Surface x-ray scattering and scanning tunneling microscopy studies at the Au(111) electrode

International Nuclear Information System (INIS)

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

1993-01-01

This chapter reviews Surface X-ray Scattering and Scanning Tunneling Microscopy results carried out at the Au(111) surface under electrochemical conditions. Results are presented for the reconstructed surface, and for bromide and thallium monolayers. These examples are used to illustrate the complementary nature of the techniques

Vanadium and molybdenum oxide thin films on Au(111). Growth and surface characterization

Energy Technology Data Exchange (ETDEWEB)

Guimond, Sebastien

2009-06-04

The growth and the surface structure of well-ordered V{sub 2}O{sub 3}, V{sub 2}O{sub 5} and MoO{sub 3} thin films have been investigated in this work. These films are seen as model systems for the study of elementary reaction steps occurring on vanadia and molybdena-based selective oxidation catalysts. It is shown that well-ordered V{sub 2}O{sub 3}(0001) thin films can be prepared on Au(111). The films are terminated by vanadyl groups which are not part of the V{sub 2}O{sub 3} bulk structure. Electron irradiation specifically removes the oxygen atoms of the vanadyl groups, resulting in a V-terminated surface. The fraction of removed vanadyl groups is controlled by the electron dose. Such surfaces constitute interesting models to probe the relative role of both the vanadyl groups and the undercoordinated V ions at the surface of vanadia catalysts. The growth of well-ordered V{sub 2}O{sub 5}(001) and MoO{sub 3}(010) thin films containing few point defects is reported here for the first time. These films were grown on Au(111) by oxidation under 50 mbar O{sub 2} in a dedicated high pressure cell. Contrary to some of the results found in the literature, the films are not easily reduced by annealing in UHV. This evidences the contribution of radiation and surface contamination in some of the reported thermal reduction experiments. The growth of ultrathin V{sub 2}O{sub 5} and MoO{sub 3} layers on Au(111) results in formation of interface-specific monolayer structures. These layers are coincidence lattices and they do not correspond to any known oxide bulk structure. They are assumed to be stabilized by electronic interaction with Au(111). Their formation illustrates the polymorphic character and the ease of coordination units rearrangement which are characteristic of both oxides. The formation of a second layer apparently precedes the growth of bulk-like crystallites for both oxides. This observation is at odds with a common assumption that crystals nucleate as soon as a

Vanadium and molybdenum oxide thin films on Au(111). Growth and surface characterization

International Nuclear Information System (INIS)

Guimond, Sebastien

2009-01-01

The growth and the surface structure of well-ordered V 2 O 3 , V 2 O 5 and MoO 3 thin films have been investigated in this work. These films are seen as model systems for the study of elementary reaction steps occurring on vanadia and molybdena-based selective oxidation catalysts. It is shown that well-ordered V 2 O 3 (0001) thin films can be prepared on Au(111). The films are terminated by vanadyl groups which are not part of the V 2 O 3 bulk structure. Electron irradiation specifically removes the oxygen atoms of the vanadyl groups, resulting in a V-terminated surface. The fraction of removed vanadyl groups is controlled by the electron dose. Such surfaces constitute interesting models to probe the relative role of both the vanadyl groups and the undercoordinated V ions at the surface of vanadia catalysts. The growth of well-ordered V 2 O 5 (001) and MoO 3 (010) thin films containing few point defects is reported here for the first time. These films were grown on Au(111) by oxidation under 50 mbar O 2 in a dedicated high pressure cell. Contrary to some of the results found in the literature, the films are not easily reduced by annealing in UHV. This evidences the contribution of radiation and surface contamination in some of the reported thermal reduction experiments. The growth of ultrathin V 2 O 5 and MoO 3 layers on Au(111) results in formation of interface-specific monolayer structures. These layers are coincidence lattices and they do not correspond to any known oxide bulk structure. They are assumed to be stabilized by electronic interaction with Au(111). Their formation illustrates the polymorphic character and the ease of coordination units rearrangement which are characteristic of both oxides. The formation of a second layer apparently precedes the growth of bulk-like crystallites for both oxides. This observation is at odds with a common assumption that crystals nucleate as soon as a monolayer is formed dur-ing the preparation of supported vanadia

Voltammetry and Electrocatalysis of Achrornobacter Xylosoxidans Copper Nitrite Reductase on Functionalized Au(111)-Electrode Surfaces

DEFF Research Database (Denmark)

Welinder, Anna C.; Zhang, Jingdong; Hansen, Allan G.

2007-01-01

A long-standing issue in protein film voltammetry (PFV), particularly electrocatalytic voltammetry of redox enzyme monolayers, is the variability of protein adsorption modes, reflected in distributions of catalytic activity of the adsorbed protein/enzyme molecules. Use of well-defined, atomically...... planar electrode surfaces is a step towards the resolution of this central issue. We report here the voltammetry of copper nitrite reductase (CNiR, Achromobacter xylosoxidons) on Au(111)-electrode surfaces modified by monolayers of a broad variety of thiol-based linker molecules. These represent......NiR thus shows highly efficient, close to ideal reversible electrocatalytic voltammetry on cysteamine-covered Au(111)-electrode surfaces, most likely due to two cysteamine orientations previously disclosed by in situ scanning tunnelling microscopy. Such a dual orientation exposes both a hydrophobic...

Mesoscopic self-organization of a self-assembled supramolecular rectangle on highly oriented pyrolytic graphite and Au(111) surfaces.

Science.gov (United States)

Gong, Jian-Ru; Wan, Li-Jun; Yuan, Qun-Hui; Bai, Chun-Li; Jude, Hershel; Stang, Peter J

2005-01-25

A self-assembled supramolecular metallacyclic rectangle was investigated with scanning tunneling microscopy on highly oriented pyrolytic graphite and Au(111) surfaces. The rectangles spontaneously adsorb on both surfaces and self-organize into well ordered adlayers. On highly oriented pyrolytic graphite, the long edge of the rectangle stands on the surface, forming a 2D molecular network. In contrast, the face of the rectangle lays flat on the Au(111) surface, forming linear chains. The structures and intramolecular features obtained through high-resolution scanning tunneling microscopy imaging are discussed.

Evolution of magnetism of Cr nanoclusters on a Au(111) surface

Science.gov (United States)

Gotsis, Harry; Kioussis, Nicholas; Papaconstantopoulos, Dimitri

2004-03-01

Advances in low-temperature scanning tunneling microscopy under ultrahigh vacuum have provided new opportunities for investigating the magnetic structures of nanoclusters adsorbed on surfaces. Recent STM studies of Cr trimers on the Au(111) surface suggest a switching between two distinct electronic states. We have carried out ab initio electronic structure calculations to investigate the structural, electronic and magnetic properties of isolated Cr atoms, Cr dimers and trimers in different geometry. We will present results for the evolution of magnetic behavior including noncollinear magnetism and provide insight in the connection between magnetism and geometry.

Interfacial Electrochemical Electron Transfer Processes in Bacterial Biofilm Environments on Au(111)

DEFF Research Database (Denmark)

Hu, Yifan; Zhang, Jingdong; Ulstrup, Jens

2010-01-01

We have studied Streptococcus mutans (S. mutans) biolilm growth and growth inhibition on Au(111)-surfaces using atomic force microscopy (AFM) and interfacial electrochemistry of a number of redox probe molecules. AFM of the biofilm growth and growth inhibition on both mica and Au(111)-surfaces wa...

A first principles study on the electronic origins of silver segregation at the Ag-Au (111) surface

Science.gov (United States)

Hoppe, Sandra; Müller, Stefan

2017-12-01

The special electronic structure of gold gives rise to many interesting phenomena, such as its color. The surface segregation of the silver-gold system has been the subject of numerous experimental and theoretical studies, yielding conflicting results ranging from strong Ag surface enrichment to Au surface segregation. Via a combined approach of density functional theory (DFT) and statistical physics, we have analyzed the segregation at the Ag-Au (111) surface with different Ag bulk concentrations. Interestingly, we observe a moderate Au surface segregation, which is due to a charge transfer from the less electronegative Ag to Au. Canonical Monte Carlo simulations suggest that the calculated concentration profile with a Au-enriched surface layer remains stable up to higher temperatures. However, the presence of adsorbed oxygen reverses the segregation behavior and leads to strong Ag enrichment of the surface layer.

Hydrogen evolution on Au(111) covered with submonolayers of Pd

DEFF Research Database (Denmark)

Björketun, Mårten; Karlberg, Gustav; Rossmeisl, Jan

2011-01-01

A theoretical investigation of electrochemical hydrogen evolution on Au(111) covered with submonolayers of Pd is presented. The size and shape of monoatomically high Pd islands formed on the Au(111) surface are determined using Monte Carlo simulations, for Pd coverages varying from 0.02 to 0.95 ML....... The energetics of adsorption and desorption of hydrogen on/from different types of sites on the Pd-Au(111) surface are assessed by means of density functional theory calculations combined with thermodynamic modeling. Based on the density functional and Monte Carlo data, the hydrogen evolution activity...... is evaluated with a micro-kinetic model. The analysis reproduces measured Pd-coverage-dependent activities for Pd submonolayers exceeding similar to 0.15 ML and enables the relative contributions from different types of electrocatalytically active sites to be determined. Finally, the implications of surface...

Adsorption and switching properties of a N-benzylideneaniline based molecular switch on a Au(111) surface

International Nuclear Information System (INIS)

Ovari, Laszlo; Luo, Ying; Haag, Rainer; Leyssner, Felix; Tegeder, Petra; Wolf, Martin

2010-01-01

High resolution electron energy loss spectroscopy has been employed to analyze the adsorption geometry and the photoisomerization ability of the molecular switch carboxy-benzylideneaniline (CBA) adsorbed on Au(111). CBA on Au(111) adopts a planar (trans) configuration in the first monolayer (ML) as well as for higher coverages (up to 6 ML), in contrast to the strongly nonplanar geometry of the molecule in solution. Illumination with UV light of CBA in direct contact with the Au(111) surface (≤1 ML) caused no changes in the vibrational structure, whereas at higher coverages (>1 ML) pronounced modifications of vibrational features were observed, which we assign to a trans→cis isomerization. Thermal activation induced the back reaction to trans-CBA. We propose that the photoisomerization is driven by a direct (intramolecular) electronic excitation of the adsorbed CBA molecules in the second ML (and above) analogous to CBA in the liquid phase.

Quantum tunneling in real space: Tautomerization of single porphycene molecules on the (111) surface of Cu, Ag, and Au

Science.gov (United States)

Kumagai, Takashi; Ladenthin, Janina N.; Litman, Yair; Rossi, Mariana; Grill, Leonhard; Gawinkowski, Sylwester; Waluk, Jacek; Persson, Mats

2018-03-01

Tautomerization in single porphycene molecules is investigated on Cu(111), Ag(111), and Au(111) surfaces by a combination of low-temperature scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations. It is revealed that the trans configuration is the thermodynamically stable form of porphycene on Cu(111) and Ag(111), whereas the cis configuration occurs as a meta-stable form. The trans → cis or cis → trans conversion on Cu(111) can be induced in an unidirectional fashion by injecting tunneling electrons from the STM tip or heating the surface, respectively. We find that the cis ↔ cis tautomerization on Cu(111) occurs spontaneously via tunneling, verified by the negligible temperature dependence of the tautomerization rate below ˜23 K. Van der Waals corrected DFT calculations are used to characterize the adsorption structures of porphycene and to map the potential energy surface of the tautomerization on Cu(111). The calculated barriers are too high to be thermally overcome at cryogenic temperatures used in the experiment and zero-point energy corrections do not change this picture, leaving tunneling as the most likely mechanism. On Ag(111), the reversible trans ↔ cis conversion occurs spontaneously at 5 K and the cis ↔ cis tautomerization rate is much higher than on Cu(111), indicating a significantly smaller tautomerization barrier on Ag(111) due to the weaker interaction between porphycene and the surface compared to Cu(111). Additionally, the STM experiments and DFT calculations reveal that tautomerization on Cu(111) and Ag(111) occurs with migration of porphycene along the surface; thus, the translational motion couples with the tautomerization coordinate. On the other hand, the trans and cis configurations are not discernible in the STM image and no tautomerization is observed for porphycene on Au(111). The weak interaction of porphycene with Au(111) is closest to the gas-phase limit and therefore the absence

Effects of chlorine and oxygen coverage on the structure of the Au(111) surface

International Nuclear Information System (INIS)

Baker, Thomas A.; Friend, Cynthia M.; Kaxiras, Efthimios

2009-01-01

We investigate the effects of Cl and O coverage on the atomic structure of the Au(111) surface using density functional theory calculations. We find that the release and incorporation of gold atoms in the adsorbate layer becomes energetically favorable only at high coverages of either O or Cl (>0.66 ML (monolayer) for O and >0.33 ML for Cl), whereas adsorption without the incorporation of gold is favorable at lower coverages. The bonding between the adsorbate and gold substrate changes significantly with coverage, becoming more covalent (less ionic) at higher Cl and O coverage. This is based on the fact that at higher coverages there is less ionic charge transfer to the adsorbate, while the electron density in the region between the adsorbate and a surface gold atom is increased. Our results illustrate that the O and Cl coverage on Au(111) can dramatically affect its structure and bonding, which are important features in any application of gold involving these adsorbates.

Electron induced conformational changes of an imine-based molecular switch on a Au(111) surface

Energy Technology Data Exchange (ETDEWEB)

Lotze, Christian; Henningsen, Nils; Franke, Katharina; Schulze, Gunnar; Pascual, Jose Ignacio [Inst. f. Experimentalphysik, Freie Universitaet Berlin (Germany); Luo, Ying; Haag, Rainer [Inst. f. Organische Chemie, Freie Universitaet Berlin (Germany)

2009-07-01

Azobenzene-based molecules exhibit a cis-trans configurational photoisomerisation in solution. Recently, the adsorption properties of azobenzene derivatives have been investigated on different metal surfaces in order to explore the possible changes in the film properties induced by external stimuli. In azobenzene, the diazo-bridge is a key group for the isomerization process. Its interaction with a metal surface is dominated through the N lone-pair electrons, which reduces the efficiency of the conformational change. In order to reduce the molecule-surface interaction, we explore an alternative molecular architecture by substituting the diazo-bridge (-N=N-) of azobenzene by an imine-group (-N=CH-). We have investigated the imine-based compound para-carboxyl-di-benzene-imine (PCI) adsorbed on a Au(111) surface. The carboxylic terminations mediates the formation of strongly bonded molecular dimers, which align in ordered rows preferentially following the fcc regions of the Au(111) herringbone reconstruction. Low temperature scanning tunneling microscopy was used to induce conformational changes between trans and cis state of individual molecules in a molecular monolayer.

Investigation of Streptococcus mutans biofilm growth on modified Au(111)-surfaces using AFM and electrochemistry

DEFF Research Database (Denmark)

Hu, Yifan; Zhang, Jingdong; Ulstrup, Jens

2011-01-01

Biofilms of the bacterium Streptococcus mutans constitute perhaps the most important direct cause of human dental caries formation. We have studied S. mutans biofilm formation and properties on Au(111)-surfaces modified by self-assembled molecular monolayers (SAMs) of different thiol-based molecu...

Solvent effects on the adsorption and self-organization of Mn12 on Au(111).

Science.gov (United States)

Pineider, Francesco; Mannini, Matteo; Sessoli, Roberta; Caneschi, Andrea; Barreca, Davide; Armelao, Lidia; Cornia, Andrea; Tondello, Eugenio; Gatteschi, Dante

2007-11-06

A sulfur-containing single molecule magnet, [Mn12O12(O2CC6H4SCH3)16(H2O)4], was assembled from solution on a Au(111) surface affording both submonolayer and monolayer coverages. The adsorbate morphology and the degree of coverage were inspected by scanning tunneling microscopy (STM), while X-ray photoelectron spectroscopy (XPS) allowed the determination of the chemical nature of the adsorbate on a qualitative and quantitative basis. The properties of the adsorbates were found to be strongly dependent on the solvent used to dissolve the magnetic complex. In particular, systems prepared from tetrahydrofuran solutions gave arrays of isolated and partially ordered clusters on the gold substrate, while samples prepared from dichloromethane exhibited a homogeneous monolayer coverage of the whole Au(111) surface. These findings are relevant to the optimization of magnetic addressing of single molecule magnets on surfaces.

Atom distribution and interactions in Ag{sub x}Pt{sub 1-x} and Au{sub x}Pt{sub 1-x} surface alloys on Pt(111)

Energy Technology Data Exchange (ETDEWEB)

Roetter, Ralf T.; Bergbreiter, Andreas; Hoster, Harry E.; Behm, R. Juergen [Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm (Germany)

2009-07-01

The atom distributions in Ag{sub x}Pt{sub 1-x}/Pt(111) and Au{sub x}Pt{sub 1-x}/Pt(111) surface alloys were studied by high resolution UHV-STM. These surfaces were prepared by submonolayer Ag (Au) metal deposition on Pt(111), followed by annealing at 900 K or 1000 K, respectively, which in both cases results in surface confined 2D alloys, with equilibrated distribution of the components. Both systems show a tendency towards two-dimensional clustering, which fits well to their known bulk immiscibility. Effective cluster interactions (ECIs) will be derived by a quantitative evaluation of the 2D atom distributions in the surface alloys. By comparing the ECIs for PtAg and PtAu on Pt(111), and considering that Ag and Au have almost similar lattice constants, the results allow conclusion on the physical origin of the tendency for clustering.

Coverage dependent molecular assembly of anthraquinone on Au(111)

Science.gov (United States)

DeLoach, Andrew S.; Conrad, Brad R.; Einstein, T. L.; Dougherty, Daniel B.

2017-11-01

A scanning tunneling microscopy study of anthraquinone (AQ) on the Au(111) surface shows that the molecules self-assemble into several structures depending on the local surface coverage. At high coverages, a close-packed saturated monolayer is observed, while at low coverages, mobile surface molecules coexist with stable chiral hexamer clusters. At intermediate coverages, a disordered 2D porous network interlinking close-packed islands is observed in contrast to the giant honeycomb networks observed for the same molecule on Cu(111). This difference verifies the predicted extreme sensitivity [J. Wyrick et al., Nano Lett. 11, 2944 (2011)] of the pore network to small changes in the surface electronic structure. Quantitative analysis of the 2D pore network reveals that the areas of the vacancy islands are distributed log-normally. Log-normal distributions are typically associated with the product of random variables (multiplicative noise), and we propose that the distribution of pore sizes for AQ on Au(111) originates from random linear rate constants for molecules to either desorb from the surface or detach from the region of a nucleated pore.

Oxygen-induced restructuring with release of gold atoms from Au(111)

International Nuclear Information System (INIS)

Min, B.K.; Deng, X.; Schalek, R.; Pinnaduwage, D.; Friend, C.M.

2005-01-01

Adsorption of oxygen atoms, achieved via electron-induced dissociation of nitrogen dioxide, induces restructuring of the 'herringbone' to a striped, soliton-wall structure accompanied by release of gold from the 'elbows' in the herringbone structure. The number density of 'elbows' (dislocations corresponding to a change in direction of the reconstruction) decreases as a function of increasing atomic oxygen coverage while the long range order observed in low energy electron diffraction (LEED) changes from (√(3)x22)-rec. to (1x22) in the limit of saturation coverage. Small islands and serrated step edges were formed due to the release of gold atoms from elbow sites of Au(111). The overall structural change of the Au(111) surface may result from the reduction of anisotropy related to the tensile stress relief of the Au(111) surface by oxygen atoms

Surface chemistry of 2-butanol and furfural on Cu, Au and Cu/Au single crystals

OpenAIRE

Megginson, Rory

2016-01-01

In this study, the adsorption of 2-butanol and furfural was investigated on Au (111), Cu (111) and Cu/Au (111) surfaces. It was hoped that by studying how these species adsorbed on these surfaces , insight would be provided into the roles of Cu and Au in the “hydrogen free” hydrogenation of furfural to furfuryl alcohol. This is a valuable process as currently furfuryl alcohol is derived from crude oil but it is possible to derive furfural from corn husk making it a greener process...

Extraordinary epitaxial alignment of graphene islands on Au(111)

International Nuclear Information System (INIS)

Wofford, Joseph M; Dubon, Oscar D; Starodub, Elena; Nie Shu; Bartelt, Norman C; Thürmer, Konrad; McCarty, Kevin F; Walter, Andrew L; Bostwick, Aaron; Rotenberg, Eli

2012-01-01

Pristine, single-crystalline graphene displays a unique collection of remarkable electronic properties that arise from its two-dimensional, honeycomb structure. Using in situ low-energy electron microscopy, we show that when deposited on the (111) surface of Au carbon forms such a structure. The resulting monolayer, epitaxial film is formed by the coalescence of dendritic graphene islands that nucleate at a high density. Over 95% of these islands can be identically aligned with respect to each other and to the Au substrate. Remarkably, the dominant island orientation is not the better lattice-matched 30° rotated orientation but instead one in which the graphene [01] and Au [011] in-plane directions are parallel. The epitaxial graphene film is only weakly coupled to the Au surface, which maintains its reconstruction under the slightly p-type doped graphene. The linear electronic dispersion characteristic of free-standing graphene is retained regardless of orientation. That a weakly interacting, non-lattice matched substrate is able to lock graphene into a particular orientation is surprising. This ability, however, makes Au(111) a promising substrate for the growth of single crystalline graphene films. (paper)

Manipulation and control of a single molecular rotor on Au (111) surface

International Nuclear Information System (INIS)

Hai-Gang, Zhang; Jin-Hai, Mao; Qi, Liu; Nan, Jiang; Hai-Tao, Zhou; Hai-Ming, Guo; Dong-Xia, Shi; Hong-Jun, Gao

2010-01-01

Three different methods are used to manipulate and control phthalocyanine based single molecular rotors on Au (111) surface: (1) changing the molecular structure to alter the rotation potential; (2) using the tunnelling current of the scanning tunnelling microscope (STM) to change the thermal equilibrium of the molecular rotor; (3) artificial manipulation of the molecular rotor to switch the rotation on or off by an STM tip. Furthermore, a molecular 'gear wheel' is successfully achieved with two neighbouring molecules. (cross-disciplinary physics and related areas of science and technology)

Surface Structures and Thermal Desorption Behaviors of Cyclopentanethiol Self-Assembled Monolayers on Au(111)

International Nuclear Information System (INIS)

Kang, Hun Gu; Kim, You Young; Park, Tae Sun; Noh, Jae Geun; Park, Joon B.; Ito, Eisuke; Hara, Masahiko

2011-01-01

The surface structures, adsorption conditions, and thermal desorption behaviors of cyclopentanethiol (CPT) self-assembled monolayers (SAMs) on Au(111) were investigated by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). STM imaging revealed that although the adsorption of CPT on Au(111) at room temperature generates disordered SAMs, CPT molecules at 50 .deg. C formed well-ordered SAMs with a (2√3 x √5)R41".deg. packing structure. XPS measurements showed that CPT SAMs at room temperature were formed via chemical reactions between the sulfur atoms and gold surfaces. TDS measurements showed two dominant TD peaks for the decomposed fragments (C_5H_9 "+, m/e = 69) generated via C-S bond cleavage and the parent molecular species (C_5H_9SH"+, m/e = 102) derived from a recombination of the chemisorbed thiolates and hydrogen atoms near 440 K. Interestingly, dimerization of sulfur atoms in n-alkanethiol SAMs usually occurs during thermal desorption and the same reaction did not happen for CPT SAMs, which may be due to the steric hindrance of cyclic rings of the CPT molecules. In this study, we demonstrated that the alicyclic ring of organic thiols strongly affected the surface structure and thermal desorption behavior of SAMs, thus providing a good method for controlling chemical and physical properties of organic thiol SAMs

Coexistence of multiple conformations in cysteamine monolayers on Au(111)

DEFF Research Database (Denmark)

Zhang, Jingdong; Bilic, A; Reimers, JR

2005-01-01

The structural organization, catalytic function, and electronic properties of cysteamine monolayers on Au(111) have been addressed comprehensively by voltammetry, in situ scanning tunneling microscopy (STM) in anaerobic environment, and a priori molecular dynamics (MD) simulation and STM image si...

Surface Structures and Thermal Desorption Behaviors of Cyclopentanethiol Self-Assembled Monolayers on Au(111)

Energy Technology Data Exchange (ETDEWEB)

Kang, Hun Gu; Kim, You Young; Park, Tae Sun; Noh, Jae Geun [Hanyang University, Seoul (Korea, Republic of); Park, Joon B. [Chonbuk National University, Jeonju (Korea, Republic of); Ito, Eisuke; Hara, Masahiko [RIKEN-HYU Collaboration Center, Saitama (Japan)

2011-04-15

The surface structures, adsorption conditions, and thermal desorption behaviors of cyclopentanethiol (CPT) self-assembled monolayers (SAMs) on Au(111) were investigated by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). STM imaging revealed that although the adsorption of CPT on Au(111) at room temperature generates disordered SAMs, CPT molecules at 50 .deg. C formed well-ordered SAMs with a (2√3 x √5)R41{sup .}deg. packing structure. XPS measurements showed that CPT SAMs at room temperature were formed via chemical reactions between the sulfur atoms and gold surfaces. TDS measurements showed two dominant TD peaks for the decomposed fragments (C{sub 5}H{sub 9} {sup +}, m/e = 69) generated via C-S bond cleavage and the parent molecular species (C{sub 5}H{sub 9}SH{sup +}, m/e = 102) derived from a recombination of the chemisorbed thiolates and hydrogen atoms near 440 K. Interestingly, dimerization of sulfur atoms in n-alkanethiol SAMs usually occurs during thermal desorption and the same reaction did not happen for CPT SAMs, which may be due to the steric hindrance of cyclic rings of the CPT molecules. In this study, we demonstrated that the alicyclic ring of organic thiols strongly affected the surface structure and thermal desorption behavior of SAMs, thus providing a good method for controlling chemical and physical properties of organic thiol SAMs.

Electrochemical Properties of Alkanethiol Monolayers Adsorbed on Nanoporous Au Surfaces

International Nuclear Information System (INIS)

Chu, Yeon Yi; Seo, Bora; Kim, Jong Won

2010-01-01

We investigated the electrochemical properties of alkanethiol monolayers adsorbed on NPG surfaces by cyclic voltammetry and electrochemical impedance spectroscopy, and the results are compared to those on flat Au surfaces. The reductive desorption of alkanethiols on NPG surfaces is observed in more negative potential regions than that on flat Au surfaces due the stronger S-Au interaction on NPG surfaces. While the electron transfer through alkanethiol monolayers on flat Au surfaces occurs via a tunneling process through the monolayer films, the redox species can permeate through the monolayers on NPG surfaces to transfer the electrons to the Au surfaces. The results presented here will help to elucidate the intrinsic electrochemical properties of alkanethiol monolayers adsorbed on curved Au surfaces, particularly on the surface of AuNPs. Self-assembled monolayers (SAMs) of thiolate molecules on Au surfaces have been the subject of intensive research for the last few decades due to their unique physical and chemical properties. The well-organized surface structures of thiolate SAMs with various end-group functionalities can be further utilized for many applications in biology and nanotechnology. In addition to the practical applications, SAMs of thiolate molecules on Au surfaces also provide unique opportunities to address fundamental issues in surface chemistry such as self-organized surface structures, electron transfer behaviors, and moleculesubstrate interactions. Although there have been numerous reports on the fundamental physical and chemical properties of thiolate SAMs on Au surfaces, most of them were investigated on flat Au surfaces, typically on well-defined Au(111) surfaces

Diffusion of 1,4-butanedithiol radicals on Au(111) and Au(100): A DFT-based comparison

Energy Technology Data Exchange (ETDEWEB)

Franke, Andreas; Pehlke, Eckhard [Institut fuer Theoretische Physik und Astrophysik, Universitaet Kiel, 24098 Kiel (Germany)

2010-07-01

Organic molecules chemisorbed on surfaces hold the perspective of surface functionalization. The 1,4-butanedithiol radical chemisorbed at the Au(111) or Au(100) surface serves as a model system for the S-Au molecule-substrate bond. Density functional total-energy calculations have been carried out for the chemisorption of the radical on the unreconstructed Au surfaces, which are both known to be stabilized under electrochemical conditions. Local minima with close-by energies indicate multi-valley potential-energy surfaces, which originate from the interplay between the two S-Au adsorbate-substrate bonds and the internal degrees of freedom of the butanedithiol radical. Diffusion paths of the radical on both Au surfaces have been calculated within DFT using VASP. The diffusion barriers for translation and rotation of the radical differ. They can be fine-tuned by varying the applied potential in the electrochemical cell. This is considered theoretically by inspecting the variation of the dipole moment along the reaction paths. Consequences for the dynamics of succeeding diffusion hops are discussed.

Substrate induced ordering of molecular adsorbates on Au(111)

International Nuclear Information System (INIS)

Schott, J.H.; White, H.S.; Arana, C.R.

1992-01-01

Using scanning tunneling microscopy in dimethylformate, [Ru(bpy) 2 (bpy-(CH 2 ) x -bpy) 2+ ] (x = 4 and 5) monolayers adsorbed on the unreconstructed and √3 x 22 reconstructed surfaces of Au(111) were imaged in this paper. The substrate had a highly ordered pattern on the reconstructed surface, but random spatial distribution on the unreconstructed surface. 17 refs., 3 figs

Controlling the stereochemistry and regularity of butanethiol self-assembled monolayers on Au(111)

DEFF Research Database (Denmark)

Yan, Jiawei; Ouyang, Runhai; Jensen, Palle Skovhus

2014-01-01

The rich stereochemistry of the self-assembled monolayers (SAMs) of four butanethiols on Au(111) is described, the SAMs containing up to 12 individual C, S, or Au chiral centers per surface unit cell. This is facilitated by synthesis of enantiomerically pure 2-butanethiol (the smallest unsubstitu......The rich stereochemistry of the self-assembled monolayers (SAMs) of four butanethiols on Au(111) is described, the SAMs containing up to 12 individual C, S, or Au chiral centers per surface unit cell. This is facilitated by synthesis of enantiomerically pure 2-butanethiol (the smallest...... when R is achiral, while adatom binding leads to rectangular plane groups that suppress long-range expression of chirality. Binding as RS• also inhibits the pitting intrinsically associated with adatom binding, desirably producing more regularly structured SAMs....

Annealing temperature effect on self-assembled Au droplets on Si (111).

Science.gov (United States)

Sui, Mao; Li, Ming-Yu; Kim, Eun-Soo; Lee, Jihoon

2013-12-13

We investigate the effect of annealing temperature on self-assembled Au droplets on Si (111). The annealing temperature is systematically varied while fixing other growth parameters such as deposition amount and annealing duration clearly to observe the annealing temperature effect. Self-assembled Au droplets are fabricated by annealing from 50°C to 850°C with 2-nm Au deposition for 30 s. With increased annealing temperatures, Au droplets show gradually increased height and diameter while the density of droplets progressively decreases. Self-assembled Au droplets with fine uniformity can be fabricated between 550°C and 800°C. While Au droplets become much larger with increased deposition amount, the extended annealing duration only mildly affects droplet size and density. The results are systematically analyzed with cross-sectional line profiles, Fourier filter transform power spectra, height histogram, surface area ratio, and size and density plots. This study can provide an aid point for the fabrication of nanowires on Si (111).

Molecular dynamics and energy landscape of decanethiolates in self-assembled monolayers on Au(111) by STM

NARCIS (Netherlands)

Sotthewes, Kai; Wu, Hairong; Kumar, Avijit; Vancso, Gyula J.; Schön, Peter Manfred; Zandvliet, Henricus J.W.

2013-01-01

The energetics and dynamics of the various phases of decanethiolate self-assembled monolayers on Au(111) surfaces were studied with scanning tunneling microscopy. We have observed five different phases of the decanethiolate monolayer on Au(111): four ordered phases (β, δ, χ*, and ) and one

RPBE-vdW Description of Benzene Adsorption on Au(111)

DEFF Research Database (Denmark)

Pedersen, Jess Wellendorff; Kelkkanen, Kari André; Mortensen, Jens Jørgen

2010-01-01

Density functional theory has become a popular methodology for the analysis of molecular adsorption on surfaces. Despite this popularity, there exist adsorption systems for which commonly used exchange-correlation functionals fail miserably. Particularly those systems where binding is due to van...... der Waals interactions. The adsorption of benzene on Au(111) is an often mentioned such system where standard density functionals predict a very weak adsorption or even a repulsion, whereas a significant adsorption is observed experimentally. We show that a considerable improvement in the description...... of the adsorption of benzene on Au(111) is obtained when using the so-called RPBE-vdW functional....

Potential-induced structural transitions of DL-homocysteine monolayers on Au(111) electrode surfaces

DEFF Research Database (Denmark)

Zhang, Jingdong; Demetriou, Anna; Welinder, Anne Christina

2005-01-01

Monolayers of homocysteine on Au(111)-surfaces have been investigated by voltammetry, in situ scanning tunnelling microscopy (STM) and subtractively normalised interfacial Fourier transform spectroscopy (SNIFTIRS). A pair of sharp voltammetric peaks build up in the potential range 0 to -0.1 V (vs...... potentials at pH 7.7. The molecules pack into highly ordered domains around the peak potential. High-resolution in situ STM reveals a (root 3 x 5) R30 degrees lattice with three homocysteine molecules in each unit cell. The adlayer changes into disordered structures on either side of the peak potential...

Ammonia synthesis on Au modified Fe(111) and Ag and Cu modified Fe(100) surfaces

DEFF Research Database (Denmark)

Lytken, Ole; Waltenburg, Hanne Neergaard; Chorkendorff, Ib

2003-01-01

In order to investigate any influence of steps and possible positive effects of making surface alloys the ammonia synthesis has been investigated over Au modified Fe(111) and Ag and Cu modified Fe(100) single crystals in the temperature range 603-773 K, using a system combining ultra-high vacuum...... and a high-pressure cell. Ammonia was synthesized from a stoichiometric (N-2:3H(2)) gas mixture at a pressure of 2 bar. By deposition of small amounts of An, the ammonia production activity of the Fe(1 1 1) surface can be enhanced. More important, for the gold modified surface, the reaction order in ammonia...

Monolayers of a De Novo Designed 4-Alpha-Helix Bundle Carboprotein and Partial Structures on Au(111)-Surfaces

DEFF Research Database (Denmark)

Brask, Jesper; Wackerbarth, Hainer; Jensen, Knud Jørgen

2002-01-01

on a galactopyranoside derivative with a thiol anchor aglycon suitable for surface immobilization on gold. The galactopyranoside with thiol anchor and the thiol anchor alone were prepared for comparison. Voltammetry of the three molecules on Au(111) showed reductive desorption peaks caused by monolayer adsorption via...... thiolate-Au bonding. In situ STM of the thiol anchor disclosed an ordered adlayer with clear domains and molecular features. This holds promise, broadly for single-molecule voltammetry and the SPM and scanning tunnelling microscopy (STM) of natural and synthetic proteins....

In situ STM imaging of the structures of pentacene molecules adsorbed on Au(111).

Science.gov (United States)

Pong, Ifan; Yau, Shuehlin; Huang, Peng-Yi; Chen, Ming-Chou; Hu, Tarng-Shiang; Yang, Yawchia; Lee, Yuh-Lang

2009-09-01

In situ scanning tunneling microscope (STM) was used to examine the spatial structures of pentacene molecules adsorbed onto a Au(111) single-crystal electrode from a benzene dosing solution containing 16-400 microM pentacene. Molecular-resolution STM imaging conducted in 0.1 M HClO(4) revealed highly ordered pentacene structures of ( radical31 x radical31)R8.9 degrees , (3 x 10), ( radical31 x 10), and ( radical7 x 2 radical7)R19.1 degrees adsorbed on the reconstructed Au(111) electrode dosed with different pentacene solutions. These pentacene structures and the reconstructed Au(111) substrate were stable between 0.2 and 0.8 V [vs reversible hydrogen electrode, RHE]. Increasing the potential to E > 0.8 V lifted the reconstructed Au(111) surface and disrupted the ordered pentacene adlattices simultaneously. Ordered pentacene structures could be restored by applying potentials negative enough to reinforce the reconstructed Au(111). At potentials negative of 0.2 V, the adsorption of protons became increasingly important to displace adsorbed pentacene admolecules. Although the reconstructed Au(111) structure was not essential to produce ordered pentacene adlayers, it seemed to help the adsorption of pentacene molecules in a long-range ordered pattern. At room temperature (25 degrees C), approximately 100 pentacene molecules seen in STM images could rotate and align themselves to a neighboring domain in 10 s, suggesting that pentacene admolecules could be mobile on Au(111) under the STM imaging conditions of -150 mV in bias voltage and 1 nA in feedback current.

In situ STM imaging and direct electrochemistry of Pyrococcus furiosus ferredoxin assembled on thiolate-modified Au(111) surfaces

DEFF Research Database (Denmark)

Zhang, Jingdong; Christensen, Hans Erik Mølager; Ooi, Bee Lean

2004-01-01

We have addressed here electron transfer (ET) of Pyrococcus furiosus ferredoxin (PfFd, 7.5 kDa) in both homogeneous solution using edge plane graphite (EPG) electrodes and in the adsorbed state by electrochemistry on surface-modified single-crystal Au(111) electrodes, This has been supported...... by surface microscopic structures of PfFd monolayers, as revealed by scanning tunneling microscopy under potential control (in situ STM). Direct ET between PfFd in phosphate buffer solution, pH 7.9, and EPG electrodes is observed in the presence of promoters. Neomycin gives rise to a pair of redox peaks...... with a formal potential of ca -430 mV (vs SCE), corresponding to [3Fe-4S](1+/0). The presence of an additional promoter, which can be propionic acid, alanine, or cysteine, induces a second pair of redox peaks at similar to-900 mV (vs SCE) arising from [3Fe-4S](0/1-). A robust neomycin-PfFd complex was detected...

Bis(triisopropylsilylethynyl)pentacene/Au(111) interface: Coupling, molecular orientation, and thermal stability

KAUST Repository

Gnoli, Andrea; Ü stü nel, Hande; Toffoli, Daniele; Yu, Liyang; Catone, D.; Turchini, Stefano; Lizzit, Silvano; Stingelin, Natalie; Larciprê te, Rosanna

2014-01-01

The assembly and the orientation of functionalized pentacene at the interface with inorganics strongly influence both the electric contact and the charge transport in organic electronic devices. In this study electronic spectroscopies and theoretical modeling are combined to investigate the properties of the bis(triisopropylsilylethynyl)pentacene (TIPS-Pc)/Au(111) interface as a function of the molecular coverage to compare the molecular state in the gas phase and in the adsorbed phase and to determine the thermal stability of TIPS-Pc in contact with gold. Our results show that in the free molecule only the acene atoms directly bonded to the ligands are affected by the functionalization. Adsorption on Au(111) leads to a weak coupling which causes only modest binding energy shifts in the TIPS-Pc and substrate core level spectra. In the first monolayer the acene plane form an angle of 33 ± 2° with the Au(111) surface at variance with the vertical geometry reported for thicker solution-processed or evaporated films, whereas the presence of configurational disorder was observed in the multilayer. The thermal annealing of the TIPS-Pc/Au(111) interface reveals the ligand desorption at ∼470 K, which leaves the backbone of the decomposed molecule flat-lying on the metal surface as in the case of the unmodified pentacene. The weak interaction with the metal substrate causes the molecular dissociation to occur 60 K below the thermal decomposition taking place in thick drop-cast films.

Bis(triisopropylsilylethynyl)pentacene/Au(111) interface: Coupling, molecular orientation, and thermal stability

KAUST Repository

Gnoli, Andrea

2014-10-02

The assembly and the orientation of functionalized pentacene at the interface with inorganics strongly influence both the electric contact and the charge transport in organic electronic devices. In this study electronic spectroscopies and theoretical modeling are combined to investigate the properties of the bis(triisopropylsilylethynyl)pentacene (TIPS-Pc)/Au(111) interface as a function of the molecular coverage to compare the molecular state in the gas phase and in the adsorbed phase and to determine the thermal stability of TIPS-Pc in contact with gold. Our results show that in the free molecule only the acene atoms directly bonded to the ligands are affected by the functionalization. Adsorption on Au(111) leads to a weak coupling which causes only modest binding energy shifts in the TIPS-Pc and substrate core level spectra. In the first monolayer the acene plane form an angle of 33 ± 2° with the Au(111) surface at variance with the vertical geometry reported for thicker solution-processed or evaporated films, whereas the presence of configurational disorder was observed in the multilayer. The thermal annealing of the TIPS-Pc/Au(111) interface reveals the ligand desorption at ∼470 K, which leaves the backbone of the decomposed molecule flat-lying on the metal surface as in the case of the unmodified pentacene. The weak interaction with the metal substrate causes the molecular dissociation to occur 60 K below the thermal decomposition taking place in thick drop-cast films.

