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Vanadium dioxide (VO2) is a well-known phase-changing material that goes from a semiconducting state to a metallic one at a critical temperature of 68 °C, which is the closest to room temperature (25 °C). The electrical transition is also accompanied by structural and optical changes. The optical transition upon heating-also known as thermochromism-makes VO2 a possible coating for “intelligent” windows. In this work, the relationship between the thermochromic performance of VO2 films and the surface morphology was investigated using Temperature-dependent Atomic Force Microscopy (T-AFM) in conjunction with the X-ray Diffraction technique and Scanning Electron Microscopy. In particular, VO2 films were deposited using the rf sputtering technique on Silicon and glass substrates at a substrate temperature of 300 °C, which is one of the lowest for this technique to grow the thermochromic monoclinic phase of VO2. It was found that upon heating (25–100 °C), there was a decrease in RMS roughness for all films independent from the substrate; the value of RMS roughness, however, varied depending on the substrate. Finally, the thermochromic parameters of the VO2 films were correlated with the surface morphology and appeared to be dependent on the kind of substrate used.

We present a new approach to formulating open superstring field theory based on the covering of the supermoduli space of super-Riemann surfaces and explicitly construct a gauge-invariant action in the Neveu-Schwarz sector up to quartic interactions. The cubic interaction takes a form of an integral over an odd modulus of disks with three punctures and the associated ghost is inserted. The quartic interaction takes a form of an integral over one even modulus and two odd moduli, and it can be interpreted as the integral over the region of the supermoduli space of disks with four punctures which is not covered by Feynman diagrams with two cubic vertices and one propagator. As our approach is based on the covering of the supermoduli space, the resulting theory naturally realizes an $A_\infty$ structure, and the two-string product and the three-string product used in defining the cubic and quartic interactions are constructed to satisfy the $A_\infty$ relations to this order., Comment: 60 pages, 3 figures; v2: minor corrections and references added; v3: a proof that the quartic vertex is unambiguously defined for general off-shell states added in appendix A.5, version published in JHEP

International audience

International audience; Long poly-diacetylene chains are excellent candidates for planar, on-surface synthesizedmolecular electronic wires. Since hexagonal-Boron Nitride (h-BN) was identified as the bestavailable atomically flat insulator for the deposition of poly-diacetylene precursors, we demonstratethe polymerization patterns and rate on it under UV-light irradiation, with subsequent polymeridentification by atomic force microscopy. The results on h-BN indicate self-sensitization whichyields blocks comprised of several polymers, unlike on the well-studied graphite/diacetylene system,where the polymers are always isolated. In addition, the photo-polymerization proceeds at least170 times faster on h-BN, where it also results in longer polymers. Both effects are explained bythe h-BN bandgap, which is larger than the diacetylene electronic excitation energy, thus allowingthe transfer of excess energy absorbed by polymerized wires to adjacent monomers, triggeringtheir polymerization. This work sets the stage for conductance measurements of single molecularpoly-diacetylene wires on h-BN.

cited By 0; International audience; Localization of atomic defect-induced electronic transport through a single graphene layer is calculated using a full-valence electronic structure description as a function of the defect density and taking into account the atomic-scale deformations of the layer. The elementary electronic destructive interferences leading to Anderson localization are analyzed. The low-voltage current intensity decreases with increasing length and defect density, with a calculated localization length ζ = 3.5 nm for a defect density of 5%. The difference from the experimental defect density of 0.5% required for an oxide surface-supported graphene to obtain the same ζ is discussed, pointing out how interactions of the graphene supporting surface and surface chemical modifications also control electronic transport localization.

cited By 1; International audience; Single crystal sapphire and diamond surfaces are used as planar, atomically flat insulating surfaces, for the deposition of the diacetylene compound 10,12-nonacosadiynoic acid. The surface assembly is compared with results on hexagonal boron nitride (h-BN), highly oriented pyrolytic graphite (HOPG) and MoS2 surfaces. A perfectly flat-lying monolayer of 10,12-nonacosadiynoic acid self-assembles on h-BN like on HOPG and MoS2. On sapphire and oxidized diamond surfaces, we observed assemblies of standing-up molecular layers. Surface assembly is driven by surface electrostatic dipoles. Surface polarity is partially controlled using a hydrogenated diamond surface or totally screened by the deposition of a graphene layer on the sapphire surface. This results in a perfectly flat and organized SAM on graphene, which is ready for on-surface polymerization of long and isolated molecular wires under ambient conditions.

