uppermost oxygen and Ti atoms underneath were, respectively, imaged by NC-AFM and STM. The NC-AFM image contrast was close to the true surface topography in (1 x 2), but reduced in (1 x 1).

  2. Direct observation of the secondary structure of unfolded pseudomonas-cytochrome c 551 by scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Liu, Z. F.; Manivannan, A.; Yanagi, H.; Ashida, M.; Fujishima, A.; Inokuchi, H.

    The denaturation of pseudomonas-cytochrome c 551 at the air-water interface was studied using scanning tunneling microscopy (STM). The STM images indicate that the native secondary and tertiary structures of this protein has been virtually lost at such interface. The polypeptide chains of the unfolded protein are nearly fully extended, and highly aggregated in a localized region, forming a crystalline or a twisted rope-like structure. Our observation demonstrates the capability of STM in studying the unfolding of proteins, and also suggests the possibility of using STM to directly sequence the amino acid residues of a protein.

  3. Direct observation of the secondary structure of unfolded pseudomonas-cytochrome c 551 by scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Liu, Z. F.; Manivannan, A.; Yanagi, H.; Ashida, M.; Fujishima, A.; Inokuchi, H.

    1993-03-01

    The denaturation of pseudomonas-cytochrome c 551 at the air-water interface was studied using scanning tunneling microscopy (STM). The STM images indicate that the native secondary and tertiary structures of this protein has been virtually lost at such interface. The polypeptide chains of the unfolded protein are nearly fully extended, and highly aggregated in a localized region, forming a crystalline or a twisted rope-like structure. Our observation demonstrates the capability of STM in studying the unfolding of proteins, and also suggests the possibility of using STM to directly sequence the amino acid residues of a protein.

  4. The Nature of Verbal Short-Term Impairment in Dyslexia: The Importance of Serial Order

    PubMed Central

    Majerus, Steve; Cowan, Nelson

    2016-01-01

    Verbal short-term memory (STM) impairment is one of the most consistent associated deficits observed in developmental reading disorders such as dyslexia. Few studies have addressed the nature of this STM impairment, especially as regards the ability to temporarily store serial order information. This question is important as studies in typically developing children have shown that serial order STM abilities are predictors of oral and written language development. Associated serial order STM deficits in dyslexia may therefore further increase the learning difficulties in these populations. In this mini review, we show that specific serial order STM impairment is frequently reported in both dyslexic children and adults with a history of dyslexia. Serial order STM impairment appears to occur for the retention of both verbal and visuo-spatial sequence information. Serial order STM impairment is, however, not a characteristic of every individual dyslexic subject and is not specific to dyslexia. Future studies need to determine whether serial order STM impairment is a risk factor which, in association with phonological processing deficits, can lead to dyslexia or whether serial order STM impairment reflects associated deficits causally unrelated to dyslexia. PMID:27752247

  5. The geometry of Bi nanolines on Si(0 0 1)

    NASA Astrophysics Data System (ADS)

    Miwa, R. H.; MacLeod, J. M.; Srivastava, G. P.; McLean, A. B.

    2005-05-01

    A study of the Bi nanoline geometry on Si(0 0 1) has been performed using a combination of ab initio theoretical technique and scanning tunnelling microscopy (STM). Our calculations demonstrate decisively that the recently proposed Haiku geometry is a lower energy configuration than any of the previously proposed line geometries. Furthermore, we have made comparisons between STM constant-current topographs of the lines and Tersoff-Haman STM simulations. Although the Haiku and the Miki geometries both reproduce the main features of the constant-current topographs, the simulated STM images of the Miki geometry have a dark stripe between the dimer rows that does not correspond well with experiment.

  6. 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.

  7. Electronic properties of the boroxine–gold interface: evidence of ultra-fast charge delocalization† †Electronic supplementary information (ESI) available: Details about the calculations, further theoretical results, STM images of the thermally annealed TPB monolayer and XPS data analysis procedure are reported. See DOI: 10.1039/c6sc05632f Click here for additional data file.