Surface characterization of sulfur and alkanethiol self-assembled monolayers on Au(111)

International Nuclear Information System (INIS)

Vericat, C; Vela, M E; Benitez, G A; Gago, J A Martin; Torrelles, X; Salvarezza, R C

2006-01-01

In the last two decades surface science techniques have decisively contributed to our present knowledge of alkanethiol self-assembled monolayers (SAMs) on solid surfaces. These organic layers have been a challenge for surface scientists, in particular because of the soft nature of the organic material (which can be easily damaged by irradiation), the large number of atoms present in the molecules, and the complex physical chemistry involved in the self-assembly process. This challenge has been motivated by the appealing technological applications of SAMs that cover many fields of the emerging area of nanotechnology. Sulfur (S) is closely related to alkanethiols and can be used to understand basic aspects of the surface structure of SAMs. In this review we focus on the atomic/molecular structures of S-containing SAMs on Au(111). Particular emphasis is given to the substrate, adsorption sites, chemical state of the S-metal bond and also to the experimental and theoretical tools used to study these structures at the atomic or molecular levels. (topical review)

Surface characterization of sulfur and alkanethiol self-assembled monolayers on Au(111)

Energy Technology Data Exchange (ETDEWEB)

Vericat, C [Instituto de Investigaciones FisicoquImicas Teoricas y Aplicadas (INIFTA), Universidad Nacional de La Plata-CONICET, Sucursal 4 Casilla de Correo 16 (1900) La Plata (Argentina); Vela, M E [Instituto de Investigaciones FisicoquImicas Teoricas y Aplicadas (INIFTA), Universidad Nacional de La Plata-CONICET, Sucursal 4 Casilla de Correo 16 (1900) La Plata (Argentina); Benitez, G A [Instituto de Investigaciones FisicoquImicas Teoricas y Aplicadas (INIFTA), Universidad Nacional de La Plata-CONICET, Sucursal 4 Casilla de Correo 16 (1900) La Plata (Argentina); Gago, J A Martin [Centro de AstrobiologIa (CSIC-INTA), 28850 Torrejon de Ardoz Madrid (Spain); Torrelles, X [Instituto de Ciencia de Materiales de Barcelona (ICMAB), Barcelona (Spain); Salvarezza, R C [Instituto de Investigaciones FisicoquImicas Teoricas y Aplicadas (INIFTA), Universidad Nacional de La Plata-CONICET, Sucursal 4 Casilla de Correo 16 (1900) La Plata (Argentina)

2006-12-06

In the last two decades surface science techniques have decisively contributed to our present knowledge of alkanethiol self-assembled monolayers (SAMs) on solid surfaces. These organic layers have been a challenge for surface scientists, in particular because of the soft nature of the organic material (which can be easily damaged by irradiation), the large number of atoms present in the molecules, and the complex physical chemistry involved in the self-assembly process. This challenge has been motivated by the appealing technological applications of SAMs that cover many fields of the emerging area of nanotechnology. Sulfur (S) is closely related to alkanethiols and can be used to understand basic aspects of the surface structure of SAMs. In this review we focus on the atomic/molecular structures of S-containing SAMs on Au(111). Particular emphasis is given to the substrate, adsorption sites, chemical state of the S-metal bond and also to the experimental and theoretical tools used to study these structures at the atomic or molecular levels. (topical review)

Ab initio molecular dynamics calculations on scattering of hyperthermal H atoms from Cu(111) and Au(111)

Energy Technology Data Exchange (ETDEWEB)

Kroes, Geert-Jan, E-mail: g.j.kroes@chem.leidenuniv.nl; Pavanello, Michele [Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden (Netherlands); Blanco-Rey, María [Departamento de Física de Materiales, Facultad de Químicas UPV/EHU, Apartado 1072, 20080 Donostia-San Sebastián (Spain); Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Alducin, Maite [Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Centro de Física de Materiales, Centro Mixto CSIC-UPV/EHU, Paseo Manuel de Lardizabal 5, 20018 Donostia-San Sebastián (Spain); Auerbach, Daniel J. [Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden (Netherlands); Max Planck Institute for Biophysical Chemistry, Göttingen (Germany); Institute for Physical Chemistry, Georg-August University of Göttingen, Göttingen (Germany)

2014-08-07

Energy loss from the translational motion of an atom or molecule impinging on a metal surface to the surface may determine whether the incident particle can trap on the surface, and whether it has enough energy left to react with another molecule present at the surface. Although this is relevant to heterogeneous catalysis, the relative extent to which energy loss of hot atoms takes place to phonons or electron-hole pair (ehp) excitation, and its dependence on the system's parameters, remain largely unknown. We address these questions for two systems that present an extreme case of the mass ratio of the incident atom to the surface atom, i.e., H + Cu(111) and H + Au(111), by presenting adiabatic ab initio molecular dynamics (AIMD) predictions of the energy loss and angular distributions for an incidence energy of 5 eV. The results are compared to the results of AIMDEFp calculations modeling energy loss to ehp excitation using an electronic friction (“EF”) model applied to the AIMD trajectories, so that the energy loss to the electrons is calculated “post” (“p”) the computation of the AIMD trajectory. The AIMD calculations predict average energy losses of 0.38 eV for Cu(111) and 0.13-0.14 eV for Au(111) for H-atoms that scatter from these surfaces without penetrating the surface. These energies closely correspond with energy losses predicted with Baule models, which is suggestive of structure scattering. The predicted adiabatic integral energy loss spectra (integrated over all final scattering angles) all display a lowest energy peak at an energy corresponding to approximately 80% of the average adiabatic energy loss for non-penetrative scattering. In the adiabatic limit, this suggests a way of determining the approximate average energy loss of non-penetratively scattered H-atoms from the integral energy loss spectrum of all scattered H-atoms. The AIMDEFp calculations predict that in each case the lowest energy loss peak should show additional energy

Ab initio molecular dynamics calculations on scattering of hyperthermal H atoms from Cu(111) and Au(111).

Science.gov (United States)

Kroes, Geert-Jan; Pavanello, Michele; Blanco-Rey, María; Alducin, Maite; Auerbach, Daniel J

2014-08-07

Energy loss from the translational motion of an atom or molecule impinging on a metal surface to the surface may determine whether the incident particle can trap on the surface, and whether it has enough energy left to react with another molecule present at the surface. Although this is relevant to heterogeneous catalysis, the relative extent to which energy loss of hot atoms takes place to phonons or electron-hole pair (ehp) excitation, and its dependence on the system's parameters, remain largely unknown. We address these questions for two systems that present an extreme case of the mass ratio of the incident atom to the surface atom, i.e., H + Cu(111) and H + Au(111), by presenting adiabatic ab initio molecular dynamics (AIMD) predictions of the energy loss and angular distributions for an incidence energy of 5 eV. The results are compared to the results of AIMDEFp calculations modeling energy loss to ehp excitation using an electronic friction ("EF") model applied to the AIMD trajectories, so that the energy loss to the electrons is calculated "post" ("p") the computation of the AIMD trajectory. The AIMD calculations predict average energy losses of 0.38 eV for Cu(111) and 0.13-0.14 eV for Au(111) for H-atoms that scatter from these surfaces without penetrating the surface. These energies closely correspond with energy losses predicted with Baule models, which is suggestive of structure scattering. The predicted adiabatic integral energy loss spectra (integrated over all final scattering angles) all display a lowest energy peak at an energy corresponding to approximately 80% of the average adiabatic energy loss for non-penetrative scattering. In the adiabatic limit, this suggests a way of determining the approximate average energy loss of non-penetratively scattered H-atoms from the integral energy loss spectrum of all scattered H-atoms. The AIMDEFp calculations predict that in each case the lowest energy loss peak should show additional energy loss in the

Effect of dispersion on surface interactions of cobalt(II) octaethylporphyrin monolayer on Au(111) and HOPG(0001) substrates: a comparative first principles study.

Science.gov (United States)

Chilukuri, Bhaskar; Mazur, Ursula; Hipps, K W

2014-07-21

A density functional theory study of a cobalt(II) octaethylporphyrin (CoOEP) monolayer on Au(111) and HOPG(0001) surfaces was performed under periodic boundary conditions. Calculations with and without dispersion corrections are performed and the effect of van der Waals forces on the interface properties is analyzed. Calculations have determined that the CoOEP molecule tends to bind at the 3-fold and the 6-fold center sites on Au(111) and HOPG(0001), respectively. Geometric optimizations at the center binding sites have indicated that the porphyrin molecules (in the monolayer) lie flat on both substrates. Calculations also reveal that the CoOEP monolayer binds slightly more strongly to Au(111) than to HOPG(0001). Charge density difference plots disclose that charge is redistributed mostly around the porphyrin plane and the first layer of the substrates. Dispersion interactions cause a larger substrate to molecule charge pushback on Au(111) than on HOPG. CoOEP adsorption tends to lower the work functions of either substrate, qualitatively agreeing with the experimental photoelectron spectroscopic data. Comparison of the density of states (DOS) of the isolated CoOEP molecule with that on gold and HOPG substrates showed significant band shifts around the Fermi energy due to intermolecular orbital hybridization. Simulated STM images were plotted with the Tersoff-Hamann approach using the local density of states, which also agree with the experimental results. This study elucidates the role of dispersion for better describing porphyrin-substrate interactions. A DFT based overview of geometric, adsorption and electronic properties of a porphyrin monolayer on conductive surfaces is presented.

A periodic mixed gaussians-plane waves DFT study on simple thiols on Au(111): adsorbate species, surface reconstruction, and thiols functionalization.

Science.gov (United States)

Rajaraman, Gopalan; Caneschi, Andrea; Gatteschi, Dante; Totti, Federico

2011-03-07

Here we present DFT calculations based on a periodic mixed gaussians/plane waves approach to study the energetics, structure, bonding of SAMs of simple thiols on Au(111). Several open issues such as structure, bonding and the nature of adsorbate are taken into account. We started with methyl thiols (MeSH) on Au(111) to establish the nature of the adsorbate. We have considered several structural models embracing the reconstructed surface scenario along with the MeS˙-Au(ad)-MeS˙ type motif put forward in recent years. Our calculations suggest a clear preference for the homolytic cleavage of the S-H bond leading to a stable MeS˙ on a gold surface. In agreement with the recent literature studies, the reconstructed models of the MeS˙ species are found to be energetically preferred over unreconstructed models. Besides, our calculations reveal that the model with 1:2 Au(ad)/thiols ratio, i.e. MeS˙-Au(ad)-MeS˙, is energetically preferred compared to the clean and 1:1 ratio models, in agreement with the experimental and theoretical evidences. We have also performed Molecular Orbital/Natural Bond Orbital, MO/NBO, analysis to understand the electronic structure and bonding in different structural motifs and many useful insights have been gained. Finally, the studies have then been extended to alkyl thiols of the RSR' (R, R' = Me, Et and Ph) type and here our calculations again reveal a preference for the RS˙ type species adsorption for clean as well as for reconstructed 1:2 Au(ad)/thiols ratio models.

Electronic and magnetic properties of Mn{sub 12} single-molecule magnets on the Au(111) surface

Energy Technology Data Exchange (ETDEWEB)

Voss, Soenke; Burgert, Michael; Fonin, Mikhail; Groth, Ulrich; Ruediger, Ulrich [Universitaet Konstanz (Germany); Michaelis, Christian; Brihuega, Ivan; Kern, Klaus [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany); Dedkov, Yury S. [Institut fuer Festkoerperphysik, Technische Universitaet Dresden (Germany)

2008-07-01

The paramount interest in single-molecule magnets (SMMs) like Mn{sub 12}-acetate and its derivatives was inspired by numerous experimental and theoretical insights indicating the feasibility of addressing quantum effects of magnetism on a molecular scale. Due to its relatively high blocking temperature ({proportional_to}3 K) combined with the ability to identify well-defined spin states, Mn{sub 12} still remains the most favoured SMM possibly allowing the detection of magnetic fingerprints in transport properties of a single molecule. In this work, the electronic properties of Mn{sub 12} molecules chemically grafted on Au(111) surfaces have been studied by means of low temperature as well as room temperature scanning tunneling microscopy and spectroscopy (STS), X-ray absorption spectroscopy and photoelectron spectroscopy. The results revealed signatures from most probably intact Mn{sub 12} molecules while STS measurements in magnetic fields indicate the possibility to identify magnetic fingerprints in scanning tunneling spectra. The results will be discussed with respect to previous attempts to perform transport measurements on Mn{sub 12} SMMs.

Triptycene-terminated thiolate and selenolate monolayers on Au(111

Directory of Open Access Journals (Sweden)

Jinxuan Liu

2017-04-01

Full Text Available To study the implications of highly space-demanding organic moieties on the properties of self-assembled monolayers (SAMs, triptycyl thiolates and selenolates with and without methylene spacers on Au(111 surfaces were comprehensively studied using ultra-high vacuum infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy and thermal desorption spectroscopy. Due to packing effects, the molecules in all monolayers are substantially tilted. In the presence of a methylene spacer the tilt is slightly less pronounced. The selenolate monolayers exhibit smaller defect densities and therefore are more densely packed than their thiolate analogues. The Se–Au binding energy in the investigated SAMs was found to be higher than the S–Au binding energy.

Spin-polarized scanning tunneling spectroscopy of self-organized nanoscale Co islands on Au(111) surfaces.

Science.gov (United States)

Schouteden, K; Muzychenko, D A; Van Haesendonck, C

2008-07-01

Magnetic monolayer and bilayer Co islands of only a few nanometer in size were grown by atomic deposition on atomically flat Au(111) films. The islands were studied in situ by scanning tunneling microscopy (STM) and spectroscopy at low temperatures. Spin-resolved tunneling spectroscopy, using an STM tip with a magnetic coating, revealed that the Co islands exhibit a net magnetization perpendicular to the substrate surface due to the presence of spin-polarized d-states. A random distribution of islands with either upward or downward pointing magnetization was observed, without any specific correlation of magnetization orientation with island size or island height.

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

Directory of Open Access Journals (Sweden)

Benedikt Uhl

2013-12-01

Full Text Available 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(trifluoromethylsulfonylimide [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.

Modification of Au and Si(111):H surfaces towards biological sensing

Energy Technology Data Exchange (ETDEWEB)

Zhang, Xin; Rappich, Joerg [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Institut fuer Si Photovoltaik, Berlin (Germany); Sun, Guoguang; Hinrichs, Karsten; Rosu, Dana; Esser, Norbert [ISAS-Institute for Analytical Sciences, Department Berlin (Germany); Hovestaedt, Marc; Ay, Bernhard; Volkmer, Rudolf [Institut fuer Medizinische Immunologie, Charite Berlin, Berlin (Germany); Janietz, Silvia [Fraunhofer-Institut fuer Angewandte Polymerforschung, Golm (Germany)

2010-07-01

Within the topics to grow functional organic surfaces for biosensors we grafted carboxylbenzene, aminobenzene and maleimidobenzene onto Au and H-terminated Si surfaces by electrochemical deposition from 4-carboxylbenzene-diazonium tetrafluoroborate (4-CBDT), 4-aminobenzene-diazonium tetrafluoroborate (4-ABDT) and 4-maleimidobenzene-diazonium tetrafluoroborate (4-MBDT).The electron injection to the diazonium compound in solution (cathodic current) leads to the formation of intermediate radicals, which further react with the surface (Au or Si:H) and the respective molecule is grafted onto the surface.The aim was to functionalise these surfaces for further reaction with corresponding amines, acids or cysteine-modified peptides. Ex-situ infrared spectroscopic ellipsometry (IRSE) was applied to inspect the surface species before and after the functionalisation.

Effects of pressure, temperature and atomic exchanges on phase separation dynamics in Au/Ni(111) surface alloy: Kinetic Monte Carlo study

Energy Technology Data Exchange (ETDEWEB)

Zvejnieks, G. [Institute for Solid State Physics, University of Latvia, Kengaraga 8, LV-1063 Riga (Latvia); Ibenskas, A., E-mail: ibenskas@pfi.lt [Center for Physical Sciences and Technology, Semiconductor Physics Institute, Gostauto 11, LT-01108 Vilnius (Lithuania); Tornau, E.E. [Center for Physical Sciences and Technology, Semiconductor Physics Institute, Gostauto 11, LT-01108 Vilnius (Lithuania)

2015-11-15

Instability of the Au/Ni(111) surface alloy is studied in different CO gas pressure, p, and temperature limits using kinetic Monte Carlo simulations. We analyze the reaction front dynamics and formation of Au clusters using the model which takes into account surface adatom pair and three-body interactions, CO adsorption and desorption, catalytic carbonyl formation reaction, Au and Ni adatom diffusion and their concerted exchange. Variation of interaction parameters allows us to identify three possible reaction front propagation limits with different pressure dependencies: (i) slow channel-like flow in agreement with experimental data [1] (step flow rate, R, increases with p), (ii) intermediate regime (weak p–dependence), and (iii) fast homogeneous flow (R decreases with p). We find that only Au–Ni exchange, contrary to both Ni–CO and Au–CO exchanges, significantly reduces the number of screened Ni atoms inside the Au clusters and stimulates the occurrence of Ni-free Au clusters. The size of Au islands depends on both pressure and temperature. At a fixed temperature it decreases with pressure due to an increased step flow rate. In the high temperature limit, despite the step flow rate exponential increase with temperature, the cluster size increases due to an enhanced Au mobility. - Highlights: • Kinetic Monte Carlo study of Au–Ni surface alloy instability to CO pressure and temperature. • Three reaction front propagation regimes. • In channel-like regime, the step flow rate increases with CO pressure as in experiment. • Ni-free Au islands are obtained when Au-Ni adatom exchange mechanism is considered. • The size of Au islands decreases with pressure and increases with temperature.

Effects of pressure, temperature and atomic exchanges on phase separation dynamics in Au/Ni(111) surface alloy: Kinetic Monte Carlo study

International Nuclear Information System (INIS)

Zvejnieks, G.; Ibenskas, A.; Tornau, E.E.

2015-01-01

Instability of the Au/Ni(111) surface alloy is studied in different CO gas pressure, p, and temperature limits using kinetic Monte Carlo simulations. We analyze the reaction front dynamics and formation of Au clusters using the model which takes into account surface adatom pair and three-body interactions, CO adsorption and desorption, catalytic carbonyl formation reaction, Au and Ni adatom diffusion and their concerted exchange. Variation of interaction parameters allows us to identify three possible reaction front propagation limits with different pressure dependencies: (i) slow channel-like flow in agreement with experimental data [1] (step flow rate, R, increases with p), (ii) intermediate regime (weak p–dependence), and (iii) fast homogeneous flow (R decreases with p). We find that only Au–Ni exchange, contrary to both Ni–CO and Au–CO exchanges, significantly reduces the number of screened Ni atoms inside the Au clusters and stimulates the occurrence of Ni-free Au clusters. The size of Au islands depends on both pressure and temperature. At a fixed temperature it decreases with pressure due to an increased step flow rate. In the high temperature limit, despite the step flow rate exponential increase with temperature, the cluster size increases due to an enhanced Au mobility. - Highlights: • Kinetic Monte Carlo study of Au–Ni surface alloy instability to CO pressure and temperature. • Three reaction front propagation regimes. • In channel-like regime, the step flow rate increases with CO pressure as in experiment. • Ni-free Au islands are obtained when Au-Ni adatom exchange mechanism is considered. • The size of Au islands decreases with pressure and increases with temperature

Growth of Single- and Bilayer ZnO on Au(111) and Interaction with Copper

Energy Technology Data Exchange (ETDEWEB)

Deng, Xingyi; Yao, Kun; Sun, Keju; Li, Wei-Xue; Lee, Junseok; Matranga, Christopher

2013-05-02

The stoichiometric single- and bi-layer ZnO(0001) have been prepared by reactive deposition of Zn on Au(111) and studied in detail with X-ray photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory calculations. Both single- and bi-layer ZnO(0001) adopt a planar, graphite-like structure similar to freestanding ZnO(0001) due to the weak van der Waals interactions dominating their adhesion with the Au(111) substrate. At higher temperature, the single-layer ZnO(0001) converts gradually to bi-layer ZnO(0001) due to the twice stronger interaction between two ZnO layers than the interfacial adhesion of ZnO with Au substrate. It is found that Cu atoms on the surface of bi-layer ZnO(0001) are mobile with a diffusion barrier of 0.31 eV, and likely to agglomerate and form nanosized particles at low coverages; while Cu atoms tend to penetrate a single layer of ZnO(0001) with a barrier of 0.10 eV, resulting in a Cu free surface.

Coverage Dependent Assembly of Anthraquinone on Au(111)

Science.gov (United States)

Conrad, Brad; Deloach, Andrew; Einstein, Theodore; Dougherty, Daniel

A study of adsorbate-adsorbate and surface state mediated interactions of anthraquinone (AnQ) on Au(111) is presented. We utilize scanning tunneling microscopy (STM) to characterize the coverage dependence of AnQ structure formation. Ordered structures are observed up to a single monolayer (ML) and are found to be strongly dependent on molecular surface density. While the complete ML forms a well-ordered close-packed layer, for a narrow range of sub-ML coverages irregular close-packed islands are observed to coexist with a disordered pore network linking neighboring islands. This network displays a characteristic pore size and at lower coverages, the soliton walls of the herringbone reconstruction are shown to promote formation of distinct pore nanostructures. We will discuss these nanostructure formations in the context of surface mediated and more direct adsorbate interactions.

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

DEFF Research Database (Denmark)

Engbæk, Jakob; Schiøtz, Jakob; Dahl-Madsen, Bjarke

2006-01-01

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

Dynamics of decanethiol self-assembled monolayers on Au(111) studied by Scanning tunnelling microscopy

NARCIS (Netherlands)

Wu, Hairong; Sotthewes, Kai; Kumar, Avijit; Vancso, Gyula J.; Schön, Peter Manfred; Zandvliet, Henricus J.W.

2013-01-01

We investigated the dynamics of decanethiol self-assembled monolayers on Au(111) surfaces using time-resolved scanning tunneling microscopy at room temperature. The expected ordered phases (β, δ, χ*, and ) and a disordered phase (ε) were observed. Current–time traces with the feedback loop disabled

Enhanced fullerene–Au(111 coupling in (2√3 × 2√3R30° superstructures with intermolecular interactions

Directory of Open Access Journals (Sweden)

Michael Paßens

2015-06-01

Full Text Available Disordered and uniform (2√3 × 2√3R30° superstructures of fullerenes on the Au(111 surface have been studied using scanning tunneling microscopy and spectroscopy. It is shown that the deposition and growth process of a fullerene monolayer on the Au(111 surface determine the resulting superstructure. The supply of thermal energy is of importance for the activation of a Au vacancy forming process and thus, one criterion for the selection of the respective superstructure. However, here it is depicted that a vacancy–adatom pair can be formed even at room temperature. This latter process results in C60 molecules that appear slightly more bright in scanning tunnelling microscopy images and are identified in disordered (2√3 x 2√3R30° superstructures based on a detailed structure analysis. In addition, these slightly more bright C60 molecules form uniform (2√3 x 2√3R30° superstructures, which exhibit intermolecular interactions, likely mediated by Au adatoms. Thus, vacancy–adatom pairs forming at room temperature directly affect the resulting C60 superstructure. Differential conductivity spectra reveal a lifting of the degeneracy of the LUMO and LUMO+1 orbitals in the uniform (2√3 x 2√3R30° superstructure and in addition, hybrid fullerene–Au(111 surface states suggest partly covalent interactions.

Molecular and electronic structure of osmium complexes confined to Au(111) surfaces using a self-assembled molecular bridge

Energy Technology Data Exchange (ETDEWEB)

Llave, Ezequiel de la; Herrera, Santiago E.; Adam, Catherine; Méndez De Leo, Lucila P.; Calvo, Ernesto J.; Williams, Federico J., E-mail: fwilliams@qi.fcen.uba.ar [INQUIMAE-CONICET, Departamento de Química Inorgánica, Analítica y Química-Física, Facultad Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, Buenos Aires C1428EHA (Argentina)

2015-11-14

The molecular and electronic structure of Os(II) complexes covalently bonded to self-assembled monolayers (SAMs) on Au(111) surfaces was studied by means of polarization modulation infrared reflection absorption spectroscopy, photoelectron spectroscopies, scanning tunneling microscopy, scanning tunneling spectroscopy, and density functional theory calculations. Attachment of the Os complex to the SAM proceeds via an amide covalent bond with the SAM alkyl chain 40° tilted with respect to the surface normal and a total thickness of 26 Å. The highest occupied molecular orbital of the Os complex is mainly based on the Os(II) center located 2.2 eV below the Fermi edge and the LUMO molecular orbital is mainly based on the bipyridine ligands located 1.5 eV above the Fermi edge.

Magnetism of coherent Co and Ni thin films on Cu(111) and Au(111) substrates: An ab initio study

Energy Technology Data Exchange (ETDEWEB)

Zelený, Martin, E-mail: zeleny@fme.vutbr.cz; Dlouhý, Ivo

2017-02-15

We present an ab initio study of structural and magnetic properties of coherent Co and Ni thin films on Cu(111) and Au(111) substrates with thicknesses of up to 6 monolayers. All studied films on Cu(111) substrates prefer structures close their ground state (hcp for Co and fcc for Ni), whereas only the hcp stacking sequence has been found for both films on Au(111) substrates. All studied films exhibit instability of the first monolayer with respect to decomposition into 2-monolayer- or 3-monolayer-high islands, which is in agreement with experimental findings. All studied films are also ferromagnetic, nevertheless the Ni/Cu(111) films reduce their magnetic moments in the layer adjacent to the substrate due to a stronger Cu–Ni interaction at the interface. The magnetic anisotropy of a Co film does not depend on the film thickness: all the studied Co/Au(111) films exhibit a perpendicular magnetic anisotropy, whereas all the Co/Cu(111) films prefer in-plane magnetization. On the other hand, both Ni films change their preference for in-plane orientation of their easy axis to out-of-plane orientation at a critical thickness of 2 monolayers, however, the magnetic anisotropy energies for films thicker than 1 monolayer are smaller than 1 meV/Ni atom. These behaviors of magnetic anisotropy do not depend on the structure of the studied films. - Highlights: • All films exhibit instability of the first monolayer and prefer grow in islands. • The Cu–Ni interaction is responsible for reduced Ni magnetic moments in Ni/Cu(111) films. • The Co/Au(111) and Co/Cu(111) films show different orientations of magnetic anisotropy. • The Ni films exhibit in-plane magnetization only for single monolayer. • Behaviors of magnetic anisotropy do not depend on the structure of the studied films.

Monolayer Iron Carbide Films on Au(111) as a Fischer–Tropsch Model Catalyst

DEFF Research Database (Denmark)

Mannie, Gilbère; Lammich, Lutz; Li, Yong-Wang

2014-01-01

-temperature exposure of Fe islands gas to C2H4 deposited on the clean Au(111) surface results in partly converted Fe/FexCy islands. Multistep flash-heating treatment of the partly converted Fe/FexCy islands at 523 and 773 K results in pure highly crystalline FexCy islands with in-plane nearest-neighbor distances of 0...

N-Heterocyclic carbenes on close-packed coinage metal surfaces: bis-carbene metal adatom bonding scheme of monolayer films on Au, Ag and Cu.

Science.gov (United States)

Jiang, Li; Zhang, Bodong; Médard, Guillaume; Seitsonen, Ari Paavo; Haag, Felix; Allegretti, Francesco; Reichert, Joachim; Kuster, Bernhard; Barth, Johannes V; Papageorgiou, Anthoula C

2017-12-01

By means of scanning tunnelling microscopy (STM), complementary density functional theory (DFT) and X-ray photoelectron spectroscopy (XPS) we investigate the binding and self-assembly of a saturated molecular layer of model N -heterocyclic carbene (NHC) on Cu(111), Ag(111) and Au(111) surfaces under ultra-high vacuum (UHV) conditions. XPS reveals that at room temperature, coverages up to a monolayer exist, with the molecules engaged in metal carbene bonds. On all three surfaces, we resolve similar arrangements, which can be interpreted only in terms of mononuclear M(NHC) 2 (M = Cu, Ag, Au) complexes, reminiscent of the paired bonding of thiols to surface gold adatoms. Theoretical investigations for the case of Au unravel the charge distribution of a Au(111) surface covered by Au(NHC) 2 and reveal that this is the energetically preferential adsorption configuration.

Vibrational properties of the Au-(√{3 }×√{3 } )/Si(111) surface reconstruction

Science.gov (United States)

Halbig, B.; Liebhaber, M.; Bass, U.; Geurts, J.; Speiser, E.; Räthel, J.; Chandola, S.; Esser, N.; Krenz, M.; Neufeld, S.; Schmidt, W. G.; Sanna, S.

2018-01-01

The vibrational properties of the Au-induced (√{3 }×√{3 })R 30∘ reconstruction of the Si(111) surface are investigated by polarized surface Raman spectroscopy and density-functional theory. The Raman measurements are performed in situ at room temperature as well as 20 K, and they reveal the presence of vibrational eigenmodes in the spectral range from 20 to 450 cm-1. In particular, two peaks of E symmetry at 75 and 183 cm-1 dominate the spectra. No substantial difference between room- and low-temperature spectra is observed, suggesting that the system does not undergo a phase transition down to 20 K. First-principles calculations are performed based on the structural models discussed in the literature. The thermodynamically stable conjugate honeycomb-chained-trimer model (CHCT) [Surf. Sci. 275, L691 (1992), 10.1016/0039-6028(92)90785-5] leads to phonon eigenvalues compatible with the experimental observations in the investigated spectral range. On the basis of the phonon eigenfrequencies, symmetries, and Raman intensities, we assign the measured spectral features to the calculated phonon modes. The good agreement between measured and calculated modes provides a strong argument in favor of the CHCT model.

An efficient Monte Carlo algorithm for the fast equilibration and atomistic simulation of alkanethiol self-assembled monolayers on a Au(111) substrate.

Science.gov (United States)

Alexiadis, Orestis; Daoulas, Kostas Ch; Mavrantzas, Vlasis G

2008-01-31

A new Monte Carlo algorithm is presented for the simulation of atomistically detailed alkanethiol self-assembled monolayers (R-SH) on a Au(111) surface. Built on a set of simpler but also more complex (sometimes nonphysical) moves, the new algorithm is capable of efficiently driving all alkanethiol molecules to the Au(111) surface, thereby leading to full surface coverage, irrespective of the initial setup of the system. This circumvents a significant limitation of previous methods in which the simulations typically started from optimally packed structures on the substrate close to thermal equilibrium. Further, by considering an extended ensemble of configurations each one of which corresponds to a different value of the sulfur-sulfur repulsive core potential, sigmass, and by allowing for configurations to swap between systems characterized by different sigmass values, the new algorithm can adequately simulate model R-SH/Au(111) systems for values of sigmass ranging from 4.25 A corresponding to the Hautman-Klein molecular model (J. Chem. Phys. 1989, 91, 4994; 1990, 93, 7483) to 4.97 A corresponding to the Siepmann-McDonald model (Langmuir 1993, 9, 2351), and practically any chain length. Detailed results are presented quantifying the efficiency and robustness of the new method. Representative simulation data for the dependence of the structural and conformational properties of the formed monolayer on the details of the employed molecular model are reported and discussed; an investigation of the variation of molecular organization and ordering on the Au(111) substrate for three CH3-(CH2)n-SH/Au(111) systems with n=9, 15, and 21 is also included.

Self-organization of S adatoms on Au(111): √3R30° rows at low coverage.

Science.gov (United States)

Walen, Holly; Liu, Da-Jiang; Oh, Junepyo; Lim, Hyunseob; Evans, J W; Kim, Yousoo; Thiel, P A

2015-07-07

Using scanning tunneling microscopy, we observe an adlayer structure that is dominated by short rows of S atoms, on unreconstructed regions of a Au(111) surface. This structure forms upon adsorption of low S coverage (less than 0.1 monolayer) on a fully reconstructed clean surface at 300 K, then cooling to 5 K for observation. The rows adopt one of three orientations that are rotated by 30° from the close-packed directions of the Au(111) substrate, and adjacent S atoms in the rows are separated by √3 times the surface lattice constant, a. Monte Carlo simulations are performed on lattice-gas models, derived using a limited cluster expansion based on density functional theory energetics. Models which include long-range pairwise interactions (extending to 5a), plus selected trio interactions, successfully reproduce the linear rows of S atoms at reasonable temperatures.

Self-organization of S adatoms on Au(111): √3R30° rows at low coverage

Energy Technology Data Exchange (ETDEWEB)

Walen, Holly, E-mail: hwalen@iastate.edu [Department of Chemistry, Iowa State University, Ames, Iowa 50011 (United States); Liu, Da-Jiang [Ames Laboratory of the USDOE, Ames, Iowa 50011 (United States); Oh, Junepyo; Lim, Hyunseob; Kim, Yousoo [RIKEN Surface and Interface Science Laboratory, Wako, Saitama 351-0198 (Japan); Evans, J. W. [Ames Laboratory of the USDOE, Ames, Iowa 50011 (United States); Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States); Thiel, P. A. [Department of Chemistry, Iowa State University, Ames, Iowa 50011 (United States); Ames Laboratory of the USDOE, Ames, Iowa 50011 (United States); Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011 (United States)

2015-07-07

Using scanning tunneling microscopy, we observe an adlayer structure that is dominated by short rows of S atoms, on unreconstructed regions of a Au(111) surface. This structure forms upon adsorption of low S coverage (less than 0.1 monolayer) on a fully reconstructed clean surface at 300 K, then cooling to 5 K for observation. The rows adopt one of three orientations that are rotated by 30° from the close-packed directions of the Au(111) substrate, and adjacent S atoms in the rows are separated by √3 times the surface lattice constant, a. Monte Carlo simulations are performed on lattice-gas models, derived using a limited cluster expansion based on density functional theory energetics. Models which include long-range pairwise interactions (extending to 5a), plus selected trio interactions, successfully reproduce the linear rows of S atoms at reasonable temperatures.

Surface structure and morphology of Cu-free and Cu-covered Au(100) and Au(111) electrodes in alkaline solution

Energy Technology Data Exchange (ETDEWEB)

Schlaup, Christian [Technical University of Denmark, Department of Physics, Fysikvey, DK-2800 Kongens Lyngby (Denmark); Friebel, Daniel [Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Rd, Menlo Park, CA 94025 (United States); Wandelt, Klaus [University of Bonn, Institute for Physical und Theoretical Chemistry, Wegelerstr. 12, D-53115 Bonn (Germany)

2011-07-01

For both Cu-free Au-electrodes three different phases were observed as a function of the applied electrode potential. While at low potentials the onset of surface reconstruction points towards an apparently adsorbate free surface and, thus, a weak interaction with species from the electrolyte, a Au-hydroxide and a Au-oxide phase are formed subsequently during potential increase. A similar phase behavior was also found for Cu-covered Au-electrodes, while at low potentials an apparently adsorbate free Cu layer is observed, a Cu-hydroxide coadsorbate phase and a Cu-oxide phase are formed under increased potential conditions. In addition the apparently adsorbate free Cu-film tends to form a Cu-Au alloy phase while keeping the electrode for a sufficient long time at low potential conditions.

Deformation of Ag clusters deposited on Au(111) - Experiment and molecular dynamics

Energy Technology Data Exchange (ETDEWEB)

Miroslawski, Natalie; Groenhagen, Niklas; Hoevel, Heinz [TU Dortmund, Experimentelle Physik I (Germany); Issendorff, Bernd von [Universitaet Freiburg, Fakultaet Physik (Germany); Jaervi, Tommi [Fraunhofer Institut fuer Werkstoffmechanik, Freiburg (Germany); Moseler, Michael [Universitaet Freiburg, Fakultaet Physik (Germany); Fraunhofer Institut fuer Werkstoffmechanik, Freiburg (Germany); Freiburger Materialforschungszentrum (Germany)

2011-07-01

Mass selected clusters from Ag{sup +}{sub 55} to Ag{sup +}{sub 147{+-}}{sub 2} were deposited with different deposition energies at 77 K on Au(111) and imaged with STM at 77 K. We observed a deformation of the cluster shape due to the strong metallic interaction between the cluster and the substrate. The clusters became epitaxial and developed a structure composed of several Ag monolayers. The number of these monolayers depends on the number of atoms in the cluster and the deposition energy. The larger the cluster mass the more monolayers the cluster develops on Au(111) and the larger the deposition energy the fewer monolayers occur. These results were verified by molecular dynamic simulations. Additionally the behaviour of Ag{sub N} clusters on Au(111) after different annealing steps was investigated.

Exotic high activity surface patterns in PtAu nanoclusters

KAUST Repository

Mokkath, Junais Habeeb

2013-05-09

The structure and chemical ordering of PtAu nanoclusters of 79, 135, and 201 atoms are studied via a combination of a basin hopping atom-exchange technique (to locate the lowest energy homotops at fixed composition), a symmetry orbit technique (to find the high symmetry isomers), and density functional theory local reoptimization (for determining the most stable homotop). The interatomic interactions between Pt and Au are derived from the empirical Gupta potential. The lowest energy structures show a marked tendency toward PtcoreAushell chemical ordering by enrichment of the more cohesive Pt in the core region and of Au in the shell region. We observe a preferential segregation of Pt atoms to (111) facets and Au atoms to (100) facets of the truncated octahedron cluster motif. Exotic surface patterns are obtained particularly for Pt-rich compositions, where Pt atoms are being surrounded by Au atoms. These surface arrangements boost the catalytic activity by creating a large number of active sites. © 2013 American Chemical Society.

Chemical vapour deposition of graphene on Nk(111) and Co(0001) and intercalation with Au to study Dirac Cone Formation and Rashba splitting

Energy Technology Data Exchange (ETDEWEB)

Sanchez-Barriga, J.; Vescovo, E.; Varykhalov, A.; Scholz, M.R.; Rader, O.; Marchenko, D.; Rybkin, A.

2010-01-01

We show in detail monitoring by photoelectron spectroscopy how graphene can be grown by chemical vapor deposition on the transition-metal surfaces Ni(111) and Co(0001) and intercalated by a monoatomic layer of Au. For both systems, a linear E(k) dispersion of massless Dirac fermions appears in the graphene {pi}-band in the vicinity of the Fermi energy. In order to study ferromagnetism and spin-orbit effects by spin- and angle-resolved photoelectron spectroscopy, the sample must be magnetized in remanence. To this end, a W(110) substrate is prepared, its cleanliness verified by photoemission from W(110) surface states and surface core levels, and epitaxial Ni(111) and Co(0001) thin films are grown on top. Spin-resolved photoemission from the {pi}-band shows that the ferromagnetic polarization of graphene/Ni(111) and graphene/Co(0001) is negligible and that graphene on Ni(111) is after intercalation of Au spin-orbit split by the Rashba effect.

An accurate full-dimensional potential energy surface for H-Au(111): Importance of nonadiabatic electronic excitation in energy transfer and adsorption.

Science.gov (United States)

Janke, Svenja M; Auerbach, Daniel J; Wodtke, Alec M; Kandratsenka, Alexander

2015-09-28

We have constructed a potential energy surface (PES) for H-atoms interacting with fcc Au(111) based on fitting the analytic form of the energy from Effective Medium Theory (EMT) to ab initio energy values calculated with density functional theory. The fit used input from configurations of the H-Au system with Au atoms at their lattice positions as well as configurations with the Au atoms displaced from their lattice positions. It reproduces the energy, in full dimension, not only for the configurations used as input but also for a large number of additional configurations derived from ab initio molecular dynamics (AIMD) trajectories at finite temperature. Adiabatic molecular dynamics simulations on this PES reproduce the energy loss behavior of AIMD. EMT also provides expressions for the embedding electron density, which enabled us to develop a self-consistent approach to simulate nonadiabatic electron-hole pair excitation and their effect on the motion of the incident H-atoms. For H atoms with an energy of 2.7 eV colliding with Au, electron-hole pair excitation is by far the most important energy loss pathway, giving an average energy loss ≈3 times that of the adiabatic case. This increased energy loss enhances the probability of the H-atom remaining on or in the Au slab by a factor of 2. The most likely outcome for H-atoms that are not scattered also depends prodigiously on the energy transfer mechanism; for the nonadiabatic case, more than 50% of the H-atoms which do not scatter are adsorbed on the surface, while for the adiabatic case more than 50% pass entirely through the 4 layer simulation slab.

Physisorption of three amine terminated molecules (TMBDA, BDA, TFBDA) on the Au(111) Surface: The Role of van der Waals Interaction

Science.gov (United States)

Aminpour, Maral; Le, Duy; Rahman, Talat S.

