Home About us Contact
|
Home About us Contact | ||
|
|
||
STM
Terms modified by STM Selected AbstractsCompiler and runtime techniques for software transactional memory optimizationCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 1 2009Peng Wu Abstract Software transactional memory (STM) systems are an attractive environment to evaluate optimistic concurrency. We describe our experience of supporting and optimizing an STM system at both the managed runtime and compiler levels. We describe the design policies of our STM system and the statistics collected by the runtime to identify performance bottlenecks and guide tuning decisions. We present an initial work on supporting automatic instrumentation of the STM primitives for C/C++ and Java programs in the IBM XL compiler and J9 Java virtual machine. We evaluate and discuss the performance of several transactional programs running on our system. Copyright © 2008 John Wiley & Sons, Ltd. [source] Orientation and Arrangement of Octaruthenium Supramolecules with Alkyl Chains on GraphiteEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 35 2007Dong-Lin Shieh Abstract The self-assemblies of octaruthenium grid-type supramolecules, {[Ru2(CO)4(NH2C16H33)2](,-O2CCO2)}4, on highly oriented pyrolytic graphite (HOPG) in air and in 1-phenyloctane were studied by scanning tunneling microscopy (STM). The surface supramolecules are arranged into rows in which the metal cores are linearly packed and the alkyl chains are parallel to the surface. With the aid of theoretical calculations in the framework of density functional theory, the electronic origin of the tunneling in the measured STM images is discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Basolateral amygdala inactivation by muscimol, but not ERK/MAPK inhibition, impairs the use of reward expectancies during working memoryEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2007Lisa M. Savage Abstract Rats were trained on a delayed matching to position (DMTP) task that embedded either a differential outcomes procedure (DOP) or a non-differential outcomes procedure (NOP). The DOP, via Pavlovian conditioning (stimulus,outcome associations), results in the use of unique reward expectancies that facilitate learning and memory performance above subjects trained with a NOP that requires subjects to retain cue information for accurate choice behavior (stimulus,response associations). This enhancement in learning and/or memory produced by the DOP is called the differential outcomes effect (DOE). After being trained on the DMTP task, rats were implanted with two cannulae aimed at the basolateral amygdala (BLA) nuclei. Rats trained with the DOP, relative to those trained with the NOP, displayed enhanced short-term memory (STM) performance under vehicle conditions (i.e. the DOE). However, injections of the ,-aminobutyric acid (GABA)A agonist muscimol into the BLA dose-dependently (0.0625 and 0.125 µg) impaired STM performance only in DOP-trained rats. These results support the role of the BLA in the use of established reward expectancies during a short-term working memory task. Despite the fact that extracellular signal-regulated kinase/mitogen-activated protein kinases (ERK/MAPK) have been shown to be necessary for amygdala-dependent long-term potentiation and some forms of long-term and STM, inhibition of the ERK/MAPK signaling cascade by U0126 (2.0 or 4.0 µg) in the BLA was not critical for updating the STM of either spatial information or reward expectation. [source] Rigid Bisphenanthrolines: Synthesis, Structure and Self-Assembly at a Solid,Liquid Interface,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2006Michael Schmittel Abstract Several rigid linear bisphenanthrolines with and without bulky groups at the bisimine sites were synthesized. For three representatives, the solid-state structures were elucidated. Their potential for self-assembled monolayers was explored by scanning tunneling microscopy (STM) at the solid,liquid interface, and the resulting architectures were found to be promising candidates for templating metal-ion nanopatterns. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Electric-Field-Assisted Nanostructuring of a Mott InsulatorADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Vincent Dubost Abstract Here, the first experimental evidence for a strong electromechanical coupling in the Mott insulator GaTa4Se8 that allows highly reproducible nanoscaled writing by means of scanning tunneling microscopy (STM) is reported. The local electric field across the STM junction is observed to have a threshold value above which the clean (100) surface of GaTa4Se8 becomes mechanically instable: at voltage biases >1.1,V, the surface suddenly inflates and comes in contact with the STM tip, resulting in nanometer-sized craters. The formed pattern can be indestructibly "read" by STM at a lower voltage bias, thus allowing 5,Tdots inch,2 dense writing/reading at room temperature. The discovery of the electromechanical coupling in GaTa4Se8 might give new clues in the understanding of the electric pulse induced resistive switching recently observed in this stoichiometric Mott insulator. [source] BDNF,triggered events