cited By 2; International audience; The electrical characterization of single-polymer chains on a surface is an important step towards novel molecular device development. The main challenge is the lack of appropriate atomically flat insulating substrates for fabricating single-polymer chains. Here, using atomic force microscopy, we demonstrate that the (0001) surface of an insulating hexagonal boron nitride (h-BN) substrate leads to a flat-lying self-assembled monolayer of diacetylene compounds. The subsequent heating or ultraviolet irradiation can initiate an on-surface polymerization process leading to the formation of long polydiacetylene chains. The frequency of photo-polymerization occurrence on h-BN(0001) is two orders of magnitude higher than that on graphite(0001). This is explained by the enhanced lifetime of the molecular excited state, because relaxation via the h-BN is suppressed due to a large band gap. We also demonstrate that on-surface polymerization on h-BN(0001) is possible even after the lithography process, which opens up the possibility of further electrical investigations.

We construct a gauge invariant action for the Neveu-Schwarz and Ramond sectors of open superstring field theory realizing a cyclic $A_\infty$ structure, providing the first complete and fully explicit solution to the classical Batalin-Vilkovisky master equation in superstring field theory. We also demonstrate the equivalence of our action to the Wess-Zumino-Witten-based construction of Kunitomo and one of the authors., 41 pages, added discussion of PCO in subsection 3.1

Although single-molecule electronic devices have been of great interest for several decades, the fabrication of practical circuits remains challenging due to the lack of reliable ways to wire individual molecules. On-surface synthesis of single conductive polymer chains will be a key technology to solve this problem. We already found that stimulating a molecular layer of diacetylene compound by the tip of scanning tunneling microscope (STM) could initiate chain polymerization. As a result, we could systematically fabricate a single conjugated polydiacetylene chain at designated positions. Subsequently, we developed a novel method (‘chemical soldering’) for connecting the conjugated polymer chains to single organic molecules. The connection of two polydiacetylene chains to a single phthalocyanine molecule was demonstrated. Nanoscale characteristics of the connection were also experimentally and theoretically investigated. Here, we briefly review tip-induced chain polymerization and the chemical soldering methods. This work will help to advance single-molecule electronics.

For the development of various molecular nanostructures such as single-molecule electronic circuits, it is very important to fix the molecular components at predetermined positions on a substrate. We report the fixation of the thiol derivatives dodecanethiol and (3-mercaptopropyl)trimethoxysilane (MPS) on a MoS2(0001) substrate at prefabricated sulfur vacancies. Scanning tunneling microscopy (STM) reveals the selective bonding of thiol groups to the Mo atoms at the vacancy defects. In addition, we report STM tip-induced dissociation of the S–C bond, which essentially results in the repair of the vacancy defects with sulfur atoms from the thiols. This is consistent with the high desulfurization reactivity of MoS2. Because of its structure and composition, MPS has a higher dissociation reactivity than that of dodecanethiol.

Key to single-molecule electronics is connecting functional molecules to each other using conductive nanowires. This involves two issues: how to create conductive nanowires at designated positions, and how to ensure chemical bonding between the nanowires and functional molecules. Here, we present a novel method that solves both issues. Relevant functional molecules are placed on a self-assembled monolayer of diacetylene compound. A probe tip of a scanning tunneling microscope is then positioned on the molecular row of the diacetylene compound to which the functional molecule is adsorbed, and a conductive polydiacetylene nanowire is fabricated by initiating chain polymerization by stimulation with the tip. Since the front edge of chain polymerization necessarily has a reactive chemical species, the created polymer nanowire forms chemical bonding with an encountered molecular element. We name this spontaneous reaction "chemical soldering". First-principles theoretical calculations are used to investigate the structures and electronic properties of the connection. We demonstrate that two conductive polymer nanowires are connected to a single phthalocyanine molecule. A resonant tunneling diode formed by this method is discussed.