2012-02-01

Recently, the electronic properties and alignment of tetramethyl-1,4-benzenediamine (TMBDA), 1,4-benzenediamine (BDA) and tetrafluro-1,4-benzenediamine (TFBDA) molecules were studied experimentally. Discrepancies were found for both the binding energy and the molecule tilt angle with respect to the surface, when results were compared with density functional theory calculations [1]. We have included the effect of vdW interactions both between the molecules and the Au(111) surface and find binding energies which are in very good agreement with experiments. We also find that at low coverages each of these molecules would adsorb almost parallel to the surface. N-Au bond lengths and charge redistribution on adsorption of the molecules are also analyzed. Our calculations are based on DFT using vdW-DF exchange correlation functionals. For BDA (since we are aware of experimental data), we show that for higher coverage, inclusion of intermolecular van der Waals interaction leads to tilting of the molecules with respect to the surface and formation of line structures. Our results demonstrate the central role played by intermolecular interaction in pattern formation on this surface.[4pt] [1] M. Dell'Angela et al, Nano Lett. 2010, 10, 2470; M. Kamenetska et al, J. Phys. Chem. C, 2011, 115, 12625

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

Science.gov (United States)

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.

Synthesis of Epitaxial Single-Layer MoS2 on Au(111).

Science.gov (United States)

Grønborg, Signe S; Ulstrup, Søren; Bianchi, Marco; Dendzik, Maciej; Sanders, Charlotte E; Lauritsen, Jeppe V; Hofmann, Philip; Miwa, Jill A

2015-09-08

We present a method for synthesizing large area epitaxial single-layer MoS2 on the Au(111) surface in ultrahigh vacuum. Using scanning tunneling microscopy and low energy electron diffraction, the evolution of the growth is followed from nanoscale single-layer MoS2 islands to a continuous MoS2 layer. An exceptionally good control over the MoS2 coverage is maintained using an approach based on cycles of Mo evaporation and sulfurization to first nucleate the MoS2 nanoislands and then gradually increase their size. During this growth process the native herringbone reconstruction of Au(111) is lifted as shown by low energy electron diffraction measurements. Within the MoS2 islands, we identify domains rotated by 60° that lead to atomically sharp line defects at domain boundaries. As the MoS2 coverage approaches the limit of a complete single layer, the formation of bilayer MoS2 islands is initiated. Angle-resolved photoemission spectroscopy measurements of both single and bilayer MoS2 samples show a dramatic change in their band structure around the center of the Brillouin zone. Brief exposure to air after removing the MoS2 layer from vacuum is not found to affect its quality.

Electrochemistry and in situ scanning tunnelling microscopy of pure and redox-marked DNA- and UNA-based oligonucleotides on Au(111)-electrode surfaces

DEFF Research Database (Denmark)

Hansen, Allan Glargaard; Salvatore, Princia; Karlsen, K.

2013-01-01

the strongest and in accord with multiple site Ru-attachment. In situ STM disclosed molecular scale features in varying coverage on addition of the metal ions. The Ru-derivatives showed a bias voltage dependent broad maximum in the tunnelling current–overpotential correlation which could be correlated......We have studied adsorption and electrochemical electron transfer of several 13- and 15-base DNA and UNA (unlocked nucleic acids) oligonucleotides (ONs) linked to Au(111)-electrode surfaces via a 50-C6-SH group using cyclic voltammetry (CV) and scanning tunnelling microscopy in aqueous buffer under...

Potential-induced structural transitions of DL-homocysteine monolayers on Au(111) electrode surfaces

International Nuclear Information System (INIS)

Zhang Jingdong; Demetriou, Anna; Welinder, Anne Christina; Albrecht, Tim; Nichols, Richard J.; Ulstrup, Jens

2005-01-01

Monolayers of homocysteine on Au(111)-surfaces have been investigated by voltammetry, in situ scanning tunnelling microscopy (STM) and subtractively normalised interfacial Fourier transform spectroscopy (SNIFTIRS). A pair of sharp voltammetric peaks build up in the potential range 0 to -0.1V (vs. SCE) in phosphate buffer pH 7.7. The peak half-widths are about 25mV at a scan rate of 10mVs -1 . This is much smaller than for a one-electron Faradaic process (90.6mV) under similar conditions. The coverage of homocysteine is 6.1 (+/-0.2)x10 -10 molcm -2 , or 5.9x10 -5 Ccm -2 , from Au-S reductive desorption at -0.8V (SCE) in 0.1M NaOH, while the charge is only about 8x10 -6 Ccm -2 (pH 7.7) for the 0 to -0.1V peak. This suggests a capacitive origin. The peak potential and shape depend on pH. At pH 7.7 both cathodic and anodic peak currents reach a maximum, but drop at both higher and lower pH. The midpoint potential shows biphasic behaviour, decreasing linearly with increasing pH until pH 10.4 towards a constant value at higher pH. The cathodic and anodic peak charges decay at pH both higher and lower than 7.7. The homocysteine monolayer was investigated by in situ STM at different potentials at pH 7.7. The molecules pack into highly ordered domains around the peak potential. High-resolution in situ STM reveals a (√3x5) R30 deg. lattice with three homocysteine molecules in each unit cell. The adlayer changes into disordered structures on either side of the peak potential. This process is reversible. We propose that the voltammetric peaks are capacitive. The ordered domains are formed only around the potential of zero charge (pzc) and dissipate at potentials on either side of the peak, inducing mirror charge flow in the metallic electrode as the charged -COO - and -NH 3 + groups approach the surface. No bands for carboxylate coordinated to the surface were observed in SNIFTIRS implying more subtle orientation changes of the charged groups on transcending the voltammetric

ATR-SEIRAS study of CO adsorption and oxidation on Rh modified Au(111-25 nm) film electrodes in 0.1 M H2SO4

International Nuclear Information System (INIS)

Xu, Qinqin; Berná, Antonio; Pobelov, Ilya V.; Rodes, Antonio; Feliu, Juan M.; Wandlowski, Thomas; Kuzume, Akiyoshi

2015-01-01

Rh modified Au(111-25 nm) electrodes, prepared by electron beam evaporation and galvanostatic deposition, were employed to study adsorption and electro-oxidation of CO on Rh in 0.1 M sulfuric acid solution by in situ attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS). The results of ATR-SEIRAS experiments were compared with those obtained by infrared reflection absorption spectroscopy on three low-index Rh single crystal surfaces. The Rh film deposited on Au(111-25 nm) electrode consists of 3D clusters forming a highly stepped [n(111) × (111)]-like surface with narrow (111) terraces. When CO was dosed at the hydrogen adsorption potential region, CO adsorbed in both atop (CO L ) and bridge (CO B ) configurations, as well as coadsorbed water species, were detected on the Rh film electrode. A partial interconversion of spectroscopic bands due to the CO displacement from bridge to atop sites was found during the anodic potential scan, revealing that there is a potential-dependent preference of CO adsorption sites on Rh surfaces. Our data indicate that CO oxidation on Rh electrode surface in acidic media involves coadsorbed water and follows the nucleation and growth model of a Langmuir-Hinshelwood type reaction

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

DEFF Research Database (Denmark)

Albrecht, Tim; Li, Wu; Haehnel, Wolfgang

2006-01-01

to the tunnelling current, apparently due to slow electron transfer kinetics. As a consequence, STM images of heme-containing and heme-free MOP-C did not reveal any notable differences in apparent height or physical extension. The apparent height of heme-containing MOP-C did not show any dependence on the substrate...... potential being varied around the redox potential of the protein. The mere presence of an accessible molecular energy level is not sufficient to result in detectable tunnelling current modulation. (c) 2006 Elsevier B.V. All rights reserved.......In the present work, we report the electrochemical characterization and in situ scanning tunnelling microscopy (STM) studies of monolayers of an artificial de novo designed heme protein MOP-C, covalently immobilized on modified Au(111) surfaces. The protein forms closely packed monolayers, which...

Infrared spectroscopy of molecular submonolayers on surfaces by infrared scanning tunneling microscopy: tetramantane on Au111.

Science.gov (United States)

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

2013-09-20

We have developed a new scanning-tunneling-microscopy-based spectroscopy technique to characterize infrared (IR) absorption of submonolayers of molecules on conducting crystals. The technique employs a scanning tunneling microscope as a precise detector to measure the expansion of a molecule-decorated crystal that is irradiated by IR light from a tunable laser source. Using this technique, we obtain the IR absorption spectra of [121]tetramantane and [123]tetramantane on Au(111). Significant differences between the IR spectra for these two isomers show the power of this new technique to differentiate chemical structures even when single-molecule-resolved scanning tunneling microscopy (STM) images look quite similar. Furthermore, the new technique was found to yield significantly better spectral resolution than STM-based inelastic electron tunneling spectroscopy, and to allow determination of optical absorption cross sections. Compared to IR spectroscopy of bulk tetramantane powders, infrared scanning tunneling microscopy (IRSTM) spectra reveal narrower and blueshifted vibrational peaks for an ordered tetramantane adlayer. Differences between bulk and surface tetramantane vibrational spectra are explained via molecule-molecule interactions.

Long-range interfacial electron transfer and electrocatalysis of molecular scale Prussian Blue nanoparticles linked to Au(111)-electrode surfaces by different chemical contacting groups

DEFF Research Database (Denmark)

Zhu, Nan; Ulstrup, Jens; Chi, Qijin

2017-01-01

We have explored interfacial electrochemical electron transfer (ET) and electrocatalysis of 5–6 nm Prussian Blue nanoparticles (PBNPs) immobilized on Au(111)-electrode surfaces via molecular wiring with variable-length, and differently functionalized thiol-based self-assembled molecular monolayers...... (SAMs). The SAMs contain positively (−NH3+) or negatively charged (–COO–) terminal group, as well an electrostatically neutral hydrophobic terminal group (–CH3). The surface microscopic structures of the immobilized PBNPs were characterized by high-resolution atomic force microscopy (AFM) directly...... in aqueous electrolyte solution under the same conditions as for electrochemical measurements. The PBNPs displayed fast and reversible interfacial ET on all the surfaces, notably in multi-ET steps as reflected in narrow voltammetric peaks. The ET kinetics can be controlled by adjusting the length of the SAM...

In situ x-ray scattering studies of the Au(111)/electrolyte interface

International Nuclear Information System (INIS)

Wang, Jia; Ocko, B.M.; Davenport, A.J.; Isaacs, H.S.

1991-01-01

The adsorption of anions at the Au(111) electrode and the subsequent effect on the gold surface structure have been investigated using x-ray specular reflectivity and grazing incident angle diffraction techniques. The top layer of gold atoms undergoes a reversible phase transition between the (1x1) bulk termination and a (23x√ bar 3) reconstructed phase on changing the potential. The shifts of the phase transition potential in NaCland NaBr solutions from the one in NaF can be understood by the anion adsorption induced charge effect. The reconstruction formation rate increases in chloride and bromide solutions due to an increase in the surface mobility with anion adsorption. Adsorbed chloride and bromide monolayers can be monitored during a potential scan by the specular reflectivity

Occupied and unoccupied electronic states on vicinal Si(111) surfaces decorated with monoatomic gold chains; Besetzte und unbesetzte elektronische Zustaende vizinaler Si(111)-Oberflaechen mit atomaren Goldketten

Energy Technology Data Exchange (ETDEWEB)

Biedermann, Kerstin

2012-07-12

In this work, the occupied and unoccupied electronic states of vicinal Si(111)-Au surfaces were investigated. The research focused on amending the experimental electronic band structure by two-photon photoemission and laser-based photoemission and bringing it in line with theoretical band structure calculations. This work dealt with the Si(553)-Au, the Si(111)-(5x2)-Au and the Si(557)-Au surface. Angle-resolved UV-photoelectron spectroscopy gave access to the occupied part of the band structure and thus to the energetic position, the dispersion and the symmetry of the occupied states. Bichromatic two-photon photoemission, however, revealed information about the energetics and, in addition, about the dynamics of unoccupied states on a femtosecond timescale. Notably, the selective polarization of the laser pulses allowed for distinguishing and classifying many of the states with respect to their symmetry. All three surfaces exhibited both surface and bulk states in the occupied part of the band structure. They could be clearly identified and separated from surface contributions by means of tight-binding calculations of the bulk band structure of silicon and by comparison to each other. An added similarity of these surfaces are the one-dimensional Rashba-split gold states, which definitely show dispersion along the chains but not perpendicular to them. All surfaces exhibit states which can easily be assigned to the gold chains. Additional features, however, cannot be attributed clearly to the characteristics of the complex surface reconstruction in all cases. An assignment to surface states was only successfully accomplished for Si(553)-Au. The primary emphasis of this photoemission study was on the Si(553)-Au surface, which shows the smallest defect density in comparison to the other surfaces and hence exhibits the sharpest peaks in the experimental spectra. In accordance with ab-initio band structure calculations this surface also displays, in addition to one

Azobenzene versus 3,3',5,5'-tetra-tert-butyl-azobenzene (TBA) at Au(111): characterizing the role of spacer groups.

Science.gov (United States)

McNellis, Erik R; Bronner, Christopher; Meyer, Jörg; Weinelt, Martin; Tegeder, Petra; Reuter, Karsten

2010-06-28

We present large-scale density-functional theory (DFT) calculations and temperature programmed desorption measurements to characterize the structural, energetic and vibrational properties of the functionalized molecular switch 3,3',5,5'-tetra-tert-butyl-azobenzene (TBA) adsorbed at Au(111). Particular emphasis is placed on exploring the accuracy of the semi-empirical dispersion correction approach to semi-local DFT (DFT-D) in accounting for the substantial van der Waals component in the surface bonding. In line with previous findings for benzene and pure azobenzene at coinage metal surfaces, DFT-D significantly overbinds the molecule, but seems to yield an accurate adsorption geometry as far as can be judged from the experimental data. Comparing the trans adsorption geometry of TBA and azobenzene at Au(111) reveals a remarkable insensitivity of the structural and vibrational properties of the -N[double bond, length as m-dash]N- moiety. This questions the established view of the role of the bulky tert-butyl-spacer groups for the switching of TBA in terms of a mere geometric decoupling of the photochemically active diazo-bridge from the gold substrate.

Theoretical study of the surface resistivity of (111) surfaces of NixPt1-x(111) alloys

International Nuclear Information System (INIS)

Rous, P. J.

2001-01-01

A layer-Korringa - Kohn - Rostoker calculation is used to study the compositional dependence of the surface resistivity of the (111) surface of Ni x Pt 1-x (111) alloys. The compositional disorder in the bulk and at the surface is described by the coherent potential approximation. If it is assumed that the atomic planes near the (111) surface Ni x Pt 1-x have the same composition as the bulk layers, then a weak Nordheim effect is observed in the compositional dependence of the surface resistivity. However, we show that surface segregation in Ni x Pt 1-x (111) causes an inverse Nordheim dependence in the actual surface resistivity as the bulk composition is varied. [copyright] 2001 American Institute of Physics

Dipole moments associated with edge atoms; a comparative study on stepped Pt, Au and W surfaces

International Nuclear Information System (INIS)

Besocke, K.; Krahl-Urban, B.; Wagner, H.

1977-01-01

Work function measurements have been performed on stepped Pt and Au surfaces with (111) terraces and on W surfaces with (110) terraces. In each case the work function decreases linearly with increasing step density and depends on the step orientation. The work function changes are attributed to dipole moments associated with the step edges. The dipole moments per unit step length are larger for open edge structures than for densely packed ones. The dipole moments for Pt are about twice as large as for Au and W. (Auth.)

Molecular monolayers and interfacial electron transfer of pseudomonas aeruginosa azurin on Au(111)

DEFF Research Database (Denmark)

Chi, Qijin; Zhang, Jingdong; Nielsen, Jens Ulrik

2000-01-01

disulfide group to form a monolayer. The adsorption of this protein on Au(111) via a gold-sulfur binding mode is further supported by XPS measurements. In situ STM images with molecular resolution have been recorded and show a dense monolayer organization of adsorbed azurin molecules. Direct electron......We provide a comprehensive approach to the formation and characterization of molecular monolayers of the blue copper protein Pseudomonas aeruginosa azurin on Au(111) in aqueous ammonium acetate solution. Main issues are adsorption patterns, reductive desorption, properties of the double layer......, and long-range electrochemical electron transfer between the electrode and the copper center. Voltammetry, electrochemical impedance spectroscopy (EIS), in situ scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS) have been employed to disclose features of these issues. Zn...

A density functional theory study of the electronic properties of Os(II) and Os(III) complexes immobilized on Au(111)

DEFF Research Database (Denmark)

O'Boyle, N.M.; Albrecht, Tim; Murgida, D.H.

2007-01-01

We present a density functional theory (DFT) study of an osmium polypyridyl complex adsorbed on Au(111). The osmium polypyridyl complex [Os(bpy)(2)(P0P)Cl](n+) [bpy is 2,2'-bipyridine, P0P is 4,4'-bipyridine, n = 1 for osmium(II), and n = 2 for osmium(III)] is bound to the surface through the fre...

Exchange interaction of strongly anisotropic tripodal erbium single-ion magnets with metallic surfaces

DEFF Research Database (Denmark)

Dreiser, Jan; Wäckerlin, Christian; Ali, Md. Ehesan

2014-01-01

We present a comprehensive study of Er(trensal) single-ion magnets deposited in ultrahigh vacuum onto metallic surfaces. X-ray photoelectron spectroscopy reveals that the molecular structure is preserved after sublimation, and that the molecules are physisorbed on Au(111) while they are chemisorbed...... on a Ni thin film on Cu(100) single-crystalline surfaces. X-ray magnetic circular dichroism (XMCD) measurements performed on Au(111) samples covered with molecular monolayers held at temperatures down to 4 K suggest that the easy axes of the strongly anisotropic molecules are randomly oriented...... pathways toward optical addressing of surface-deposited single-ion magnets....

Interaction of Au with thin ZrO2 films: influence of ZrO2 morphology on the adsorption and thermal stability of Au nanoparticles.

Science.gov (United States)

Pan, Yonghe; Gao, Yan; Kong, Dandan; Wang, Guodong; Hou, Jianbo; Hu, Shanwei; Pan, Haibin; Zhu, Junfa

2012-04-10

The model catalysts of ZrO(2)-supported Au nanoparticles have been prepared by deposition of Au atoms onto the surfaces of thin ZrO(2) films with different morphologies. The adsorption and thermal stability of Au nanoparticles on thin ZrO(2) films have been investigated using synchrotron radiation photoemission spectroscopy (SRPES) and X-ray photoelectron spectroscopy (XPS). The thin ZrO(2) films were prepared by two different methods, giving rise to different morphologies. The first method utilized wet chemical impregnation to synthesize the thin ZrO(2) film through the procedure of first spin-coating a zirconium ethoxide (Zr(OC(2)H(5))(4)) precursor onto a SiO(2)/Si(100) substrate at room temperature followed by calcination at 773 K for 12 h. Scanning electron microscopy (SEM) investigations indicate that highly porous "sponge-like nanostructures" were obtained in this case. The second method was epitaxial growth of a ZrO(2)(111) film through vacuum evaporation of Zr metal onto Pt(111) in 1 × 10(-6) Torr of oxygen at 550 K followed by annealing at 1000 K. The structural analysis with low energy electron diffraction (LEED) of this film exhibits good long-range ordering. It has been found that Au forms smaller particles on the porous ZrO(2) film as compared to those on the ordered ZrO(2)(111) film at a given coverage. Thermal annealing experiments demonstrate that Au particles are more thermally stable on the porous ZrO(2) surface than on the ZrO(2)(111) surface, although on both surfaces, Au particles experience significant sintering at elevated temperatures. In addition, by annealing the surfaces to 1100 K, Au particles desorb completely from ZrO(2)(111) but not from porous ZrO(2). The enhanced thermal stability for Au on porous ZrO(2) can be attributed to the stronger interaction of the adsorbed Au with the defects and the hindered migration or coalescence resulting from the porous structures. © 2012 American Chemical Society

Cysteine adsorption on the Au(111) surface and the electron transfer in configuration of a scanning tunneling microscope: A quantum-chemical approach

DEFF Research Database (Denmark)

Nazmutdinov, R.R.; Manyurov, I.R.; Zinkicheva, T.T.

2007-01-01

Adsorption of two forms, molecule and radical, of amino acid L-cysteine (Cys) on the Au-12 cluster that simulates the (111) face of single-crystal gold is studied in the framework of the density functional theory. Effects of solvation of adsorbed Cys particles and lateral interaction in a monolay...

Characterization and methanol electrooxidation studies of Pt(111)/Os surfaces prepared by spontaneous deposition.

Science.gov (United States)

Johnston, Christina M; Strbac, Svetlana; Lewera, Adam; Sibert, Eric; Wieckowski, Andrzej

2006-09-12

Catalytic activity of the Pt(111)/Os surface toward methanol electrooxidation was optimized by exploring a wide range of Os coverage. Various methods of surface analyses were used, including electroanalytical, STM, and XPS methods. The Pt(111) surface was decorated with nanosized Os islands by spontaneous deposition, and the Os coverage was controlled by changing the exposure time to the Os-containing electrolyte. The structure of Os deposits on Pt(111) was characterized and quantified by in situ STM and stripping voltammetry. We found that the optimal Os surface coverage of Pt(111) for methanol electrooxidation was 0.7 +/- 0.1 ML, close to 1.0 +/- 0.1 Os packing density. Apparently, the high osmium coverage Pt(111)/Os surface provides more of the necessary oxygen-containing species (e.g., Os-OH) for effective methanol electrooxidation than the Pt(111)/Os surfaces with lower Os coverage (vs e.g., Ru-OH). Supporting evidence for this conjecture comes from the CO electrooxidation data, which show that the onset potential for CO stripping is lowered from 0.53 to 0.45 V when the Os coverage is increased from 0.2 to 0.7 ML. However, the activity of Pt(111)/Os for methanol electrooxidation decreases when the Os coverage is higher than 0.7 +/- 0.1 ML, indicating that Pt sites uncovered by Os are necessary for sustaining significant methanol oxidation rates. Furthermore, osmium is inactive for methanol electrooxidation when the platinum substrate is absent: Os deposits on Au(111), a bulk Os ingot, and thick films of electrodeposited Os on Pt(111), all compare poorly to Pt(111)/Os. We conclude that a bifunctional mechanism applies to the methanol electrooxidation similarly to Pt(111)/Ru, although with fewer available Pt sites. Finally, the potential window for methanol electrooxidation on Pt(111)/Os was observed to shift positively versus Pt(111)/Ru. Because of the difference in the Os and Ru oxophilicity under electrochemical conditions, the Os deposit provides fewer

Diffusion of single Au, Ag and Cu atoms inside Si(111)-(7 × 7) half unit cells: A comparative study

Energy Technology Data Exchange (ETDEWEB)

Liu, Qin [Department of Physics, Southern University of Science and Technology, Shenzhen, Guangdong 518055 (China); Department of Physics, The Chinese University of Hong Kong, Shatin, New Territory, Hong Kong (China); Science and Technology on Surface Physics and Chemistry Laboratory, Mianyang, Sichuan 621908 (China); Fu, Qiang [Institut für Physik and IRIS Adlershof, Humboldt-Universität zu Berlin, Zum Großen Windkanal 6, 12489 Berlin (Germany); Shao, Xiji; Ma, Xuhang; Wu, Xuefeng [Department of Physics, Southern University of Science and Technology, Shenzhen, Guangdong 518055 (China); Wang, Kedong, E-mail: wangkd@sustc.edu.cn [Department of Physics, Southern University of Science and Technology, Shenzhen, Guangdong 518055 (China); Xiao, Xudong, E-mail: xdxiao@phy.cuhk.edu.hk [Department of Physics, The Chinese University of Hong Kong, Shatin, New Territory, Hong Kong (China)

2017-04-15

Highlights: • Diffusions of Au, Ag and Cu atoms in the half unit cells of Si(111)-(7×7) have been studied by using a STM-based I-t method. • Despite their similar absorption sites, the diffusion dynamics show obvious differences between Ag and the other two. • Theoretical calculations suggest that different potential energy profiles are responsible for the observed differences. - Abstract: The diffusion behaviors of single Au, Ag and Cu atoms on Si(111)-(7 × 7) half unit cells have been investigated via combining scanning tunneling microscopy and first-principles calculations. Despite the similar adsorption sites between both half unit cells among these elements, the diffusion dynamics show obvious differences between Ag and the other two. Although obvious asymmetry has been found in the diffusion behaviors of Au and Cu atoms in two half unit cells of Si(111)-(7 × 7), the asymmetry behaves in a way different from that of Ag atoms and no dual-time character has been observed for the diffusions of Au and Cu in both half unit cells. Theoretical calculations suggest a different potential energy profile caused by the stronger hybridization between d states of Au (Cu) and Si states make the concept of basin useless for the diffusion of Au and Cu atoms inside the half unit cells of Si(111)-(7 × 7).

Adsorption and dehydrogenation of tetrahydroxybenzene on Cu(111)

DEFF Research Database (Denmark)

Bebensee, Fabian; Svane, K.; Bombis, Christian

2013-01-01

Adsorption of tetrahydroxybenzene (THB) on Cu(111) and Au(111) surfaces is studied using a combination of STM, XPS, and DFT. THB is deposited intact, but on Cu(111) it undergoes gradual dehydrogenation of the hydroxyl groups as a function of substrate temperature, yielding a pure dihydroxy......-benzoquinone phase at 370 K. Subtle changes to the adsorption structure upon dehydrogenation are explained from differences in molecule–surface bonding....

Hydrogen-bonded clusters of 1, 1'-ferrocenedicarboxylic acid on Au(111) are initially formed in solution

Science.gov (United States)

Quardokus, Rebecca C.; Wasio, Natalie A.; Brown, Ryan D.; Christie, John A.; Henderson, Kenneth W.; Forrest, Ryan P.; Lent, Craig S.; Corcelli, Steven A.; Alex Kandel, S.

2015-03-01

Low-temperature scanning tunneling microscopy is used to observe self-assembled structures of ferrocenedicarboxylic acid (Fc(COOH)2) on the Au(111) surface. The surface is prepared by pulse-deposition of Fc(COOH)2 dissolved in methanol, and the solvent is evaporated before imaging. While the rows of hydrogen-bonded dimers that are common for carboxylic acid species are observed, the majority of adsorbed Fc(COOH)2 is instead found in six-molecule clusters with a well-defined and chiral geometry. The coverage and distribution of these clusters are consistent with a random sequential adsorption model, showing that solution-phase species are determinative of adsorbate distribution for this system under these reaction conditions.

Influence of Au Nanoparticle Shape on Au@Cu2O Heterostructures

Directory of Open Access Journals (Sweden)

Jie Zhu

2015-01-01

Full Text Available Synthesis of metal-semiconductor heterostructures may allow the combination of function of the corresponding components and/or the enhanced performance resulting from the interactions between all the components. In this paper, Au@Cu2O core-shell heterostructures are prepared by a seed-growth method, using different-shaped Au nanocrystals as the seeds such as nanorods, octahedra, decahedra, dots, and nanocubes. The results revealed that the final structure of Au@Cu2O was greatly influenced by the shape of the seeds used. Exposure of Cu2O{111} and Cu2O{001} favored when the overgrowth happened on Au{111} and Au{001} surface, respectively. The size of the product can also be tuned by the amount of the seeds. The results reported here provide a thinking clue to modulate the shape and size of core-shell nanocrystals, which is useful in developing new materials with desired performance.

Mechanical and charge transport properties of alkanethiol self-assembled monolayers on Au (111) surface: The Role of Molecular Tilt

Energy Technology Data Exchange (ETDEWEB)

Mulleregan, Alice; Qi, Yabing; Ratera, Imma; Park, Jeong Y.; Ashby, Paul D.; Quek, Su Ying; Neaton, J. B.; Salmeron, Miquel

2007-11-12

The relationship between charge transport and mechanical properties of alkanethiol self-assembled monolayers (SAM) on Au(111) films has been investigated using an atomic force microscope with a conductive tip. Molecular tilts induced by the pressure applied by the tip cause stepwise increases in film conductivity. A decay constant {beta} = 0.57 {+-} 0.03 {angstrom}{sup -1} was found for the current passing through the film as a function of tip-substrate separation due to this molecular tilt. This is significantly smaller than the value of {approx} 1 {angstrom}{sup -1} found when the separation is changed by changing the length of the alkanethiol molecules. Calculations indicate that for isolated dithiol molecules S-bonded to hollow sites, the junction conductance does not vary significantly as a function of molecular tilt. The impact of S-Au bonding on SAM conductance is discussed.

Systematic Control of Self-Assembled Au Nanoparticles and Nanostructures Through the Variation of Deposition Amount, Annealing Duration, and Temperature on Si (111).

Science.gov (United States)

Li, Ming-Yu; Sui, Mao; Pandey, Puran; Zhang, Quanzhen; Kim, Eun-Soo; Lee, Jihoon

2015-12-01

The size, density, and configurations of Au nanoparticles (NPs) can play important roles in controlling the electron mobility, light absorption, and localized surface plasmon resonance, and further in the Au NP-assisted nanostructure fabrications. In this study, we present a systematical investigation on the evolution of Au NPs and nanostructures on Si (111) by controlling the deposition amount (DA), annealing temperature (AT), and dwelling time (DT). Under an identical growth condition, the morphologies of Au NPs and nanostructures drastically evolve when the DA is only slightly varied, based on the Volmer-Weber and coalescence models: i.e. I: mini NPs, II: mid-sized round dome-shaped Au NPs, III: large Au NPs, and IV: coalesced nanostructures. With the AT control, three distinctive ranges are observed: i.e., NP nucleation, Au NPs maturation and melting. The gradual dimensional expansion of Au NPs is always compensated with the density reduction, which is explained with the thermodynamic theory. The DT effect is relatively minor on Au NPs, a sharp contrast to other metallic NPs, which is discussed based on the Ostwald-ripening.

Surface photovoltage investigation of gold chains on Si(111) by two-photon photoemission

Energy Technology Data Exchange (ETDEWEB)

Otto, Sebastian; Biedermann, Kerstin; Fauster, Thomas [Lehrstuhl fuer Festkoerperphysik, Universitaet Erlangen-Nuernberg, Staudtstr. 7, D-91058 Erlangen (Germany)

2011-07-01

We present surface photovoltage measurements on Si(111)-(7 x 7) with monoatomic gold chains. The gold coverage was varied between zero and 0.6 ML, where the Si(111)-(5 x 2)-Au reconstruction covers the surface completely. During the two-photon photoemission experiments the p- or n-doped samples were illuminated by infrared (IR, E{sub IR}=1.55 eV) and ultraviolet (UV, E{sub UV}=4.65 eV) laser pulses. For all coverages the photovoltage was determined for sample temperatures of 90 K and 300 K by variation of the IR and UV laser power. P-doped as well as n-doped Si(111) wafers show a linear dependence of the photovoltage on gold coverage. This stands in contrast to scanning tunneling spectroscopy measurements, which show a coverage-independent photovoltage over a wide coverage range for n-doped wafers. While for p-doped wafers our experimentally determined photovoltage is in agreement with previous reports, for n-doped wafers the observed values are lower than expected.

In situ surface X-ray diffraction study of ultrathin epitaxial Co films on Au(111) in alkaline solution

International Nuclear Information System (INIS)

Reikowski, Finn; Maroun, Fouad; Di, Nan; Allongue, Philippe; Ruge, Martin; Stettner, Jochim; Magnussen, Olaf M.

2016-01-01

The oxidation behavior of ultrathin electrodeposited Co films on Au(111) in alkaline electrolyte was studied using in situ surface X-ray scattering techniques employing synchrotron radiation and complementary optical reflectivity and electrochemical measurements. The films are formed at pH 4 and consist of (001)-oriented hcp Co crystallites that are several nm high, a few ten nm in diameter, and remain largely unchanged after electrolyte exchange to pH 12 solution. In the pre-oxidation peak only minor changes were observed in the diffraction studies, excluding the formation of Co(OH)_2 layers. In the potential regime of Co hydroxide formation a rapid reduction of the amount of Co is observed, while the characteristic height of the islands decreases only slightly. On longer times scales, growth of 3D crystals of Co(OH)_2 occurs as well as irreversible Co dissolution into the electrolyte is found. On the basis of the structural observations oxidation of the Co film is proposed to proceed via fast formation of an ultrathin passivating layer, followed by nucleation and growth of 3D hydroxide crystals at the grain boundaries in the Co deposit.

Ballistic Electron Emission Microscopy (BEEM) of Au/Pr{sub 2}O{sub 3}/Si structures; Ballistische Elektronen Emissions Mikroskopie (BEEM) an Au/Si und Au/Pr{sub 2}O{sub 3}/Si-Strukturen

Energy Technology Data Exchange (ETDEWEB)

Mauch, I.

2007-05-15

This thesis describes Ballistic Electron Emission Microscopy (BEEM) measurements of Au/Si(111) and Au/Pr{sub 2}O{sub 3}/Si(111) structures. This technique is based on Scanning Tunnelling Microscopy (STM). It measures the ballistic transport of hot electrons through parts of the sample and across an interface, which provides a potential barrier. One part of this work was to modify the BEEM apparatus and to implement a lock in method, which modulates the tunnel current with a small frequency. In this way it is possible to study samples with very low resistance (as low as 30 k{omega}), which widely enlarges the number of samples which are appropriate for BEEM measurement at room temperature. Both types of samples studied in this thesis had low resistance and were therefore studied using the lock in method. For the classical BEEM system Au/Si(111), we observed a pronounced dependence of the sample resistance of Au/Si(111)-7 x 7 on the preparation temperature. We developed a model for the resistance of thermal prepared Au/Si(111)-7 x 7 samples. The model identifies that the low resistance is due to the surface conductivity of the reconstructed silicon surface. If the surface is prepared at a lower temperature (but still high enough that the surface is cleaned and the silicon dioxide desorbed) rough areas remain on the surface, which reduce the surface conductivity. For BEEM measurements flat areas of the sample surface are selected. The low temperature prepared samples we were able to obtain BEEM spectra as well as images at room temperature using the lock in method. The sesquioxide of praseodymium (Pr{sub 2}O{sub 3}) is currently discussed as a possible candidate for a gate oxide in semiconductor devices, since it has some of the required material properties such as a high dielectric constant, low leakage current and epitaxial growth on Si(100). We have for the first time performed BEEM measurement of praseodymium oxide. Despite a low resistance of the structures we

Emergence of chirality in hexagonally packed monolayers of hexapentyloxytriphenylene on Au(111): a joint experimental and theoretical study.

Science.gov (United States)

Sleczkowski, Piotr; Katsonis, Nathalie; Kapitanchuk, Oleksiy; Marchenko, Alexandr; Mathevet, Fabrice; Croset, Bernard; Lacaze, Emmanuelle

2014-11-11

We investigate the expression of chirality in a monolayer formed spontaneously by 2,3,6,7,10,11-pentyloxytriphenylene (H5T) on Au(111). We resolve its interface morphology by combining scanning tunneling microscopy (STM) with theoretical calculations of intermolecular and interfacial interaction potentials. We observe two commensurate structures. While both of them belong to a hexagonal space group, analogical to the triangular symmetry of the molecule and the hexagonal symmetry of the substrate surface, they surprisingly reveal a 2D chiral character. The corresponding breaking of symmetry arises for two reasons. First it is due to the establishment of a large molecular density on the substrate, which leads to a rotation of the molecules with respect to the molecular network crystallographic axes to avoid steric repulsion between neighboring alkoxy chains. Second it is due to the molecule-substrate interactions, leading to commensurable large crystallographic cells associated with the large size of the molecule. As a consequence, molecular networks disoriented with respect to the high symmetry directions of the substrate are induced. The high simplicity of the intermolecular and molecule-substrate van der Waals interactions leading to these observations suggests a generic character for this kind of symmetry breaking. We demonstrate that, for similar molecular densities, only two kinds of molecular networks are stabilized by the molecule-substrate interactions. The most stable network favors the interfacial interactions between terminal alkoxy tails and Au(111). The metastable one favors a specific orientation of the triphenylene core with its symmetry axes collinear to the Au⟨110⟩. This specific orientation of the triphenylene cores with respect to Au(111) appears associated with an energy advantage larger by at least 0.26 eV with respect to the disoriented core.

Metal-organic extended 2D structures: Fe-PTCDA on Au(111)

International Nuclear Information System (INIS)

Alvarez, Lucia; Caillard, Renaud; MartIn-Gago, Jose A; Mendez, Javier; Pelaez, Samuel; Serena, Pedro A

2010-01-01

In this work we combine organic molecules of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) with iron atoms on an Au (111) substrate in ultra-high vacuum conditions at different temperatures. By means of scanning tunnelling microscopy (STM) we study the formation of stable 2D metal-organic structures. We show that at certain growth conditions (temperature, time and coverage) stable 'ladder-like' nanostructures are obtained. These are the result of connecting together two metal-organic chains through PTCDA molecules placed perpendicularly, as rungs of a ladder. These structures, stable up to 450 K, can be extended in a 2D layer covering the entire surface and presenting different rotation domains. STM images at both polarities show a contrast reversal between the two molecules at the unit cell. By means of density functional theory (DFT) calculations, we confirm the stability of these structures and that their molecular orbitals are placed separately at the different molecules.

High-temperature morphology of stepped gold surfaces

International Nuclear Information System (INIS)

Bilalbegovic, G.; Tosatti, E.; Ercolessi, F.

1992-04-01

Molecular dynamics simulations with a classical many-body potential are used to study the high-temperature stability of stepped non-melting metal surfaces. We have studied in particular the Au(111) vicinal surfaces in the (M+1, M-1, M) family and the Au(100) vicinals in the (M, 1, 1) family. Some vicinal orientations close to the non-melting Au(111) surface become unstable close to the bulk melting temperature and facet into a mixture of crystalline (111) regions and localized surface-melted regions. On the contrary, we do not find high-temperature faceting for vicinals close to Au(100), also a non-melting surface. These (100) vicinal surfaces gradually disorder with disappearance of individual steps well below the bulk melting temperature. We have also studied the high-temperature stability of ledges formed by pairs of monoatomic steps of opposite sign on the Au(111) surface. It is found that these ledges attract each other, so that several of them merge into one larger ledge, whose edge steps then act as a nucleation site for surface melting. (author). 43 refs, 8 figs

Ab initio simulations of scanning-tunneling-microscope images with embedding techniques and application to C58-dimers on Au(111).

Science.gov (United States)

Wilhelm, Jan; Walz, Michael; Stendel, Melanie; Bagrets, Alexei; Evers, Ferdinand

2013-05-14

We present a modification of the standard electron transport methodology based on the (non-equilibrium) Green's function formalism to efficiently simulate STM-images. The novel feature of this method is that it employs an effective embedding technique that allows us to extrapolate properties of metal substrates with adsorbed molecules from quantum-chemical cluster calculations. To illustrate the potential of this approach, we present an application to STM-images of C58-dimers immobilized on Au(111)-surfaces that is motivated by recent experiments.