in the rat hippocampus are required for both short- and long-term memory formationHIPPOCAMPUS, Issue 4 2002Mariana Alonso Abstract Information storage in the brain is a temporally graded process involving different memory types or phases. It has been assumed for over a century that one or more short-term memory (STM) processes are involved in processing new information while long-term memory (LTM) is being formed. Because brain-derived neutrophic factor (BDNF) modulates both short-term synaptic function and activity-dependent synaptic plasticity in the adult hippocampus, we examined the role of BDNF in STM and LTM formation of a hippocampal-dependent one-trial fear-motivated learning task in rats. Using a competitive RT-PCR quantitation method, we found that inhibitory avoidance training is associated with a rapid and transient increase in BDNF mRNA expression in the hippocampus. Bilateral infusions of function-blocking anti-BDNF antibody into the CA1 region of the dorsal hippocampus decreased extracellular signal,regulated kinase 2 (ERK2) activation and impaired STM retention scores. Inhibition of ERK1/2 activation by PD098059 produced similar effects. In contrast, intrahippocampal administration of recombinant human BDNF increased ERK1/2 activation and facilitated STM. The infusion of anti-BDNF antibody impaired LTM when given 15 min before or 1 and 4 hr after training, but not at 0 or 6 hr posttraining, indicating that two hippocampal BDNF-sensitive time windows are critical for LTM formation. At the same time points, PD098059 produced no LTM deficits. Thus, our results indicate that endogenous BDNF is required for both STM and LTM formation of an inhibitory avoidance learning. Additionally, they suggest that this requirement involves ERK1/2-dependent and -independent mechanisms. Hippocampus 2002;12:551,560. © 2002 Wiley-Liss, Inc. [source] Evidence for Band-Like Transport in Graphene-Based Organic MonolayersADVANCED MATERIALS, Issue 3 2010Daniel Käfer Evidence for a band-like, lateral transport of electrons through the cores of HBC-thiolates, forming a highly ordered self-assembled monolayer (SAM) containing a very regular array of HBC-cores, is provided based on a detailed analysis of temperature-dependent scanning tunneling microscopy (STM) data recorded for islands of aromatic SAMs immersed in an insulating matrix. [source] The Quest for Nanoscale Magnets: The example of [Mn12] Single Molecule MagnetsADVANCED MATERIALS, Issue 43 2009Guillaume Rogez Abstract Recent advances on the organization and characterization of [Mn12] single molecule magnets (SMMs) on a surface or in 3D are reviewed. By using nonconventional techniques such as X-ray magnetic circular dichroism (XMCD) and scanning tunneling microscopy (STM), it is shown that [Mn12]-based SMMs deposited on a surface lose their SMM behavior, even though the molecules seem to be structurally undamaged. A new approach is reported to get high-density information-storage devices, based on the 3D assembling of SMMs in a liquid crystalline phase. The 3D nanostructure exhibits the anisotropic character of the SMMs, thus opening the way to address micrometric volumes by two photon absorption using the pump-probe technique. We present recent developments such as µ-SQUID, magneto-optical Kerr effect (MOKE), or magneto-optical circular dichroism (MOCD), which enable the characterization of SMM nanostructures with exceptional sensitivity. Further, the spin-polarized version of the STM under ultrahigh vacuum is shown to be the key tool for addressing not only single molecule magnets, but also magnetic nano-objects. [source] Verbal memory performance improved via an acute administration of D -amphetamineHUMAN PSYCHOPHARMACOLOGY: CLINICAL AND EXPERIMENTAL, Issue 5 2007Inge Zeeuws Abstract Background An improved long-term retention of verbal memory was observed after an acute D -amphetamine administration. It was proposed that D -amphetamine modulates consolidation, but a possible drug effect on retrieval could not be rejected. Objectives We want to provide additional support for the consolidation hypothesis, and investigate whether an influence on intervening retrieval can be refuted. Methods Thirty-six male paid volunteers participated in a double blind, counterbalanced, placebo-controlled design in which the number of intermediate free recall tests was manipulated. Results A significant D -amphetamine facilitation effect on recall performance emerged 1 h and 1 day after list learning. In line with the consolidation hypothesis, no effect was found on immediate tests. Importantly, the number of intermediate retrievals did not affect the magnitude of the drug effect, suggesting that the D -amphetamine facilitation effect is independent of retrieval. Conclusion The D -amphetamine facilitation effect on verbal memory does not involve a modulation of the initial encoding or short-term memory (STM) processes. Moreover, the drug does not enhance long-term retention by acting on intervening retrieval processes. The current findings are in line with the conjecture of an involvement of the consolidation process in the D -amphetamine facilitation effect on verbal memory in healthy humans. Copyright © 2007 John Wiley & Sons, Ltd. [source] Dynamic Processes at Solid-liquid InterfacesIMAGING & MICROSCOPY (ELECTRONIC), Issue 1 2006Video-STM Images Nanoscale Dynamics Scanning tunnelling microscopy (STM) not only provides unsurpassed resolution, enabling real-space imaging of individual surface atoms, but also is capable to operate in a wide range of environments, ranging from ultrahigh vacuum to gases and liquids. The latter allows studies of processes at solidliquid interfaces with a time resolution that can be as low as some 10 msec. in modern instruments. This is sufficiently fast to study elementary transport processes at these interfaces, such as surface diffusion or crystal growth, directly on the atomic scale. [source] The Inner Shell Influence on the Electronic Structure of Double-Walled Carbon Nanotubes,ADVANCED MATERIALS, Issue 1 2008Y. Tison We present STM and STS results obtained for double-walled carbon nanotubes. In the case displayed here, the STS results exhibit the Van Hove singularities corresponding to semi conducting tubes for both the outer and the inner shell and a finite density of states at the Fermi level (EF) is observed for a DWNT. We associate this behavior to the presence of an intershell interaction. [source] Theory of tip-dependent imaging of adsorbates in the STM: CO on Cu(111)INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2006D. Drakova Abstract The processes of local electron injection or extraction in the scanning tunneling microscopy (STM) and spectroscopy (STS) lead to the creation of short-lived excited states localized at the electrode surfaces. The dynamic relaxation of the transient negative or positive ion resonances, due to both local and long-range interactions, is the clue to the understanding of numerous phenomena in STM/STS ranging from the "anomalously" large tip height corrugation amplitudes on clean metal surfaces to the observation of quantum mirages and features in the STS, which are not observed with the help of other surface spectroscopies. Quantum nanodynamics theory (QND) has been applied to calculate the interaction potential of a single CO molecule with the Cu(111) surface, with a transient negative ion resonance formed when an electron is injected from the tip, and the tunneling conductance on the clean and CO covered Cu(111) surface using a clean metal tip Al/Al(111) and a Pt(111) tip with an adsorbed CO molecule at the apex. Within QND and three-dimensional scattering theory, regarding the tunneling as an excited-state problem, we provide the explanation of the tip-dependent STM image of a single CO molecule on Cu(111). The appearance of the CO molecule as an indentation, using a clean metal tip and as a protrusion with a tip terminated by a CO molecule, is understood as a result of tunneling through two competing channels. Tunneling via adsorbate-induced ion resonances enhances the tunneling conductance. In contrast, tunneling via metal ion resonances only leads to attenuation of the conductance in the presence of the adsorbate. The current in the vicinity of the adsorbed CO molecule is reduced when a clean metal tip is used; i.e., CO appears dark in the STM image, because metal ion resonances on Cu(111) derive from the surface states with image state components coupling to plasmons and are therefore very diffuse. With a CO-terminated tip, the major current channel is, for symmetry reasons, from the 2,-derived orbital of the tip CO molecule, via the diffuse 2,-derived orbital of the CO molecule on the sample, hence adsorbed CO appears bright. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Computation of STM images of carbon nanotubesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4-5 2003P. Lambin Abstract Scanning tunneling microscopy (STM) is the only probing technique that allows for the investigation of both the topography and the electronic structure of carbon nanosystems at a subnanometer resolution. The interpretation of the STM images of carbon nanostructures involves complications that are normally absent in the study of planar crystalline surfaces. The complications typically appear from a number of quantum effects responsible for distortions in the microscope image of a nano-object. Because of these difficulties, computer simulation plays an extremely important role in the analysis of experimental data. In the current article, we report on two theoretical approaches developed for aiding in the interpretation and understanding of the formation of the STM image of a nanotube: first, the quantum mechanical dynamics of a wave packet, which allows for the modeling of the flow of the tunneling current between a tip and a nanotube supported by a substrate; and, second, a tight-binding perturbation theory that allows for the explicit calculation of realistic STM images and scanning tunneling spectra of carbon nanostructures. An atlas of computed STM images is provided for a series of 27 single-wall nanotubes with diameter around 1.3 nm. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 [source] Metal Objects Mapping After Small Charge Explosions.JOURNAL OF FORENSIC SCIENCES, Issue 3 2006A Study on AISI 304Cu Steel with Two Different Grain Sizes ABSTRACT: Evidence of exposure of a metal component to a small charge explosion can be detected by observing microstructural modifications; they may be present even if the piece does not show noticeable overall plastic deformations. Particularly, if an austenitic stainless steel (or another metal having a face-centered cubic structure and a low stacking fault energy) is exposed to an explosive shock wave, high-speed deformation induces primarily mechanical twinning, whereas, in nonexplosive events, a lower velocity plastic deformation first induces slip. The occurrence of mechanical twins can be detected even if the surface is damaged or oxidized in successive events. In the present research, optical metallography (OM) and scanning electron microscopy (SEM), and scanning tunneling microscopy (STM) were used to detect microstructural modifications caused on AISI 304Cu steel disks by small-charge explosions. Spherical charges of 54.5 or 109 g TNT equivalent mass were used at explosive-to-target distances from 6.5 to 81.5 cm, achieving peak pressures from 160 to 0.5 MPa. Explosions induced limited or no macro-deformation. Two alloy grain sizes were tested. Surface OM and SEM evidenced partial surface melting, zones with recrystallization phenomena, and intense mechanical twinning, which was also detected by STM and X-ray diffraction. In the samples' interior, only twins were seen, up to some distance from the explosion impinged surface and again, at the shortest charge-to-sample distances, in a thin layer around the reflecting surface. For forensic science locating purposes after explosions, the maximum charge-to-target distance at which the phenomena disappear was singled out for each charge or grain size and related to the critical resolved shear stress for twinning. [source] Adlayer structure of octa-alkoxy-substituted copper(II) phthalocyanine on Au(111) by electrochemical scanning tunneling microscopyMICROSCOPY RESEARCH AND TECHNIQUE, Issue 1 2008Li Wang Abstract Electrochemical scanning tunneling microscopy (ECSTM) has been used to examine the adlayer of octa-alkoxy-substituted copper(II) phthalocyanines (CuPc(OC8H17)8) on Au(111) in 0.1 M HClO4, where the molecular adlayer was prepared by spontaneous adsorption from a benzene solution containing this molecule. Topography STM scans revealed long-range ordered, interweaved arrays of CuPc(OC8H17)8 with coexistent rectangular and hexagonal symmetries. High-quality STM molecular resolution yielded the internal molecular structure and the orientation of CuPc(OC8H17)8 admolecules. These STM results could shed insight into the method of generating ordered molecular assemblies of phthalocyanine molecules with long-chained substitutes on metal surface. Microsc. Res. Tech., 2008. © 2007 Wiley-Liss, Inc. [source] Identification of Xenorhabdus nematophila genes required for mutualistic colonization of Steinernema carpocapsae nematodesMOLECULAR MICROBIOLOGY, Issue 5 2002Kurt Heungens Summary One stage in the symbiotic interaction between the bacterium Xenorhabdus nematophila and its nematode host, Steinernema carpocapsae, involves the species-specific colonization of the nematode intestinal vesicle by the bacterium. To characterize the bacterial molecular determinants that are essential for vesicle colonization, we adapted and applied a signature-tagged mutagenesis (STM) screen to this system. We identified 15 out of 3000 transposon mutants of X. nematophila with at least a 15-fold reduction in average vesicle colonization. These 15 mutants harbour disruptions in nine separate loci. Three of these loci have predicted open reading frames (ORFs) with similarity to genes (rpoS, rpoE, lrp) encoding regulatory proteins; two have predicted ORFs with similarity to genes (aroA, serC) encoding amino acid biosynthetic enzymes; one, designated nilB (nematode intestine localization), has an ORF with similarity to a gene encoding a putative outer membrane protein (OmpU) in Neisseria; and three, nilA, nilC and nilD, have no apparent homologues in the public database. nilA, nilB and nilC are linked on a single 4 kb locus. nilB and nilC are > 104 -fold reduced in their ability to colonize the nematode vesicle and are predicted to encode membrane-localized proteins. The nilD locus contains an extensive repeat region and several small putative ORFs. Other than reduced colonization, the nilB, nilC and nilD mutants did not display alterations in any other phenotype tested, suggesting a specific role for these genes in allowing X. nematophila to associate with the nematode host. [source] Genetic analysis of Escherichia coli K1 gastrointestinal colonizationMOLECULAR MICROBIOLOGY, Issue 6 2000J. Martindale Strains of Escherichia coli expressing the K1 polysaccharide capsule colonize the large intestine of newborn infants, and are the leading cause of Gram-negative septicaemia and meningitis in the neonatal period. We used signature-tagged mutagenesis (STM) to identify genes that E. coli K1 requires to colonize the gastrointestinal (GI) tract. A total of 2140 mTn5 mutants was screened for their capacity to colonize the GI tract of infant rats, and 16 colonization defective mutants were identified. The mutants have