Spontaneous chain polymerization of molecules initiated by a scanning tunneling microscope tip is studied with a focus on its rate-determining factors. Such chain polymerization that happens in self-assembled monolayers (SAM) of diacetylene compound molecules, which results in a π-conjugated linear polydiacetylene nanowire, varies in its rate P depending on domains in the SAM and substrate materials. While the arrangement of diacetylene molecules is identical in every domain on a graphite substrate, it varies in different domains on a MoS(2) substrate. This structural variation enables us to investigate how P is affected by molecular geometry. An important determining factor of P is the distance between two carbon atoms which are to be bound by polymerization reaction, R; as R decreases by 0.1 nm, P increases ∼2 times. P for a MoS(2) substrate is ∼4 times higher (with the same value of R) than that for a graphite substrate because of higher mobility of molecules. The exciting correlation of the chain polymerization rate to the geometrical structure of the diacetylene molecules brings a deeper understanding of the mechanism of chain polymerization kinetics. In addition, the fabrication of one-dimensional conjugated polymer nanowires on a semiconducting MoS(2) substrate as demonstrated here may be of immense importance in the realization of future molecular devices.

Chain polymerizations of diacetylene compound multilayer films on graphite substrates were examined with a scanning tunneling microscope (STM) at the liquid/solid interface of the phenyloctane solution. The first layer grew very quickly into many small domains. This was followed by the slow formation of the piled up layers into much larger domains. Chain polymerization on the topmost surface layer could be initiated by applying a pulsed voltage between the STM tip and the substrate, usually producing a long polymer of submicrometer length. In contrast, polymerizations on the underlying layer were never observed. This can be explained by a conformation model in which the polymer backbone is lifted up.

To realize novel nanodevices beyond today's silicon-based transistors, a method is needed that will allow us to create nanowires at designated positions. In this review article, we introduce our method for creating a conjugated polymer nanowire by initiating a chain polymerization of organic molecules using the tip of a scanning tunneling microscope. We have demonstrated this method using a self-ordered monomolecular layer of amphiphilic diacetylene compound adsorbed on a graphite surface. The termination of the chain polymerization can also be controlled by making an artificial defect in advance. [DOI: 10.1380/ejssnt.2004.99]

Chain polymerization of amphiphilic diacetylene compounds in a monomolecular layer on a graphite substrate can be observed and controlled at a nanometer scale using a scanning tunneling microscope (STM). The wavelength dependence of photoreactivity suggests that the graphite substrate sensitizes the photoreaction. The chain polymerization can be initiated not only by irradiating light, but also by applying stimulation using an STM tip. We can also control the termination of chain polymerization by an artificial defect, so that we can create a polydiacetylene nanowire of designated length at any designated position.

The chain polymerization in a monomolecular layer of unsaturated organic compounds on a surface is investigated using a scanning tunneling microscope (STM). We used self-ordered layers of 10,12-pentacosadiynoic acid or 10,12-nonacosadiynoic acid of diacetylene compounds on a graphite substrate. Ultraviolet light irradiation on the molecular layer induced the chain polymerization, and the created polymers can be clearly imaged by STM. The tunneling electrons from an STM tip can also excite a molecule, and the excited molecule initiates the extended chain reaction. The termination of chain reaction can also be controlled by making an artificial defect in advance using an STM tip. As a result, we can control the initiation and termination of chain polymerization with a spatial precision of the order of 1 nm.