Bonding and orientation of 1,4-benzenedimethanethiol on Au(111) prepared from solution and from gas phase

International Nuclear Information System (INIS)

Pasquali, L; Terzi, F; Zanardi, C; Seeber, R; Paolicelli, G; Mahne, N; Nannarone, S

2007-01-01

The orientation and bonding of 1,4-benzenedimethanethiol molecules on Au(111) is studied by means of x-ray and ultraviolet (UV) photoemission, x-ray absorption and metastable deexcitation spectroscopy. The organic films are prepared both from solution and by exposing the clean substrate to the vapours of the substance in an evacuated environment. This leads to two different growth modes: when self-assembled monolayers (SAMs) are prepared from solution, the molecules tend to form a bilayer film with the molecules standing upright and with the molecular axis forming an angle of about 30 0 with respect to the substrate normal; when growth is carried out from the gas phase, the molecules tend to assume at the earliest stages of exposure a flat-lying configuration, with both sulfur end-groups bonding to Au; at increasing exposure the surface coverage presents a saturation and the chemisorbed molecules tend to assume an upright arrangement

Antibacterial Au nanostructured surfaces

Science.gov (United States)

Wu, Songmei; Zuber, Flavia; Brugger, Juergen; Maniura-Weber, Katharina; Ren, Qun

2016-01-01

We present here a technological platform for engineering Au nanotopographies by templated electrodeposition on antibacterial surfaces. Three different types of nanostructures were fabricated: nanopillars, nanorings and nanonuggets. The nanopillars are the basic structures and are 50 nm in diameter and 100 nm in height. Particular arrangement of the nanopillars in various geometries formed nanorings and nanonuggets. Flat surfaces, rough substrate surfaces, and various nanostructured surfaces were compared for their abilities to attach and kill bacterial cells. Methicillin-resistant Staphylococcus aureus, a Gram-positive bacterial strain responsible for many infections in health care system, was used as the model bacterial strain. It was found that all the Au nanostructures, regardless their shapes, exhibited similar excellent antibacterial properties. A comparison of live cells attached to nanotopographic surfaces showed that the number of live S. aureus cells was flat and rough reference surfaces. Our micro/nanofabrication process is a scalable approach based on cost-efficient self-organization and provides potential for further developing functional surfaces to study the behavior of microbes on nanoscale topographies.We present here a technological platform for engineering Au nanotopographies by templated electrodeposition on antibacterial surfaces. Three different types of nanostructures were fabricated: nanopillars, nanorings and nanonuggets. The nanopillars are the basic structures and are 50 nm in diameter and 100 nm in height. Particular arrangement of the nanopillars in various geometries formed nanorings and nanonuggets. Flat surfaces, rough substrate surfaces, and various nanostructured surfaces were compared for their abilities to attach and kill bacterial cells. Methicillin-resistant Staphylococcus aureus, a Gram-positive bacterial strain responsible for many infections in health care system, was used as the model bacterial strain. It was found that all

Self-assembled GaN nano-column grown on Si(111) substrate using Au+Ga alloy seeding method by metalorganic chemical vapor deposition

International Nuclear Information System (INIS)

Shim, Byung-Young; Ko, Eun-A; Song, Jae-Chul; Kang, Dong-Hun; Kim, Dong-Wook; Lee, In-Hwan; Kannappan, Santhakumar; Lee, Cheul-Ro

2007-01-01

Single-crystal GaN nano-column arrays were grown on Au-coated silicon (111) substrate by Au-Ga alloy seeding method using metalorganic chemical vapor deposition (MOCVD). The nano-column arrays were studied as a function of growth parameters and Au thin film thickness. The diameter and length of the as-grown nano-column vary from 100 to 500 nm and 4 to 6 μm, respectively. The surface morphology and optical properties of the nano-columns were investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), cathodoluminescence (CL) and photoluminescence (PL). The Au+Ga alloy droplets were found to be uniformly distributed on silicon surface. Further, SEM image reveals a vertical growth and cylindrical in shape GaN nano-column. The chemical composition of the nano-column, which composed of gallium and nitrogen ions, was estimated by EDX. CL reveals a strong band edge emission from the GaN nano-column. PL spectra show a peak at 365.7 nm with a full-width half maximum (FWHM) of 65 meV which indicates good optical quality GaN nano-column with low dislocation density. Our results suggest that single crystal GaN nano-column can be grown on Au+Ga alloy on silicon substrate with a low dislocation density for better device performances. (author)

Dehydrogenation of benzene on Pt(111) surface

Science.gov (United States)

Gao, W.; Zheng, W. T.; Jiang, Q.

2008-10-01

The dehydrogenation of benzene on Pt(111) surface is studied by ab initio density functional theory. The minimum energy pathways for benzene dehydrogenation are found with the nudge elastic band method including several factors of the associated barriers, reactive energies, intermediates, and transient states. The results show that there are two possible parallel minimum energy pathways on the Pt(111) surface. Moreover, the tilting angle of the H atom in benzene can be taken as an index for the actual barrier of dehydrogenation. In addition, the properties of dehydrogenation radicals on the Pt(111) surface are explored through their adsorption energy, adsorption geometry, and electronic structure on the surface. The vibrational frequencies of the dehydrogenation radicals derived from the calculations are in agreement with literature data.

First-principles study of surface plasmons on Ag(111) and H/Ag(111)

DEFF Research Database (Denmark)

Yan, Jun; Jacobsen, Karsten Wedel; Thygesen, Kristian Sommer

2011-01-01

Linear-response time-dependent density functional theory is used to investigate the relation between molecular bonding and surface plasmons for the model system H/Ag(111). We employ an orbital-dependent exchange-correlation functional to obtain a correct description of the Ag 3d band, which...... is crucial to avoid overscreening the plasmon by the s-d interband transitions. For the clean surface, this approach reproduces the experimental plasmon energies and dispersion to within 0.15 eV. Adsorption of hydrogen shifts and damps the Ag(111) surface plasmon and induces a new peak in the loss function...... at 0.6 eV below the Ag(111) plasmon peak. This feature originates from interband transitions between states located on the hydrogen atoms and states on the Ag surface atoms....

Binary molecular layers of C-60 and copper phthalocyanine on Au(111) : Self-organized nanostructuring

NARCIS (Netherlands)

Stöhr, Meike; Wagner, Thorsten; Gabriel, Markus; Weyers, Bastian; Möller, Rolf

The binary molecular system of C-60 and copper phthalocyanine(CuPc) molecules has been investigated by scanning tunneling microscopy (STM) at room temperature and at 50 K. As substrate Au(111) was chosen. When C-60 and CuPc molecules are sequentially deposited, it is found that well-ordered domains

Modification of Au surfaces using new ferrocene derivatives

International Nuclear Information System (INIS)

Diaz-Ortiz, Tanya L.; Malave-Leon, Maria; Rivera-Claudio, Mirna; Castillo-Ramirez, Jorge; Cabrera-Martinez, Carlos R.; Brito-Gomez, Rosa; Tremont, Rolando J.

2008-01-01

Gold surfaces have been modified by self-assembled techniques. Here the adsorption time of diasteroisomers (1R, 3S)-1-ferrocenyl-3-methyl-4,4-diphenyl-2,5-dioxacyclopentane and (1S, 3S)-1-ferrocenyl-3-methyl-4,4-diphenyl-2,5-dioxacyclopentane (, 3a and 3b) at a Au surface in ethanol solution was controlled. This study was followed by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) analysis. The method used for the surface modification was the control of exposure time of a Au surface in the modifier/ethanol solution. It was demonstrated by EIS and XPS that the Au surface was modified with mixture of compounds 3a + 3b, avoiding the electron transference in the interface. It was also observed that the organometallic molecule indeed had been adsorbed on the Au surface. In addition, evidence seems to conclude that the molecule-Au interaction is through the electrons of cyclopentadienyl moiety, where the oxygen atoms are near the air-molecule interface and the iron atom is near the Au surface. This type of interaction of the ferrocene derivatives with gold surfaces has not been reported by any other author

Computational investigation of CO adsorbed on Aux, Agx and (AuAg)x nanoclusters (x = 1 - 5, 147) and monometallic Au and Ag low-energy surfaces*

Science.gov (United States)

Gould, Anna L.; Catlow, C. Richard A.; Logsdail, Andrew J.

2018-02-01

Density functional theory calculations have been performed to investigate the use of CO as a probe molecule for the determination of the structure and composition of Au, Ag and AuAg nanoparticles. For very small nanoclusters (x = 1 - 5), the CO vibrational frequencies can be directly correlated to CO adsorption strength, whereas larger 147-atom nanoparticles show a strong energetic preference for CO adsorption at a vertex position but the highest wavenumbers are for the bridge positions. We also studied CO adsorption on Au and Ag (100) and (111) surfaces, for a 1 monolayer coverage, which proves to be energetically favourable on atop only and bridge positions for Au (100) and atop for Ag (100); vibrational frequencies of the CO molecules red-shift to lower wavenumbers as a result of increased metal coordination. We conclude that CO vibrational frequencies cannot be solely relied upon in order to obtain accurate compositional analysis, but we do propose that elemental rearrangement in the core@shell nanoclusters, from Ag@Au (or Au@Ag) to an alloy, would result in a shift in the CO vibrational frequencies that indicate changes in the surface composition. Contribution to the Topical Issue "Shaping Nanocatalysts", edited by Francesca Baletto, Roy L. Johnston, Jochen Blumberger and Alex Shluger.Supplementary material in the form of one pdf file available from the Journal web page at http://https://doi.org/10.1140/epjb/e2017-80280-7

Surface Chemistry Involved in Epitaxy of Graphene on 3C-SiC(111/Si(111

Directory of Open Access Journals (Sweden)

Abe Shunsuke

2010-01-01

Full Text Available Abstract Surface chemistry involved in the epitaxy of graphene by sublimating Si atoms from the surface of epitaxial 3C-SiC(111 thin films on Si(111 has been studied. The change in the surface composition during graphene epitaxy is monitored by in situ temperature-programmed desorption spectroscopy using deuterium as a probe (D2-TPD and complementarily by ex situ Raman and C1s core-level spectroscopies. The surface of the 3C-SiC(111/Si(111 is Si-terminated before the graphitization, and it becomes C-terminated via the formation of C-rich (6√3 × 6√3R30° reconstruction as the graphitization proceeds, in a similar manner as the epitaxy of graphene on Si-terminated 6H-SiC(0001 proceeds.

Antibacterial Au nanostructured surfaces.

Science.gov (United States)

Wu, Songmei; Zuber, Flavia; Brugger, Juergen; Maniura-Weber, Katharina; Ren, Qun

2016-02-07

We present here a technological platform for engineering Au nanotopographies by templated electrodeposition on antibacterial surfaces. Three different types of nanostructures were fabricated: nanopillars, nanorings and nanonuggets. The nanopillars are the basic structures and are 50 nm in diameter and 100 nm in height. Particular arrangement of the nanopillars in various geometries formed nanorings and nanonuggets. Flat surfaces, rough substrate surfaces, and various nanostructured surfaces were compared for their abilities to attach and kill bacterial cells. Methicillin-resistant Staphylococcus aureus, a Gram-positive bacterial strain responsible for many infections in health care system, was used as the model bacterial strain. It was found that all the Au nanostructures, regardless their shapes, exhibited similar excellent antibacterial properties. A comparison of live cells attached to nanotopographic surfaces showed that the number of live S. aureus cells was flat and rough reference surfaces. Our micro/nanofabrication process is a scalable approach based on cost-efficient self-organization and provides potential for further developing functional surfaces to study the behavior of microbes on nanoscale topographies.

Silicon and Germanium (111) Surface Reconstruction

Science.gov (United States)

Hao, You Gong

Silicon (111) surface (7 x 7) reconstruction has been a long standing puzzle. For the last twenty years, various models were put forward to explain this reconstruction, but so far the problem still remains unsolved. Recent ion scattering and channeling (ISC), scanning tunneling microscopy (STM) and transmission electron diffraction (TED) experiments reveal some new results about the surface which greatly help investigators to establish better models. This work proposes a silicon (111) surface reconstruction mechanism, the raising and lowering mechanism which leads to benzene -like ring and flower (raised atom) building units. Based on these building units a (7 x 7) model is proposed, which is capable of explaining the STM and ISC experiment and several others. Furthermore the building units of the model can be used naturally to account for the germanium (111) surface c(2 x 8) reconstruction and other observed structures including (2 x 2), (5 x 5) and (7 x 7) for germanium as well as the (/3 x /3)R30 and (/19 x /19)R23.5 impurity induced structures for silicon, and the higher temperature disordered (1 x 1) structure for silicon. The model is closely related to the silicon (111) surface (2 x 1) reconstruction pi-bonded chain model, which is the most successful model for the reconstruction now. This provides an explanation for the rather low conversion temperature (560K) of the (2 x 1) to the (7 x 7). The model seems to meet some problems in the explanation of the TED result, which is explained very well by the dimer, adatom and stacking fault (DAS) model proposed by Takayanagi. In order to explain the TED result, a variation of the atomic scattering factor is proposed. Comparing the benzene-like ring model with the DAS model, the former needs more work to explain the TED result and the later has to find a way to explain the silicon (111) surface (1 x 1) disorder experiment.

Sudden Intensity Increases and Radial Gradient Changes of Cosmic Ray Mev Electrons and Protons Observed at Voyager 1 Beyond 111 AU in the Heliosheath

Science.gov (United States)

Webber, W. R.; Mcdonald, F. B.; Cummings, A. C.; Stone, E. C.; Heikkila, B.; Lal, N.

2012-01-01

Voyager 1 has entered regions of different propagation conditions for energetic cosmic rays in the outer heliosheathat a distance of about 111 AU from the Sun. The low energy 614 MeV galactic electron intensity increased by 20over a time period 10 days and the electron radial intensity gradient abruptly decreased from 19AU to 8AU at2009.7 at a radial distance of 111.2 AU. At about 2011.2 at a distance of 116.6 AU a second abrupt intensity increase of25 was observed for electrons. After the second sudden electron increase the radial intensity gradient increased to18AU. This large positive gradient and the 13 day periodic variations of 200 MeV particles observed near theend of 2011 indicate that V1 is still within the overall heliospheric modulating region. The implications of these resultsregarding the proximity of the heliopause are discussed.

Surface Relaxation and Electronic States of Pt(111) Surface with Varying Slab Thickness

International Nuclear Information System (INIS)

Kaushal, Ashok K.; Mullick, Shanta; Ahluwalia, P. K.

2011-01-01

Surface relaxation and electronic DOS's of Pt(111) surface have been studied with varying slab thickness using ab-initio SIESTA method. We found the expansion in the top layer and contraction in the subsurface layers of Pt(111) surface. Our results match with the experimental results. Also observing electronic density of states we found that as we increase the thickness of slab, the PDOS of Pt(111) surface goes towards the bulk density of states and Fermi energy shifts towards the bulk fermi energy.

State-to-state time-of-flight measurements of NO scattering from Au(111): direct observation of translation-to-vibration coupling in electronically nonadiabatic energy transfer.

Science.gov (United States)

Golibrzuch, Kai; Shirhatti, Pranav R; Altschäffel, Jan; Rahinov, Igor; Auerbach, Daniel J; Wodtke, Alec M; Bartels, Christof

2013-09-12

Translational motion is believed to be a spectator degree of freedom in electronically nonadiabatic vibrational energy transfer between molecules and metal surfaces, but the experimental evidence available to support this view is limited. In this work, we have experimentally determined the translational inelasticity in collisions of NO molecules with a single-crystal Au(111) surface-a system with strong electronic nonadiabaticity. State-to-state molecular beam surface scattering was combined with an IR-UV double resonance scheme to obtain high-resolution time-of-flight data. The measurements include vibrationally elastic collisions (v = 3→3, 2→2) as well as collisions where one or two quanta of molecular vibration are excited (2→3, 2→4) or de-excited (2→1, 3→2, 3→1). In addition, we have carried out comprehensive measurements of the effects of rotational excitation on the translational energy of the scattered molecules. We find that under all conditions of this work, the NO molecules lose a large fraction (∼0.45) of their incidence translational energy to the surface. Those molecules that undergo vibrational excitation (relaxation) during the collision recoil slightly slower (faster) than vibrationally elastically scattered molecules. The amount of translational energy change depends on the surface temperature. The translation-to-rotation coupling, which is well-known for v = 0→0 collisions, is found to be significantly weaker for vibrationally inelastic than elastic channels. Our results clearly show that the spectator view of the translational motion in electronically nonadiabatic vibrational energy transfer between NO and Au(111) is only approximately correct.

Effects of Cu intercalation on the graphene/Ni(111) surface: density-functional calculations

International Nuclear Information System (INIS)

Kwon, Se Gab; Kang, Myung Ho

2012-01-01

The Cu-intercalated graphene/Ni(111) surface has been studied by using density-functional theory calculations. We find that (1) the intercalation-induced decoupling between graphene and the Ni(111) substrate begins sharply at a Cu coverage of about 0.75 ML, (2) at the optimal Cu coverage of 1 ML, graphene recovers an almost ideal Dirac-cone band structure with no band gap, and (3) the Dirac point is located at 0.17 eV below the Fermi level, indicating a small charge transfer from the substrate. Cu thus plays essentially the same role as Au in realizing quasi-free-standing graphene by intercalation. Our charge character analysis shows that the Dirac-cone bands near the Fermi level reveal a weakening of their π character when crossing the Ni d bands, suggesting that the resulting low Dirac-cone intensity could possibly be the origin of the recent photoemission report of a relatively large band gap of 0.18 eV.

In situ observation of a deprotonation driven phase transformation-4,4'-Biphenyldicarboxylic acide on Au(111)

NARCIS (Netherlands)

Schwarz, Daniel; van Gastel, Raoul; Zandvliet, Henricus J.W.; Poelsema, Bene

2013-01-01

We have studied the growth of 4,4′-biphenyldicarboxylic acid (BDA) domains on Au(111) by means of low-energy electron microscopy (LEEM) and selective area low-energy electron diffraction (μLEED). Between 300 and 400 K, BDA forms three different 2-D crystalline phases, which are attributed to

Sulfur dimers adsorbed on Au(111) as building blocks for sulfur octomers formation: A density functional study

International Nuclear Information System (INIS)

Hernandez-Tamargo, Carlos E.; Montero-Alejo, Ana Lilian; Pujals, Daniel Codorniu; Mikosch, Hans; Hernández, Mayra P.

2014-01-01

Experimental scanning tunneling microscopy (STM) studies have shown for more than two decades rectangular formations when sulfur atoms are deposited on Au(111) surfaces. The precursors have ranged from simple molecules or ions, such as SO 2 gas or sulfide anions, to more complex organosulfur compounds. We investigated, within the framework of the Density Functional Theory, the structure of these rectangular patterns assuming them entirely composed of sulfur atoms as the experimental evidence suggests. The sulfur coverage at which the simulations were carried out (0.67 ML or higher) provoked that the sulfur-sulfur association had to be taken into account for achieving a good agreement between the sets of simulated and experimental STM images. A combination of four sulfur dimers per rectangular formation properly explained the trends obtained by the experimental STM analysis which were related with the rectangles' size and shape fluctuations together with sulfur-sulfur distances within these rectangles. Finally, a projected density of states analysis showed that the dimers were capable of altering the Au(5d) electronic states at the same level as atomic sulfur adsorbed at low coverage. Besides, sulfur dimers states were perfectly distinguished, whose presence near and above the Fermi level can explain both: sulfur-sulfur bond elongation and dimers stability when they stayed adsorbed on the surface at high coverage

Sulfur dimers adsorbed on Au(111) as building blocks for sulfur octomers formation: A density functional study

Energy Technology Data Exchange (ETDEWEB)

Hernandez-Tamargo, Carlos E.; Montero-Alejo, Ana Lilian [Laboratory of Computational and Theoretical Chemistry (LQCT), Faculty of Chemistry, Havana University, Havana 10400 (Cuba); Pujals, Daniel Codorniu [Higher Institute of Technologies and Applied Sciences (InSTEC), Havana 10400 (Cuba); Mikosch, Hans [Institute of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9/E164-EC, 1060 Vienna (Austria); Hernández, Mayra P., E-mail: mayrap@imre.oc.uh.cu [Instituto de Ciencias y Tecnologías de Materiales (IMRE), Havana 10400 (Cuba)

2014-07-28

Experimental scanning tunneling microscopy (STM) studies have shown for more than two decades rectangular formations when sulfur atoms are deposited on Au(111) surfaces. The precursors have ranged from simple molecules or ions, such as SO{sub 2} gas or sulfide anions, to more complex organosulfur compounds. We investigated, within the framework of the Density Functional Theory, the structure of these rectangular patterns assuming them entirely composed of sulfur atoms as the experimental evidence suggests. The sulfur coverage at which the simulations were carried out (0.67 ML or higher) provoked that the sulfur-sulfur association had to be taken into account for achieving a good agreement between the sets of simulated and experimental STM images. A combination of four sulfur dimers per rectangular formation properly explained the trends obtained by the experimental STM analysis which were related with the rectangles' size and shape fluctuations together with sulfur-sulfur distances within these rectangles. Finally, a projected density of states analysis showed that the dimers were capable of altering the Au(5d) electronic states at the same level as atomic sulfur adsorbed at low coverage. Besides, sulfur dimers states were perfectly distinguished, whose presence near and above the Fermi level can explain both: sulfur-sulfur bond elongation and dimers stability when they stayed adsorbed on the surface at high coverage.

Electronic structure and electron dynamics at an organic molecule/metal interface: interface states of tetra-tert-butyl-imine/Au(111)

International Nuclear Information System (INIS)

Hagen, Sebastian; Wolf, Martin; Tegeder, Petra; Luo Ying; Haag, Rainer

2010-01-01

Time- and angle-resolved two-photon photoemission (2PPE) spectroscopies have been used to investigated the electronic structure, electron dynamics and localization at the interface between tetra-tert-butyl imine (TBI) and Au(111). At a TBI coverage of one monolayer (ML), the two highest occupied molecular orbitals, HOMO and HOMO-1, are observed at an energy of -1.9 and -2.6 eV below the Fermi level (E F ), respectively, and coincide with the d-band features of the Au substrate. In the unoccupied electronic structure, the lowest unoccupied molecular orbital (LUMO) has been observed at 1.6 eV with respect to E F . In addition, two delocalized states that arise from the modified image potential at the TBI/metal interface have been identified. Their binding energies depend strongly on the adsorption structure of the TBI adlayer, which is coverage dependent in the submonolayer (≤1 ML) regime. Thus the binding energy of the lower interface state (IS) shifts from 3.5 eV at 1.0 ML to 4.0 eV at 0.5 ML, which is accompanied by a pronounced decrease in its lifetime from 100 fs to below 10 fs. This is a result of differences in the wave function overlap with electronic states of the Au(111) substrate at different binding energies. This study shows that in order to fully understand the electronic structure of organic adsorbates at metal surfaces, not only adsorbate- and substrate-induced electronic states have to be considered but also ISs, which are the result of a potential formed by the interaction between the adsorbate and the substrate.

In-situ quartz crystal microgravimetric studies of molecular adsorbates containing thiol and hydroquinone moieties bound to Au(111) surfaces in aqueous electrolytes

Energy Technology Data Exchange (ETDEWEB)

Mo, Y.; Sukenik, C.; Sandifer, M. [Case Western Univ., Cleveland, OH (United States); Barriga, R.J.; Soriaga, M.P.; Scherson, D. [Texas A& M Univ., College Station, TX (United States)

1995-12-01

The microgravimetric properties of monolayers of 2, 5-dihydroxythiophenol, 2,5-dihydroxybenzyl mercaptan, and 2, 5-dihydroxy-4-methylbenzyl mercaptan adsorbed on Au(111) single crystal electrodes were examined by in situ quartz crystal microbalance techniques in aqueous perchloric acid electrolytes. The results obtained are consistent with the reversible loss of an average of about three waters per adsorbed molecule as the layers are oxidized and subsequently reduced. These observations provide evidence for discrete changes in the extent of bound water within the hydroquinone/quinone layer as the oxidation state of the monolayer is changed. 9 refs., 4 figs.

Pentacene Multilayers On Ag(111) Surface

International Nuclear Information System (INIS)

Mete, E.

2010-01-01

The structural profiles and electronic properties of pentacene (C 2 2H 1 4) multilayers on Ag(111) surface has been studied within the density functional theory (DFT) framework. We have performed first-principle total energy calculations based on the projector augmented wave (PAW) method to investigate the initial growth patterns of pentacene (Pn) on Ag(111) surface. In its bulk phase, pentacene crystallizes with a triclinic symmetry while a thin film phase having an orthorhombic unit cell is energetically less favorable by 0.12 eV/cell. Pentacene prefers to stay planar on Ag(111) surface and aligns perfectly along lattice vector (1,-1,0) without any molecular deformation at a height of 3.9 angstroms. At one monolayer (ML) coverage the separation between the molecular layer and the surface plane extends to 4.1 angstroms due to intermolecular interactions weakening surface-pentacene attraction. While the first ML remains flat, the molecules on a second full pentacene layer deposited on the surface rearrange so that they become skewed with respect to each other. This adsorption mode is energetically more preferable than the one for which the molecules form a flat pentacene layer by an energy difference similar to that obtained for bulk and thin film phases. Moreover, as new layers added, pentacenes assemble to maintain this skewness for 3 and 4 ML similar to its bulk phase while the first ML always remains flat. Therefore, our calculations indicate bulk-like initial stages for the growth pattern.

Electrodéposition et la caractérisation de nanofilms palladium sur Au (111) pour le stockage d'hydrogène Electro-deposition and characterization of palladium nanofilms on Au (111) for hydrogen storage

OpenAIRE

Wang , Liang

2012-01-01

This thesis focused on electro-deposition, characterization andhydrogen strorage of ultrathin palladium film over Au(111). Theelectrochemical characterization of the nanofilms in sulphuric mediumshows well-defined features evolving with the deposit thickness. Wecould assign each peak to a specific reaction, in agreement with thegrowth mechanisms revealed by in situ SXRD measurements. Thepseudomorphic growth of the 1st layer firstly undergoes an adsorptionstep, followed by nucleation and growt...

Controlled Synthesis of Au@AgAu Yolk-Shell Cuboctahedra with Well-Defined Facets.

Science.gov (United States)

Londono-Calderon, Alejandra; Bahena, Daniel; Yacaman, Miguel J

2016-08-02

The synthesis of Au@AgAu yolk-shell cuboctahedra nanoparticles formed by galvanic replacement in a seed-mediated method is described. Initially, single-crystal Au seeds are used for the formation of Au@Ag core-shell nanocubes, which serve as the template material for the deposition of an external Au layer. The well-controlled synthesis yields the formation of cuboctahedra nanoparticles with smooth inner and outer Au/Ag surfaces. The deposition/oxidation process is described to understand the formation of cuboctahedra and octahedra nanoparticles. The Au core maintains the initial morphology of the seed and remains static at the center of the yolk-shell because of residual Ag. Structural analysis of the shell indicates intrinsic stacking faults (SFs) near the surface. Energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) compositional analysis show an Au-Ag nonordered alloy forming the shell. The three-dimensional structure of the nanoparticles presented open facets on the [111] as observed by electron tomography SIRT reconstruction over a stack of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images. The geometrical model was validated by analyzing the direction of streaks in coherent nanobeam diffraction (NBD). The catalytic activity was evaluated using a model reaction based on the reduction of 4-nitrophenol (4-NTP) by NaBH4 in the presence of Au@AgAu yolk-shell nanoparticles.

Sensitivity of photoelectron diffraction to conformational changes of adsorbed molecules: Tetra-tert-butyl-azobenzene/Au(111

Directory of Open Access Journals (Sweden)

A. Schuler

2017-01-01

Full Text Available Electron diffraction is a standard tool to investigate the atomic structure of surfaces, interfaces, and adsorbate systems. In particular, photoelectron diffraction is a promising candidate for real-time studies of structural dynamics combining the ultimate time resolution of optical pulses and the high scattering cross-sections for electrons. In view of future time-resolved experiments from molecular layers, we studied the sensitivity of photoelectron diffraction to conformational changes of only a small fraction of molecules in a monolayer adsorbed on a metallic substrate. 3,3′,5,5′-tetra-tert-butyl-azobenzene served as test case. This molecule can be switched between two isomers, trans and cis, by absorption of ultraviolet light. X-ray photoelectron diffraction patterns were recorded from tetra-tert-butyl-azobenzene/Au(111 in thermal equilibrium at room temperature and compared to patterns taken in the photostationary state obtained by exposing the surface to radiation from a high-intensity helium discharge lamp. Difference patterns were simulated by means of multiple-scattering calculations, which allowed us to determine the fraction of molecules that underwent isomerization.

First-principle study of Mg adsorption on Si(111) surfaces

International Nuclear Information System (INIS)

Min-Ju, Ying; Ping, Zhang; Xiao-Long, Du

2009-01-01

We have carried out first-principle calculations of Mg adsorption on Si(111) surfaces. Different adsorption sites and coverage effects have been considered. We found that the threefold hollow adsorption is energy-favoured in each coverage considered, while for the clean Si(111) surface of metallic feature, we found that 0.25 and 0.5 ML Mg adsorption leads to a semiconducting surface. The results for the electronic behaviour suggest a polarized covalent bonding between the Mg adatom and Si(111) surface. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

The electro-oxidation of the mixture of formaldehyde and 2-propanol on gold (100 and (111 single crystal planes in alkaline medium

Directory of Open Access Journals (Sweden)

BRANISLAV Z. NIKOLIC

2000-12-01

Full Text Available The effect of formaldehyde on the oxidation of 2-propanol and vice versa on gold single crystal planes (100 and 111 was studied. An activating effect in the reaction of the simultaneous oxidation of 2-propanol and formaldehyde was obtained on a gold (100 plane. In the case of a gold (111 electrode, the activation effect was not obtained. It was concluded that the adsorption of formaldehyde on the electrode surface prevents the adsorption of poisoning species formed during the electro-oxidation of 2-propanol on the Au(100 plane, while this is not the case on the Au(111 plane. The different behaviour is caused by the difference in the symmetry of the surface atoms of these two Au single-crystal planes.

The importance of accurate adiabatic interaction potentials for the correct description of electronically nonadiabatic vibrational energy transfer: A combined experimental and theoretical study of NO(v = 3) collisions with a Au(111) surface

Energy Technology Data Exchange (ETDEWEB)

Golibrzuch, Kai; Shirhatti, Pranav R.; Kandratsenka, Alexander; Wodtke, Alec M.; Bartels, Christof [Institute for Physical Chemistry, Georg August University of Göttingen, Göttingen 37077 (Germany); Max Planck Institute for Biophysical Chemistry, Göttingen 37077 (Germany); Rahinov, Igor [Department of Natural Sciences, The Open University of Israel, Ra' anana 4353701 (Israel); Auerbach, Daniel J. [Institute for Physical Chemistry, Georg August University of Göttingen, Göttingen 37077 (Germany); Max Planck Institute for Biophysical Chemistry, Göttingen 37077 (Germany); Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, California 93106 (United States)

2014-01-28

We present a combined experimental and theoretical study of NO(v = 3 → 3, 2, 1) scattering from a Au(111) surface at incidence translational energies ranging from 0.1 to 1.2 eV. Experimentally, molecular beam–surface scattering is combined with vibrational overtone pumping and quantum-state selective detection of the recoiling molecules. Theoretically, we employ a recently developed first-principles approach, which employs an Independent Electron Surface Hopping (IESH) algorithm to model the nonadiabatic dynamics on a Newns-Anderson Hamiltonian derived from density functional theory. This approach has been successful when compared to previously reported NO/Au scattering data. The experiments presented here show that vibrational relaxation probabilities increase with incidence energy of translation. The theoretical simulations incorrectly predict high relaxation probabilities at low incidence translational energy. We show that this behavior originates from trajectories exhibiting multiple bounces at the surface, associated with deeper penetration and favored (N-down) molecular orientation, resulting in a higher average number of electronic hops and thus stronger vibrational relaxation. The experimentally observed narrow angular distributions suggest that mainly single-bounce collisions are important. Restricting the simulations by selecting only single-bounce trajectories improves agreement with experiment. The multiple bounce artifacts discovered in this work are also present in simulations employing electronic friction and even for electronically adiabatic simulations, meaning they are not a direct result of the IESH algorithm. This work demonstrates how even subtle errors in the adiabatic interaction potential, especially those that influence the interaction time of the molecule with the surface, can lead to an incorrect description of electronically nonadiabatic vibrational energy transfer in molecule-surface collisions.

Observation of dynamic water microadsorption on Au surface

Energy Technology Data Exchange (ETDEWEB)

Huang, Xiaokang, E-mail: xiaokang.huang@tqs.com; Gupta, Gaurav; Gao, Weixiang; Tran, Van; Nguyen, Bang; McCormick, Eric; Cui, Yongjie; Yang, Yinbao; Hall, Craig; Isom, Harold [TriQuint Semiconductor, Inc., 500 W Renner Road, Richardson, Texas 75080 (United States)

2014-05-15

Experimental and theoretical research on water wettability, adsorption, and condensation on solid surfaces has been ongoing for many decades because of the availability of new materials, new detection and measurement techniques, novel applications, and different scales of dimensions. Au is a metal of special interest because it is chemically inert, has a high surface energy, is highly conductive, and has a relatively high melting point. It has wide applications in semiconductor integrated circuitry, microelectromechanical systems, microfluidics, biochips, jewelry, coinage, and even dental restoration. Therefore, its surface condition, wettability, wear resistance, lubrication, and friction attract a lot of attention from both scientists and engineers. In this paper, the authors experimentally investigated Au{sub 2}O{sub 3} growth, wettability, roughness, and adsorption utilizing atomic force microscopy, scanning electron microscopy, reflectance spectrometry, and contact angle measurement. Samples were made using a GaAs substrate. Utilizing a super-hydrophilic Au surface and the proper surface conditions of the surrounding GaAs, dynamic microadsorption of water on the Au surface was observed in a clean room environment. The Au surface area can be as small as 12 μm{sup 2}. The adsorbed water was collected by the GaAs groove structure and then redistributed around the structure. A model was developed to qualitatively describe the dynamic microadsorption process. The effective adsorption rate was estimated by modeling and experimental data. Devices for moisture collection and a liquid channel can be made by properly arranging the wettabilities or contact angles of different materials. These novel devices will be very useful in microfluid applications or biochips.

Adsorption of human insulin on single-crystal gold surfaces investigated by in situ scanning tunnelling microscopy and electrochemistry

DEFF Research Database (Denmark)

Welinder, Anna Christina; Zhang, Jingdong; Steensgaard, D.B.

2010-01-01

sweep, LSV, cyclic, CV, and square wave (SQWV) voltammetry. Multifarious electrochemical patterns were observed. Most attention was given to reductive desorption caused by insulin binding to the Au-surfaces via up to three disulfide groups per insulin monomer, presumably converted to single Au-S links....... SQWV suggested the Au-S bond strength order Au(111) > Au(110) > Au(100) based on the reductive desorption potentials. The voltammetric diversity was paralleled by different in situ STM insulin adsorption modes on the three surfaces. Single-molecule resolution was achieved in all cases. The coverage...... followed the order Au(110) > Au(100) > Au(111) and differs from the reductive desorption order that records the Au-S bonding element. Evenly distributed single molecules were scattered over large Au(111)-terraces, with intriguing molecular arrays disclosed near the terrace edges. In comparison, high...

Organisation and Control of Nanoscale Structures on Au(111)

DEFF Research Database (Denmark)

Zhang, Jingdong; Chi, Qijin; Andersen, Jens Enevold Thaulov

2001-01-01

system is IDe arnino acid cystine in the adsorbed state. Af ter dissociation of its disulfide band cystine farms a highly ordered pattem controlled by adsorption via IDe liberated sulfur atoms and intermolecular hydrogen bonding. Further organisation at three different leveis by lateral interactions can...... constitutes a new case for the lise of in situ STM as a tool for manufacturing nanoscale pit structures on IDe Au(lll) surface at small bias voltage. Individually and in combination these data hold perspectives for preparation of atornically planar electrochernical surfaces willi controlled functionalisation...

Scanning tunnelling microscopy of a foldamer prototype at the liquid/solid interface : water/Au(111) versus 1-octanol/graphite

NARCIS (Netherlands)

Klymchenko, Andrey S.; Schuurmans, Norbert; van der Auweraer, Mark; Feringa, Ben L.; van Esch, Jan; De Feyter, Steven

2006-01-01

We report the design and synthesis of a catechol based foldamer containing amide functionalized alkyl chains, and its monolayer formation at the liquid/solid interface. By scanning tunnelling microscopy, both at the 1-octanol/graphite interface as well as at the water/Au( 111) interface, the

Adsorptive behavior of dimethylglyoxime on Au(111).

Science.gov (United States)

Kim, Jandee; Kim, Sechul; Rhee, Choong Kyun

2011-12-06

Dimethylglyoxime (DMG) adsorbed on Au(111) was investigated using electrochemical scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). STM experiments revealed three different structures of adsorbed DMG at open circuit potential (~0.07 V versus Ag/AgCl): (2√3×2√3)R30°-α, (2√3×4√3)R30°-β, and (2√3×4√3)R30°-γ. The coverage of adsorbed DMG obtained using XPS was 0.33. A combination of structural and quantitative information identified the adsorbed DMG as an anionic tetramer, held together by intermolecular hydrogen bonding and arrayed in three ordered patterns. Domains of adsorbed DMG underwent phase transitions between the observed structures, most likely due to the influence of the STM tip. However, a significant correlation between the observed structures and the imaging conditions was not found. The ordered layers existed only at open circuit potential as evidenced by their disappearance when the potential was shifted to 0.2 or -0.15 V. The ordered layers were also removed by immersion in a solution of Ni(2+), implying that the adsorbed DMG was converted to a soluble dimer complex with the Ni(2+) ion. This particular observation is discussed in terms of the rigidity of the organic network. © 2011 American Chemical Society

Fermi surfaces properties of AuAl2, AuGa2, and AuIn2 with the CaF2-type cubic structure

Science.gov (United States)

Nishimura, K.; Kakihana, M.; Suzuki, F.; Yara, T.; Hedo, M.; Nakama, T.; Ōnuki, Y.; Harima, H.

2018-05-01

We grew high-quality single crystals of AuAl2, AuGa2, and AuIn2 with the fluorite (CaF2)-type cubic structure and determined the Fermi surface properties by the de Haas-van Alphen (dHvA) experiments using full-potential LAPW bad calculations. The Fermi surface and optical properties for three compounds were once studied from an interest of colors because AuAl2 has a striking bright reddish-purple color, whereas AuGa2 and AuIn2 are, respectively, neutral and bluish. The detected dHvA frequencies in the present study are found to be in a wide range of (0.1-13)×107 Oe. The main dHvA branches for three compounds are in excellent agreement with the theoretical ones, but some dHvA branches with small dHvA frequencies are slightly deviated from the theoretical ones, especially in AuGa2 and AuIn2.

Thermovoltage in scanning tunnelling microscopy. Study of heterogeneous metal surfaces on atomic scale; Thermospannung in der Rastertunnelmikroskopie. Untersuchung heterogener Metalloberflaechen auf atomarer Skala

Energy Technology Data Exchange (ETDEWEB)

Weyers, B.

2005-07-01

In this thesis the thermovoltage has been studied via a tunnel barrier under different aspects. Au(111) has been chosen as substrate. The mean free path of the electrons on the Au(111) surface was determined by a comparison of the standing waves on stage edges with the theoretical prediction. The measurements were performed at different temperatures. Detailed studies were performed on Au(111), Cu(111), and Cu(110) in order to examine the question whether the cause for strong signal on the stage edges lies in the surface state itself or in the band gap. The mani theme of this thesis is the study of a binary metal system, in this case silver on Au(111).

The interplay between surface-water and hydrogen bonding in a water adlayer on Pt(111) and Ag(111)

Energy Technology Data Exchange (ETDEWEB)

Delle Site, Luigi [Max-Planck-Institut fuer Polymerforschung, Ackermannweg 10, D-55128 Mainz (Germany); Ghiringhelli, Luca M [Max-Planck-Institut fuer Polymerforschung, Ackermannweg 10, D-55128 Mainz (Germany); Andreussi, Oliviero [Scuola Normale Superiore, Piazza dei Cavalieri 7, 56100 Pisa (Italy); Donadio, Davide [Computational Science, Department of Chemistry and Applied Biosciences, ETH Zurich, USI-Campus, via Giuseppe Buffi 13, CH-6900 Lugano (Switzerland); Parrinello, Michele [Scuola Normale Superiore, Piazza dei Cavalieri 7, 56100 Pisa (Italy)

2007-06-20

The structure of a water adlayer on a Pt(111) surface is investigated by means of extensive first-principles calculations. Allowing for proton disorder, the ground state energy for the {radical}3 x {radical}3R30{sup o} structure can be found. This results from an interplay between water/metal chemical bonding and the hydrogen bonding of the water network. This picture is supported by substituting Pt(111) with Ag(111): the almost inert surface allows for the reconstruction of the hydrogen network. (fast track communication)

The interplay between surface-water and hydrogen bonding in a water adlayer on Pt(111) and Ag(111)

International Nuclear Information System (INIS)

Delle Site, Luigi; Ghiringhelli, Luca M; Andreussi, Oliviero; Donadio, Davide; Parrinello, Michele

2007-01-01

The structure of a water adlayer on a Pt(111) surface is investigated by means of extensive first-principles calculations. Allowing for proton disorder, the ground state energy for the √3 x √3R30 o structure can be found. This results from an interplay between water/metal chemical bonding and the hydrogen bonding of the water network. This picture is supported by substituting Pt(111) with Ag(111): the almost inert surface allows for the reconstruction of the hydrogen network. (fast track communication)

Identification of Non-Faradaic Processes by Measurement of the Electrochemical Peltier Heat during the Silver Underpotential Deposition on Au(111).

Science.gov (United States)

Frittmann, Stefan; Halka, Vadym; Schuster, Rolf

2016-04-04

We measured the heat which is reversibly exchanged during the course of an electrochemical surface reaction, i.e., the deposition/dissolution of the first two monolayers of Ag on a Au(111) surface in (bi)sulfate and perchlorate containing electrolytes. The reversibly exchanged heat corresponds to the Peltier heat of the reaction and is linearly related to its entropy change, including also non-Faradaic side processes. Hence, the measurement of the Peltier heat provides thermodynamic information on the electrochemical processes which is complementary to the current-potential relations usually obtained by conventional electrochemical methods. From the variation of the molar Peltier heat during the various stages of the deposition reaction we inferred that co-adsorption processes of anions and Ag do not play a prominent role, while we find strong indications for a charge neutral substitution reaction of adsorbed anions by hydroxide, which would not show up in cyclic voltammetry. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Bifunctional chelates of Rh-105 and Au-199 as potential radiotherapeutic agents

International Nuclear Information System (INIS)

Troutner, D.E.; Schlemper, E.O.