transposon insertions in genes affecting the synthesis of cell surface structures, membrane transporters, transcriptional regulators, enzymes in metabolic pathways, and in genes of unknown function, designated dgc (defective in GI colonization). Three dgcs are absent from the whole genome sequence of E. coli K-12, although related sequences are found in other pathogenic strains of E. coli and in Shigella flexneri. Additionally, immunohistochemistry was used to define the nature of the colonization defect in five mutants including all dgc mutants. STM was successfully applied to examine the factors involved in E. coli K1 colonization, and the findings are relevant to the pathogenesis of other enteric infections. [source] Molecular rectification in metal,bridge molecule,metal junctionsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2010Yaqing Liu Abstract Molecular bridged nanocontacts allow direct electrical addressing of electroactive molecules, which is of interest for the development of molecular based electronic devices. In the present paper, the electroactive molecule 6-ferrocenyl-1-hexanethiol (Fc-HT) was integrated into metal,bridge,metal (MBM) junctions assembled in a scanning tunneling microscope (STM) setup. A diode-like behavior was observed from the current/bias (It/Vb) signal through Au (substrate)/Fc-HT/Au (tip) junction, which presented an asymmetric current response due to the resonant tunneling between metal electrode and ferrocenylthiol molecules. With gate electrode modulation, the enhancement of the tunneling current can be controlled, which allows to tune the direction of the current rectification. Our investigations demonstrated that ferrocenylthiol bridged MBM nanostructure has potential applications in the future design of higher-order heterojunctions components in combination with electrochemical logic gates. [source] Influence of substrate and temperature on the shape of deposited Fe, Co, and FeCo nanoparticlesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2010Wolfgang Rosellen Abstract In situ scanning tunneling measurements have been carried out on mass-filtered supported Fe, Co, and FeCo alloy nanoparticles with diameters between 4 and 14,nm. These nanoparticles are prepared from the gas phase using a continuously working cluster source and are subsequently deposited on bare W(110) and Ni(111)/W(110) surfaces. The size and the crystallographic structure before deposition are determined by high resolution transmission electron microscopy (HRTEM), the height of the nanoparticles on the substrate by scanning tunneling microscopy (STM). Depending on the substrate the particles do not maintain their spherical shape after deposition. The melting at elevated temperatures results in an anisotropic elongation along the [001] direction of the W(110) substrate. STM illustration of large Co nanoparticles deposited on an atomically flat W(110)-surface. [source] Crystallographically oriented high resolution lithography of graphene nanoribbons by STM lithographyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2010G. Dobrik Abstract Due to its exciting physical properties and sheet-like geometry graphene is in the focus of attention both from the point of view of basic science and of potential applications. In order to fully exploit the advantage of the sheet-like geometry very high resolution, crystallographicaly controlled lithography has to be used. Graphene is a zero gap semiconductor, so that a field effect transistor (FET) will not have an "off" state unless a forbidden gap is created. Such a gap can be produced confining the electronic wave functions by etching narrow graphene nanoribbons (GNRs) typically of a few nanometers in width and with well defined crystallographic orientation. We developed the first lithographic method able to achieve GNRs that have both nanometer widths and well defined crystallographic orientation. The lithographic process is carried out by the local oxidation of the sample surface under the tip of a scanning tunneling microscopy (STM). Crystallographic orientation is defined by acquiring atomic resolution images of the surface to be patterned. The cutting of trenches with controlled depth and of a few nanometer in width, folding and manipulation of single graphene layers is demonstrated. The narrowest GNR cut by our method is of 2.5,nm width, scanning tunneling spectroscopy (STS) showed that it has a gap of 0.5,eV, comparable to that of germanium, which allows room temperature operation of graphene nanodevices. [source] Density functional study of graphene overlayers on SiCPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2008Alexander Mattausch Abstract Despite the ongoing "graphene boom" of the last three years our understanding of epitaxial graphene grown on SiC substrate is only beginning to emerge. Along with experimental methods such as low energy electron diffraction (LEED), scanning tunneling microscopy (STM) and angle resolved photoemission spectroscopy (ARPES), ab initio calculations help to uncover the geometric and electronic structure of the graphene/SiC interface. In this chapter we describe the density-functional calculations we performed for single and