Initiation and termination of chain polymerization of amphiphilic diacetylene compounds in a monomolecular layer on a graphite substrate were observed and controlled at nanometer scale using a scanning tunneling microscope (STM). A polydiacetylene molecule of a desired length, which has a unique molecular conformation, can be created at desired positions.

cited By 14; International audience; Bottom-up creation of huge molecular complexes by covalently interconnecting functional molecules and conductive polymers is a key technology for constructing nanoscale electronic circuits. In this study, we have created an array of molecule–polymer nanojunctions from C60 molecules and polydiacetylene (PDA) nanowires at designated positions on solid surfaces by controlling self-assemblies and intermolecular chemical reactions of molecular ingredients predeposited onto the surfaces. In the proposed method, the construction of each nanojunction spontaneously proceeds via two types of chemical reactions: a chain polymerization among self-assembled diacetylene compound molecules for creating a single PDA nanowire and a subsequent cycloaddition reaction between the propagating forefront part of the PDA backbone and a single C60 molecule adsorbed on the surface. Scanning tunneling microscopy has proved that the C60 molecule is covalently connected to each end of the π-conjugated PDA backbone. Furthermore, the decrease in the energy gap of the C60 molecule in nanojunctions is observed as compared with that of pristine C60 molecules, which is considered to be due to the covalent interaction between the PDA edge and the C60 molecule.

A conjugated polymer nanowire can be created at any designated position in a monomolecular layer by initiating chain polymerization using a scanning tunneling microscope tip with a spatial precision of the order of 1 nm. The demonstration has been presented for a self-ordered monomolecular layer of 10,12-pentacosadiynoic acid, which is a diacetylene compound, adsorbed on a graphite surface. The polymer nanowires created have a length ranging from 5 to 300 nm, the length being controlled by domain boundaries or artificial defects in the molecular layer. The frequency of occurrence of chain polymerization is measured against the pulsed bias voltage, which suggests that the excitation of the molecule is caused by the inelastically tunneling electrons.

The one-loop effective action for general trajectories of D-particles in Matrix theory is calculated in the expansion with respect to the number of derivatives up to six, which gives the equation of motion consistently. The result shows that the terms with six derivatives vanish for straight-line trajectories, however, they do not vanish in general. This provides a concrete example that non-renormalization of twelve-fermion terms does not necessarily imply that of six-derivative terms., 18 pages, LaTeX2e, no figures, v2: a coefficient in (3.32) and the corresponding one in (3.33) corrected and a minor change

Aggregation of Cu and Ni adatoms on oxygen preadsorbed Cu(100) was studied by STM. Cu deposited on a Cu(100) c(2×2)-O surface agglomerate into anisotropic islands with a (2 2 × 2 )R45°-O structure, while Ni deposited on a c(2×2)-O surface forms isotropic Ni islands with c(2×2)-O structure. On the other hand, Ni on a (2 2 × 2 )R45°-O structure undergoes extremely anisotropic aggregation, which forms Ni-wires with a c(2×2)-O structure. Formation of Ni-wire on a (2 2 × 2 )R45°-O structure has been inferred by a preferential nucleation along the Cu atom missing trough inlaid with Ni.

Nano-scale patterning of the metal surfaces was attained by the adsorption and the reaction of metal atoms. Growth of metal islands on the metal surfaces was markedly influenced by preparing the surface with preadsorption and/or by the reconstruction. Adsorption of oxygen on Cu(100) form randomly coalesced nano-size c(2 x 2)-O which undergoes the (2√2 x √2)R45° reconstruction with increasing the oxygen coverage. In contrast, N-atoms on Cu(100) make well ordered array of squared c(2 X 2)-N patches of ca. 50 A 2 . Cu atoms deposited on the nano-size c(2 X 2)-O Cu(100) form one atomic height rectangular Cu islands but Ni atoms undergo no orientational growth of Ni islands. Ni atoms deposited on the (2√2 x √2)R45°-C Cu(100) surface, however, gave an extremely anisotropic growth of Ni-wire. In contrast, when Ni atom was deposited on a Cu(100) surface having a super-grid like pattem made by the boundaries of squared c(2 x 2)-N patches, one atomic height Ni islands grew at the crossings of the super-grid. These phenomena are distinctive from the chemical reaction of surface atoms which provides various quasi-compounds. The reaction of Cu with (-Ag-O-) strings on Ag(110) provided a new quasi-compound of (-Cu-O-) on Ag(110), which undergoes a reversible reaction of (-Cu-O-)⇄ (Cu) 6 + O 2 . In addition, the (-Ag-O-) strings on Ag(110) undergo selective photo-erasing. These results suggest that chemical reaction is a promising tool for making atomic-scale pattern on the surface.