1990-01-01

Since last year we have: continued the synthesis of pentadentate bifunctional chelating agents based on diethylene triamine; studied the chelation Rh-105, Au-198 (as model for Au-199) and Tc-99m with these agents as well as chelation of Pd-109, Cu-67, In-111, and Co-57 with some of them; synthesized a new class of potential bifunctional chelating agents based on phenylene diamine; investigated the behavior of Au-198 as a model for Au-199; begun synthesis of bifunctional chelating agents based on terpyridly and similar ligands; and continued attempts to produce tetradentate bifunctional chelates based on diaminopropane. Each of these will be addressed in this report

Study of Alkylthiolate Self-assembled Monolayers on Au(111) Using a Semilocal meta-GGA Density Functional

DEFF Research Database (Denmark)

Ferrighi, Lara; Pan, Yun-xiang; Grönbeck, Henrik

2012-01-01

We present a density functional theory study of the structure and stability of self-assembled monolayers (SAMs) of alkylthiolate on Au(111) as a function of the alkyl chain length. The most favorable structure of the SAMs involves an RS–Au–SR complex (S being sulfur, R being an alkyl chain) forme....... In particular, the use of M06-L yields an increased stability of the SAMs with increasing alkyl chain length and an increased attractive interaction between RS–Au–SR complexes at shorter distances....... through sandwiching one Au adatom by two alkylthiolates (RSs). Comparing a generalized gradient (GGA-PBE) and a meta-GGA (MGGA-M06-L) exchange-correlation functional we find that only the meta-GGA functional predicts the experimentally observed attractive intermolecular interactions within the SAMs...

Theoretical study of the noble metals on semiconductor surfaces and Ti-base shape memory alloys

International Nuclear Information System (INIS)

Ding, Yungui.

1994-01-01

The electronic and structural properties of the (√3 x √3) R30 degrees Ag/Si(111) and (√3 x √3) R30 degrees Au/Si(111) surfaces are investigated using first principles total energy calculations. We have tested almost all experimentally proposed structural models for both surfaces and found the energetically most favorable model for each of them. The lowest energy model structure of the (√3 x √3) R30 degrees Ag/Si(111) surface consists of a top layer of Ag atoms arranged as ''honeycomb-chained-trimers'' lying above a distorted ''missing top layer'' Si(111) substrate. The coverage of Ag is 1 monolayer (ML). We find that the honeycomb structure observed in STM images arise from the electronic charge densities of an empty surface band near the Fermi level. The electronic density of states of this model gives a ''pseudo-gap'' around the Fermi level, which is consistent with experimental results. The lowest energy model for the (√3 x √3) R30 degrees Au/Si(111) surface is a conjugate honeycomb-chained-trimer (CHCT-1) configuration which consists of a top layer of trimers formed by 1 ML Au atoms lying above a ''missing top layer'' Si(111) substrate with a honeycomb-chained-trimer structure for its first layer. The structures of Au and Ag are in fact quite similar and belong to the same class of structural models. However, small variation in the structural details gives rise to quite different observed STM images, as revealed in the theoretical calculations. The electronic charge density from bands around the Fermi level for the (√3 x √3) R30 degrees, Au/Si(111) surface also gives a good description of the images observed in STM experiments. First principles calculations are performed to study the electronic and structural properties of a series of Ti-base binary alloys TiFe, TiNi, TiPd, TiMo, and TiAu in the B2 structure

New bonding configuration on Si(111) and Ge(111) surfaces induced by the adsorption of alkali metals

DEFF Research Database (Denmark)

Lottermoser, L.; Landemark, E.; Smilgies, D.M.

1998-01-01

The structure of the (3×1) reconstructions of the Si(111) and Ge(111) surfaces induced by adsorption of alkali metals has been determined on the basis of surface x-ray diffraction and low-energy electron diffraction measurements and density functional theory. The (3×1) surface results primarily f...... from the substrate reconstruction and shows a new bonding configuration consisting of consecutive fivefold and sixfold Si (Ge) rings in 〈11̅ 0〉 projection separated by channels containing the alkali metal atoms. © 1998 The American Physical Society...

Two-Dimensional Cysteine and Cystine Cluster Networks on Au(111) Disclosed by Voltammetry and in Situ Scanning Tunneling Microscopy

DEFF Research Database (Denmark)

Zhang, Jingdong; Chi, Qijin; Nielsen, Jens Ulrik

2000-01-01

Microscopic structures for molecular monolayers of L-cysteine and L-cystine assembled on Au(111) have been disclosed by employing electrochemistry and in situ scanning tunneling microscopy (STM). HighresolutionSTMimages show that the adlayers of both cyteine and cystine exhibit highly......-ordered networklike clusters with (3x3 6)R30° structure. By combining the surface coverage estimated from voltammetric data, each cluster is demonstrated to include six individual cysteine molecules or three cystine molecules. As a comparison, no cluster structure is observed for the 1-butanethiol adlayer prepared...... and examined under the same conditions as those for cysteine and cystine. This suggests that intermolecular and intramolecular hydrogen bonds among adsorbed cysteine or cystine molecules could be responsible for the origin of the cluster-network structures for the adlayers. Several models are proposed and used...

Surface structure of AU3Cu(001)

DEFF Research Database (Denmark)

Eckstein, G.A.; Maupai, S.; Dakkouri, A.S.

1999-01-01

The surface morphology, composition, and structure of Au3Cu(001) as determined by scanning tunneling microscopy and surface x-ray diffraction are presented. Atomic resolution STM images reveal distinctive geometric features. The analysis of the surface x-ray diffraction data provides clear evidence...... for the surface structure. [S0163-1829(99)04535-X]....

Ag on Si(111) from basic science to application

Energy Technology Data Exchange (ETDEWEB)

Belianinov, Aleksey [Iowa State Univ., Ames, IA (United States)

2012-01-01

In our work we revisit Ag and Au adsorbates on Si(111)-7x7, as well as experiment with a ternary system of Pentacene, Ag and Si(111). Of particular interest to us is the Si(111)-(√3x√3)R30°}–Ag (Ag-Si-√3 hereafter). In this thesis I systematically explore effects of Ag deposition on the Ag-Si-√3 at different temperatures, film thicknesses and deposition fluxes. The generated insight of the Ag system on the Si(111) is then applied to generate novel methods of nanostructuring and nanowire growth. I then extend our expertise to the Au system on the Ag-Si(111) to gain insight into Au-Si eutectic silicide formation. Finally we explore behavior and growth modes of an organic molecule on the Ag-Si interface.

The role of charge transfer in the oxidation state change of Ce atoms in the TM13-CeO2(111) systems (TM = Pd, Ag, Pt, Au): a DFT + U investigation.

Science.gov (United States)

Tereshchuk, Polina; Freire, Rafael L H; Ungureanu, Crina G; Seminovski, Yohanna; Kiejna, Adam; Da Silva, Juarez L F

2015-05-28

Despite extensive studies of transition metal (TM) clusters supported on ceria (CeO2), fundamental issues such as the role of the TM atoms in the change in the oxidation state of Ce atoms are still not well understood. In this work, we report a theoretical investigation based on static and ab initio molecular dynamics density functional theory calculations of the interaction of 13-atom TM clusters (TM = Pd, Ag, Pt, Au) with the unreduced CeO2(111) surface represented by a large surface unit cell and employing Hubbard corrections for the strong on-site Coulomb correlation in the Ce f-electrons. We found that the TM13 clusters form pyramidal-like structures on CeO2(111) in the lowest energy configurations with the following stacking sequence, TM/TM4/TM8/CeO2(111), while TM13 adopts two-dimensional structures at high energy structures. TM13 induces a change in the oxidation state of few Ce atoms (3 of 16) located in the topmost Ce layer from Ce(IV) (itinerant Ce f-states) to Ce(III) (localized Ce f-states). There is a charge flow from the TM atoms to the CeO2(111) surface, which can be explained by the electronegativity difference between the TM (Pd, Ag, Pt, Au) and O atoms, however, the charge is not uniformly distributed on the topmost O layer due to the pressure induced by the TM13 clusters on the underlying O ions, which yields a decrease in the ionic charge of the O ions located below the cluster and an increase in the remaining O ions. Due to the charge flow mainly from the TM8-layer to the topmost O-layer, the charge cannot flow from the Ce(IV) atoms to the O atoms with the same magnitude as in the clean CeO2(111) surface. Consequently, the effective cationic charge decreases mainly for the Ce atoms that have a bond with the O atoms not located below the cluster, and hence, those Ce atoms change their oxidation state from IV to III. This increases the size of the Ce(III) compared with the Ce(IV) cations, which builds-in a strain within the topmost Ce layer, and

On the influence of the aliphatic linker on fabrication of highly ordered and orientated self-assembled monolayers of aromatic selenols on AU(111)

KAUST Repository

Azzam, Waleed

2014-03-06

Self-assembled monolayers (SAMs) formed by adsorption of 1,2-dibenzyldiselenide (DPMSe) and 1,2-diphenyldiselenide (DBSe) on Au(111) substrates at room temperature have been characterized using scanning tunnelling microscopy, X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and low-energy electron diffraction. Upon adsorption, the Se-Se bonds in DPMSe and DBSe were cleaved on the gold surface to form phenylmethaneselenolate (PMSe) and benzeneselenolate (BSe) species, respectively. Although both PMSe and BSe molecular entities only differ in their structure (an additional methyl group in PMSe), the resulting monolayer films revealed noteworthy dissimilarities regarding their adlayer SAM structure and surface morphology. The molecular adlayer structure and orientation of PMSe and BSe species were found to vary significantly with the immersion time (IT). The resulting PMSe films were poorly organized, and the structure was described by a (4√3 × 2) rectangular unit cell for the SAMs prepared with 24 h of IT. Moreover, the PMSe-SAMs were found to be unstable upon exposure to air for a long time. Our results showed that exposure to air for 48 h results in the formation of small bright ad-islands, which have a height corresponding to that of a single atomic step on the Au(111). Contrary, BSe-SAMs exhibited densely packed and well-ordered monolayers, and two different structural phases were resolved at short and long ITs. The most densely packed structure was obtained for SAMs prepared with very short ITs (10 min). Upon increasing the IT, the SAMs exhibited structural changes to a lower density of molecular packing structure. The spectroscopic data also confirmed this structural transformation by suggesting an upright orientation for BSe-SAMs prepared after short ITs and strongly inclined adsorption geometry for SAMs prepared after long ITs. © 2014 American Chemical Society.

Influence of the solution pH in the 6-mercaptopurine self-assembled monolayer (6MP-SAM) on a Au(111) single-crystal electrode.

Science.gov (United States)

Madueño, Rafael; García-Raya, Daniel; Viudez, Alfonso J; Sevilla, José M; Pineda, Teresa; Blázquez, Manuel

2007-10-23

Self-assembled monolayers (SAMs) of 6-mercaptopurine (6MP) have been prepared on a Au(111) single-crystal electrode by immersion of the metal surface in a 100 microM 6MP and 0.01 M HClO4 solution. The 6MP-SAM Au(111) single-crystal electrodes were transferred to the cell and allowed to equilibrate with the different aqueous working solutions before the electrochemical experiments. The influence of the solution pH was studied by cyclic voltammetry, double layer capacitance curves, and electrochemical impedance spectroscopy. The electrochemical behavior of the 6MP-SAM in acetic acid at pH 4 presents important differences in comparison to that obtained in 0.1 M KOH solutions. Cyclic voltammograms for the reductive desorption process in acid medium are broad and show some features that can be explained by a phase transition between a chemisorbed and a physisorbed state of the 6MP molecules. The low solubility of these molecules in acid medium could explain this phenomenon and the readsorption of the complete monolayer when the potential is scanned in the positive direction. The variation of the double-layer capacitance values in the potential range of monolayer stability with the pH suggests that the acid-base chemistry of the 6MP molecules is playing a role. This fact has been studied by following the variations of the electron-transfer rate constant of the highly charged redox probes as are Fe(CN)(6)-3/-4 and Ru(NH3)(6)+3/+2 as a function of solution pH. The apparent surface pKa value for the 6MP-SAM (pKa approximately 8) is explained by the total conversion of the different 6MP tautomers that exist in solution to the thiol species in the adsorbed state.

Nitrogen adsorption on Fe(111), (100), and (110) surfaces

DEFF Research Database (Denmark)

Mortensen, Jens Jørgen; Ganduglia-Pirovano, Veronica; Hansen, Lars Bruno

1999-01-01

Adsorption energies and structures for N atoms on three low-index surfaces of Fe have been calculated using density functional theory (DFT) and the generalized gradient approximation (GGA). At low N coverage the adsorption energy on Fe(100) is found to be similar to 0.7 eV higher than on the (111......) and (110) surfaces - particularly the c(2 x 2)-N/Fe(100) structure with the N atoms in four-fold sites is very stable. We attribute the differences in adsorption energy to the lack of four-fold sites on the (111) and (110) surfaces, We suggest that at higher N coverages, islands with a structure similar...

HREM of metallized {111} iron oxide nanoparticle surfaces

International Nuclear Information System (INIS)

Lovely, G R; Brown, A P; Brydson, R; Kirkland, A I; Meyer, R; Chang, L Y; Jefferson, D A; Falke, M; Bleloch, A

2006-01-01

Mixed phase Fe 3 O 4 - γ-Fe 2 O 3 (magnetite-maghemite) nanoparticles have been fabricated by colloidal routes. HR(S)TEM images, taken on both aberration corrected and uncorrected (S)TEMs, and indirect reconstruction of images of the nanoparticles show the presence of {111} facets that terminate with enhanced contrast. This extra contrast is shown to be real and is due to additional octahedral cations occupying the {111} surfaces

SFG investigation of adsorbed CO and NO on NiO(111) surface

Energy Technology Data Exchange (ETDEWEB)

Bandara, Athula; Dobashi, Shinsaku; Kubota, Jun; Onda, Ken; Wada, Akihide; Domen, Kazunari; Hirose, Chiaki [Tokyo Inst. of Tech., Yokohama (Japan). Research Lab. of Resources Utilization; Kano, S.S.

1997-07-01

Adsorption structures of CO and NO on the NiO(111) film grown on Ni(111) crystal have been investigated by sum frequency generation (SFG) spectroscopy and infrared reflection absorption spectroscopy (IRAS). The CO stretching band of adsorbed CO on NiO(111) was observed at 2144 cm{sup -1} on the SFG spectra for both p- and s-polarized visible light. However, adsorbed NO on NiO(111) was observed at 1805 cm{sup -1} on the SFG spectra only for the p-polarized visible light. The results suggest that the adsorbed CO molecule was tilted from the surface normal but the NO molecule was perpendicular to the surface. These orientations of CO and NO reflect the surface structure of NiO(111) which has (2 x 2)-reconstructed microfacets. Adsorption of CO on Ni(111) instead of NiO(111) was also examined by SFG and IRAS. Absorption bands due to linear and bridged CO were observed at 2076 and 1918 cm{sup -1}, respectively, by IRAS. On the other hand, the linear CO molecules on Ni(111) gave an SFG peak at 2076 cm{sup -1} only for the p-polarized visible light indicating the CO molecules are perpendicular to the surface, and bridged CO molecules did not give any SFG signal. The absence of the bridged CO signal is believed to be due to the smaller Raman tensor of bridged CO. (author)

SFG investigation of adsorbed CO and NO on NiO(111) surface

International Nuclear Information System (INIS)

Bandara, Athula; Dobashi, Shinsaku; Kubota, Jun; Onda, Ken; Wada, Akihide; Domen, Kazunari; Hirose, Chiaki; Kano, S.S.

1997-01-01

Adsorption structures of CO and NO on the NiO(111) film grown on Ni(111) crystal have been investigated by sum frequency generation (SFG) spectroscopy and infrared reflection absorption spectroscopy (IRAS). The CO stretching band of adsorbed CO on NiO(111) was observed at 2144 cm -1 on the SFG spectra for both p- and s-polarized visible light. However, adsorbed NO on NiO(111) was observed at 1805 cm -1 on the SFG spectra only for the p-polarized visible light. The results suggest that the adsorbed CO molecule was tilted from the surface normal but the NO molecule was perpendicular to the surface. These orientations of CO and NO reflect the surface structure of NiO(111) which has (2 x 2)-reconstructed microfacets. Adsorption of CO on Ni(111) instead of NiO(111) was also examined by SFG and IRAS. Absorption bands due to linear and bridged CO were observed at 2076 and 1918 cm -1 , respectively, by IRAS. On the other hand, the linear CO molecules on Ni(111) gave an SFG peak at 2076 cm -1 only for the p-polarized visible light indicating the CO molecules are perpendicular to the surface, and bridged CO molecules did not give any SFG signal. The absence of the bridged CO signal is believed to be due to the smaller Raman tensor of bridged CO. (author)

A first-principles study of oxygen adsorption on Ir(111) surface

Energy Technology Data Exchange (ETDEWEB)

Gao, Hengjiao, E-mail: gaohengjiao@163.com; Xiong, Yuqing, E-mail: xiongyq@hotmail.com; Liu, Xiaoli, E-mail: shantianzi@126.com; Zhao, Dongcai, E-mail: zhaodongc@163.com; Feng, Yudong, E-mail: yudong_feng@sina.com; Wang, Lanxi, E-mail: wanglanxi@live.com; Wang, Jinxiao, E-mail: coldwind716@gmail.com

2016-12-15

Highlights: • Adsorption of oxygen on Ir(111) surface was studied by density functional theory. • The most stable adsorption site was determined by adsorption energy calculation. • Adsorption of oxygen at bridge and top site on Ir surface was the most stable ones. • Interaction of O 2p and Ir 5d orbits is relatively strong and formed hybridization. - Abstract: In order to understand deposition mechanism of iridium thin film by atomic layer deposition, the adsorption of oxygen on Ir(111) surface was studied by use of density functional theory and a periodical slab model. By calculating the adsorption energy and structure of oxygen at four adsorption sites (top, bridge, fcc-hollow and hcp-hollow) on Ir(111) surface, the most stable adsorption site was determined. On this basis, the banding mechanism of O and Ir atoms was studied by density of states of oxygen and iridium atoms. Oxygen adsorbed at hcp(parallel) site on Ir(111) surface was the most stable one according to the adsorption energy calculation results. Orbital charge analysis indicate that charge transferred from 5p and 5d orbit to 2p orbit of adsorbed O atoms, and 6s orbit of iridium atoms. Meanwhile, density of state study indicated that adsorption of oxygen on Ir(111) surface is mainly due to the interaction between 2p orbit of O atoms and 5d orbit of iridium atoms.

Alloying Au surface with Pd reduces the intrinsic activity in catalyzing CO oxidation

KAUST Repository

Qian, Kun

2016-03-30

© 2016. Various Au-Pd/SiO2 catalysts with a fixed Au loading but different Au:Pd molar ratios were prepared via deposition-precipitation method followed by H2 reduction. The structures were characterized and the catalytic activities in CO oxidation were evaluated. The formation of Au-Pd alloy particles was identified. The Au-Pd alloy particles exhibit enhanced dispersions on SiO2 than Au particles. Charge transfer from Pd to Au within Au-Pd alloy particles. Isolated Pd atoms dominate the surface of Au-Pd alloy particles with large Au:Pd molar ratios while contiguous Pd atoms dominate the surface of Au-Pd alloy particles with small Au:Pd molar ratios. Few synergetic effect of Au-Pd alloy occurs on catalyzing CO oxidation under employed reaction conditions. Alloying Au with Pd reduces the intrinsic activity in catalyzing CO oxidation, and contiguous Pd atoms on the Au-Pd alloy particles are capable of catalyzing CO oxidation while isolated Pd atoms are not. These results advance the fundamental understandings of Au-Pd alloy surfaces in catalyzing CO oxidation.

An axis-specific rotational rainbow in the direct scatter of formaldehyde from Au(111) and its influence on trapping probability.

Science.gov (United States)

Park, G Barratt; Krüger, Bastian C; Meyer, Sven; Kandratsenka, Alexander; Wodtke, Alec M; Schäfer, Tim

2017-08-02

The conversion of translational to rotational motion often plays a major role in the trapping of small molecules at surfaces, a crucial first step for a wide variety chemical processes that occur at gas-surface interfaces. However, to date most quantum-state resolved surface scattering experiments have been performed on diatomic molecules, and little detailed information is available about how the structure of nonlinear polyatomic molecules influences the mechanisms for energy exchange with surfaces. In the current work, we employ a new rotationally resolved 1 + 1' resonance-enhanced multiphoton ionization (REMPI) scheme to measure the rotational distribution in formaldehyde molecules directly scattered from the Au(111) surface at incidence kinetic energies in the range 0.3-1.2 eV. The results indicate a pronounced propensity to excite a-axis rotation (twirling) rather than b- or c-axis rotation (tumbling or cartwheeling), and are consistent with a rotational rainbow scattering model. Classical trajectory calculations suggest that the effect arises-to zeroth order-from the three-dimensional shape of the molecule (steric effects). Analysis suggests that the high degree of rotational excitation has a substantial influence on the trapping probability of formaldehyde at incidence translational energies above 0.5 eV.

Controlling the Nanoscale Patterning of AuNPs on Silicon Surfaces

Directory of Open Access Journals (Sweden)

Chris J. Allender

2013-03-01

Full Text Available This study evaluates the effectiveness of vapour-phase deposition for creating sub-monolayer coverage of aminopropyl triethoxysilane (APTES on silicon in order to exert control over subsequent gold nanoparticle deposition. Surface coverage was evaluated indirectly by observing the extent to which gold nanoparticles (AuNPs deposited onto the modified silicon surface. By varying the distance of the silicon wafer from the APTES source and concentration of APTES in the evaporating media, control over subsequent gold nanoparticle deposition was achievable to an extent. Fine control over AuNP deposition (AuNPs/μm2 however, was best achieved by adjusting the ionic concentration of the AuNP-depositing solution. Furthermore it was demonstrated that although APTES was fully removed from the silicon surface following four hours incubation in water, the gold nanoparticle-amino surface complex was stable under the same conditions. Atomic force microscopy (AFM and X-ray photoelectron spectroscopy (XPS were used to study these affects.

Magnetic order of Au nanoparticle with clean surface

Energy Technology Data Exchange (ETDEWEB)

Sato, Ryuju; Ishikawa, Soichiro; Sato, Hiroyuki; Sato, Tetsuya, E-mail: satoh@appi.keio.ac.jp

2015-11-01

Au nanoparticles, which are kept in vacuum after the preparation by gas evaporation method, show ferromagnetism even in 1.7 nm in diameter. The intrinsic magnetism is examined by detecting the disappearance of spontaneous magnetization in Au bulk prepared by heating the nanoparticles without exposure to the air. The temperature dependence of spontaneous magnetization is not monotonic and the increase in magnetization is observed after Au nanoparticles are exposed to the air. The magnetic behavior can be interpreted by the ferrimagnetic-like core–shell structure with shell thickness of 0.16±0.01 nm and magnetic moment of (1.5±0.1)×10{sup −2} μ{sub B}/Au atom, respectively. - Highlights: • Au nanoparticles with clean surface were prepared by the gas evaporation method. • The spontaneous magnetization was observed in Au nanoparticles. • Temperature dependent spontaneous magnetization of smaller Au particles was not monotonic. • The magnetic behavior was interpreted by the ferrimagnetic-like core–shell model. • The shell thickness and the magnetic moment per Au atom were estimated.

Fabricating a Homogeneously Alloyed AuAg Shell on Au Nanorods to Achieve Strong, Stable, and Tunable Surface Plasmon Resonances

KAUST Repository

Huang, Jianfeng

2015-08-13

Colloidal metal nanocrystals with strong, stable, and tunable localized surface plasmon resonances (SPRs) can be useful in a corrosive environment for many applications including field-enhanced spectroscopies, plasmon-mediated catalysis, etc. Here, a new synthetic strategy is reported that enables the epitaxial growth of a homogeneously alloyed AuAg shell on Au nanorod seeds, circumventing the phase segregation of Au and Ag encountered in conventional synthesis. The resulting core–shell structured bimetallic nanorods (AuNR@AuAg) have well-mixed Au and Ag atoms in their shell without discernible domains. This degree of mixing allows AuNR@AuAg to combine the high stability of Au with the superior plasmonic activity of Ag, thus outperforming seemingly similar nanostructures with monometallic shells (e.g., Ag-coated Au NRs (AuNR@Ag) and Au-coated Au NRs (AuNR@Au)). AuNR@AuAg is comparable to AuNR@Ag in plasmonic activity, but that it is markedly more stable toward oxidative treatment. Specifically, AuNR@AuAg and AuNR@Ag exhibit similarly strong signals in surface-enhanced Raman spectroscopy that are some 30-fold higher than that of AuNR@Au. When incubated with a H2O2 solution (0.5 m), the plasmonic activity of AuNR@Ag immediately and severely decayed, whereas AuNR@AuAg retained its activity intact. Moreover, the longitudinal SPR frequency of AuNR@AuAg can be tuned throughout the red wavelengths (≈620–690 nm) by controlling the thickness of the AuAg alloy shell. The synthetic strategy is versatile to fabricate AuAg alloyed shells on different shaped Au, with prospects for new possibilities in the synthesis and application of plasmonic nanocrystals.

Gold Mining by Alkanethiol Radicals: Vacancies and Pits in the Self-Assembled Monolayers of 1-Propanethiol and 1-Butanethiol on Au(111)

DEFF Research Database (Denmark)

Wang, Yun; Chi, Qijin; Hush, Noel S.

2011-01-01

Scanning-tunneling microscopy (STM) under electrochemical control (in situ STM) in aqueous solution, combined with a priori density functional theory (DFT) image simulations at room temperature, reveals the atomic nature of the interface between Au(111) and self-assembled monolayers (SAMs) of 1-p...

Molecular self assembly and chiral recognition of copper octacyanophthalocyanine on Au(111): Interplay of intermolecular and molecule-substrate interactions.

Science.gov (United States)

Sk, Rejaul; Dhara, Barun; Miller, Joel; Deshpande, Aparna

Submolecular resolution scanning tunneling microscopy (STM) of copper octacyanophthalocyanine, CuPc(CN)8, at 77 K demonstrates that these achiral molecules form a two dimensional (2D) tetramer-based self-assembly upon evaporation onto an atomically flat Au(111) substrate. They assemble in two different structurally chiral configurations upon adsorption on Au(111). Scanning tunneling spectroscopy (STS),acquired at 77 K, unveils the HOMO and LUMO energy levels of this self-assembly. Voltage dependent STM images show that each molecule in both the structurally chiral configurations individually becomes chiral by breaking the mirror symmetry due to the enhanced intermolecular dipolar coupling interaction at the LUMO energy while the individual molecules remain achiral at the HOMO energy and within the HOMO-LUMO gap. At the LUMO energy, the handedness of the each chiral molecule is decided by the direction of the dipolar coupling interaction in the tetramer unit cell. This preference for LUMO energy indicates that this chirality is purely electronic in nature and it manifests on top of the organizational chirality that is present in the self-assembly independent of the orbital energy. Supported by IISER Pune and DAE-BRNS, India (Project No. 2011/20/37C/17/BRNS).

High-temperature stability of Au/Pd/Cu and Au/Pd(P)/Cu surface finishes

Science.gov (United States)

Ho, C. E.; Hsieh, W. Z.; Lee, P. T.; Huang, Y. H.; Kuo, T. T.

2018-03-01

Thermal reliability of Au/Pd/Cu and Au/Pd(4-6 wt.% P)/Cu trilayers in the isothermal annealing at 180 °C were investigated by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and transmission electron microscopy (TEM). The pure Pd film possessed a nanocrystalline structure with numerous grain boundaries, thereby facilitating the interdiffusion between Au and Cu. Out-diffusion of Cu through Pd and Au grain boundaries yielded a significant amount of Cu oxides (CuO and Cu2O) over the Au surface and gave rise to void formation in the Cu film. By contrast, the Pd(P) film was amorphous and served as a good diffusion barrier against Cu diffusion. The results of this study indicated that amorphous Pd(P) possessed better oxidation resistance and thermal reliability than crystalline Pd.

Ultraflat Au nanoplates as a new building block for molecular electronics.

Science.gov (United States)

Jeong, Wooseok; Lee, Miyeon; Lee, Hyunsoo; Lee, Hyoban; Kim, Bongsoo; Park, Jeong Young

2016-05-27

We demonstrate the charge transport properties of a self-assembled organic monolayer on Au nanoplates with conductive probe atomic force microscopy (CP-AFM). Atomically flat Au nanoplates, a few hundred micrometers on each side, that have only (111) surfaces, were synthesized using the chemical vapor transport method; these nanoplates were employed as the substrates for hexadecanethiol (HDT) self-assembled monolayers (SAMs). Atomic-scale high-resolution images show (√3 x √3) R30° molecular periodicity, indicating a well-ordered structure of the HDT on the Au nanoplates. We observed reduced friction and adhesion forces on the HDT SAMs on Au nanoplates, compared with Si substrates, which is consistent with the lubricating nature of HDT SAMs. The electrical properties, such as I-V characteristics and current as a function of load, were measured using CP-AFM. We obtained a tunneling decay constant (β) of 0.57 Å(-1), including through-bond (βtb = 0.99 Å(-1)) and through-space (βts = 1.36 Å(-1)) decay constants for the two-pathway model. This indicates that the charge transport properties of HDT SAMs on Au nanoplates are consistent with those on a Au (111) film, suggesting that SAMs on nanoplates can provide a new building block for molecular electronics.

Epitaxial growth of zigzag PtAu alloy surface on Au nano-pentagrams with enhanced Pt utilization and electrocatalytic performance toward ethanol oxidation reaction

International Nuclear Information System (INIS)

Du, Cheng; Gao, Xiaohui; Zhuang, Zhihua; Cheng, Chunfeng; Zheng, Fuqin; Li, Xiaokun; Chen, Wei

2017-01-01

Highlights: • PtAu nanoalloy surface is heteroepitaxially grown on the pre-synthesized Au nano-pentagrams. • The PtAu/Au nano-pentagrams exhibit excellent electrocatalytic activity for ethanol oxidation. • The charge transfer resistance of PtAu/Au is lower than that of commercial Pt/C. • The durability and anti-poisoning ability of PtAu/Au is much better than those of commercial Pt/C - Abstract: Improving Pt utilization is of fundamental importance for many significant processes in energy conversion, which is strongly dependent on the surface structure of used catalysts. Based on the traditional Pt-on-Au system which has been proved to be an ideal nanostructure for improving the catalytic activity and stability of Pt, and the recent follow-up studies on this system, we introduce here a new strategy for fabricating Pt surface with high-index facets over the Pt-on-Au system. To achieve this goal, we elaborately designed and fabricated a unique zigzag PtAu alloy nanosurface on Au nano-pentagrams (PtAu/Au NPs) through epitaxial growth of Pt along the high-index facets on the pre-synthesized Au nano-pentagrams. Owing to the surface electronic interaction between Au and Pt and the exposed high-index facets from the unique morphology of zigzag PtAu alloy nanosurface, the as-prepared PtAu/Au NPs exhibited excellent electrocatalytic performance toward ethanol oxidation reaction (EOR) in alkaline condition. The specific activity (8.3 mA cm"−"2) and mass activity (4.4 A mg"−"1) obtained from PtAu/Au NPs are about 5.2 and 5.5 times, respectively, higher than those from commercial Pt/C for EOR.

Image-potential states on the metallic (111) surface of bismuth

International Nuclear Information System (INIS)

Muntwiler, Matthias; Zhu, X-Y

2008-01-01

An extended series (up to n=6, in quantum beats) of image-potential states (IPS) is observed in time-resolved two-photon photoelectron (TR-2PPE) spectroscopy of the Bi(111) surface. Although mainly located in the vacuum, these states probe various properties of the electronic structure of the surface as reflected in their energetics and dynamics. Based on the observation of IPS a projected gap in the surface normal direction is inferred in the region from 3.57 to 4.27 eV above the Fermi level. Despite this band gap, the lifetimes of the IPS are shorter than on comparable metals, which is an indication of the metallic character of the Bi(111) surface.

Selection of conformational states in surface self-assembly for a molecule with eight possible pairs of surface enantiomers

DEFF Research Database (Denmark)

Nuermaimaiti, Ajiguli; Schultz-Falk, Vickie; Lind Cramer, Jacob

2016-01-01

Self-assembly of a molecule with many distinct conformational states, resulting in eight possible pairs of surface enantiomers, is investigated on a Au(111) surface under UHV conditions. The complex molecule is equipped with alkyl and carboxyl moieties to promote controlled self-assembly of lamel......Self-assembly of a molecule with many distinct conformational states, resulting in eight possible pairs of surface enantiomers, is investigated on a Au(111) surface under UHV conditions. The complex molecule is equipped with alkyl and carboxyl moieties to promote controlled self......-assembly of lamellae structures. From statistical analysis of Scanning Tunnelling Microscopy (STM) data we observe a clear selection of specific conformational states after self-assembly. Using Density Functional Theory (DFT) calculations we rationalise how this selection is correlated to the orientation of the alkyl...

Surface-enhanced Raman spectroscopy with Au-nanoparticle substrate fabricated by using femtosecond pulse

Science.gov (United States)

Zhang, Wending; Li, Cheng; Gao, Kun; Lu, Fanfan; Liu, Min; Li, Xin; Zhang, Lu; Mao, Dong; Gao, Feng; Huang, Ligang; Mei, Ting; Zhao, Jianlin

2018-05-01

Au-nanoparticle (Au-NP) substrates for surface-enhanced Raman spectroscopy (SERS) were fabricated by grid-like scanning a Au-film using a femtosecond pulse. The Au-NPs were directly deposited on the Au-film surface due to the scanning process. The experimentally obtained Au-NPs presented local surface plasmon resonance effect in the visible spectral range, as verified by finite difference time domain simulations and measured reflection spectrum. The SERS experiment using the Au-NP substrates exhibited high activity and excellent substrate reproducibility and stability, and a clearly present Raman spectra of target analytes, e.g. Rhodamine-6G, Rhodamine-B and Malachite green, with concentrations down to 10‑9 M. This work presents an effective approach to producing Au-NP SERS substrates with advantages in activity, reproducibility and stability, which could be used in a wide variety of practical applications for trace amount detection.

Passivation of Si(111) surfaces with electrochemically grafted thin organic films

Science.gov (United States)

Roodenko, K.; Yang, F.; Hunger, R.; Esser, N.; Hinrichs, K.; Rappich, J.

2010-09-01

Ultra thin organic films (about 5 nm thick) of nitrobenzene and 4-methoxydiphenylamine were deposited electrochemically on p-Si(111) surfaces from benzene diazonium compounds. Studies based on atomic force microscopy, infrared spectroscopic ellipsometry and x-ray photoelectron spectroscopy showed that upon exposure to atmospheric conditions the oxidation of the silicon interface proceed slower on organically modified surfaces than on unmodified hydrogen passivated p-Si(111) surfaces. Effects of HF treatment on the oxidized organic/Si interface and on the organic layer itself are discussed.

Laser-induced desorption determinations of surface diffusion on Rh(111)

International Nuclear Information System (INIS)

Seebauer, E.G.; Schmidt, L.D.

1987-01-01

Surface diffusion of hydrogen, deuterium and CO on Rh(111) has been investigated by laser-induced thermal desorption (LITD) and compared with previous results for these species on Pt(111) and on other metals. For deuterium in the coverage range 0.02 0 - 8 x 10 -2 cm 2 /s, with a diffusion activation energy 3.7 0 rises from 10 -3 to 10 -2 cm 2 /s between θ = 0.01 and 0.40. Values of E/sub diff/ on different surfaces appear to correlate with differences in heats of adsorption in different binding states which form saddle point configurations in surface diffusion. In addition, oxidation reactions on Rh and on several other transition metal surfaces may be limited to CO or H surface diffusion. 30 refs., 3 figs., 1 tab

Surface tension estimation of high temperature melts of the binary alloys Ag-Au

Science.gov (United States)

Dogan, Ali; Arslan, Hüseyin

2017-11-01

Surface tension calculation of the binary alloys Ag-Au at the temperature of 1381 K, where Ag and Au have similar electronic structures and their atomic radii are comparable, are carried out in this study using several equations over entire composition range of Au. Apparently, the deviations from ideality of the bulk solutions, such as activities of Ag and Au are small and the maximum excess Gibbs free energy of mixing of the liquid phase is for instance -4500 J/mol at XAu = 0.5. Besides, the results obtained in Ag-Au alloys that at a constant temperature the surface tension increases with increasing composition while the surface tension decreases as the temperature increases for entire composition range of Au. Although data about surface tension of the Ag-Au alloy are limited, it was possible to make a comparison for the calculated results for the surface tension in this study with the available experimental data. Taken together, the average standard error analysis that especially the improved Guggenheim model in the other models gives the best agreement along with the experimental results at temperature 1383 K although almost all models are mutually in agreement with the other one.

Adsorption of 1,3-butadiene on Si(111)7x7 surface

International Nuclear Information System (INIS)

An, K.-S.; Kim, Y.; Baik, J.Y.; Park, C.-Y.; Kim, B.

2004-01-01

Full text: The adsorption of 1,3-butadiene (BD : C 4 H 10 ) on the Si(111)7x7 surface has been investigated using synchrotron radiation photoemission spectroscopy and scanning tunneling microscopy. BD adsorbs on the Si(111)7x7 surface at room temperature, not only adatom-rest-atom bridging but also adatom-adatom bridging type. In the valence band spectrum for the Si(111)7x7 surface, the adatom and rest-atom states were observed at the binding energies of about 0.2 and 0.8 eV, respectively. With increasing BD exposure, the adatom state is completely quenched at an initial exposure, while the rest-atom state disappears at higher exposure. This indicates two different reaction pathways of BD on the Si(111)7x7 surface. STM shows three different adsorption types on the 7x7 surface, two adatom-adatom bridging and one adatom-rest-atom bridging types. By comparing the valence band and Si 2p core level spectra with STM images, it was found that the chemical reactivity of BD molecule with the adatom-rest-atom pair is strongly higher than the adatom-adatom pair

Water dissociation on Ni(100) and Ni(111): Effect of surface temperature on reactivity

International Nuclear Information System (INIS)

Seenivasan, H.; Tiwari, Ashwani K.

2013-01-01

Water adsorption and dissociation on Ni(100) and Ni(111) surfaces are studied using density functional theory calculations. Water adsorbs on top site on both the surfaces, while H and OH adsorb on four fold hollow and three fold hollow (fcc) sites on Ni(100) and Ni(111), respectively. Transition states (TS) on both surfaces are identified using climbing image-nudged elastic band method. It is found that the barrier to dissociation on Ni(100) surface is slightly lower than that on Ni(111) surface. Dissociation on both the surfaces is exothermic, while the exothermicity on Ni(100) is large. To study the effect of lattice motion on the energy barrier, TS calculations are performed for various values of Q (lattice atom coordinate along the surface normal) and the change in the barrier height and position is determined. Calculations show that the energy barrier to reaction decreases with increasing Q and increases with decreasing Q on both the surfaces. Dissociation probability values at different surface temperatures are computed using semi-classical approximation. Results show that the influence of surface temperature on dissociation probability on the Ni(100) is significantly larger compared to that of Ni(111). Moreover, on Ni(100), a dramatic shift in energy barrier to lower incident energy values is observed with increasing surface temperature, while the shift is smaller in the case of Ni(111)

Surface acidity scales: Experimental measurements of Brønsted acidities on anatase TiO2 and comparison with coinage metal surfaces

Science.gov (United States)

Silbaugh, Trent L.; Boaventura, Jaime S.; Barteau, Mark A.

2016-08-01

The first quantitative surface acidity scale for Brønsted acids on a solid surface is presented through the use of titration-displacement and equilibrium experiments on anatase TiO2. Surface acidities of species on TiO2 correlated with gas phase acidities, as was previously observed in qualitative studies of Brønsted acid displacement on Ag(110), Cu(110) and Au(111). A 90% compression of the surface acidity scale relative to the gas phase was observed due to compensation from the covalent component of the conjugate base - surface bond. Adsorbed conjugate bases need not be completely anionic for correlations with gas phase acidities to hold. Positive and negative substituent effects, such as substituted fluorine and hydrocarbon sidechain dispersion interactions with the surface, may modify the surface acidity scale, in agreement with previous experimental and theoretical work on Au(111).