double graphene layers on Si- and C-terminated 6H-SiC surfaces. Experimental data reveal a pronounced difference between the two surface terminations. On a Si-terminated surface the interface adopts a 6,3 × 6,3 unit cell whereas the C-face supports misoriented (turbostratic) graphene layers. It has been recently realized that, on the Si-face, the large commensurate cell is subdivided into patches of coherently matching to the substrate carbon atoms. In our calculations we assumed the "coherent match" geometry for the whole interface plane. This reduces the periodic unit to the ,3 × ,3R 30° cell but requires a substantial stretching of the graphene sheet. Although simplified, the model provides a qualitative picture of the bonding and of the interface electron energy spectrum. We find that the covalent bonding between the carbon layer and the substrate destroys the massless "relativistic" electron energy spectrum, the hallmark of a freestanding graphene. Hence the first carbon layer cannot be responsible for the graphene-type electron spectrum observed by ARPES and rather plays a role of a buffer between the substrate and the subsequent carbon sheets. The "true" graphene spectrum appears with the second carbon layer which exhibits a weak van der Waals bonding to the underlying structure. For Si-terminated substrate, we find that the Fermi level is pinned by the interface state at 0.45 eV above the graphene Dirac point, in agreement with experimental data. This renders the interface metallic. On the contrary, for a C-face the "coherent match" model predicts the Fermi level exactly at the Dirac point. However, this does not necessarily apply to the turbostratic graphene layers that normally grow on the C-terminated substrate. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Inhomogeneous surface electronic properties and charge ordering in epitaxial Fe3O4 films on MgO(001)PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2007A. Subagyo Abstract We report scanning tunneling microscopy (STM) study of surface electronic properties and charge ordering of epitaxially grown magnetite, Fe3O4, (001) films exhibiting high density of antiphase domain boundaries (APBs). STM measurements using a W tip reveal surface termination at B-sites. Fe ions with a 0.3 nm periodicity, i.e., a single atomic distance are observed. Current imaging tunneling spectroscopy reveals the alternation of two kinds of current peaks with a 0.6 nm periodicty indicating the presence of charge ordering consisted of Fe dimers with different charge states. STM measurements using a magnetic Ni tip provide higher contrast of the charge ordering. The APBs can modify the charge ordering as ordered and disordered areas are observed on adjacent domains separated by an APB. These strongly indicate that APBs can induce inhomogeneous properties on the surface of Fe3O4(001) films. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Scanning tunneling microscopy of monoatomic gold chains on vicinal Si(335) surface: experimental and theoretical studyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2005M. Krawiec Abstract We study electronic and topographic properties of the Si(335) surface, containing Au wires parallel to the steps. We use scanning tunneling microscopy (STM) supplemented by reflection of high energy electron diffraction (RHEED) technique. The STM data show the space and voltage dependent oscillations of the distance between STM tip and the surface which can be explained within one band tight binding Hubbard model. We calculate the STM current using nonequilibrium Keldysh Green function formalism. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Video-rate scanning probe control challenges: setting the stage for a microscopy revolutionASIAN JOURNAL OF CONTROL, Issue 2 2009M. J. Rost Abstract Scanning probe microscopy is at the verge of revolutionizing microscopy once again. Video-rate scanning tunneling microscope (STM) and video-rate atomic force microscope (AFM) technology will enable the direct observation of many dynamic processes that are impossible to observe today, such as atom or molecule diffusion, real time film growth, or catalytic reactions. In this paper we discuss the critical aspects that have to be taken into account when working on increasing the imaging speed of scanning probe microscopes. We highlight the state-of-the-art developments in the control of the piezoelectric scanning elements and describe the latest innovations regarding the design and construction of the whole mechanical loop including new scanner geometries. We identify critical aspects for which no obvious solution exists and aspects where advanced control engineering can help, like piezo non-linearities, the acceleration limit and the challenging technical requirements for the preamplifiers that are needed for measuring a tunneling current. Finally, we provide an overview of a number of new directions that are being pursued to solve the problems currently encountered in scanning probe technology. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Unexpected Deformations Induced by Surface Interaction and Chiral Self-Assembly of CoII -Tetraphenylporphyrin (Co-TPP) Adsorbed on Cu(110): A Combined STM and Periodic DFT StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 38 2010Philip Donovan Abstract In a combined scanning tunnelling microscopy (STM) and periodic density functional theory (DFT) study, we present the first comprehensive picture of the energy costs and gains that drive the adsorption and chiral self-assembly of highly distorted CoII -tetraphenylporphyrin (Co-TPP) conformers on the Cu(110) surface. Periodic, semi-local DFT calculations reveal a strong energetic preference for Co-TPP molecules to adsorb at the short-bridge site when organised within a domain. At this adsorption site, a substantial chemical interaction between the molecular core and the surface causes the porphyrin macrocycle to accommodate close to the surface and in a flat geometry, which induces considerable tilting distortions in the phenyl groups. Experimental STM images can be explained in terms of these conformational changes and adsorption-induced electronic effects. For the ordered structure we unambiguously show that the substantial energy gain from the molecule,surface interaction recuperates the high cost of the induced molecular and surface deformations as compared with gas phase molecules. Conversely, singly adsorbed molecules prefer a long-bridge adsorption site and adopt a non-planar, saddle-shape conformation. By using a van der Waals density functional correction scheme, we found that the intermolecular ,,, interactions make the distorted conformer more stable than the saddle conformer within the organic assembly. These interactions drive supramolecular assembly and also generate chiral expression in the system, pinning individual molecules in a propeller-like conformation and directing their assembly along non-symmetric directions that lead to the coexistence of mirror-image chiral domains. Our observations reveal that a strong macrocycle,surface interaction can trigger and stabilise highly unexpected deformations of the molecular structure and thus substantially extend the range of chemistries possible within these systems. [source] Self-Assembled Monolayers of Alkoxy-Substituted Octadehydrodibenzo[12]annulenes on a Graphite Surface: Attempts at peri -Benzopolyacene Formation by On-Surface PolymerizationCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2010Kazukuni Tahara Dr. Abstract Self-assembled monolayers of a series of tetraalkoxy-substituted octadehydrodibenzo[12]annulene (DBA) derivatives 1,c,g possessing butadiyne linkages were studied at the 1,2,4-trichlorobenzene (TCB) or 1-phenyloctane/graphite interface by scanning tunneling microscopy (STM). The purpose of this research is not only to investigate the structural variation of two-dimensional (2D) monolayers, but also to assess a possibility for peri -benzopolyacene formation by two-dimensionally controlled polymerization on a surface. As a result, the formation of three structures, porous, linear, and lamella structures, were observed by changing the alkyl chain length and the solute concentration. The formation of multilayers of the lamella structure was often observed for all compounds. The selection of molecular networks is basically ascribed to intermolecular and molecule,substrate interactions per unit area and network density. The selective appearance of the linear structure of 1,d is attributed to favorable epitaxial registry matching between the substrate lattice and the overlayer lattice. Even though the closest interatomic distance between the diacetylenic units of the DBAs in the lamella structure (,0.6,nm) is slightly larger compared to the typical distances necessary for topochemical polymerization, the reactivity toward external stimuli (electronic-pulse irradiation from an STM tip and UV irradiation) was investigated. Unfortunately, no evidence for polymerization of the DBAs on the surface was observed. The present results indicate the necessity for further designing a suitable system for the on-surface construction of structurally novel conjugated polymers, which are otherwise difficult to prepare. [source] Modification of Supramolecular Binding Motifs Induced By Substrate Registry: Formation of Self-Assembled Macrocycles and Chain-Like PatternsCHEMISTRY - A EUROPEAN JOURNAL, Issue 42 2009Leslie-Anne Fendt Abstract The self-assembly properties of two ZnII porphyrin isomers on Cu(111) are studied at different coverage by means of scanning tunneling microscopy (STM). Both isomers are substituted in their meso -positions by two voluminous 3,5-di(tert -butyl)phenyl and two rod-like 4,-cyanobiphenyl groups, respectively. In the trans -isomer, the two 4,-cyanobiphenyl groups are opposite to each other, whereas they are located at right angle in the cis -isomer. For coverage up to one monolayer, the cis- substituted porphyrins self-assemble to form oligomeric macrocycles held together by antiparallel CN,,,CN dipolar interactions and CN,,,H-C(sp2) hydrogen bonding. Cyclic trimers and tetramers occur most frequently but everything from cyclic dimers to hexamers can be observed. Upon annealing of the samples at temperatures >150,°C, dimeric macrocyclic structures are observed, in which the two porphyrins are bridged by Cu