Oxygen adsorbed on Cu(100) induces results in phase coalesced nano-sized c(2×2)-O domains with high density of anti-phase domain boundaries when the coverage is lower than ca. 0.3 ML. When the coverage exceeds 0.3 ML, however, large c(2×2)-O domains are formed among the nano-sized c(2×2)-O domains, that is, two nano-sized c(2×2)-O domains are coalesced into one large c(2×2)-O domain by adsorbing oxygen at a boundary. Interestingly, one-by-one release of Cu atoms is brought about on the large c(2×2)-O domain and the (2 2 × 2 ) R 45°− O reconstruction is established, where a large c(2×2)-O domain is a transitive phase to the (2 2 × 2 )R45°−O reconstruction. When Cu atoms are deposited on a nano-sized c(2×2)-O Cu(100) surface, rectangular Cu islands with (2 2 × 2 )R45°−O structure are grown in the [010] and [001] directions. These phenomena are well rationalized by the stress induced by the adsorption of oxygen four-fold hollow sites.

A (–Cu–O–) string on a Ag(110) surface defined by scanning tunneling microscopy (STM) was studied using the x-ray photoelectron spectroscopy (XPS), high resolution electron energy loss spectroscopy (HREELS). These data give the information about bonding properties which cannot be derived from the STM images. The combinative studies could show the structure as well as the growth mechanism of (–Cu–O–) strings on the Ag(110) surface. Deposition of Cu atoms on a p(2×1)-O Ag(110) surface resulted in a new O(1s) peak at 529.9 eV in the XPS and a new electron energy loss peak at 35 meV in the HREELS. These new peaks are assignable to the (Cu–O) bonding state on Ag(110), which is corresponding to the growth of new (–Cu–O–) strings in the [110] direction shown by the STM. These results suggest a stoichiometric reaction producing (–Cu–O–) strings according to an equation of (–Ag–O–)+Cu→(–Cu–O–)+Ag on the Ag(110) surface. The fact that the Ag atoms released by the chemical reaction make layered Ag islands and the (...

Adsorption of an oxygen atom at the four-fold hollow site of a Cu(100) surface forces the displacement of the nearest four Cu atoms laterally away from the oxygen atom, which induces stress in the substrate surface. When oxygen coverage exceeds a critical value (ca 0.3 ML), Cu atoms are regularly missed and the (2√2 × √2)R45° reconstruction is established. Contrary to this, when a Cu(110) surface is exposed to O2, the chemical reaction of Cu atoms produces a quasi-compound of (CuO) strings along the [001] direction which have a tendency to agglomerate into a (2 × 1) structure. The reconstruction assisted by chemical reaction is called “chemical reconstruction”. By reacting a quasi-compound of (AgO) strings on Ag(110) with Cu atoms, a (CuO) string grows on the Ag(110) surface in a zigzag manner along the [110] direction. The new quasi-compound of (CuO) strings grown on the Ag(110) surface undergo a reversible reaction of (CuO)⇄(Cu)6+O2. It was found that the chemical transportation of Cu atoms from a W-tip onto the Ag(110) surface is also assisted by the formation of a quasi-compound. Photo chemical reaction of quasi-compounds suggested the feasibility of the nano-scale photo fabrication of the surface.