General aspects of surface alloy formation

Energy Technology Data Exchange (ETDEWEB)

Bergbreiter, Andreas; Engstfeld, Albert K.; Roetter, Ralf T.; Hoster, Harry E.; Behm, R. Juergen [Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm (Germany); Berko, Andras

2010-07-01

Surface confined alloys are excellent model systems for studies of structure-property relationships of bimetallic surfaces. They are formed by deposition of a guest metal B onto a substrate A, followed by annealing to a temperature, where place exchange between adatoms and atoms from the underlying surface layer becomes possible and diffusion into the bulk is sufficiently slow. We exemplarily confirmed by scanning tunneling microscopy and Auger electron spectroscopy for PtRu/Ru(0001), PdRu/Ru(0001), AuPt/Pt(111), AgPt/Pt(111), and AgPd/Pd(111), surface alloys are obtained for systems where metal B has a negative surface segregation energy within metal A. By exchanging A and B, however, AB surface alloys are most likely overgrown by metal B, which we demonstrate for RuPt/Pt(111) in comparison to PtRu/Ru(0001).

Growth and structure of Co/Au magnetic thin films; Croissance et structure des couches minces magnetiques Co/Au

Energy Technology Data Exchange (ETDEWEB)

Marsot, N

1999-01-14

We have studied the growth and the crystallographic structure of magnetic ultra thin cobalt/gold films (Co/Au), in order to investigate the correlations between their magnetic and structural properties. Room temperature (R.T.) Co growth on Au (111) proceeds in three stages. Up to 2 Co monolayers (ML), a bilayer island growth mode is observed. Between 2 and 5 ML, coalescence of the islands occurs, covering the substrate surface and a Co/Au mixing is observed resulting from the de-construction of the Herringbone reconstruction. Finally, beyond 5 ML, the CoAu mixing is buried and the Co growth continues in a 3-D growth. Annealing studies at 600 K on this system show a smoothing effect of the Co film, and at the same time, segregation of Au atoms. The quality of the Co/Au interface (sharpness) is not enhanced by the annealing. The local order was studied by SEXAFS and the long range order by GIXRD showing that the Co film has a hexagonal close packed structure, with an easy magnetization axis perpendicular to the surface. From a local order point of view, the Co grows with an incoherent epitaxy and keeps its own bulk parameters. The GIXRD analysis shows a residual strain in the Co film of 4%. The difference observed between the local order analysis and the long range order results is explained in terms of the low dimensions of the diffracting domains. The evolution of film strains, as a function of the Co coverage, shows a marked deviation from the elastic strain theory. Modification of the strain field in the Co film as a function of the Au coverage is studied by GIXRD analysis. The Au growth study, at R.T., shows no evidence of a Au/Co mixing in the case of the Au/Co interface. The Au overlayer adopts a twinned face centred cubic structure on the rough Co film surface. (author)

Electronic structure of graphene on Ni surfaces with different orientation

International Nuclear Information System (INIS)

Pudikov, D.A.; Zhizhin, E.V.; Rybkin, A.G.; Rybkina, A.A.; Zhukov, Y.M.; Vilkov, O. Yu.; Shikin, A.M.

2016-01-01

An experimental study of the graphene, synthesized by propylene cracking on Ni surfaces with different orientation: (100) and (111), using angle-resolved photoemission, has been performed. It has been shown that graphene on Ni(111) had a perfect lateral structure due to consistency of their lattices, whereas graphene/Ni(100) consisted of a lot of domains. For both systems electronic structure was quite similar and demonstrated a strong bonding of graphene to the underlying Ni surface. After Au intercalation the electronic structure of graphene in both systems was shifted to the Fermi level and became linear in the vicinity of the K point of the Brillouin zone. - Highlights: • Graphene on Ni(111) is well-ordered, whereas on Ni(100) – multi-domain. • Graphene on Ni(111) and Ni(100) is strongly bonded with substrate. • Intercalation of Au atoms restores the linearity in dispersion and makes graphene quasi-free on both Ni(100) and Ni(111).

Computer studies of surface structure of NiAl(111)

International Nuclear Information System (INIS)

Takeuchi, Wataru; Yamamura, Yasunori

1994-01-01

The 180 neutral impact-collision ion scattering spectroscopy (NICISS) data have been analyzed using the ACOCT program code based on the binary collision approximation (BCA). The computer simulations are performed for the case of 2 keV He + ions incident along the [ anti 12 anti 1] direction of a NiAl(111) surface. It is found that the experimental results are well reproduced by the ACOCT simulations including the inward relaxation of 40% of the first interlayer spacing on Ni terminated layer at the NiAl(111) surface and including the Moliere approximation of the Thomas-Fermi potential with a reduced Firsov screening length, multiplied by a factor of 0.60. (orig.)

A scanning tunneling microscopy study of the electronic and spin states of bis(phthalocyaninato)terbium(iii) (TbPc2) molecules on Ag(111).

Science.gov (United States)

Ara, Ferdous; Qi, Zhi Kun; Hou, Jie; Komeda, Tadahiro; Katoh, Keiichi; Yamashita, Masahiro

2016-10-25

In this article, we investigate a single molecule magnet bis(phthalocyaninato)terbium(iii) (TbPc 2 ) molecule film by using low temperature STM. In order to investigate the effect of molecule-substrate interaction on the electronic and spin properties of the adsorbed molecule, we tune the molecule-substrate coupling by switching the substrate between Au(111) and Ag(111), the latter of which provides stronger interaction with the molecule than the former. Despite the enhanced chemical reactivity of the Ag(111) surface compared with Au(111), a well-organized pseudo-square film is formed. In addition, a checker-board type contrast variation is identified, which is well explained by the existence of two types of molecules whose rotational angle between the top and bottom Pc is θ = 45° (bright molecule) and θ = 30° (dark molecule). The expected stronger molecule-substrate interaction, however, appears as an intriguing dI/dV mapping image which reveals the spatial distribution of the density of states (DOS). We identify the contrast reversal in the dI/dV mapping for the molecules of θ = 45° and θ = 30° at the sample voltages of V = 0.7 eV and 1.1 eV. Combined with the density functional theory (DFT) calculation, we attribute this change to the shift of an electronic state due to the rotation of the mutual angle between the top and bottom Pc. For the spin behavior, we previously observed a Kondo resonance for the TbPc 2 molecule adsorbed on the Au(111) surface. On the Ag(111) surface, the Kondo resonance is hardly observed, which is due to the annihilation of the π radical spin by the charge transfer from the substrate to the molecule. Instead we observe a Kondo peak for the molecule on the second layer, for which the spin recovers due to the reduction of the coupling with the substrate. In addition, when a magnetic field of 2 T normal to the surface is applied, the second layer molecule shows a sharp dip at the Fermi level. We attribute this to the inelastic

Switching and sensing spin states of co-porphyrin in bimolecular reactions on Au111 using scanning tunneling microscopy.

Science.gov (United States)

Kim, Howon; Chang, Yun Hee; Lee, Soon-Hyeong; Kim, Yong-Hyun; Kahng, Se-Jong

2013-10-22

Controlling and sensing spin states of magnetic molecules at the single-molecule level is essential for spintronic molecular device applications. Here, we demonstrate that spin states of Co-porphyrin on Au(111) can be reversibly switched over by binding and unbinding of the NO molecule and can be sensed using scanning tunneling microscopy and spectroscopy (STM and STS). Before NO exposure, Co-porphryin showed a clear zero-bias peak, a signature of Kondo effect in STS, whereas after NO exposures, it formed a molecular complex, NO-Co-porphyrin, that did not show any zero-bias feature, implying that the Kondo effect was switched off by binding of NO. The Kondo effect could be switched back on by unbinding of NO through single-molecule manipulation or thermal desorption. Our density functional theory calculation results explain the observations with pairing of unpaired spins in dz(2) and ppπ* orbitals of Co-porphyrin and NO, respectively. Our study opens up ways to control molecular spin state and Kondo effect by means of enormous variety of bimolecular binding and unbinding reactions on metallic surfaces.

Alkyl-terminated Si(111) surfaces: A high-resolution, core level photoelectron spectroscopy study

Energy Technology Data Exchange (ETDEWEB)

Terry, J.; Linford, M.R.; Wigren, C.; Cao, R.; Pianetta, P.; Chidsey, C.E. [Stanford University, Stanford, California 94309 (United States)

1999-01-01

The bonding of alkyl monolayers to Si(111) surfaces has been studied with high-resolution core level photoelectron spectroscopy (PES). Two very different wet-chemical methods have been used to prepare the alkyl monolayers: (i) Olefin insertion into the H{endash}Si bond of the H{endash}Si(111) surface, and (ii) replacement of Cl on the Cl{endash}Si(111) surface by an alkyl group from an alkyllithium reagent. In both cases, PES has revealed a C 1s component shifted to lower binding energy and a Si 2p component shifted to higher binding energy. Both components are attributed to the presence of a C{endash}Si bond at the interface. Along with photoelectron diffraction data [Appl. Phys. Lett. {bold 71}, 1056, (1997)], these data are used to show that these two synthetic methods can be used to functionalize the Si(111) surface. {copyright} {ital 1999 American Institute of Physics.}

Adsorption and reaction of propanal, 2-propenol and 1-propanol on Ni/Pt(111) bimetallic surfaces

Science.gov (United States)

Murillo, Luis E.; Chen, Jingguang G.

2008-07-01

The hydrogenation of acrolein (CH 2dbnd CH sbnd CH dbnd O) can lead to the formation of three hydrogenation products, 2-propenol (CH 2dbnd CH sbnd CH 2sbnd OH), propanal (CH 3sbnd CH 2sbnd CH dbnd O), and 1-propanol (CH 3sbnd CH 2sbnd CH 2sbnd OH). In the current study the adsorption and reaction of these three molecules were investigated on Ni/Pt(111) surfaces to understand the different hydrogenation pathways of acrolein, using temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS). TPD experiments showed that 2-propenol underwent isomerization toward propanal on Pt(111) and the Pt sbnd Ni sbnd Pt(111) bimetallic surface, with a dominant decarbonylation pathway on the Pt(111) surface. A self-hydrogenation (disproportionation) pathway toward 1-propanol was observed on the Ni(111) film, however, the decarbonylation pathway was found to be the most dominant on this surface. Unlike 2-propenol, propanal did not undergo isomerization or self-hydrogenation pathways on any of the surfaces, with the dominant pathway being primarily the decarbonylation on Pt(111) and Ni(111). In contrast, 1-propanol underwent mainly molecular desorption from all three surfaces. These results provided additional understanding of previous studies of hydrogenation pathways of acrolein on the Ni/Pt(111) surfaces.

Alloying Au surface with Pd reduces the intrinsic activity in catalyzing CO oxidation

KAUST Repository

Qian, Kun; Luo, Liangfeng; Jiang, Zhiquan; Huang, Weixin

2016-01-01

were evaluated. The formation of Au-Pd alloy particles was identified. The Au-Pd alloy particles exhibit enhanced dispersions on SiO2 than Au particles. Charge transfer from Pd to Au within Au-Pd alloy particles. Isolated Pd atoms dominate the surface

Decomposition mechanism of formic acid on Cu (111) surface: A theoretical study

Energy Technology Data Exchange (ETDEWEB)

Jiang, Zhao, E-mail: jiangzhao@mail.xjtu.edu.cn; Qin, Pei; Fang, Tao

2017-02-28

Highlights: • Adsorption and decomposition mechanism of HCOOH on Cu (111) were investigated using DFT calculations. • The stable co-adsorption configurations of related intermediates were identified. • Five dissociation pathways of HCOOH via initial H−O, C−H and C−O bond scissions were considered and analyzed. - Abstract: The study of formic acid decomposition on transition metal surfaces is important to obtain useful information for vapor phase catalysis involving HCOOH and for the development of direct formic acid fuel cells. In this study, periodic density functional theory calculations have been employed to investigate the dissociation pathways of HCOOH on Cu (111) surface. About adsorption, it is found that the adsorption of HCOO, COOH, HCO, CO, OH and H on Cu (111) are considered chemisorption, whereas HCOOH, CO{sub 2}, H{sub 2}O and H{sub 2} have the weak interaction with Cu (111) surface. Furthermore, the minimum energy pathways are analyzed for the decomposition of HCOOH to CO{sub 2} and CO through the scission of H−O, C−H and C−O bonds. It is found that HCOOH, HCOO and COOH prefer to dissociate in the related reactions rather than desorb. For the decomposition, it is indicated that HCO and COOH are the main dissociated intermediates of trans-HCOOH, CO{sub 2} is the main dissociated intermediates of bidentate-HCOO, and CO is the main dissociated product of cis-COOH. The co-adsorbed H atom is beneficial for the formation of CO{sub 2} from cis-COOH. Besides, it is found that the most favorable path for HCOOH decomposition on Cu (111) surface is HCOOH-HCO-CO (Path 5), where the step of CO formation from HCO dehydrogenation is considered to be the rate-determining step. The results also show that CO is preferentially formed as the dominant product of HCOOH on Cu (111) surface.

HREEL study of c(53x9)rect-N structure on Ni(111) surface

International Nuclear Information System (INIS)

Papagno, M.; Pacile, D.; Giallombardo, C.; Cupolillo, A.; Papagno, L.

2005-01-01

In this work we have prepared and characterized by low energy electron diffraction (LEED) and high-resolution electron energy loss spectroscopy (HREELS) the Ni(111)-c(53x9)rect-N surface structure formed by saturating the Ni(111) surface with nitrogen atoms. This structure was obtained by the ion-gauge assisted N 2 exposure method. The loss spectra show features at 50 and 25meV assigned to the N-Ni vibration and to a phonon of the reconstructed surface, respectively. We also investigated the case in which the Ni(111) surface was covered with a low coverage of N atoms

Stick–slip behaviour on Au(111 with adsorption of copper and sulfate

Directory of Open Access Journals (Sweden)

Nikolay Podgaynyy

2015-03-01

Full Text Available Several transitions in the friction coefficient with increasing load are found on Au(111 in sulfuric acid electrolyte containing Cu ions when a monolayer (or submonolayer of Cu is adsorbed. At the corresponding normal loads, a transition to double or multiple slips in stick–slip friction is observed. The stick length in this case corresponds to multiples of the lattice distance of the adsorbed sulfate, which is adsorbed in a √3 × √7 superstructure on the copper monolayer. Stick–slip behaviour for the copper monolayer as well as for 2/3 coverage can be observed at FN ≥ 15 nN. At this normal load, a change from a small to a large friction coefficient occurs. This leads to the interpretation that the tip penetrates the electrochemical double layer at this point. At the potential (or point of zero charge (pzc, stick–slip resolution persists at all normal forces investigated.

Efficient H2 production over Au/graphene/TiO2 induced by surface plasmon resonance of Au and band-gap excitation of TiO2

International Nuclear Information System (INIS)

Liu, Yang; Yu, Hongtao; Wang, Hua; Chen, Shuo; Quan, Xie

2014-01-01

Highlights: • Both surface plasmon resonance and band-gap excitation were used for H 2 production. • Au/Gr/TiO 2 composite photocatalyst was synthesized. • Au/Gr/TiO 2 exhibited enhancement of light absorption and charge separation. • H 2 production rate of Au/Gr/TiO 2 was about 2 times as high as that of Au/TiO 2 . - Abstract: H 2 production over Au/Gr/TiO 2 composite photocatalyst induced by surface plasmon resonance of Au and band-gap excitation of TiO 2 using graphene (Gr) as an electron acceptor has been investigated. Electron paramagnetic resonance study indicated that, in this composite, Gr collected electrons not only from Au with surface plasmon resonance but also from TiO 2 with band-gap excitation. Surface photovoltage and UV–vis absorption measurements revealed that compared with Au/TiO 2 , Au/Gr/TiO 2 displayed more effective photogenerated charge separation and higher optical absorption. Benefiting from these advantages, the H 2 production rate of Au/Gr/TiO 2 composite with Gr content of 1.0 wt% and Au content of 2.0 wt% was about 2 times as high as that of Au/TiO 2 . This work represents an important step toward the efficient application of both surface plasmon resonance and band-gap excitation on the way to converting solar light into chemical energy

Surface diffusion coefficient of Au atoms on single layer graphene grown on Cu

Energy Technology Data Exchange (ETDEWEB)

Ruffino, F., E-mail: francesco.ruffino@ct.infn.it; Cacciato, G.; Grimaldi, M. G. [Dipartimento di Fisica ed Astronomia-Universitá di Catania, via S. Sofia 64, 95123 Catania, Italy and MATIS IMM-CNR, via S. Sofia 64, 95123 Catania (Italy)

2014-02-28

A 5 nm thick Au film was deposited on single layer graphene sheets grown on Cu. By thermal processes, the dewetting phenomenon of the Au film on the graphene was induced so to form Au nanoparticles. The mean radius, surface-to-surface distance, and surface density evolution of the nanoparticles on the graphene sheets as a function of the annealing temperature were quantified by scanning electron microscopy analyses. These quantitative data were analyzed within the classical mean-field nucleation theory so to obtain the temperature-dependent Au atoms surface diffusion coefficient on graphene: D{sub S}(T)=[(8.2±0.6)×10{sup −8}]exp[−(0.31±0.02(eV)/(at) )/kT] cm{sup 2}/s.

GaAs (111) and (1'-.2m''.3m bar ' '.2m''-.3m' 1'-.2m''.3m bar ' '.2m''-.3m' 1'-.2m''.3m bar ' '.2m''-.3m' ) surfaces and the GaAs/AlAs (111) heterojunction studied using a local energy density

International Nuclear Information System (INIS)

Chetty, N.; Martin, R.M.

1992-01-01

We use a local energy density scrE(r) within density-functional theory to study GaAs (111) and (bar 1 bar 1 bar 1) surfaces, and the GaAs/AlAs (111) heterojunction. We use scrE(r) to calculate the formation enthalpy of a single isolated GaAs (111) and (bar 1 bar 1 bar 1) surface, which is not possible with the use of conventional total-energy methods. We are able to address questions related to the stability of these surfaces. Our methods also apply to heterojunctions where we consider GaAs/AlAs (111) as a prototype. We use scrE(r) to calculate the formation enthalpy of the Ga-rich and Al-rich interfaces, which are distinct and which are both inherent in the supercell geometry

Laterally enhanced growth of electrodeposited Au to form ultrathin films on nonconductive surfaces

International Nuclear Information System (INIS)

Kobayashi, Chiaki; Saito, Mikiko; Homma, Takayuki

2012-01-01

We investigated the laterally enhanced growth of electrodeposited Au for fabricating nanogap electrodes. To enhance the lateral growth, we carried out electrodeposition over patterned electrodes onto a SiO 2 surface modified with self-assembled monolayers (SAMs) or dendrimers with amine groups. The morphology and thickness of the Au films were controlled by adjusting deposition conditions such as duration, applied potential, and Au ion concentration in the bath. To investigate the mechanism of the laterally enhanced growth, the surface states of SAM- or dendrimer-modified SiO 2 were analyzed by X-ray photoelectron spectroscopy (XPS). The XPS results indicate the existence of organic molecules and Au ions on the SiO 2 surface, which suggests that laterally enhanced growth is induced by the Au ions coordinated on the amine groups of the organic molecules. To further analyze the mechanism of the laterally enhanced growth, we investigated the relationship between the morphology of the laterally enhanced growth of Au and the amount of Au ions on organic molecules. The laterally enhanced growth of Au is expected to be useful for fabricating thin film nanogap electrodes.

Revisiting the adsorption of copper-phthalocyanine on Au(111) including van der Waals corrections

International Nuclear Information System (INIS)

Lüder, Johann; Eriksson, Olle; Sanyal, Biplab; Brena, Barbara

2014-01-01

We have studied the adsorption of copper-phthalocyanine on Au(111) by means of van der Waals corrected density functional theory using the Tkatchenko-Scheffler method. We have compared the element and site resolved adsorption distances to recent experimental normal-incident X-ray standing wave measurements. The measured adsorption distances could be reproduced within a deviation of 1% for the Cu atom, 1% for the C atoms, and 2% for the N atoms. The molecule was found to have a magnetic moment of 1 μ B distributed over the Cu and the N atoms of the pyrrole ring. Simulated scanning tunnel microscopy images based on the total and on the spin-resolved differential charge densities are provided for bias voltages of −1.45 and 1.45 eV

Novel surface diffusion characteristics for a robust pentacene derivative on Au(1 1 1) surfaces

Science.gov (United States)

Miller, Ryan A.; Larson, Amanda; Pohl, Karsten

2017-06-01

Molecular dynamics simulations have been performed in both the ab initio and classical mechanics frameworks of 5,6,7-trithiapentacene-13-one (TTPO) molecules on flat Au(1 1 1) surfaces. Results show new surface diffusion characteristics including a strong preference for the molecule to align its long axis parallel to the sixfold Au(1 1 1) symmetry directions and subsequently diffuse along these close-packed directions, and a calculated activation energy for diffusion of 0.142 eV, about four times larger than that for pure pentacene on Au. The temperature-dependent diffusion coefficients were calculated to help quantify the molecular mobility during the experimentally observed process of forming self-assembled monolayers on gold electrodes.

C6H6/Au(111): Interface dipoles, band alignment, charging energy, and van der Waals interaction

International Nuclear Information System (INIS)

Abad, E.; Martinez, J. I.; Flores, F.; Ortega, J.; Dappe, Y. J.

2011-01-01

We analyze the benzene/Au(111) interface taking into account charging energy effects to properly describe the electronic structure of the interface and van der Waals interactions to obtain the adsorption energy and geometry. We also analyze the interface dipoles and discuss the barrier formation as a function of the metal work-function. We interpret our DFT calculations within the induced density of interface states (IDIS) model. Our results compare well with experimental and other theoretical results, showing that the dipole formation of these interfaces is due to the charge transfer between the metal and benzene, as described in the IDIS model.

Oxidation-reduction induced roughening of platinum (111) surface

International Nuclear Information System (INIS)

You, H.; Nagy, Z.

1993-06-01

Platinum (111) single crystal surface was roughened by repeated cycles of oxidation and reduction to study dynamic evolution of surface roughening. The interface roughens progressively upon repeated cycles. The measured width of the interface was fit to an assumed pow law, W ∼t β , with β = 0.38(1). The results are compared with a simulation based on a random growth model. The fraction of the singly stepped surface apparently saturates to 0. 25 monolayer, which explains the apparent saturation to a steady roughness observed in previous studies

(Tl, Sb) and (Tl, Bi) binary surface reconstructions on Ge(111) substrate

Science.gov (United States)

Gruznev, D. V.; Bondarenko, L. V.; Tupchaya, A. Y.; Yakovlev, A. A.; Mihalyuk, A. N.; Zotov, A. V.; Saranin, A. A.

2018-03-01

2D compounds made of Group-III and Group-V elements on the surface of silicon and germanium attract considerable attention due to prospects of creating III-V binary monolayers, which are predicted to hold advanced physical properties. In the present work, we have investigated two such systems, (Tl, Sb)/Ge(111) and (Tl, Bi)/Ge(111) using scanning tunneling microscopy, low energy electron diffraction observations and density-functional-theory calculations. In addition to the previously reported surface structures of 2D (Tl, Sb) and (Tl, Bi) compounds on Si(111), we found new ones, namely, √{ 7} × √{ 7} and 3 × 3. Formation processes and plausible models of their atomic arrangements are discussed.

Exotic high activity surface patterns in PtAu nanoclusters

KAUST Repository

Mokkath, Junais Habeeb; Schwingenschlö gl, Udo

2013-01-01

of the truncated octahedron cluster motif. Exotic surface patterns are obtained particularly for Pt-rich compositions, where Pt atoms are being surrounded by Au atoms. These surface arrangements boost the catalytic activity by creating a large number of active

Site-specific growth of Au-Pd alloy horns on Au nanorods: A platform for highly sensitive monitoring of catalytic reactions by surface enhancement raman spectroscopy

KAUST Repository

Huang, Jianfeng

2013-06-12

Surface-enhanced Raman scattering (SERS) is a highly sensitive probe for molecular detection. The aim of this study was to develop an efficient platform for investigating the kinetics of catalytic reactions with SERS. To achieve this, we synthesized a novel Au-Pd bimetallic nanostructure (HIF-AuNR@AuPd) through site-specific epitaxial growth of Au-Pd alloy horns as catalytic sites at the ends of Au nanorods. Using high-resolution electron microscopy and tomography, we successfully reconstructed the complex three-dimensional morphology of HIF-AuNR@AuPd and identified that the horns are bound with high-index {11l} (0.25 < l < 0.43) facets. With an electron beam probe, we visualized the distribution of surface plasmon over the HIF-AuNR@AuPd nanorods, finding that strong longitudinal surface plasmon resonance concentrated at the rod ends. This unique crystal morphology led to the coupling of high catalytic activity with a strong SERS effect at the rod ends, making HIF-AuNR@AuPd an excellent bifunctional platform for in situ monitoring of surface catalytic reactions. Using the hydrogenation of 4-nitrothiophenol as a model reaction, we demonstrated that its first-order reaction kinetics could be accurately determined from this platform. Moreover, we clearly identified the superior catalytic activity of the rod ends relative to that of the rod bodies, owing to the different SERS activities at the two positions. In comparison with other reported Au-Pd bimetallic nanostructures, HIF-AuNR@AuPd offered both higher catalytic activity and greater detection sensitivity. © 2013 American Chemical Society.

Atomic structure of diamond {111} surfaces etched in oxygen water vapor

International Nuclear Information System (INIS)

Theije, F.K. de; Reedijk, M.F.; Arsic, J.; Enckevort, W.J.P. van; Vlieg, E.

2001-01-01

The atomic structure of the {111} diamond face after oxygen-water-vapor etching is determined using x-ray scattering. We find that a single dangling bond diamond {111} surface model, terminated by a full monolayer of -OH fits our data best. To explain the measurements it is necessary to add an ordered water layer on top of the -OH terminated surface. The vertical contraction of the surface cell and the distance between the oxygen atoms are generally in agreement with model calculations and results on similar systems. The OH termination is likely to be present during etching as well. This model experimentally confirms the atomic-scale mechanism we proposed previously for this etching system

Equilibrium binding studies of mono, di and triisocyanide ligands on Au powder surfaces

Energy Technology Data Exchange (ETDEWEB)

Ontko, Alyn [Iowa State Univ., Ames, IA (United States)

1997-10-08

The author`s group has previously shown that isocyanides are readily adsorbed from solutions to Au powder and bind to the Au surface in an end-on fashion through the terminal carbon. Later work demonstrated that the equilibrium constants for the reversible adsorption of electronically inequivalent isocyanides could be obtained using the Langmuir isotherm technique. This dissertation describes two projects completed which complement the initial findings of this group. Initially, several alkylisocyanides were synthesized to examine the effect of tail length on Au powder adsorption. It was observed that the length of the alkyl chain affected not only the Au surface binding affinity, but also the rate of surface saturation and saturation coverage values. Direct competition studies were also studied using a <sup>13</sup>C-labeled isocyanide. These studies demonstrated the stabilization afforded by substrate-substrate packing forces in SAM`s formed by the longer chain isocyanides. In a second study, di and triisocyanides were synthesized to determine the effect that the length of the connecting link and the number of isocyanide groups (as points of attachment) have on Au adsorption stability. The work in this area describes the binding modes, relative binding affinities and surface coverage values for a series of flexible alkyl and xylyldiisocyanides on Au powder surfaces. This report contains only the introductory material, and general summary. Two chapters have been processed separately. 56 refs.

The Au modified Ge(1 1 0) surface

Science.gov (United States)

Zhang, L.; Kabanov, N. S.; Bampoulis, P.; Saletsky, A. M.; Zandvliet, H. J. W.; Klavsyuk, A. L.

2018-05-01

The pristine Ge(1 1 0) surface is composed of Ge pentagons, which are arranged in relatively large (16 × 2) and c(8 × 10) unit cells. The deposition of sub-monolayer amounts of Au and mild annealing results into de-reconstructed Ge(1 1 0) regions completely free of Ge pentagons and regions composed of nanowires that are aligned along the high symmetry [ 1 1 bar 0 ] direction of the Ge(1 1 0) surface. The de-reconstructed Ge(1 1 0) regions consist of atomic rows that are aligned along the [ 1 1 bar 0 ] direction. A substantial fraction of these substrate rows are straight and resemble the atom rows of the unreconstructed, i.e. bulk terminated, Ge(1 1 0) surface, whereas the other substrate rows have a meandering appearance. These meandering atom rows are comprised of two types of atoms, one type that appears dim, whereas the other type appears bright in filled-state scanning tunneling microscopy images. Using density functional theory calculations, we have tested more than 20 different atomic models for the meandering atom rows. The density functional theory calculations reveal that it is energetically favorable for the deposited Au atoms to exchange position with Ge atoms in the first layer. Based on these findings we conclude that the bright atoms are Ge atoms, whereas the dim atoms are Au atoms.

Architecture-dependent surface chemistry for Pt monolayers on carbon-supported Au.

Science.gov (United States)

Cheng, Shuang; Rettew, Robert E; Sauerbrey, Marc; Alamgir, Faisal M

2011-10-01

Pt monolayers were grown by surface-limited redox replacement (SLRR) on two types of Au nanostructures. The Au nanostructures were fabricated electrochemically on carbon fiber paper (CFP) by either potentiostatic deposition (PSD) or potential square wave deposition (PSWD). The morphology of the Au/CFP heterostructures, examined using scanning electron microscopy (SEM), was found to depend on the type of Au growth method employed. The properties of the Pt deposit, as studied using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and cyclic voltammetry (CV), were found to depend strongly on the morphology of the support. Specifically, it was found that smaller Au morphologies led to a higher degree of cationicity in the resulting Pt deposit, with Pt(4+) and Pt(2+) species being identified using XPS and XAS. For fuel-cell catalysts, the resistance of ultrathin catalyst deposits to surface area loss through dissolution, poisoning, and agglomeration is critical. This study shows that an equivalent of two monolayers (ML) is the low-loading limit of Pt on Au. At 1 ML or below, the Pt film decreases in activity and durability very rapidly due to presence of cationic Pt. © 2011 American Chemical Society

Surface morphology of laser superheated Pb(111)

Energy Technology Data Exchange (ETDEWEB)

Zhang, Z. H.; Lin, Bo; Zeng, X. L.; Elsayed-Ali, H. E.

1998-05-01

The step density on the vicinal Pb(111) surface after laser superheating and melting is investigated using reflection high-energy electron diffraction. The (00) beam profiles parallel and perpendicular to the incident beam are analyzed. For laser heating with ˜100 ps laser pulses, surface superheating does not significantly change the density of the steps and step edge roughness. A sudden increase in the average terrace width is observed after laser surface melting. The average terrace width and the string length at the step edge become as large as those at room temperature. The average terrace width at 573 K changes from 38±15 to 64±19 Å after laser surface melting, while the average string length at the step edge changes from 50±12 to 250±38 Å.

Modification of Ni(111) reactivity toward CH4, CO, and D2 by two-dimensional alloying

DEFF Research Database (Denmark)

Holmblad, Peter Mikal; Nielsen, Jane Hvolbæk; Chorkendorff, Ib

1996-01-01

. In TPD spectra of deuterium saturated surface alloys a new clearly resolved desorption state is observed at 180-220 K with maximum intensity around theta(Au)=0.3-0.4 ML. This state is clearly related to chemisorption sites involving both Au and Ni. A site model based on mean field statistics adequately......Alloying Au into the outermost atomic layer of Ni(111) significantly alters the physical and chemical properties of the surface. The reactivity is investigated by the use of seeded supersonic molecular beams of CH4 and it is found that the nobleness of Au reduces the overall reactivity toward CH4....... This is accounted for in an ensemble model resolving the sticking probability on Ni atoms having different nearest neighbor surroundings. Although a mean field description of site distributions is found to be a very good approximation it is improved by using experimentally determined ensemble statistics from STM...

Effect of Au proximity on the LSMO surface: An ab initio study

International Nuclear Information System (INIS)

Petti, D.; Stroppa, A.; Picozzi, S.; Brivio, S.; Cantoni, M.; Bertacco, R.

2012-01-01

The effect of the proximity of Au on the electronic and magnetic properties of La 0.66 Sr 0.33 MnO 3 (LSMO) has been investigated by means of ab initio calculations within the density-functional theory. The calculations show an orbital reconstruction of the interfacial Mn, which is due more to the presence of a discontinuity rather than to a real chemical interaction with Au atoms. In fact, the same orbital reconstruction is found in the free LSMO surface. In both cases of Au/LSMO and LSMO surface, the Mn magnetic moments change very little with respect to the bulk case. In general, the calculations show a negligible influence of the Au atomic layer on LSMO at an ideal interface, with the LSMO surface magnetic and electronic properties essentially unchanged. - Highlights: ► Three structures considered: bulk LSMO, Au/LSMO and vacuum LSMO interfaces. ► At the two interfaces the formation of a discontinuity creates an orbital ordering. ► DFT calculations point toward an enhancement of the magnetization at the interface. ► Negligible chemical interaction with gold is seen for a 2D ideal interface. ► Crucial role of the 3D nature of Au on LSMO in depressing LSMO magnetic properties.

The phases of Pb/Ge(111): A surface X-ray diffraction study

International Nuclear Information System (INIS)

Grey, F.

1988-03-01

This report describes the results of several surface X-ray diffraction measurements of a chemisorbed overlayer of Pb on the Ge(111) surface. Three phases of Pb/Ge(111) exist in the monolayer regime: the α- and β-phases with a √3x√3R30 0 unit cell, and a high-temperature 1x1 phase. In the 1x1 phase of Pb/Ge(111), isotropic X-ray scattering is observed consistent with a two-dimensional liquid phase. Measurements of the integer-order Bragg reflections through the √3x√3R30 0 →1x1 transition confirm the liquid-like nature of the 1x1 phase, and show that the liquid layer is modulated by the periodic potential of the substrate. By measuring variations of the (2/3,2/3) surface Bragg reflection from the √3x√3R30 0 phase as a function of temperature and coverage, a simple phase diagram for Pb/Ge(111) is deduced. Below 1/3ML (where 1 ML is one Pb atom per Ge surface atom) the α-phase coexists with the 1x1 phase. Between 1/3ML and 4/3ML, α- and β-phases form a two-phase system displaying phase separation. Analogies with simple theoretical phase diagrams are emphasized. (orig.) With 11 tabs., 40 figs., 67 refs

Surface Pourbaix diagrams and oxygen reduction activity of Pt, Ag and Ni(111) surfaces studied by DFT

DEFF Research Database (Denmark)

Hansen, Heine Anton; Rossmeisl, Jan; Nørskov, Jens Kehlet

2008-01-01

The electrochemical most stable surface structures is investigated as function of pH and potential for Pt, Ag and Ni based on DFT calculations and constructed surface Pourbaix diagrams. It is also explained why metals such as Ag and Ni may be used successfully in alkaline fuel cells but not in ac......The electrochemical most stable surface structures is investigated as function of pH and potential for Pt, Ag and Ni based on DFT calculations and constructed surface Pourbaix diagrams. It is also explained why metals such as Ag and Ni may be used successfully in alkaline fuel cells...... but not in acidic PEM fuel cells. Based on density functional theory calculations we investigate the electrochemically most stable surface structures as a function of pH and electrostatic potential for Pt(111), Ag(111) and Ni(111), and we construct surface Pourbaix diagrams. We study the oxygen reduction reaction......, on the other hand, is constant vs. the standard hydrogen electrode (SHE). For Ag, this means that where the potential for dissolution and ORR are about the same at pH = 0, Ag becomes more stable relative to RHE as pH is increased. Hence the pH dependent stability offers an explanation for the possible use...

Surface-imprinted core–shell Au nanoparticles for selective detection of bisphenol A based on surface-enhanced Raman scattering

International Nuclear Information System (INIS)

Xue, Jin-Qun; Li, Da-Wei; Qu, Lu-Lu; Long, Yi-Tao

2013-01-01

Graphical abstract: -- Highlights: •The molecularly imprinted polymer capped core–shell AuNPs (MIP-ir-AuNPs) were fabricated as a specific functional SERS substrate. •MIP-ir-AuNPs could be utilized in rapid and selective detection of BPA. •MIP-ir-AuNPs displayed good capability for determination of BPA in real samples. -- Abstract: Surface-imprinted core–shell Au nanoparticles (AuNPs) were explored for the highly selective detection of bisphenol A (BPA) by surface-enhanced Raman scattering (SERS). A triethoxysilane-template complex (BPA-Si) was synthesized and then utilized to fabricate a molecularly imprinted polymer (MIP) layer on the AuNPs via a sol–gel process. The imprinted BPA molecules were removed by a simple thermal treatment to generated the imprint-removed material, MIP-ir-AuNPs, with the desired recognition sites that could selectively rebind the BPA molecules. The morphological and polymeric characteristics of MIP-ir-AuNPs were investigated by transmission electron microscopy and Fourier-transform infrared spectroscopy. The results demonstrated that the MIP-ir-AuNPs were fabricated with a 2 nm MIP shell layer within which abundant amine groups were generated. The rebinding kinetics study showed that the MIP-ir-AuNPs could reach the equilibrium adsorption for BPA within 10 min owning to the advantage of ultrathin core–shell nanostructure. Moreover, a linear relationship between SERS intensity and the concentration of BPA on the MIP-ir-AuNPs was observed in the range of 0.5–22.8 mg L −1 , with a detection limit of 0.12 mg L −1 (blank ± 3 × s.d.). When applied to SERS detection, the developed surface-imprinted core–shell MIP-ir-AuNPs could recognize BPA and prevent interference from the structural analogues such as hexafluorobisphenol A (BPAF) and diethylstilbestrol (DES). These results revealed that the proposed method displayed significant potential utility in rapid and selective detection of BPA in real samples

All-(111) surface silicon nanowire field effect transistor devices: Effects of surface preparations

NARCIS (Netherlands)

Masood, M.N.; Carlen, Edwin; van den Berg, Albert

2014-01-01

Etching/hydrogen termination of All-(111) surface silicon nanowire field effect (SiNW-FET) devices developed by conventional photolithography and plane dependent wet etchings is studied with X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and

Chemical modifications of Au/SiO2 template substrates for patterned biofunctional surfaces.

Science.gov (United States)

Briand, Elisabeth; Humblot, Vincent; Landoulsi, Jessem; Petronis, Sarunas; Pradier, Claire-Marie; Kasemo, Bengt; Svedhem, Sofia

2011-01-18

The aim of this work was to create patterned surfaces for localized and specific biochemical recognition. For this purpose, we have developed a protocol for orthogonal and material-selective surface modifications of microfabricated patterned surfaces composed of SiO(2) areas (100 μm diameter) surrounded by Au. The SiO(2) spots were chemically modified by a sequence of reactions (silanization using an amine-terminated silane (APTES), followed by amine coupling of a biotin analogue and biospecific recognition) to achieve efficient immobilization of streptavidin in a functional form. The surrounding Au was rendered inert to protein adsorption by modification by HS(CH(2))(10)CONH(CH(2))(2)(OCH(2)CH(2))(7)OH (thiol-OEG). The surface modification protocol was developed by testing separately homogeneous SiO(2) and Au surfaces, to obtain the two following results: (i) SiO(2) surfaces which allowed the grafting of streptavidin, and subsequent immobilization of biotinylated antibodies, and (ii) Au surfaces showing almost no affinity for the same streptavidin and antibody solutions. The surface interactions were monitored by quartz crystal microbalance with dissipation monitoring (QCM-D), and chemical analyses were performed by polarization modulation-reflexion absorption infrared spectroscopy (PM-RAIRS) and X-ray photoelectron spectroscopy (XPS) to assess the validity of the initial orthogonal assembly of APTES and thiol-OEG. Eventually, microscopy imaging of the modified Au/SiO(2) patterned substrates validated the specific binding of streptavidin on the SiO(2)/APTES areas, as well as the subsequent binding of biotinylated anti-rIgG and further detection of fluorescent rIgG on the functionalized SiO(2) areas. These results demonstrate a successful protocol for the preparation of patterned biofunctional surfaces, based on microfabricated Au/SiO(2) templates and supported by careful surface analysis. The strong immobilization of the biomolecules resulting from the described

Catalytically favorable surface patterns in Pt-Au nanoclusters

KAUST Repository

Mokkath, Junais Habeeb

2013-01-01

Motivated by recent experimental demonstrations of novel PtAu nanoparticles with highly enhanced catalytic properties, we present a systematic theoretical study that explores principal catalytic indicators as a function of the particle size and composition. We find that Pt electronic states in the vicinity of the Fermi level combined with a modified electron distribution in the nanoparticle due to Pt-to-Au charge transfer are the origin of the outstanding catalytic properties. From our model we deduce the catalytically favorable surface patterns that induce ensemble and ligand effects. © The Royal Society of Chemistry 2013.