atoms, originating from the surface, under formation of two CN,,,Cu,,,NC coordination bonds. The trans -isomer builds up linear chains on Cu(111) at low coverage, whereas for higher coverage the molecules assemble in a periodic, densely packed structure. Both cis - and trans -bis(4,-cyanobiphenyl)-substituted ZnII porphyrins behave very differently on Cu(111) compared to similar porphyrins in literature on less reactive surfaces such as Au(111) and Ag(111). On the latter surfaces, there is no signal visible between molecular orientation and the crystal directions of the substrate, whereas on Cu(111), very strong adsorbate,substrate interactions have a dominating influence on all observed structures. This strong porphyrin,substrate interaction enables a much broader variety of structures, including also less favorable intermolecular bonding motifs and geometries. [source] Current,Voltage Characteristics of a Homologous Series of Polycyclic Aromatic HydrocarbonsCHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2007Thilo Böhme Dr. Abstract A novel alkyl-substituted polycyclic aromatic hydrocarbon (PAH) with D2h symmetry and 78 carbon atoms in the aromatic core (C78) was synthesized, thereby completing a homologous series of soluble PAH compounds with increasing size of the aromatic , system (42, 60, and 78 carbon atoms). The optical band gaps were determined by UV/Vis and fluorescence spectroscopy in solution. Scanning tunneling microscopy (STM) and spectroscopy (STS) revealed diode-like current versus voltage (I,V) characteristics through individual aromatic cores in monolayers at the interface between the solution and the basal plane of graphite. The asymmetry of the current,voltage (I,V) characteristics increases with the increasing size of the aromatic core, and the concomitantly decreasing HOMO,LUMO gap. This is attributed to resonant tunneling through the HOMO of the adsorbed molecule, and an asymmetric position of the molecular species in the tunnel junction. Consistently, submolecularly resolved STM images at negative substrate bias are in good agreement with the calculated pattern for the electron densities of the HOMOs. The analysis provides the basis for tailoring rectification with a single molecule in an STM junction. [source] Electrochemically Assisted Fabrication of Metal Atomic Wires and Molecular Junctions by MCBJ and STM-BJ Methods,CHEMPHYSCHEM, Issue 13 2010Dr. Jing-Hua Tian Abstract Atomic wires (point contacts) and molecular junctions are two fundamental units in the fields of nanoelectronics and devices. This Minireview introduces our recent approaches aiming to develop versatile methods to fabricate and characterize these unique metallic and molecular structures reliably. Electrochemical methods are coupled with mechanically controllable break junction (EC-MCBJ) or scanning tunneling microscopy (STM) break junction (EC-STMBJ) methods to fabricate metallic point contacts and metal/molecule/metal junctions. With the designed electrodeposition method, the metal of interest (e.g. Au, Cu, Fe or Pd) is deposited in a controlled way on the original electrode pair, on a chip for MCBJ or on the STM tip, to make the metallic contact. Then, various metal atomic wires and molecular junctions can be fabricated and characterized systematically. Herein, we measured the quantized conductance through the construction of histograms of these metal atomic point contacts and of single molecules including benzene-1,4-dithiol (BDT), ferrocene-bisvinylphenylmethyl dithiol (Fc-VPM), 4,4,-bipyridine (BPY), 1,2-di(pyridin-4-yl)ethene (BPY-EE), and 1,2-di(pyridin-4-yl)ethane (BPY-EA). Finally, we briefly discussed the future of EC-MCBJ and EC-STM for nanoelectronics and devices, for example, for the formation of heterogeneous metal-based atomic point contacts and molecular junctions. [source] Two-Dimensional Self-Assembly of a Porphyrin,Polypyridyl Ruthenium(II) Hybrid on HOPG Surface through Metal,Ligand InteractionsCHEMPHYSCHEM, Issue 9 2010Aimei Gao Dr. Abstract The synthesis and self-assembly behavior of porphyrin,polypyridyl ruthenium(II) hybrid, which consists of a flexible alkyl chain attached with two conjugated moieties is described. The electronic absorption spectrum and emission spectra show that the [C8 -TPP-(ip)Ru(phen)2](ClO4)2, abbreviated as (C8ip)TPPC has optical properties. Scanning tunneling microscopy (STM) studies found that the ,,, interaction and metal,ligand interaction allow (C8ip)TPPC to form self-assembled structure and have an edge-on orientation on the highly oriented pyrolytic graphite (HOPG) surface. The multidentate structure in (C8ip)TPPC molecules act as linkers between the molecules and form metal,ligand coordination, which forces the assembly process in the direction of stable columnar arrays. In addition, although the sample was stored for two months in ambient conditions, STM experiments showed that the order of (C8ip)TPPC self-assembly only slightly decreased which indicates that the self-assembled monolayer is stable. This work demonstrates that introducing a metal-ligand in the porphyrin-polypyridyl compound is a useful strategy to obtain novel surface assemblies. [source] | |||||||||||||||||||||||||