    PubMed Central

    Toffoli, Daniele; Stredansky, Matus; Feng, Zhijing; Balducci, Gabriele; Furlan, Sara; Stener, Mauro; Ustunel, Hande; Cvetko, Dean; Kladnik, Gregor; Morgante, Alberto; Verdini, Alberto; Dri, Carlo; Comelli, Giovanni

    2017-01-01

    We performed a combined experimental and theoretical study of the assembly of phenylboronic acid on the Au(111) surface, which is found to lead to the formation of triphenylboroxines by spontaneous condensation of trimers of molecules. The interface between the boroxine group and the gold surface has been characterized in terms of its electronic properties, revealing the existence of an ultra-fast charge delocalization channel in the proximity of the oxygen atoms of the heterocyclic group. More specifically, the DFT calculations show the presence of an unoccupied electronic state localized on both the oxygen atoms of the adsorbed triphenylboroxine and the gold atoms of the topmost layer. By means of resonant Auger electron spectroscopy, we demonstrate that this interface state represents an ultra-fast charge delocalization channel. Boroxine groups are among the most widely adopted building blocks in the synthesis of covalent organic frameworks on surfaces. Our findings indicate that such systems, typically employed as templates for the growth of organic films, can also act as active interlayers that provide an efficient electronic transport channel bridging the inorganic substrate and organic overlayer. PMID:28580111

  8. Coexistence of two electronic nano-phases on a CH3NH3PbI3–xClx surface observed in STM measurements

    SciTech Connect

    Yost, Andrew J.; Pimachev, Artem; Ho, Chun -Chih; Darling, Seth B.; Wang, Leeyih; Su, Wei -Fang; Dahnovsky, Yuri; Chien, TeYu

    2016-10-10

    Scanning tunneling microscopy is utilized to investigate the local density of states of a CH3NH3PbI3-xClx perovskite in cross-sectional geometry. Two electronic phases, 10-20 nm in size, with different electronic properties inside the CH3NH3PbI3-xClx perovskite layer are observed by the dI/ dV mapping and point spectra. A power law dependence of the dI/dV point spectra is revealed. In addition, the distinct electronic phases are found to have preferential orientations close to the normal direction of the film surface. Density functional theory calculations indicate that the observed electronic phases are associated with local deviation of I/Cl ratio, rather than different orientations of the electric dipole moments in the ferroelectric phases. Furthermore, by comparing the calculated results with experimental data we conclude that phase A (lower contrast in dI/dV mapping at -2.0 V bias) contains a lower I/Cl ratio than that in phase B (higher contrast in dI/dV).

  9. Coexistence of two electronic nano-phases on a CH3NH3PbI3–xClx surface observed in STM measurements

    SciTech Connect

    Yost, Andrew J.; Pimachev, Artem; Ho, Chun -Chih; Darling, Seth B.; Wang, Leeyih; Su, Wei -Fang; Dahnovsky, Yuri; Chien, TeYu

    2016-10-10

    Scanning tunneling microscopy is utilized to investigate the local density of states of a CH3NH3PbI3-xClx perovskite in cross-sectional geometry. Two electronic phases, 10-20 nm in size, with different electronic properties inside the CH3NH3PbI3-xClx perovskite layer are observed by the dI/ dV mapping and point spectra. A power law dependence of the dI/dV point spectra is revealed. In addition, the distinct electronic phases are found to have preferential orientations close to the normal direction of the film surface. Density functional theory calculations indicate that the observed electronic phases are associated with local deviation of I/Cl ratio, rather than different orientations of the electric dipole moments in the ferroelectric phases. Furthermore, by comparing the calculated results with experimental data we conclude that phase A (lower contrast in dI/dV mapping at -2.0 V bias) contains a lower I/Cl ratio than that in phase B (higher contrast in dI/dV).

  10. 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.

  11. 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.

  12. Overexpression of Salmonella enterica serovar Typhi recA gene confers fluoroquinolone resistance in Escherichia coli DH5α

    PubMed Central

    Yassien, M.A.M.; Elfaky, M.A.