First principles investigation of the activity of thin film Pt, Pd and Au surface alloys for oxygen reduction

DEFF Research Database (Denmark)

Tripkovic, Vladimir; Hansen, Heine Anton; Rossmeisl, Jan

2015-01-01

driving force for surface segregation, diffusion to defects or surface self-assembling. On the basis of stability and activity analysis we conclude that the near surface alloy of Pd in Pt and some PdAu binary and PtPdAu ternary thin films with a controlled amount of Au are the best catalysts for oxygen......Further advances in fuel cell technologies are hampered by kinetic limitations associated with the sluggish cathodic oxygen reduction reaction. We have investigated a range of different formulations of binary and ternary Pt, Pd and Au thin films as electrocatalysts for oxygen reduction. The most...... active binary thin films are near-surface alloys of Pt with subsurface Pd and certain PdAu and PtAu thin films with surface and/or subsurface Au. The most active ternary thin films are with pure metal Pt or Pd skins with some degree of Au in the surface and/or subsurface layer and the near-surface alloys...

Growth and structure of Co/Au magnetic thin films

International Nuclear Information System (INIS)

Marsot, N.

1999-01-01

We have studied the growth and the crystallographic structure of magnetic ultra thin cobalt/gold films (Co/Au), in order to investigate the correlations between their magnetic and structural properties. Room temperature (R.T.) Co growth on Au (111) proceeds in three stages. Up to 2 Co monolayers (ML), a bilayer island growth mode is observed. Between 2 and 5 ML, coalescence of the islands occurs, covering the substrate surface and a Co/Au mixing is observed resulting from the de-construction of the Herringbone reconstruction. Finally, beyond 5 ML, the CoAu mixing is buried and the Co growth continues in a 3-D growth. Annealing studies at 600 K on this system show a smoothing effect of the Co film, and at the same time, segregation of Au atoms. The quality of the Co/Au interface (sharpness) is not enhanced by the annealing. The local order was studied by SEXAFS and the long range order by GIXRD showing that the Co film has a hexagonal close packed structure, with an easy magnetization axis perpendicular to the surface. From a local order point of view, the Co grows with an incoherent epitaxy and keeps its own bulk parameters. The GIXRD analysis shows a residual strain in the Co film of 4%. The difference observed between the local order analysis and the long range order results is explained in terms of the low dimensions of the diffracting domains. The evolution of film strains, as a function of the Co coverage, shows a marked deviation from the elastic strain theory. Modification of the strain field in the Co film as a function of the Au coverage is studied by GIXRD analysis. The Au growth study, at R.T., shows no evidence of a Au/Co mixing in the case of the Au/Co interface. The Au overlayer adopts a twinned face centred cubic structure on the rough Co film surface. (author)

Nitrogen ion induced nitridation of Si(111) surface: Energy and fluence dependence

Energy Technology Data Exchange (ETDEWEB)

Kumar, Praveen [Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064 (India); ISOM, Universidad Politecnia de Madrid, 28040 (Spain); Kumar, Mahesh [Physics and Energy Harvesting Group, National Physical Laboratory, New Delhi 110012 (India); Nötzel, R. [ISOM, Universidad Politecnia de Madrid, 28040 (Spain); Shivaprasad, S.M., E-mail: smsprasad@jncasr.ac.in [Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064 (India)

2014-06-01

We present the surface modification of Si(111) into silicon nitride by exposure to energetic N{sub 2}{sup +} ions. In-situ UHV experiments have been performed to optimize the energy and fluence of the N{sub 2}{sup +} ions to form silicon nitride at room temperature (RT) and characterized in-situ by X-ray photoelectron spectroscopy. We have used N{sub 2}{sup +} ion beams in the energy range of 0.2–5.0 keV of different fluence to induce surface reactions, which lead to the formation of Si{sub x}N{sub y} on the Si(111) surface. The XPS core level spectra of Si(2p) and N(1s) have been deconvoluted into different oxidation states to extract qualitative information, while survey scans have been used for quantifying of the silicon nitride formation, valence band spectra show that as the N{sub 2}{sup +} ion fluence increases, there is an increase in the band gap. The secondary electron emission spectra region of photoemission is used to evaluate the change in the work function during the nitridation process. The results show that surface nitridation initially increases rapidly with ion fluence and then saturates. - Highlights: • A systematic study for the formation of silicon nitride on Si(111). • Investigation of optimal energy and fluence for energetic N{sub 2}{sup +} ions. • Silicon nitride formation at room temperature on Si(111)

Substrate-dependent Au{sub x} cluster: A new insight into Au{sub x}/CeO{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Zhu, Kong-Jie; Yang, Yan-Ju [School of Chemistry and Life Science, Zhejiang Normal University, Jinhua 321004 (China); Lang, Jia-Jian [School of Chemistry and Life Science, Zhejiang Normal University, Jinhua 321004 (China); Engineering Laboratory of Specialty Fibers and Nuclear Energy Materials, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, Zhejiang 315201 (China); Teng, Bo-Tao, E-mail: tbt@zjnu.cn [School of Chemistry and Life Science, Zhejiang Normal University, Jinhua 321004 (China); Wu, Feng-Min [School of Chemistry and Life Science, Zhejiang Normal University, Jinhua 321004 (China); Du, Shi-Yu [Engineering Laboratory of Specialty Fibers and Nuclear Energy Materials, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, Zhejiang 315201 (China); Wen, Xiao-Dong, E-mail: wxd@sxicc.ac.cn [State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001 (China)

2016-11-30

Graphical abstract: 2D Au{sub x} (x < 10) on CeO{sub 2}(110) are more stable than 3D ones, while the stability trend changes for x ≥ 10; Au{sub x} (x ≤ 4) prefer to monatomically disperse on CeO{sub 2}(100) and aggregate to 3D clusters for x > 4. - Highlights: • The stable structures of Au{sub x}/CeO{sub 2} are dependent of index surfaces of CeO{sub 2}. • Au{sub x} prefers to monatomically disperse on CeO{sub 2}(100) at low coverage. • Au{sub x} aggregates to 3D clusters on CeO{sub 2}(100) at high coverage. • 2D Au{sub x} (x < 10) are more stable than the 3D ones on CeO{sub 2}(110). • The effects on the stability of Au{sub x}/CeO{sub 2} are systematically discussed. - Abstract: To theoretically study the structures of metal clusters on oxides is very important and becomes one of the most challenging works in computational heterogeneous catalysis since many factors affect their structures and lead to various possibilities. In this work, it is very interesting to find that the stable structures and stability evolution of Au{sub x} clusters on ceria are varied with different index surfaces of CeO{sub 2}. The corresponding reasons in chemical, geometric and electronic properties are systematically explored. Au{sub x} (x = 1–4) clusters prefer to separately disperse at the O-O bridge sites on CeO{sub 2}(100) due to the low coordination number of surface O; while aggregate due to the strong Au–Au attractions when x is larger than 4. Owing to the uniform distribution of O-O bridge sites on CeO{sub 2}(111) and (100), the most stable configurations of Au{sub x} are 3D structures with bottom atoms more than top ones when x is larger than 4. However, 2D configurations of Au{sub x}/CeO{sub 2}(110) (x < 10) are more stable than the corresponding 3D structures due to the particular O-O arrangement on CeO{sub 2}(110). 3D Au{sub x} clusters across O-O-Y lines are suggested as the most stable configurations for Au{sub x}/CeO{sub 2}(110) (x ≥ 10). The present

Pulsed melting of silicon (111) and (100) surfaces simulated by molecular dynamics

International Nuclear Information System (INIS)

Abraham, F.F.; Broughton, J.Q.

1986-01-01

The pulsed heating of Si (100) and (111) surfaces has been simulated by molecular dynamics. The (111) crystal-melt interface propagates by layer-by-layer growth whereas the (100) interface grows in a continuous fashion. The equilibrium crystal-melt interface is sharp for the (111) orientation and broad for the (100) orientation. These simulations are the first use of nonpairwise potentials to study interfaces between condensed phases, and the results support models of interfaces which heretofore had to be deduced from indirect experimental information

Angular dependence of Auger signals from a GaAs (111) surface

International Nuclear Information System (INIS)

Barnard, W.O.

1984-03-01

This dissertation is concerned with the angular dependence of the L 3 M 4 M 4 1067 eV Ga and L 3 M 4 M 4 1228 eV As Auger electron signals from a (111) GaAs surface, using a system which is equipped with a cylindrical mirror analyser. Following a detailed discussion of the Auger process, a review is given of angular effects in the emission excitation and detection of Auger signals. Present theories are discussed and an empirical theory is developed to test the experimental results obtained in this study. The experimental procedures and equipment used are presented. It was found that the Auger signals show a strong variation with the angle of rotation about the normal of a GaAs surface. Furthermore, the nature of the angular spectra of the Ga and As signals are interchanged when the electron beam incident surface is changed from (111) to (111). The main features of the angular variation of the quasi-elastic backscattered signal is reflected in the corresponding Ga and As Auger angular spectra. The angular dependence of the quasi-elastic backscattered signal can be explained semi-quantitatively in terms of the empirical theory. Theoretical arguments are presented which suggest that the Auger signals should show an angular dependence similar to the quasi-elastic backscattered signal. Evidence was found that geometric screening-off of underlying atoms by surface and near surface atoms influence the Auger yield

Gold surfaces and nanoparticles are protected by Au(0)-thiyl species and are destroyed when Au(I)-thiolates form

DEFF Research Database (Denmark)

Reimers, Jeffrey R.; Ford, Michael J.; Halder, Arnab

2016-01-01

that it is the noble character of gold and nanoparticle surfaces that destabilizes Au(I)-thiolates. Bonding results from large van der Waals forces, influenced by covalent bonding induced through s-d hybridization and charge polarization effects that perturbatively mix in some Au(I)-thiolate character. A simple method...

Enhanced absorption in Au nanoparticles/a-Si:H/c-Si heterojunction solar cells exploiting Au surface plasmon resonance

Energy Technology Data Exchange (ETDEWEB)

Losurdo, Maria; Giangregorio, Maria M.; Bianco, Giuseppe V.; Sacchetti, Alberto; Capezzuto, Pio; Bruno, Giovanni [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR, via Orabona 4, 70126 Bari (Italy)

2009-10-15

Au nanoparticles (NPs)/(n-type)a-Si:H/(p-type)c-Si heterojunctions have been deposited combining plasma-enhanced chemical-vapour deposition (PECVD) with Au sputtering. We demonstrate that a density of {proportional_to}1.3 x 10{sup 11} cm{sup -2} of Au nanoparticles with an approximately 20 nm diameter deposited onto (n-type)a-Si:H/(p-type)c-Si heterojunctions enhance performance exploiting the improved absorption of light by the surface plasmon resonance of Au NPs. In particular, Au NPs/(n-type)a-Si:H/(p-type)c-Si show an enhancement of 20% in the short-circuit current, J{sub SC}, 25% in the power output, P{sub max} and 3% in the fill factor, FF, compared to heterojunctions without Au NPs. Structures have been characterized by spectroscopic ellipsometry, atomic force microscopy and current-voltage (I-V) measurements to correlate the plasmon resonance-induced enhanced absorption of light with photovoltaic performance. (author)

Single-molecule conductivity of non-redox and redox molecules at pure and gold-mined Au(111)-electrode surfaces

DEFF Research Database (Denmark)

Zhang, Jingdong; Chi, Qijin; Ulstrup, Jens

The structure, two-dimensional organization, and function of molecules immobilized on solid surfaces can be addressed in a degree of detail that has reached the level of the single-molecule. In this context redox molecules are “smart” molecules adding sophisticated electronic function. Redox meta...

Surface reactivity of Ge[111] for organic functionalization by means of a radical-initiated reaction: A DFT study

Energy Technology Data Exchange (ETDEWEB)

Rubio-Pereda, Pamela, E-mail: rubio.pereda@gmail.com [Centro de Investigación Científica y de Educación Superior de Ensenada 3918, Código Postal 22860, Ensenada, Baja California (Mexico); Takeuchi, Noboru, E-mail: takeuchi@cnyn.unam.mx [Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, Apartado Postal 14, Código Postal 22800, Ensenada, Baja California (Mexico)

2016-08-30

Highlights: • The surface reactivity of the Ge [111] surface is studied with DFT for the attachment of organic molecules by means of a radical-initiated reaction. • A hydrogen vacancy in the hydrogen terminated Ge [111] surface exhibits an accumulation of charge and electron pairing. • These characteristics make the hydrogen vacancy less reactive for the attachment of unsaturated organic molecules. • The adsorption of acetylene is probable to occur while the adsorption of ethylene and styrene is substantially less probable to occur. • The hydrogen terminated Ge [111] surface is found to be less reactive than its two-dimensional analogue, the hydrogen-terminated germanene. - Abstract: The study of interfacial chemistry at semiconductor surfaces has become an important area of research. Functionalities such as molecular recognition, biocompatibility of surfaces, and molecular computing, could be achieved by the combinations of organic chemistry with the semiconductor technology. One way to accomplish this goal is by means of organic functionalization of semiconductor surfaces such as the bulk-terminated germanium surfaces, more specifically the Ge[111]. In this work, we theoretically study, by applying density functional theory, the surface reactivity of the bulk-terminated Ge[111] surface for organic functionalization by means of a radical-initiated reaction of unsaturated molecules such as acetylene, ethylene and styrene with a hydrogen vacancy on a previously hydrogen-terminated Ge[111] surface. Results derived from this work are compared with those obtained in our previous calculations on the germanene surface, following the same chemical route. Our calculations show an accumulation of electronic charge at the H-vacancy having as a result electron pairing due to strong lattice-electron coupling and therefore a diminished surface reactivity. Calculation of the transition states for acetylene and ethylene indicates that the surface reactivity of the

One-pot reaction for the preparation of biofunctionalized self-assembled monolayers on gold surfaces

Energy Technology Data Exchange (ETDEWEB)

Raigoza, Annette F.; Fies, Whitney; Lim, Amber; Onyirioha, Kristeen; Webb, Lauren J., E-mail: lwebb@cm.utexas.edu

2017-02-01

Highlights: • One-pot synthesis of α-helical-terminated self-assembled monolayers on Au(111). • Synthesis of high density, structured, and covalently bound α-helices on Au(111). • Characterization by surface-averaged and single molecule techniques. • Peptide-terminated surfaces for fabrication of biomaterials and sensors. - Abstract: The Huisgen cycloaddition reaction (“click” chemistry) has been used extensively to functionalize surfaces with macromolecules in a straightforward manner. We have previously developed a procedure using the copper(I)-catalyzed click reaction to tether synthetic α-helical peptides carrying two alkyne groups to a well-ordered azide-terminated alkanethiol self-assembled monolayer (SAM) on a Au(111) surface. While convenient, click-based strategies potentially pose significant problems from reagents, solvents, and reaction temperatures that may irreversibly damage some molecules or substrates. Tuning click chemistry conditions would allow individual optimization of reaction conditions for a wide variety of biomolecules and substrate materials. Here, we explore the utility of simultaneous SAM formation and peptide-attachment chemistry in a one-pot reaction. We demonstrate that a formerly multistep reaction can be successfully carried out concurrently by mixing azide-terminated alkanethiols, CuCl, and a propargylglycine-containing peptide over a bare gold surface in ethanol and reacting at 70 °C. X-ray photoelectron spectroscopy (XPS), surface infrared spectroscopy, surface circular dichroic (CD) spectroscopy, and scanning tunneling microscopy (STM) were used to determine that this one-pot reaction strategy resulted in a high density of surface-bound α-helices without aggregation. This work demonstrates the simplicity and versatility of a SAM-plus-click chemistry strategy for functionalizing Au surfaces with structured biomolecules.

Electron transfer and redox metalloenzyme catalysis at the single-molecule level

DEFF Research Database (Denmark)

Hansen, Allan Glargaard; Zhang, Jingdong; Christensen, Hans Erik Mølager

2004-01-01

transfer (ET). Image interpretation requires, however, theoretical support, as STM represents both electronic and topographic features. Molecules with accessible redox levels offer other insight into electron tunneling mechanisms, addressed in detail for ET metalloproteins. We present here in situ STM...... of the blue redox metalloenzyme copper nitrite reductase (Achromobacter xylosoxidans, AxCuNiR) on Au(111) electrode surfaces modified by a self-assembled cysteamine monolayer. AxCuNiR displays strong nitrite reduction waves in this environment. AxCuNiR/cysteamine/ Au(111) surfaces were imaged at KNO2...

Adsorption of carbon monoxide on the Si(111)-7 × 7 surface

Energy Technology Data Exchange (ETDEWEB)

Shong, Bonggeun, E-mail: bshong@cnu.ac.kr

2017-05-31

Highlights: • Detailed chemistry of CO with the Si(111)-7 × 7 surface is computationally studied. • On-top on rest-atoms and back-bond insertion on adatoms are suggested geometries. • The two structures exhibit no activation barrier for adsorption and significant stability. • Geometrical and spectroscopic properties of CO adsorbates are predicted. • Direction of the interfacial charge transfer depends on the bonding configuration. - Abstract: The adsorption of CO and surface chemistry of Si are well-understood topics in surface science. However, research into the adsorption of CO on the Si(111)-7 × 7 surface is deficient. In this study, the adsorption of CO on Si(111)-7 × 7 is investigated via high-level density functional theory calculations using cluster model. Two adsorption configurations are found to be kinetically and thermodynamically viable: on-top on rest-atoms and back-bond insertion on adatoms, both binding to the surface via C atom. Structural, electronic, and spectroscopic properties of the adsorbates indicate a σ-donating/π-accepting nature of the CO−Si bonds in both configurations. The domination of σ-donation in the on-top configuration results in a net positive charge on the on-top adsorbate, and the opposite situation yields a net negative charge on the back-bond insertion adsorbates. Our study provides a detailed understanding of the previous experimental observations of fundamental surface chemical phenomena, suggesting possible applications of Si surface functionalization using CO.

Analysis of the Si(111) surface prepared in chemical vapor ambient for subsequent III-V heteroepitaxy

International Nuclear Information System (INIS)

Zhao, W.; Steidl, M.; Paszuk, A.; Brückner, S.; Dobrich, A.; Supplie, O.; Kleinschmidt, P.; Hannappel, T.

2017-01-01

Highlights: • We investigate the Si(111) surface prepared in CVD ambient at 1000 °C in 950 mbar H_2. • UHV-based XPS, LEED, STM and FTIR as well as ambient AFM are applied. • After processing the Si(111) surface is free of contamination and atomically flat. • The surface exhibits a (1 × 1) reconstruction and monohydride termination. • Wet-chemical pretreatment and homoepitaxy are required for a regular step structure. - Abstract: For well-defined heteroepitaxial growth of III-V epilayers on Si(111) substrates the atomic structure of the silicon surface is an essential element. Here, we study the preparation of the Si(111) surface in H_2-based chemical vapor ambient as well as its atomic structure after contamination-free transfer to ultrahigh vacuum (UHV). Applying complementary UHV-based techniques, we derive a complete picture of the atomic surface structure and its chemical composition. X-ray photoelectron spectroscopy measurements after high-temperature annealing confirm a Si surface free of any traces of oxygen or other impurities. The annealing in H_2 ambient leads to a monohydride surface termination, as verified by Fourier-transform infrared spectroscopy. Scanning tunneling microscopy confirms a well ordered, atomically smooth surface, which is (1 × 1) reconstructed, in agreement with low energy electron diffraction patterns. Atomic force microscopy reveals a significant influence of homoepitaxy and wet-chemical pretreatment on the surface morphology. Our findings show that wet-chemical pretreatment followed by high-temperature annealing leads to contamination-free, atomically flat Si(111) surfaces, which are ideally suited for subsequent III-V heteroepitaxy.

Influences of H on the Adsorption of a Single Ag Atom on Si(111-7 × 7 Surface

Directory of Open Access Journals (Sweden)

Lin Xiu-Zhu

2009-01-01

Full Text Available Abstract The adsorption of a single Ag atom on both clear Si(111-7 × 7 and 19 hydrogen terminated Si(111-7 × 7 (hereafter referred as 19H-Si(111-7 × 7 surfaces has been investigated using first-principles calculations. The results indicated that the pre-adsorbed H on Si surface altered the surface electronic properties of Si and influenced the adsorption properties of Ag atom on the H terminated Si surface (e.g., adsorption site and bonding properties. Difference charge density data indicated that covalent bond is formed between adsorbed Ag and H atoms on 19H-Si(111-7 × 7 surface, which increases the adsorption energy of Ag atom on Si surface.

Clean Os(0001) electronic surface states: A first-principle fully relativistic investigation

Science.gov (United States)

Urru, Andrea; Dal Corso, Andrea

2018-05-01

We analyze the electronic structure of the Os(0001) surface by means of first-principle calculations based on Fully Relativistic (FR) Density Functional Theory (DFT) and a Projector Augmented-Wave (PAW) approach. We investigate surface states and resonances analyzing their spin-orbit induced energy splitting and their spin polarization. The results are compared with previously studied surfaces Ir(111), Pt(111), and Au(111). We do not find any surface state in the gap similar to the L-gap of the (111) fcc surfaces, but find Rashba split resonances that cross the Fermi level and, as in the recently studied Ir(111) surface, have a characteristic downward dispersion. Moreover, for some selected surface states we study the spin polarization with respect to k∥, the wave-vector parallel to the surface. In some cases, such as the Rashba split resonances, the spin polarization shows a smooth behavior with slow rotations, in others the rotation is faster, due to mixing and anti-crossing of the states.

Temperature and coverage effects on the stability of epitaxial silicene on Ag(111) surfaces

Energy Technology Data Exchange (ETDEWEB)

Liu, Hongsheng; Han, Nannan; Zhao, Jijun, E-mail: zhao_jijun@hotmail.com

2017-07-01

Highlights: • Chemical potential phase diagrams of silicene/Ag(111) at varied temperatures. • The priorities of various silicene phases in experiments are explained. • A proper experimental condition to obtain homogeneous 4 × 4 silicene is recommended. - Abstract: Silicene, the single layer of silicon atoms arranged in a honeycomb lattice, has been synthesized in recent experiments and attracted significant attentions. Silicene is promising in future nanoelectronic devices due to its outstanding electronic properties. In experiments, however, different silicene superstructures coexist on Ag(111) substrate. For the device applications, homogenous silicene sheet with large scale and high quality is highly desired. Here, for the first time, we investigate both the temperature and the coverage effects on the thermal stability of epitaxial silicene on Ag(111) surface by ab initio molecular dynamics simulations. The relationship between the stability of various silicene superstructures and the growth conditions, including temperature and coverage of silicon atoms, is revealed by plotting the chemical potential phase diagram of silicene on Ag(111) surfaces at different temperatures. Our results are helpful for understanding the observed diversity of silicene phases on Ag(111) surfaces and provide some useful guidance for the synthesis of homogenous silicene phase in experiments.

Adsorbate-induced facetting reconstruction and self-organized domain patterning of vicinal Ag(111) surfaces; Adsorbatinduzierte richtungsabhaengige Facettierung und selbstorganisierte Domaenen-Musterbildung auf vizinalen Ag(111)-Oberflaechen

Energy Technology Data Exchange (ETDEWEB)

Schmitt, Stefan

2007-02-05

This thesis investigates structural aspects of adsorbate-induced facetting of vicinal Ag(111) surfaces. It is mainly based on scanning tunneling microscope (STM) and low energy electron diffraction (LEED) experiments performed under UHV conditions. The planar dye-molecule perylene-3,4,9,10-tetracarboxilicacid-dianhydride (PTCDA) adsorbs preferentially at the step edges of the 8.5 Ag(111) vicinal surfaces used in the experiments. It causes a facetting reconstruction by the formation of (111) terraces and facets with a high step density. Moreover, two distinct preferential inclinations of facets were observed, which can only be explained by the selective influence of the adsorbate superstructure. In terms of thermodynamics, the facetting reconstruction can be described as an orientational phase separation, adapted to the constraints of planar surfaces. This concept is capable of explaining the local facetting phenomena. The formalism used predicts an important role of nucleation kinetics. This aspect is taken into account by introducing an additional phase of mobile molecules (2D molecular gas), which cannot be measured directly. Furthermore, strong arguments for the appearance of a critical island size for the PTCDA/ Ag(111) superstructure were found. This work presents structural information of all stable superstructures of PTCDA on vicinal Ag(111) surfaces. Altogether 16 such superstructures were found, 3 of which had been observed and published before. Density and commensurability were found to systematically depend on the step-structure. The two preferred inclinations of facets are related to two characteristic types of domain boundaries of the herringbone superstructure to the adjacent (111)-terrace. On the (111) terraces, small islands of metastable superstructures were found. Facets and (111) terraces form a regular grating-like domain pattern with a variable structural width of 5 to 75 nm. STM measurements show direct evidence for a long-range interaction

Predicting supramolecular self-assembly on reconstructed metal surfaces

Science.gov (United States)

Roussel, Thomas J.; Barrena, Esther; Ocal, Carmen; Faraudo, Jordi

2014-06-01

The prediction of supramolecular self-assembly onto solid surfaces is still challenging in many situations of interest for nanoscience. In particular, no previous simulation approach has been capable to simulate large self-assembly patterns of organic molecules over reconstructed surfaces (which have periodicities over large distances) due to the large number of surface atoms and adsorbing molecules involved. Using a novel simulation technique, we report here large scale simulations of the self-assembly patterns of an organic molecule (DIP) over different reconstructions of the Au(111) surface. We show that on particular reconstructions, the molecule-molecule interactions are enhanced in a way that long-range order is promoted. Also, the presence of a distortion in a reconstructed surface pattern not only induces the presence of long-range order but also is able to drive the organization of DIP into two coexisting homochiral domains, in quantitative agreement with STM experiments. On the other hand, only short range order is obtained in other reconstructions of the Au(111) surface. The simulation strategy opens interesting perspectives to tune the supramolecular structure by simulation design and surface engineering if choosing the right molecular building blocks and stabilising the chosen reconstruction pattern.The prediction of supramolecular self-assembly onto solid surfaces is still challenging in many situations of interest for nanoscience. In particular, no previous simulation approach has been capable to simulate large self-assembly patterns of organic molecules over reconstructed surfaces (which have periodicities over large distances) due to the large number of surface atoms and adsorbing molecules involved. Using a novel simulation technique, we report here large scale simulations of the self-assembly patterns of an organic molecule (DIP) over different reconstructions of the Au(111) surface. We show that on particular reconstructions, the molecule

Reaction pathways of furfural, furfuryl alcohol and 2-methylfuran on Cu(111) and NiCu bimetallic surfaces

Science.gov (United States)

Xiong, Ke; Wan, Weiming; Chen, Jingguang G.

2016-10-01

Hydrodeoxygenation (HDO) is an important reaction for converting biomass-derived furfural to value-added 2-methylfuran, which is a promising fuel additive. In this work, the HDO of furfural to produce 2-methylfuran occurred on the NiCu bimetallic surfaces prepared on either Ni(111) or Cu(111). The reaction pathways of furfural were investigated on Cu(111) and Ni/Cu(111) surfaces using density functional theory (DFT) calculations, temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) experiments. These studies provided mechanistic insights into the effects of bimetallic formation on enhancing the HDO activity. Specifically, furfural weakly adsorbed on Cu(111), while it strongly adsorbed on Ni/Cu(111) through an η2(C,O) configuration, which led to the HDO of furfural on Ni/Cu(111). The ability to dissociate H2 on Ni/Cu(111) is also an important factor for enhancing the HDO activity over Cu(111).

Analysis of the Si(111) surface prepared in chemical vapor ambient for subsequent III-V heteroepitaxy

Energy Technology Data Exchange (ETDEWEB)

Zhao, W.; Steidl, M.; Paszuk, A. [Technische Universität Ilmenau, Institut für Physik, 98693 Ilmenau (Germany); Brückner, S. [Technische Universität Ilmenau, Institut für Physik, 98693 Ilmenau (Germany); Helmholtz-Zentrum Berlin, Institut für Solare Brennstoffe, 14109 Berlin (Germany); Dobrich, A. [Technische Universität Ilmenau, Institut für Physik, 98693 Ilmenau (Germany); Supplie, O. [Technische Universität Ilmenau, Institut für Physik, 98693 Ilmenau (Germany); Helmholtz-Zentrum Berlin, Institut für Solare Brennstoffe, 14109 Berlin (Germany); Kleinschmidt, P. [Technische Universität Ilmenau, Institut für Physik, 98693 Ilmenau (Germany); Hannappel, T., E-mail: thomas.hannappel@tu-ilmenau.de [Technische Universität Ilmenau, Institut für Physik, 98693 Ilmenau (Germany); Helmholtz-Zentrum Berlin, Institut für Solare Brennstoffe, 14109 Berlin (Germany)

2017-01-15

Highlights: • We investigate the Si(111) surface prepared in CVD ambient at 1000 °C in 950 mbar H{sub 2}. • UHV-based XPS, LEED, STM and FTIR as well as ambient AFM are applied. • After processing the Si(111) surface is free of contamination and atomically flat. • The surface exhibits a (1 × 1) reconstruction and monohydride termination. • Wet-chemical pretreatment and homoepitaxy are required for a regular step structure. - Abstract: For well-defined heteroepitaxial growth of III-V epilayers on Si(111) substrates the atomic structure of the silicon surface is an essential element. Here, we study the preparation of the Si(111) surface in H{sub 2}-based chemical vapor ambient as well as its atomic structure after contamination-free transfer to ultrahigh vacuum (UHV). Applying complementary UHV-based techniques, we derive a complete picture of the atomic surface structure and its chemical composition. X-ray photoelectron spectroscopy measurements after high-temperature annealing confirm a Si surface free of any traces of oxygen or other impurities. The annealing in H{sub 2} ambient leads to a monohydride surface termination, as verified by Fourier-transform infrared spectroscopy. Scanning tunneling microscopy confirms a well ordered, atomically smooth surface, which is (1 × 1) reconstructed, in agreement with low energy electron diffraction patterns. Atomic force microscopy reveals a significant influence of homoepitaxy and wet-chemical pretreatment on the surface morphology. Our findings show that wet-chemical pretreatment followed by high-temperature annealing leads to contamination-free, atomically flat Si(111) surfaces, which are ideally suited for subsequent III-V heteroepitaxy.

Communication: Surface-to-bulk diffusion of isolated versus interacting C atoms in Ni(111) and Cu(111) substrates: A first principle investigation

Energy Technology Data Exchange (ETDEWEB)

Harpale, Abhilash; Panesi, Marco; Chew, Huck Beng, E-mail: hbchew@illinois.edu [Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

2015-02-14

Using first principle calculations, we study the surface-to-bulk diffusion of C atoms in Ni(111) and Cu(111) substrates, and compare the barrier energies associated with the diffusion of an isolated C atom versus multiple interacting C atoms. We find that the preferential Ni-C bonding over C–C bonding induces a repulsive interaction between C atoms located at diagonal octahedral voids in Ni substrates. This C–C interaction accelerates C atom diffusion in Ni with a reduced barrier energy of ∼1 eV, compared to ∼1.4-1.6 eV for the diffusion of isolated C atoms. The diffusion barrier energy of isolated C atoms in Cu is lower than in Ni. However, bulk diffusion of interacting C atoms in Cu is not possible due to the preferential C–C bonding over C–Cu bonding, which results in C–C dimer pair formation near the surface. The dramatically different C–C interaction effects within the different substrates explain the contrasting growth mechanisms of graphene on Ni(111) and Cu(111) during chemical vapor deposition.

Communication: Surface-to-bulk diffusion of isolated versus interacting C atoms in Ni(111) and Cu(111) substrates: A first principle investigation.

Science.gov (United States)

Harpale, Abhilash; Panesi, Marco; Chew, Huck Beng

2015-02-14

Using first principle calculations, we study the surface-to-bulk diffusion of C atoms in Ni(111) and Cu(111) substrates, and compare the barrier energies associated with the diffusion of an isolated C atom versus multiple interacting C atoms. We find that the preferential Ni-C bonding over C-C bonding induces a repulsive interaction between C atoms located at diagonal octahedral voids in Ni substrates. This C-C interaction accelerates C atom diffusion in Ni with a reduced barrier energy of ∼1 eV, compared to ∼1.4-1.6 eV for the diffusion of isolated C atoms. The diffusion barrier energy of isolated C atoms in Cu is lower than in Ni. However, bulk diffusion of interacting C atoms in Cu is not possible due to the preferential C-C bonding over C-Cu bonding, which results in C-C dimer pair formation near the surface. The dramatically different C-C interaction effects within the different substrates explain the contrasting growth mechanisms of graphene on Ni(111) and Cu(111) during chemical vapor deposition.

First principles investigation of the activity of thin film Pt, Pd and Au surface alloys for oxygen reduction

DEFF Research Database (Denmark)

Tripkovic, Vladimir; Hansen, Heine Anton; Rossmeisl, Jan

2015-01-01

Further advances in fuel cell technologies are hampered by kinetic limitations associated with the sluggish cathodic oxygen reduction reaction. We have investigated a range of different formulations of binary and ternary Pt, Pd and Au thin films as electrocatalysts for oxygen reduction. The most...... active binary thin films are near-surface alloys of Pt with subsurface Pd and certain PdAu and PtAu thin films with surface and/or subsurface Au. The most active ternary thin films are with pure metal Pt or Pd skins with some degree of Au in the surface and/or subsurface layer and the near-surface alloys...

Red-Light-Driven Water Splitting by Au(Core)-CdS(Shell) Half-Cut Nanoegg with Heteroepitaxial Junction.

Science.gov (United States)

Naya, Shin-Ichi; Kume, Takahiro; Akashi, Ryo; Fujishima, Musashi; Tada, Hiroaki

2018-01-31

A key material for artificial photosynthesis including water splitting is heteronanostructured (HNS) photocatalysts. The photocatalytic activity depends on the geometry and dimension, and the quality of junctions between the components. Here we present a half-cut Au(core)-CdS(shell) (HC-Au@CdS) nanoegg as a new HNS plasmonic photocatalyst for water splitting. UV-light irradiation of Au nanoparticle (NP)-loaded ZnO (Au/ZnO) at 50 °C induces the selective deposition of hexagonal CdS on the Au surface of Au/ZnO with an epitaxial (EPI) relation of CdS{0001}/Au{111}. The subsequent selective dissolution of the ZnO support at room temperature yields HC-Au@CdS with the Au NP size and EPI junction (#) retained. Red-light irradiation (λ ex = 640 nm) of HC-Au@#CdS gives rise to continuous stoichiometric water splitting with an unprecedentedly high external quantum yield of 0.24%.

Atomic and molecular oxygen adsorbed on (111) transition metal surfaces: Cu and Ni

Energy Technology Data Exchange (ETDEWEB)

López-Moreno, S., E-mail: sinlopez@uacam.mx [Centro de Investigación en Corrosión, Universidad Autónoma de Campeche, Av. Héroe de Nacozari 480, Campeche, Campeche 24029 (Mexico); Romero, A. H. [Physics Department, West Virginia University, Morgantown, West Virginia 26506-6315 (United States)

2015-04-21

Density functional theory is used to investigate the reaction of oxygen with clean copper and nickel [111]-surfaces. We study several alternative adsorption sites for atomic and molecular oxygen on both surfaces. The minimal energy geometries and adsorption energies are in good agreement with previous theoretical studies and experimental data. From all considered adsorption sites, we found a new O{sub 2} molecular precursor with two possible dissociation paths on the Cu(111) surface. Cross barrier energies for the molecular oxygen dissociation have been calculated by using the climbing image nudge elastic band method, and direct comparison with experimental results is performed. Finally, the structural changes and adsorption energies of oxygen adsorbed on surface when there is a vacancy nearby the adsorption site are also considered.

Atomic and molecular oxygen adsorbed on (111) transition metal surfaces: Cu and Ni

Science.gov (United States)

López-Moreno, S.; Romero, A. H.

2015-04-01

Density functional theory is used to investigate the reaction of oxygen with clean copper and nickel [111]-surfaces. We study several alternative adsorption sites for atomic and molecular oxygen on both surfaces. The minimal energy geometries and adsorption energies are in good agreement with previous theoretical studies and experimental data. From all considered adsorption sites, we found a new O2 molecular precursor with two possible dissociation paths on the Cu(111) surface. Cross barrier energies for the molecular oxygen dissociation have been calculated by using the climbing image nudge elastic band method, and direct comparison with experimental results is performed. Finally, the structural changes and adsorption energies of oxygen adsorbed on surface when there is a vacancy nearby the adsorption site are also considered.

Atomic and molecular oxygen adsorbed on (111) transition metal surfaces: Cu and Ni

International Nuclear Information System (INIS)

López-Moreno, S.; Romero, A. H.

2015-01-01

Density functional theory is used to investigate the reaction of oxygen with clean copper and nickel [111]-surfaces. We study several alternative adsorption sites for atomic and molecular oxygen on both surfaces. The minimal energy geometries and adsorption energies are in good agreement with previous theoretical studies and experimental data. From all considered adsorption sites, we found a new O 2 molecular precursor with two possible dissociation paths on the Cu(111) surface. Cross barrier energies for the molecular oxygen dissociation have been calculated by using the climbing image nudge elastic band method, and direct comparison with experimental results is performed. Finally, the structural changes and adsorption energies of oxygen adsorbed on surface when there is a vacancy nearby the adsorption site are also considered

Shape-Selective Syntheses of Gold and Copper Nanostructures: Insights From Density-Functional Theory and Molecular Dynamics

Science.gov (United States)

Liu, Shih-Hsien

Density-functional theory (DFT) and molecular dynamics (MD) were used to resolve the origins of shape-selective syntheses of {111}-faceted Au nanostructures mediated by polyvinylpyrrolidone (PVP) as well as {100}-faceted Cu nanostructures mediated by hex- adecylamine(HDA) seen in experiment. For the work in PVP on Au surfaces, the hexagonal reconstruction of Au(100) was considered. DFT results indicate that the Au(111) surface covered by the PVP segment, 2-pyrrolidone (2P), has a lower surface energy than the 2P- covered (5 x 1) Au(100)-hex surface, and that PVP may exhibit a binding affinity for Au(111) comparable to or greater than (5 x 1) Au(100)-hex. With MD, it is shown that the PVP-covered Au(111) surface has a lower surface energy than the PVP-covered (5 x 1) Au(100)-hex surface, and that the atactic PVP isosamer chains have a binding affinity for Au(111) comparable to (5 x 1) Au(100)-hex. Also, the (5 x 1) Au(100)-hex surface may have a higher flux of Au atoms than the Au(111) surface. Therefore, the Au(111) surface would be thermodynamically and kinetically favored in PVP-mediated syntheses, leading to {111}-faceted Au nanostructures. For the work in HDA on Cu surfaces, DFT results show that the HDA-covered Cu(100) surface has a slightly higher surface energy than the HDA- covered Cu(111) surface. However, HDA has a significant binding preference on Cu(100) over Cu(111). Therefore, the Cu(100) surface would be kinetically favored in HDA-mediated syn- theses, leading to {100}-faceted Cu nanostructures. Further, a metal-organic many-body (MOMB) force field for HDA-Cu interactions was developed based on the DFT work, and the force field was used to resolve the HDA binding patterns on Cu(100) at molecular level. With MD, it is found that decylamine (DA) may be used as an effective capping agent in the synthesis of {100}-faceted Cu nanostructures since DA as well as HDA are organized on Cu surfaces and have the same binding preference on Cu(100) over Cu(111

Photoelectric emission from negative-electron-affinity diamond (111) surfaces: Exciton breakup versus conduction-band emission

International Nuclear Information System (INIS)

Bandis, C.; Pate, B.B.

1995-01-01

We have recently reported that bound electron-hole pairs (Mott-Wannier excitons) are the dominant source of photoelectron emission from specially prepared [''as-polished'' C(111)-(1x1):H] negative-electron-affinity diamond surfaces for near-band-gap excitation up to 0.5 eV above threshold [C. Bandis and B. B. Pate, Phys. Rev. Lett. 74, 777 (1995)]. It was found that photoexcited excitons transport to the surface, break up, and emit their electron. In this paper, we extend the study of exciton-derived emission to include partial yield (constant final-state) analysis as well as angular distribution measurements of the photoelectric emission. In addition, we find that exciton-derived emission does not always dominate. Photoelectric emission properties of the in situ ''rehydrogenated'' (111)-(1x1):H diamond surface are characteristically different than emission observed from the as-polished (111)-(1x1):H surface. The rehydrogenated surface has additional downward band bending as compared to the as-polished surface. In confirmation of the assignment of photoelectric yield to exciton breakup emission, we find a significant enhancement of the total electron yield when the downward band bending of the hydrogenated surface is increased. The functional form of the observed total electron yield demonstrates that, in contrast to the as-polished surface, conduction-band electrons are a significant component of the observed photoelectric yield from the in situ hydrogenated (111)-(1x1):H surface. Furthermore, electron emission characteristics of the rehydrogenated surface confirms our assignment of a Fan phonon-cascade mechanism for thermalization of excitons

Quasi-one-dimensional metals on semiconductor surfaces with defects

International Nuclear Information System (INIS)

Hasegawa, Shuji

2010-01-01

Several examples are known in which massive arrays of metal atomic chains are formed on semiconductor surfaces that show quasi-one-dimensional metallic electronic structures. In this review, Au chains on Si(557) and Si(553) surfaces, and In chains on Si(111) surfaces, are introduced and discussed with regard to the physical properties determined by experimental data from scanning tunneling microscopy (STM), angle-resolved photoemission spectroscopy (ARPES) and electrical conductivity measurements. They show quasi-one-dimensional Fermi surfaces and parabolic band dispersion along the chains. All of them are known from STM and ARPES to exhibit metal-insulator transitions by cooling and charge-density-wave formation due to Peierls instability of the metallic chains. The electrical conductivity, however, reveals the metal-insulator transition only on the less-defective surfaces (Si(553)-Au and Si(111)-In), but not on a more-defective surface (Si(557)-Au). The latter shows an insulating character over the whole temperature range. Compared with the electronic structure (Fermi surfaces and band dispersions), the transport property is more sensitive to the defects. With an increase in defect density, the conductivity only along the metal atomic chains was significantly reduced, showing that atomic-scale point defects decisively interrupt the electrical transport along the atomic chains and hide the intrinsic property of transport in quasi-one-dimensional systems.