An idea of the chemical reconstruction caused by the formation of quasi-compounds and their self-assembly is defined. New surfaces were fabricated by combining the reaction of the quasi-compounds and their self-assembly. A quasi-compound of (CuO) strings was grown in the [110] direction on Ag(110) by the reaction of (AgO) strings with Cu atoms, which brought about a reversible reaction of (CuO)⇄(Cu)6+O2. By the reaction of (AgO) strings with CO2, a composite structure of (AgO) and (AgCO3) was established on the Ag(110) surface. When Cu atoms were vaporized on this composite surface, the (AgO) strings reacted selectively with Cu atoms, and (CuO) strings grew in the [110] direction. Interestingly, an opposite selective reaction occurred when the composite surface was scanned with a W tip coated with Cu; that is, Cu atoms react selectively with carbonate species. These phenomena suggest that the chemical reaction and the chemical transportation reaction will make realize atomic scale surface fabrication possible. The photochemical reaction of a quasi-compound was also attained on a composite surface of (AgO) and (Ag2N) strings on the Ag(110) surface, where the (AgO) strings were selectively erased by illumination.

Oxygen-induced reconstruction of a PtRh(100) alloy surface was studied by scanning tunneling microscopy (STM). When a clean Pt-enriched PtRh(100) surface was exposed to O2 at more than 600 K, oxygen-induced reconstruction took place with segregation of Rh atoms to the surface. Depending on the coverage of oxygen, two types of reconstruction on the PtRh(100) alloy surface are induced. A p(3 × 1)-O structure appeared at relatively low oxygen coverage, and the TPD spectrum of the p(3 × 1)-O surface gave a desorption peak of O2 at ca. 930 K. The p(3 × 1)-O structure showed several different STM images depending on the tip condition, from which we could distinguish the two component metals, RhO rows and Pt rows. Based on this, a model structure was deduced. At a high oxygen coverage, more Rh atoms were segregated to the surface and the STM image suggests a c(2 × 20)-O structure. The c(2 × 20)-O surface changed into the p(3 × 1)-O by heating with the concomitant desorption of O2 at ca. 830 K. The STM images for this c(2 × 20)-O surface is analogous to the arrangement of Rh atoms on the top layer of a Rh(111) hexagonal lattice. Due to the lattice mismatch between the quasi-Rh(111) overlayer and PtRh(100) substrate, a moire pattern with 20 times periodicity along the 〈111〉 directions was observed. Both the p(3 × 1)-O and c(2 × 20)-O surfaces are easily reduced by H2 even at room temperature.

CH 2 (a) species are mainly formed by the hydrogenation of a (1 × 1) submonolayer of carbidic carbon on a Ni(100) surface with H 2 , but CH(a) species are predominantly formed when a p4g(2 × 2) carbide on Ni(100) is hydrogenated with H atoms. The p4g(2 × 2) structure is relaxed into a c(2 × 2) structure by forming CH species, and this c(2 × 2) structure accelerates the formation of two-dimensional graphite on the Ni(100) surface.

We found before that a stimulation with the probe tip of a scanning tunneling microscope (STM) could initiate a chain polymerization of diacetylene compound. Based on these previous studies, here we report a novel method for single molecular wiring, which we call “chemical soldering.” This method enables us to connect single conjugated polymer chains to single functional molecules, which would be an important step in advancing the development of single-molecule electronic circuitry.

Ordered arrays of metal nanoparticles are important for nanoelectronic and nanophotonic applications. Here, we report the formation of self-assembled arrays of gold nanoparticles on molecular layers of diacetylene compounds on a MoS2(0001) substrate. The arrangement of gold nanoparticles is observed using scanning tunneling microscopy. When gold is deposited on a self-assembled monolayer of 10,12-nonacosadiynoic acid or 10,12-octadecadiynoic acid on a MoS2(0001) substrate, the ordered array of diacetylene moieties in the molecular layer serves as a template for the formation of ordered arrays of gold nanoparticles. In contrast, when gold is deposited on a pristine MoS2(0001) surface or on a molecular layer of stearic acid, the gold nanoparticles are randomly distributed on the surface. It is found that the arrangement of gold nanoparticles is largely determined by the deposition rate; faster deposition results in more ordered arrays of gold nanoparticles. Our observations confirm the role of unsaturated π systems in molecules acting as a template for the regular arrangement of gold nanoparticles; this work will open up new possibilities for interfacial nanoarchitectonics.