    2015-01-01

    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

  13. 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…

  14. 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…

  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. Relations between Short-term Memory Deficits, Semantic Processing, and Executive Function

    PubMed Central

    Allen, Corinne M.; Martin, Randi C.; Martin, Nadine

    2012-01-01

    Background Previous research has suggested separable short-term memory (STM) buffers for the maintenance of phonological and lexical-semantic information, as some patients with aphasia show better ability to retain semantic than phonological information and others show the reverse. Recently, researchers have proposed that deficits to the maintenance of semantic information in STM are related to executive control abilities. Aims The present study investigated the relationship of executive function abilities with semantic and phonological short-term memory (STM) and semantic processing in such patients, as some previous research has suggested that semantic STM deficits and semantic processing abilities are critically related to specific or general executive function deficits. Method and Procedures 20 patients with aphasia and STM deficits were tested on measures of short-term retention, semantic processing, and both complex and simple executive function tasks. Outcome and Results In correlational analyses, we found no relation between semantic STM and performance on simple or complex executive function tasks. In contrast, phonological STM was related to executive function performance in tasks that had a verbal component, suggesting that performance in some executive function tasks depends on maintaining or rehearsing phonological codes. Although semantic STM was not related to executive function ability, performance on semantic processing tasks was related to executive function, perhaps due to similar executive task requirements in both semantic processing and executive function tasks. Conclusions Implications for treatment and interpretations of executive deficits are discussed. PMID:22736889

  17. Conformation Manipulation and Motion of a Double Paddle Molecule on an Au(111) Surface.

    PubMed

    Soe, We-Hyo; Shirai, Yasuhiro; Durand, Corentin; Yonamine, Yusuke; Minami, Kosuke; Bouju, Xavier; Kolmer, Marek; Ariga, Katsuhiko; Joachim, Christian; Nakanishi, Waka

    2017-09-01

    The molecular conformation of a bisbinaphthyldurene (BBD) molecule is manipulated using an LT-UHV STM on an Au(111) surface. BBD has two binaphthyl groups at both ends connected to a central durene leading to anti/syn/flat conformers. In solution, dynamic NMR indicated the fast interexchange between the anti and syn conformers as confirmed by DFT calculations. After deposition in a sub-monolayer on an Au(111) surface, only the syn conformers were observed forming small islands of self-assembled syn dimers. The syn dimers can be separated in 2 syn monomers by STM molecular manipulations. A flat conformer can also be prepared but using a peculiar mechanical unfolding of a syn monomer by STM manipulations. The experimental STM dI/dV and theoretical ESQC maps of the low lying tunneling resonances confirmed the flat conformer BBD molecule STM production. The key BBD electronic states for a step by step STM inelastic excitation lateral motion on the Au(111) are presented requiring no mechanical interactions between the STM tip apex and the BBD. On the BBD molecular board, selected STM tip apex positions for this inelastic tunneling excitation enable the flat BBD to move controllably on Au(111) by step of 0.29 nm per bias voltage ramp.

  18. 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…

  19. Nonverbal Visual Short-Term Memory as a Function of Age and Dimensionality in Learning Disabled Children.

    ERIC Educational Resources Information Center

    Swanson, Lee

    Evaluated with two age groups (mean age 8.1 years or 10.6 years) totaling 22 learning disabled children was whether there is an age related increase in recognition for visual nonverbal short term memory (STM) and the effects on STM of stimulus dimensionality, primacy, recency, and second choice responses. A serial recognition task was used to…

  20. Verbal Short-Term Memory Reflects the Organization of Long-Term Memory: Further Evidence from Short-Term Memory for Emotional Words

    ERIC Educational Resources Information Center

    Majerus, Steve; D'Argembeau, Arnaud

    2011-01-01

    Many studies suggest that long-term lexical-semantic knowledge is an important determinant of verbal short-term memory (STM) performance. This study explored the impact of emotional valence on word immediate serial recall as a further lexico-semantic long-term memory (LTM) effect on STM. This effect is particularly interesting for the study of…