The Berkovits formulation of open superstring field theory is based on the large Hilbert space of the superconformal ghost sector. We discuss its relation to the Witten formulation based on the small Hilbert space. We introduce a one-parameter family of conditions for partial gauge fixing of the Berkovits formulation such that the cubic interaction of the theory under the partial gauge fixing reduces to that of the Witten formulation in a singular limit. The local picture-changing operator at the open-string midpoint in the Witten formulation is regularized in our approach, and the divergence in on-shell four-point amplitudes coming from collision of picture-changing operators is resolved. The quartic interaction inherited from the Berkovits formulation plays a role of adjusting different behaviors of the picture-changing operators in the $s$ channel and in the $t$ channel of Feynman diagrams with two cubic vertices, and correct amplitudes in the world-sheet theory are reproduced. While gauge invariance at the second order in the coupling constant is obscured in the Witten formulation by collision of picture-changing operators, it is well defined in our approach and is recovered by including the quartic interaction inherited from the Berkovits formulation., Comment: 50 pages, 2 figures; v2: references added, minor changes, version published in JHEP

Oxygen-induced p(3 × 1) reconstruction of a Pt 0.25 Rh 0.75 (100) alloy surface was studied by scanning tunneling microscopy (STM). When a Pt-enriched (1 × 1) PtRh(100) alloy surface was exposed to O 2 , a clear p(3 × 1) LEED pattern appeared at temperatures higher than ca. 400 K, and segregation of Rh atoms was observed by STM. Once the p(3 × 1) PtRh(100) surface is established at T ≥ 400 K, a reversible interconversion, p(3 × 1)→p(1 × 1) by H 2 and p(1 × 1)→p(3 × 1) by O 2 , is brought about at room temperature. The p(3 × 1) surface showed three different STM images, depending on the tip condition, from which a model structure was deduced. The first formation of the p(3 × 1) structure requires the segregation of Rh atoms, but the interconversion between the p(3 × 1) and p(1 × 1) structures is responsible for the oxygen-induced array of Rh atoms along the 〈011tdirections.

Fine gold particles grown on the electrode in various acid solutions at different electrode potentials have been studied by means of transmission electron microscopy. It was found that the octahedral f.c.c. single crystal particles are grown at positive electrode potentials (SCE), but the pentagonal decahedron and hexagonal icosahedron particles are grown preferentially at negative electrode potentials (SCE). Different shapes and structures of gold particles formed at different electrode potentials are attributed to the surface energy of the growing particles, which may be influenced by the electrode potential. The (1 × 1) structure may correspond to lower surface energy structure at positive electrode potentials, but the surface at negative electrode potentials prefers to take the hexagonal arrangement of the atoms to lower the surface energy. Anions showed different influences on the growth of particles, so the effect of anions is discussed in this paper.

A p(2×3)-N Ag(110) surface obtained by N+ and/or N2+ ion bombardment gave a desorption peak of N2 at 530 K. When this p(2×3)-N Ag(110) surface was exposed to O2 at room temperature, the LEED patter...

The formation of carbonate species by a reaction of AgO added rows with CO2 was investigated by scanning tunneling microscopy (STM). STM observation during the reaction revealed that the AgO added rows were compressed from a (4 × 1) to a (2 × 1) phase, according to the growth of carbonate domains. Though the carbonate domains give a (1 × 2) diffraction pattern, STM images of this domain do not show a (1 × 2) structure, which indicates that the Ag substrate reconstructs to a (1 × 2) structure. Though the CO3 species thermally decompose at a lower temperature than AgO added rows, the AgO added rows can be selectively decomposed by ultraviolet irradiation.

An ordered alloy surface of Pt 3 Co(100) has been studied by low energy electron diffraction (LEED), Auger electron spectroscopy (AES), thermal desorption spectroscopy (TDS) and temperature programmed reaction (TPR). The clean surface exhibited a c(2 × 2) LEED structure, when the sample was carefully annealed at temperatures lower than the critical temperature for order-disorder transition of the bulk. With NO adsorption, the surface structure was reconstructed to a (1 × 1) LEED structure and was changed back to the c(2 × 2) structure by reaction with hydrogen at 500 K. From the results of LEED and AES studies combined with the H 2 + D 2 → 2HD reaction, it was deduced that the reconstructed (1 × 1) surface is terminated by a Pt-enriched layer, and that the clean c(2 × 2) surface reveals an ordered PtCo outmost layer. Furthermore, compared with the reaction of N 2 O and the adsorption of nitrogen activated by high frequency discharge, it was shown that the surface reconstruction originated from adsorbed surface nitrogen and not from surface oxygen.

Growth of Cu O chains and their ordering on Ag(110) surface were monitored by scanning tunneling microscopy (STM). When Cu atoms were deposited on a (2 × 1)Ag O/Ag(110) surface at room temperature, the Ag O chains in the [001] direction diminished and new strings of Cu O grew along the [110] direction and yield a (2 × 2) p2mg ordering. When a Ag(110) surface with coexisting Ag O and Cu O chains was exposed to CO at room temperature, the Ag O chains were selectively reduced.

A simple, statistical-mechanical model is introduced to analyze fluctuating rows of adatoms observed on the oxygen adsorbed Ag(110) surface. By assuming that the fluctuations occur in thermal equilibrium, it is shown that the average sizes of straight segments of fluctuating rows provide certain information on the effective interaction between adatoms.

The (AgO) chains grown along the 〈001〉 direction on Ag(110) disappeared by the reaction with Cu atoms at room temperature, and new one-dimensional chains grew in the 〈110〉 direction. The STM images at different bias potentials suggest the growth of (CuO) chains in the 〈110〉 direction on the Ag(110) surface. The (CuO) chains on the Ag(110) surface disappeared by heating to 470 K, but they reappeared by exposing to O2 at room temperature.

The crystal characteristics of gold particles grown on an amorphous carbon film in a 10−3–10−5 M HAuCl4 solution at different electrode potentials have been studied by means of electron microscopy and electron diffraction. The results show that the gold particles grown at different electrode potentials have different shapes, i.e., the particles formed at negative potential (versus SCE) consist mainly of icosahedral and decahedral particles, while at positive potential (versus SCE) fcc octahedral single crystal particles are dominant. Decahedral particles grown to 80 nm and icosahedral particles grown to 32 nm were observed at negative potentials. At positive potentials the icosahedral and decahedral particles only grew to about 10 nm. From these results it is clear that at negative potentials the gold particles prefer the growth of decahedral and icosahedral structures, but at positive potentials the fcc crystal structure is preferred. The characteristics of the gold particles depend upon the electrode potential at which the particles are grown, but it is not influenced by the concentration of the HAuCl4 electrolyte. The results will be discussed in relation to the potential-dependent surface reconstruction of Au(111), Au(110) and Au(100) surfaces.

We construct a complete action for open superstring field theory that includes the Neveu-Schwarz sector and the Ramond sector. For the Neveu-Schwarz sector, we use the string field in the large Hilbert space of the superconformal ghost sector, and the action in the Neveu-Schwarz sector is the same as the Wess-Zumino-Witten-like action of the Berkovits formulation. For the Ramond sector, it is known that the BRST cohomology on an appropriate subspace of the small Hilbert space reproduces the correct spectrum, and we use the string field projected to this subspace. We show that the action is invariant under gauge transformations that are consistent with the projection for the string field in the Ramond sector.

The WZW form of open superstring field theory has linearized gauge invariances associated with the BRST operator Q and the zero mode η [subscript 0] of the picture minus-one fermionic superconformal ghost. We discuss gauge fixing of the free theory in a simple class of gauges using the Faddeev-Popov method. We find that the world-sheet ghost number of ghost and antighost string fields ranges over all integers, except one, and at any fixed ghost number, only a finite number of picture numbers appear. We calculate the propagators in a variety of gauges and determine the field-antifield content and the free master action in the Batalin-Vilkovisky formalism. Unlike the case of bosonic string field theory, the resulting master action is not simply related to the original gauge-invariant action by relaxing the constraint on the ghost and picture numbers., United States. Dept. of Energy (Cooperative rRsearch Agreement DE-FG02-05ER41360.)