Above-surface neutralization of multicharged ions incident on a cesiated Au target

International Nuclear Information System (INIS)

Meyer, F.W.; Hughes, I.G.; Overbury, S.H.

1992-01-01

The critical distance above the surface at which conduction band electrons can start to neutralize incident multicharged projectiles by classical overbarrier transitions is inversely proportional to the metal work function. By varying the amount of Cs coverage on a Au single crystal target between O and 1 monolayers, the authors have been able to verify an up to 3.3 eV decrease of the surface work function, corresponding to more than a factor of two decrease relative to that tabulated for clean Au. This change should result in more than doubling the above-surface interaction time. At larger above-surface distances, however, the electron capture most likely occurs into higher principal quantum numbers of the projectile. The subsequent de-excitation cascade by which inner shells of the projectiles are populated may thus require more time. The authors have investigated the overall effect that lowering the work function has on the above-surface component of projectile K-Auger electron emission for grazing incidence N 6+ ions interacting with cesiated Au single crystals. They will present results showing that an enhancement of this component is indeed observed, and that it is strongly dependent on incidence angle

Multiscale modeling of interaction of alane clusters on Al(111) surfaces : a reactive force field and infrared absorbtion spectroscopy approach

NARCIS (Netherlands)

Ojwang, J.G.O.; Chaudhuri, S.; Duin, van A.C.T.; Chabal, Y.J.; Veyan, J.-F.; Santen, van R.A.; Kramer, G.J.; Goddard III, W.A.

2010-01-01

We have used reactive force field (ReaxFF) to investigate the mechanism of interaction of alanes on Al(111) surface. Our simulations show that, on the Al(111) surface, alanes oligomerize into larger alanes. In addition, from our simulations, adsorption of atomic hydrogen on Al(111) surface leads to

Degradation effects in the one-band-tunneling Au/CaF{sub 2}/n-Si(111) MIS structures

Energy Technology Data Exchange (ETDEWEB)

Vexler, M.I.; Suturin, S.M.; Tyaginov, S.E.; Banshchikov, A.G. [A.F. Ioffe Physical-Technical Institute of the Russian Academy of Sciences, 26 Polytechnicheskaya Str., 194021 St.-Petersburg (Russian Federation); Sokolov, N.S. [A.F. Ioffe Physical-Technical Institute of the Russian Academy of Sciences, 26 Polytechnicheskaya Str., 194021 St.-Petersburg (Russian Federation)], E-mail: nsokolov@fl.ioffe.ru

2008-10-01

High quality Au/CaF{sub 2}/n-Si(111) metal-insulator-semiconductor structures with thin (< 2.5 nm) epitaxial fluorite layers were fabricated. Damage of such structures due to electrical overload has been investigated in this work. Current-voltage characteristics of these structures before and in process of degradation are measured. A mechanism explaining the pronounced breakdown at reverse bias is suggested. This mechanism relies on the potentially possible bistability arising from the one-band character of tunneling in the studied devices. Some comparisons with the degradation scenario in SiO{sub 2}-based samples are made. Wear-out fields for CaF{sub 2} films are estimated. The changes in behaviour of fresh and damaged structures under visible light irradiation are treated.

First-principles investigations of O2 dissociation on low-coordinated Pd ensembles over stepped Au surfaces

International Nuclear Information System (INIS)

Yuan, D.W.; Liu, Z.R.; Xu, Y.

2012-01-01

The adsorption and dissociation of O 2 on Pd monomer or trimer incorporated into Au(322) and Au(321) surfaces are systematically investigated by first-principles calculations and nudged-elastic-band simulations. We found that the contiguous low-coordinated Pd ensembles alloyed into step edges of Au surfaces are required for O 2 dissociation with an enhanced adsorption energy (∼−1.00 eV). The dissociative barrier of O 2 is mainly related to the size of Pd ensembles, and the activation energy is about 1.00 eV on Pd trimers. However, the Pd monomer is less active for the adsorption and dissociation of O 2 . Additionally, the O spillover from Pd to Au sites only occurs at elevated temperature, and the diffusion processes are highly endothermic. The calculated results indicate that the Pd-modified Au step edge with a contiguous Pd ensemble is the reactive center for supplying atomic oxygen on Pd-doped Au catalysts. -- Highlights: ► Our results reveal the mechanism of O 2 dissociation on Pd-decorated stepped Au surfaces. ► The adsorption energy of O 2 is related to both coordination numbers and geometrical arrangements of Pd atoms alloyed into Au surface. ► The Pd-modified Au step with a contiguous Pd ensemble is the reactive center for O 2 dissociation. ► Our results are important for understanding the catalytic properties of Pd-modified nanoporous gold, especially for those catalytic reactions related to O 2 activation.

Observation of the adsorption and desorption of vibrationally excited molecules on a metal surface

Science.gov (United States)

Shirhatti, Pranav R.; Rahinov, Igor; Golibrzuch, Kai; Werdecker, Jörn; Geweke, Jan; Altschäffel, Jan; Kumar, Sumit; Auerbach, Daniel J.; Bartels, Christof; Wodtke, Alec M.

2018-06-01

The most common mechanism of catalytic surface chemistry is that of Langmuir and Hinshelwood (LH). In the LH mechanism, reactants adsorb, become thermalized with the surface, and subsequently react. The measured vibrational (relaxation) lifetimes of molecules adsorbed at metal surfaces are in the range of a few picoseconds. As a consequence, vibrational promotion of LH chemistry is rarely observed, with the exception of LH reactions occurring via a molecular physisorbed intermediate. Here, we directly detect adsorption and subsequent desorption of vibrationally excited CO molecules from a Au(111) surface. Our results show that CO (v = 1) survives on a Au(111) surface for 1 × 10-10 s. Such long vibrational lifetimes for adsorbates on metal surfaces are unexpected and pose an interesting challenge to the current understanding of vibrational energy dissipation on metal surfaces. They also suggest that vibrational promotion of surface chemistry might be more common than is generally believed.

Plasma processing of the Si(0 0 1) surface for tuning SPR of Au/Si-based plasmonic nanostructures

Energy Technology Data Exchange (ETDEWEB)

Giangregorio, Maria M. [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM sez. Bari, Via Orabona 4, 70125 Bari (Italy)]. E-mail: michelaria.giangregorio@ba.imip.cnr.it; Losurdo, Maria [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM sez. Bari, Via Orabona 4, 70125 Bari (Italy); Sacchetti, Alberto [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM sez. Bari, Via Orabona 4, 70125 Bari (Italy); Capezzuto, Pio [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM sez. Bari, Via Orabona 4, 70125 Bari (Italy); Bruno, Giovanni [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM sez. Bari, Via Orabona 4, 70125 Bari (Italy)

2006-12-15

Au nanoclusters have been deposited on Si(0 0 1) surfaces by sputtering of a metallic Au target using an Ar plasma. Different wet and dry treatments of the Si(0 0 1) surface, including dipping in HF solution and exposure to H{sub 2} and N{sub 2} plasmas, have been applied and the effects of these treatments on the Au nanoparticles/Si interface, the Au nanoclusters aspect ratio and the surface plasmon resonance (SPR) energy and amplitude are investigated exploiting spectroscopic ellipsometry and atomic force microscopy. It is found that the Au nanoclusters aspect ratio depends on the extent of the Au-Si intermixing. The thicker the Au-Si interface layer, the larger the Au nanoparticles aspect ratio and the red-shift of the SPR peak. Furthermore, SiO{sub 2} and the H{sub 2} plasma treatment inhibit the Si-Au intermixing, while HF-dipping and the N{sub 2} plasma treatment favour Au-Si intermixing, yielding silicide formation which increases the Si wetting by Au.

Initial Reduction of CO2 on Pd-, Ru-, and Cu-Doped CeO2(111) Surfaces: Effects of Surface Modification on Catalytic Activity and Selectivity.

Science.gov (United States)

Guo, Chen; Wei, Shuxian; Zhou, Sainan; Zhang, Tian; Wang, Zhaojie; Ng, Siu-Pang; Lu, Xiaoqing; Wu, Chi-Man Lawrence; Guo, Wenyue

2017-08-09

Surface modification by metal doping is an effective treatment technique for improving surface properties for CO 2 reduction. Herein, the effects of doped Pd, Ru, and Cu on the adsorption, activation, and reduction selectivity of CO 2 on CeO 2 (111) were investigated by periodic density functional theory. The doped metals distorted the configuration of a perfect CeO 2 (111) by weakening the adjacent Ce-O bond strength, and Pd doping was beneficial for generating a highly active O vacancy. The analyses of adsorption energy, charge density difference, and density of states confirmed that the doped metals were conducive for enhancing CO 2 adsorption, especially for Cu/CeO 2 (111). The initial reductive dissociation CO 2 → CO* + O* on metal-doped CeO 2 (111) followed the sequence of Cu- > perfect > Pd- > Ru-doped CeO 2 (111); the reductive hydrogenation CO 2 + H → COOH* followed the sequence of Cu- > perfect > Ru- > Pd-doped CeO 2 (111), in which the most competitive route on Cu/CeO 2 (111) was exothermic by 0.52 eV with an energy barrier of 0.16 eV; the reductive hydrogenation CO 2 + H → HCOO* followed the sequence of Ru- > perfect > Pd-doped CeO 2 (111). Energy barrier decomposition analyses were performed to identify the governing factors of bond activation and scission along the initial CO 2 reduction routes. Results of this study provided deep insights into the effect of surface modification on the initial reduction mechanisms of CO 2 on metal-doped CeO 2 (111) surfaces.

Surface assisted oxidation of flat lying organic molecules - a real-time STM study

Energy Technology Data Exchange (ETDEWEB)

Waldmann, Thomas; Roos, Michael; Breitruck, Achim; Hoster, Harry E.; Behm, R. Juergen [Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm (Germany); Kuenzel, Daniela; Gross, Axel [Institute of Theoretical Chemistry, Ulm University, D-89069 Ulm (Germany)

2010-07-01

Using time resolved scanning tunneling microscopy (STM), we tested the interaction of O{sub 2} from gas-phase with ordered adlayers of the Bis(terpyridine) derivative 2,4'-BTP on Au(111), Ag(111) and graphite (HOPG) surfaces at T = 300 K. At an O{sub 2} pressure of 10{sup -5} mbar, the adlayers on Ag(111) undergo chemical and structural changes. These include modifications of the 2-pyridyl rings of individual 2,4'-BTP adsorbates and rearrangements of the hydrogen bonded adlayer. Since we do not observe similar changes on HOPG and Au(111), we assume that Ag(111) acts as catalyst for the underlying processes. Based on our STM data in combination with DFT calculations, we conclude that the observed reaction is pyridyl-N-oxide formation. Furthermore, we derive reaction yields, enantiomeric excess, reaction rates and reaction orders from the time-resolved STM data.

Alloy formation and chemisorption at Zn/Pt(111) bimetallic surfaces using alkali ISS, XPD, and TPD.

Science.gov (United States)

Ho, Chih-Sung; Martono, Eddie; Banerjee, Santanu; Roszell, John; Vohs, John; Koel, Bruce E

2013-11-21

Alloy formation and chemisorption at bimetallic surfaces formed by vapor-depositing Zn on a Pt(111) single crystal were investigated primarily by using X-ray photoelectron diffraction (XPD), X-ray photoelectron spectroscopy (XPS), low-energy alkali ion scattering spectroscopy (ALISS), low electron energy diffraction (LEED), and temperature programmed desorption (TPD). A wide range of conditions were investigated to explore whether deposition and annealing of Zn films could produce well-defined, ordered alloy surfaces, similar to those encountered for Sn/Pt(111) surface alloys. These attempts were unsuccessful, although weak, diffuse (2 × 2) spots were observed under special conditions. The particular PtZn bimetallic alloy created by annealing one monolayer of Zn on Pt(111) at 600 K, which has a Zn composition in the surface layer of about 5 at. %, was investigated in detail by using XPD and ALISS. Only a diffuse (1 × 1) pattern was observed from this surface by LEED, suggesting that no long-range, ordered alloy structure was formed. Zn atoms were substitutionally incorporated into the Pt(111) crystal to form a near-surface alloy in which Zn atoms were found to reside primarily in the topmost and second layers. The alloyed Zn atoms in the topmost layer are coplanar with the Pt atoms in the surface layer, without any "buckling" of Zn, that is, displacement in the vertical direction. This result is expected because of the similar size of Pt and Zn, based on previous studies of bimetallic Pt alloys. Zn atoms desorb upon heating rather than diffusing deep into the bulk of the Pt crystal. Temperature programmed desorption (TPD) measurements show that both CO and NO have lower desorption energies on the PtZn alloy surface compared to that on the clean Pt(111) surface.

Polytetrafluorethylene-Au as a substrate for surface-enhanced Raman spectroscopy

Directory of Open Access Journals (Sweden)

Siegel Jakub

2011-01-01

Full Text Available Abstract This study deals with preparation of substrates suitable for surface-enhanced Raman spectroscopy (SERS applications by sputtering deposition of gold layer on the polytetrafluorethylene (PTFE foil. Time of sputtering was investigated with respect to the surface properties. The ability of PTFE-Au substrates to enhance Raman signals was investigated by immobilization of biphenyl-4,4'-dithiol (BFD from the solutions with various concentrations. BFD was also used for preparation of sandwich structures with Au or Ag nanoparticles by two different procedures. Results showed that PTFE can be used for fabrication of SERS active substrate with easy handle properties at low cost. This substrate was sufficient for the measurement of SERS spectrum of BFD even at 10-8 mol/l concentration.

Adsorption/desorption kinetics of Na atoms on reconstructed Si (111)-7 x 7 surface

International Nuclear Information System (INIS)

Chauhan, Amit Kumar Singh; Govind; Shivaprasad, S.M.

2010-01-01

Self-assembled nanostructures on a periodic template are fundamentally and technologically important as they put forward the possibility to fabricate and pattern micro/nano-electronics for sensors, ultra high-density memories and nanocatalysts. Alkali-metal (AM) nanostructure grown on a semiconductor surface has received considerable attention because of their simple hydrogen like electronic structure. However, little efforts have been made to understand the fundamental aspects of the growth mechanism of self-assembled nanostructures of AM on semiconductor surfaces. In this paper, we report organized investigation of kinetically controlled room-temperature (RT) adsorption/desorption of sodium (Na) metal atoms on clean reconstructed Si (111)-7 x 7 surface, by X-ray photoelectron spectroscopy (XPS). The RT uptake curve shows a layer-by-layer growth (Frank-vander Merve growth) mode of Na on Si (111)-7 x 7 surfaces and a shift is observed in the binding energy position of Na (1s) spectra. The thermal stability of the Na/Si (111) system was inspected by annealing the system to higher substrate temperatures. Within a temperature range from RT to 350 o C, the temperature induced mobility to the excess Na atoms sitting on top of the bilayer, allowing to arrange themselves. Na atoms desorbed over a wide temperature range of 370 o C, before depleting the Si (111) surface at temperature 720 o C. The acquired valence-band (VB) spectra during Na growth revealed the development of new electronic-states near the Fermi level and desorption leads the termination of these. For Na adsorption up to 2 monolayers, decrease in work function (-1.35 eV) was observed, whereas work function of the system monotonically increases with Na desorption from the Si surface as observed by other studies also. This kinetic and thermodynamic study of Na adsorbed Si (111)-7 x 7 system can be utilized in fabrication of sensors used in night vision devices.

Surface structural determination of UO2(111) using MeV ions

International Nuclear Information System (INIS)

Thompson, K.A.; Ellis, W.P.; Taylor, T.N.; Valone, S.M.; Maggiore, C.J.

1983-01-01

The UO 2 (111) surface was studied using MeV ions incident along the and directions. In addition, this surface was well characterized by LEED and Auger analysis. A resonance at 3.05 MeV for 4 He elastic scattering from 16 O made it possible to study the surface peaks for uranium and oxygen simultaneously. By combining previous surface studies with detailed analysis of the surface peaks and rocking curves for this compound material, an outward relaxation of 0.19 A +- 0.01 A was determined for uranium

Scattering of Hyperthermal Nitrogen Atoms from the Ag(111) Surface

NARCIS (Netherlands)

Ueta, H.; Gleeson, M. A.; Kleyn, A. W.

2009-01-01

Measurements on scattering of hyperthermal N atoms from the Ag(111) Surface at temperatures of 500, 600, and 730 K are presented. The scattered atoms have a two-component angular distribution. One of the N components is very broad. In contrast, scattered Ar atoms exhibit only a sharp,

Novel anti-reflection technology for GaAs single-junction solar cells using surface patterning and Au nanoparticles.

Science.gov (United States)

Kim, Youngjo; Lam, Nguyen Dinh; Kim, Kangho; Kim, Sangin; Rotermund, Fabian; Lim, Hanjo; Lee, Jaejin

2012-07-01

Single-junction GaAs solar cell structures were grown by low-pressure MOCVD on GaAs (100) substrates. Micro-rod arrays with diameters of 2 microm, 5 microm, and 10 microm were fabricated on the surfaces of the GaAs solar cells via photolithography and wet chemical etching. The patterned surfaces were coated with Au nanoparticles using an Au colloidal solution. Characteristics of the GaAs solar cells with and without the micro-rod arrays and Au nanoparticles were investigated. The short-circuit current density of the GaAs solar cell with 2 microm rod arrays and Au nanoparticles increased up to 34.9% compared to that of the reference cell without micro-rod arrays and Au nanoparticles. The conversion efficiency of the GaAs solar cell that was coated with Au nanoparticles on the patterned surface with micro-rod arrays can be improved from 14.1% to 19.9% under 1 sun AM 1.5G illumination. These results show that micro-rod arrays and Au nanoparticle coating can be applied together in surface patterning to achieve a novel cost-effective anti-reflection technology.

Chemisorption on the (111) and (100) faces of platinum-tin bimetallic surfaces

Science.gov (United States)

Panja, Chameli

2000-10-01

Chemisorption and reaction of CH3OH (methanol), C2H 5OH (ethanol), and H2O (water) on Pt(111) and Sn/Pt(111) alloys, and CO (carbon monoxide), NO (nitric oxide), and C2D 2 (acetylene) on Pt(100) and Sn/Pt(100) have been studied under ultrahigh vacuum conditions using temperature programmed desorption (TPD), Auger electron spectroscopy (AES), low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS). Small organic molecules like CH3OH and C2H5OH are potential fuels for low-temperature hydrocarbon fuel cells and it is important to understand the role of tin as a promoter in electrooxidation of these molecules. Also, the catalytic reactions of CO, NO and C2H2 are of considerable interest for improving of automotive exhaust-gas catalytic converters and other heterogeneous catalysts. Ordered Pt-Sn alloys can be prepared by vapor deposition of Sn on Pt surfaces. A (2 x 2) structure (theta Sn = 0.25) and a (√3x√/3)R30° structure are formed on Pt(111), and a c(2 x 2) and (3√2x√2)R45° structures with theta Sn = 0.5 and 0.67, respectively, are formed on Pt(100). CH3OH, C2H5OH and H2O are all weakly bound and reversibly adsorbed on Pt(111) and both of the Sn/Pt(111) alloys under UHV conditions. Alloying Sn into the Pt(111) surface weakens the adsorption of these molecules from that on Pt(111) and leads to a lower reactivity as the surface concentration of Sn increases. TPD measurements reveal a reduction in the saturation coverage and chemisorption bond energy for CO, NO and C2HL chemisorption, on the two Sn/Pt(100)alloys compared to that on Pt(100). CO chemisorption is completely reversible on these two Sn/Pt(100) alloys. However, NO is partially reduced to form N2O on these alloys, so that N2O along with NO and O2 desorption was observed. We propose that dinitrosyl species, i.e., two NO molecules bound to one Pt atom, are intermediates in N2O formation from adsorbed NO on these Sn

Surface treatment effect on Si (111) substrate for carbon deposition using DC unbalanced magnetron sputtering

Energy Technology Data Exchange (ETDEWEB)

Aji, A. S., E-mail: aji.ravazes70@gmail.com; Sahdan, M. F.; Hendra, I. B.; Dinari, P.; Darma, Y. [Quantum Semiconductor and Devices Lab., Physics of Material Electronics Research Division, Department of Physics, Institut Teknologi Bandung (Indonesia)

2015-04-16

In this work, we studied the effect of HF treatment in silicon (111) substrate surface for depositing thin layer carbon. We performed the deposition of carbon by using DC Unbalanced Magnetron Sputtering with carbon pallet (5% Fe) as target. From SEM characterization results it can be concluded that the carbon layer on HF treated substrate is more uniform than on substrate without treated. Carbon deposition rate is higher as confirmed by AFM results if the silicon substrate is treated by HF solution. EDAX characterization results tell that silicon (111) substrate with HF treatment have more carbon fraction than substrate without treatment. These results confirmed that HF treatment on silicon Si (111) substrates could enhance the carbon deposition by using DC sputtering. Afterward, the carbon atomic arrangement on silicon (111) surface is studied by performing thermal annealing process to 900 °C. From Raman spectroscopy results, thin film carbon is not changing until 600 °C thermal budged. But, when temperature increase to 900 °C, thin film carbon is starting to diffuse to silicon (111) substrates.

Self-Assembled Si(111) Surface States: 2D Dirac Material for THz Plasmonics

Science.gov (United States)

Wang, Z. F.; Liu, Feng

2015-07-01

Graphene, the first discovered 2D Dirac material, has had a profound impact on science and technology. In the last decade, we have witnessed huge advances in graphene related fundamental and applied research. Here, based on first-principles calculations, we propose a new 2D Dirac band on the Si(111) surface with 1 /3 monolayer halogen coverage. The s p3 dangling bonds form a honeycomb superstructure on the Si(111) surface that results in an anisotropic Dirac band with a group velocity (˜106 m /s ) comparable to that in graphene. Most remarkably, the Si-based surface Dirac band can be used to excite a tunable THz plasmon through electron-hole doping. Our results demonstrate a new way to design Dirac states on a traditional semiconductor surface, so as to make them directly compatible with Si technology. We envision this new type of Dirac material to be generalized to other semiconductor surfaces with broad applications.

Self-Assembled Si(111) Surface States: 2D Dirac Material for THz Plasmonics.

Science.gov (United States)

Wang, Z F; Liu, Feng

2015-07-10

Graphene, the first discovered 2D Dirac material, has had a profound impact on science and technology. In the last decade, we have witnessed huge advances in graphene related fundamental and applied research. Here, based on first-principles calculations, we propose a new 2D Dirac band on the Si(111) surface with 1/3 monolayer halogen coverage. The sp(3) dangling bonds form a honeycomb superstructure on the Si(111) surface that results in an anisotropic Dirac band with a group velocity (∼10(6)  m/s) comparable to that in graphene. Most remarkably, the Si-based surface Dirac band can be used to excite a tunable THz plasmon through electron-hole doping. Our results demonstrate a new way to design Dirac states on a traditional semiconductor surface, so as to make them directly compatible with Si technology. We envision this new type of Dirac material to be generalized to other semiconductor surfaces with broad applications.

Electrochemical formation and characterization of Au nanostructures on a highly ordered pyrolytic graphite surface

International Nuclear Information System (INIS)

Arroyo Gómez, José J.; Zubieta, Carolina; Ferullo, Ricardo M.; García, Silvana G.

2016-01-01

Graphical abstract: - Highlights: • The electrodeposition of Au on HOPG tends to follow the response predicted for a 3D instantaneous nucleation mechanism in the potential range considered. • By choosing suitable nucleation and growth pulses, one-dimensional deposits were possible, preferentially located on step edges of the HOPG substrate. • Quantum-mechanical calculations confirmed the tendency of Au atoms to join selectively on the HOPG step edges, at the early stages of Au electrodeposition. - Abstract: The electrochemical formation of Au nanoparticles on a highly ordered pyrolytic graphite (HOPG) substrate using conventional electrochemical techniques and ex-situ AFM is reported. From the potentiostatic current transients studies, the Au electrodeposition process on HOPG surfaces was described, within the potential range considered, by a model involving instantaneous nucleation and diffusion controlled 3D growth, which was corroborated by the microscopic analysis. Initially, three-dimensional (3D) hemispherical nanoparticles distributed on surface defects (step edges) of the substrate were observed, with increasing particle size at more negative potentials. The double potential pulse technique allowed the formation of rounded deposits at low deposition potentials, which tend to form lines of nuclei aligned in defined directions leading to 3D ordered structures. By choosing suitable nucleation and growth pulses, one-dimensional (1D) deposits were possible, preferentially located on step edges of the HOPG substrate. Quantum-mechanical calculations confirmed the tendency of Au atoms to join selectively on surface defects, such as the HOPG step edges, at the early stages of Au electrodeposition.

Communication: Methane dissociation on Ni(111) surface: Importance of azimuth and surface impact site

International Nuclear Information System (INIS)

Shen, Xiangjian; Zhang, Zhaojun; Zhang, Dong H.

2016-01-01

Understanding the role of reactant ro-vibrational degrees of freedom (DOFs) in reaction dynamics of polyatomic molecular dissociation on metal surfaces is of great importance to explore the complex chemical reaction mechanism. Here, we present an expensive quantum dynamics study of the dissociative chemisorption of CH 4 on a rigid Ni(111) surface by developing an accurate nine-dimensional quantum dynamical model including the DOF of azimuth. Based on a highly accurate fifteen-dimensional potential energy surface built from first principles, our simulations elucidate that the dissociation probability of CH 4 has the strong dependence on azimuth and surface impact site. Some improvements are suggested to obtain the accurate dissociation probability from quantum dynamics simulations.

Density functional study of a typical thiol tethered on a gold surface: ruptures under normal or parallel stretch

International Nuclear Information System (INIS)

Wang, Guan M; Sandberg, William C; Kenny, Steven D

2006-01-01

The mechanical and dynamical properties of a model Au(111)/thiol surface system were investigated by using localized atomic-type orbital density functional theory in the local density approximation. Relaxing the system gives a configuration where the sulfur atom forms covalent bonds to two adjacent gold atoms as the lowest energy structure. Investigations based on ab initio molecular dynamics simulations at 300, 350 and 370 K show that this tethering system is stable. The rupture behaviour between the thiol and the surface was studied by displacing the free end of the thiol. Calculated energy profiles show a process of multiple successive ruptures that account for experimental observations. The process features successive ruptures of the two Au-S bonds followed by the extraction of one S-bonded Au atom from the surface. The force required to rupture the thiol from the surface was found to be dependent on the direction in which the thiol was displaced, with values comparable with AFM measurements. These results aid the understanding of failure dynamics of Au(111)-thiol-tethered biosurfaces in microfluidic devices where fluidic shear and normal forces are of concern

Use of low energy alkali ion scattering as a probe of surface structure

International Nuclear Information System (INIS)

Overbury, S.H.

1986-01-01

An overview is given of the use of low energy ion scattering as a probe of surface structure with emphasis on work done using alkali ions. Various schemes for extracting structural information from the ion energy and angle distributions are discussed in terms of advantages and disadvantages of each. The scattering potential which is the primary non-structural parameter needed for analysis, is discussed in terms of recent experimental results. The structure of clean and reconstructed surfaces are discussed, with examples of measurements of layer relaxations on the Mo(111) surface and missing row reconstructions on the Au(110) and Pt(110) surfaces. Studies of adsorbate covered surfaces are presented with respect to location of the adsorbate and its effect on the structure of the underlying substrate. Finally, examples are given which demonstrate the sensitivity of ion scattering to surface defects and disordering on reconstructed Au(110) and Pt(110) surfaces and unreconstructed Mo(111) surfaces, and to ordering of adsorbates on Mo(001). 47 refs., 12 figs

Synthesis of Au nanoparticles at the surface and embedded in carbonaceous matrix by 150 keV Ar ion irradiation

International Nuclear Information System (INIS)

Prakash, Jai; Tripathi, Jalaj; Tripathi, A; Kumar, P; Asokan, K; Avasthi, D K; Rigato, V; Pivin, J C; Chae, Keun Hwa; Gautam, Sanjeev

2011-01-01

We report on synthesis of spherical Au nanoparticles at the surface and embedded in carbonaceous matrix by 150 keV Ar ion irradiation of thin Au film on polyethyleneterepthlate (PET). The pristine and irradiated samples are characterized by Rutherford backscattering spectrometry (RBS), atomic force microscopy, scanning electron microscopy and transmission electron microscopy (TEM) techniques. RBS spectra reveal the sputtering of Au film and interface mixing, increasing with increasing fluence. Surface morphology shows that at the fluence of 5 x 10 15 ions cm -2 , dewetting of thin Au film begins and partially connected nanostructures are formed whereas, at the higher fluence of 5 x 10 16 ions cm -2 , isolated spherical Au nanoparticles (45 ± 20 nm) are formed at the surface. Cross-sectional TEM observations also evidence the Au nanoparticles at the surface and mixed metal-polymer region indicating the formation of nanocomposites with small Au nanoparticles. The results are explained by the crater formation, sputtering followed by dewetting of the thin Au film and interdiffusion at the interface, through molten zones due to thermal spike induced by Ar ions.

Clarification of the interaction between Au atoms and the anatase TiO2 (112) surface using density functional theory

Science.gov (United States)

Tada, Kohei; Koga, Hiroaki; Okumura, Mitsutaka; Tanaka, Shingo

2018-04-01

A model (112) surface slab of anatase TiO2 (112) was optimized, and the adsorption of Au atoms onto the (112) surface was investigated by first-principles calculations based on DFT (density functional theory) with the generalized gradient approximation (GGA). Furthermore, the results were compared with those of Au/anatase TiO2 (101) system. The (112) surface has a ridge and a groove (zig-zag structure). The Au atoms were strongly adsorbed in the grooves but became unstable as they climbed toward the ridges, and the promotion of electrons in the 5d orbitals to the 6s and 6p orbitals in the absorbed Au atom occurred. At the Au/anatase TiO2 interface, the Au-Ti4+ coordinate bond in the (112) system is stronger than that in the (101) system because the promotion of electrons is greater in the former interaction than the latter. The results suggest that Au/anatase TiO2 catalysts with a higher dispersion of Au nanoparticles could be prepared when the (112) surface is preferentially exposed.

Cluster-surface collisions: Characteristics of Xe55- and C20 - Si[111] surface bombardment

International Nuclear Information System (INIS)

Cheng, H.

1999-01-01

Molecular dynamics (MD) simulations are performed to study the cluster-surface collision processes. Two types of clusters, Xe 55 and C 20 are used as case studies of materials with very different properties. In studies of Xe 55 - Si[111] surface bombardment, two initial velocities, 5.0 and 10.0 km/s (normal to the surface) are chosen to investigate the dynamical consequences of the initial energy or velocity in the cluster-surface impact. A transition in the speed of kinetic energy propagation, from subsonic velocities to supersonic velocities, is observed. Energy transfer, from cluster translational motion to the substrate, occurs at an extremely fast rate that increases as the incident velocity increases. Local melting and amorphous layer formation in the surfaces are found via energetic analysis of individual silicon atoms. For C 20 , the initial velocity ranges from 10 to 100 km/s. The clusters are damaged immediately upon impact. Similar to Xe 55 , increase in the potential energy is larger than the increase in internal kinetic energy. However, the patterns of energy distribution are different for the two types of clusters. The energy transfer from the carbon clusters to Si(111) surface is found to be slower than that found in the Xe clusters. Fragmentation of the carbon cluster occurs when the initial velocity is greater than 30 km/s. At 10 km/s, the clusters show recrystallization at later times. The average penetration depth displays a nonlinear dependence on the initial velocity. Disturbance in the surface caused by C 20 is discussed and compared to the damage caused by Xe 55 . Energetics, structures, and dynamics of these systems are fully analyzed and characterized. copyright 1999 American Institute of Physics

Surface Reconstruction for Preparation of Plasmonic Au/TiO₂ Nanoparticle with Perfect Hetero Interface and Improved Photocatalytic Capacity.

Science.gov (United States)

Yuan, Guoqiu; Ping, Chen; Zhao, Qin; Cao, Min; Jin, Yonglong; Ge, Cunwang

2018-07-01

The photocatalytic activity of plasmonic Au/TiO2 nanoparticles (NPs) is dependent on distances between Au and TiO2. The preparation of plasmonic NPs is still a challenge because of an inherent lattice mismatch on heterogeneous interfaces. The combination between Au and TiO2 NPs often exhibits physical adsorption, which affect block the electron transferring process by photo-induction from TiO2 to Au NPs and weaken the photocatalytic activity. In this work an approach for preparing plasmonic Au/TiO2 NPs with perfect hetero-interface was proposed based on reconstruction of anatase TiO2 with (101) surface and in-situ reduction of Au NPs. Under UV-irradiation, anatase TiO2 NPs with a high percentage of (001) facets in formaldehyde solution undergo photochemical reactions to reconstruct the (101) surface of TiO2 and simultaneously allow polyformaldehyde to absorb on the same surface. Thus, Au(OH)-4 ions could be adsorbed on the (101) surfaces of TiO2 through electrostatic adsorption and reduced to form nano-Au in situ after recrystallization at 180 °C. The high-resolution transmission electron microscopy (HRTEM) images showed clear nanoscale lattice transition on heterogeneous interfaces of Au/TiO2 NPs. The surface structure of TiO2 NPs and the growth mechanism of Au/TiO2 NPs were evaluated with HRTEM, X-ray photoelectron spectra (XPS) and Fourier transform infrared spectroscopy (FTIR). It was demonstrated that the as-prepared plasmonic Au/TiO2 NPs had higher photocatalytic activity and corrosion resistance in comparison with primary TiO2 NPs by photo-electrochemical measurements. The reinforcing mechanism could be interpreted with Mott-Schottky analysis in terms of quantum mechanics. Our study implied that the reconstruction based synthesis may open up more opportunities to obtain lattice-mismatch nanomaterials for photocatalysis.

Investigation of the Si(111) surface in uhv: oxidation and the effect of surface phosphorus

International Nuclear Information System (INIS)

Tom, H.W.K.; Zhu, X.D.; Shen, Y.R.; Somorjai, G.A.

1984-06-01

We have studied the initial stages of oxidation, the segregation of phosphorus, and the effect of phosphorus on oxidation of the Si(111) 7 x 7 surface using optical second-harmonic generation. We have also observed a (√3 x √3)R30 0 LEED pattern for P on Si

Tunneling spectroscopy of a phosphorus impurity atom on the Ge(111)-(2 × 1) surface

Energy Technology Data Exchange (ETDEWEB)

Savinov, S. V.; Oreshkin, A. I., E-mail: oreshkin@spmlab.phys.msu.su, E-mail: oreshkin@spmlab.ru [Moscow State University (Russian Federation); Oreshkin, S. I. [Moscow State University, Sternberg Astronomical Institute (Russian Federation); Haesendonck, C. van [Laboratorium voor Stoffysica en Magnetisme (Belgium)

2015-06-15

We numerically model the Ge(111)-(2 × 1) surface electronic properties in the vicinity of a P donor impurity atom located near the surface. We find a notable increase in the surface local density of states (LDOS) around the surface dopant near the bottom of the empty surface state band π*, which we call a split state due to its limited spatial extent and energetic position inside the band gap. We show that despite the well-established bulk donor impurity energy level position at the very bottom of the conduction band, a surface donor impurity on the Ge(111)-(2 × 1) surface might produce an energy level below the Fermi energy, depending on the impurity atom local environment. It is demonstrated that the impurity located in subsurface atomic layers is visible in a scanning tunneling microscope (STM) experiment on the Ge(111)-(2 × 1) surface. The quasi-1D character of the impurity image, observed in STM experiments, is confirmed by our computer simulations with a note that a few π-bonded dimer rows may be affected by the presence of the impurity atom. We elaborate a model that allows classifying atoms on the experimental low-temperature STM image. We show the presence of spatial oscillations of the LDOS by the density-functional theory method.

In situ fabrication of quasi-free-standing epitaxial graphene nanoflakes on gold.

Science.gov (United States)

Leicht, Philipp; Zielke, Lukas; Bouvron, Samuel; Moroni, Riko; Voloshina, Elena; Hammerschmidt, Lukas; Dedkov, Yuriy S; Fonin, Mikhail

2014-04-22

Addressing the multitude of electronic phenomena theoretically predicted for confined graphene structures requires appropriate in situ fabrication procedures yielding graphene nanoflakes (GNFs) with well-defined geometries and accessible electronic properties. Here, we present a simple strategy to fabricate quasi-free-standing GNFs of variable sizes, performing temperature programmed growth of graphene flakes on the Ir(111) surface and subsequent intercalation of gold. Using scanning tunneling microscopy (STM), we show that epitaxial GNFs on a perfectly ordered Au(111) surface are formed while maintaining an unreconstructed, singly hydrogen-terminated edge structure, as confirmed by the accompanying density functional theory (DFT) calculations. Using tip-induced lateral displacement of GNFs, we demonstrate that GNFs on Au(111) are to a large extent decoupled from the Au(111) substrate. The direct accessibility of the electronic states of a single GNF is demonstrated upon analysis of the quasiparticle interference patterns obtained by low-temperature STM. These findings open up an interesting playground for diverse investigations of graphene nanostructures with possible implications for device fabrication.

Positronic probe of vacancy defects on surfaces of Au nanoparticles embedded in MgO

International Nuclear Information System (INIS)

Xu, Jun; Moxom, J.; Somieski, B.; White, C. W.; Mills, A. P.; Suzuki, R.; Ishibashi, S.

2001-01-01

Clusters of four atomic vacancies were found in Au nanoparticle-embedded MgO by positron lifetime spectroscopy [Phys. Rev. Lett. 83, 4586 (1999)]. These clusters were also suggested to locate at the surface of Au nanoparticles by one-detector measurements of Doppler broadening of annihilation radiation. In this work we provide evidence, using two-detector coincidence experiments of Doppler broadening (2D-DBAR), to clarify that these vacancy clusters reside on the surfaces of Au nanoparticles. This work also demonstrates a method for identifying defects at nanomaterials interfaces: a combination of both positron lifetime spectroscopy, which tells the type of the defects, and 2D-DBAR measurements, which reveals chemical environment of the defects

Positronic probe of vacancy defects on surfaces of Au nanoparticles embedded in MgO

Science.gov (United States)

Xu, Jun; Moxom, J.; Somieski, B.; White, C. W.; Mills, A. P., Jr.; Suzuki, R.; Ishibashi, S.

2001-09-01

Clusters of four atomic vacancies were found in Au nanoparticle-embedded MgO by positron lifetime spectroscopy [Phys. Rev. Lett. 83, 4586 (1999)]. These clusters were also suggested to locate at the surface of Au nanoparticles by one-detector measurements of Doppler broadening of annihilation radiation. In this work we provide evidence, using two-detector coincidence experiments of Doppler broadening (2D-DBAR), to clarify that these vacancy clusters reside on the surfaces of Au nanoparticles. This work also demonstrates a method for identifying defects at nanomaterials interfaces: a combination of both positron lifetime spectroscopy, which tells the type of the defects, and 2D-DBAR measurements, which reveals chemical environment of the defects.

Adsorption properties of AlN on Si(111) surface: A density functional study

Science.gov (United States)

Yuan, Yinmei; Zuo, Ran; Mao, Keke; Tang, Binlong; Zhang, Zhou; Liu, Jun; Zhong, Tingting

2018-04-01

In the process of preparing GaN on Si substrate by MOCVD, an AlN buffer layer is very important. In this study, we conducted density functional theory calculations on the adsorption of AlN molecule on Si(111)-(2 × 2) surface, with the AlN molecule located horizontally or vertically above Si(111) surface at different adsorption sites. The calculations revealed that the lowest adsorption energy was at the N-top-Al-bridge site in the horizontal configuration, with the narrowest band gap, indicating that it was the most preferential adsorption growth status of AlN. In the vertical configurations, N adatom was more reactive and convenient to form bonds with the topmost Si atoms than Al adatom. When the N-end of the AlN molecule was located downward, the hollow site was the preferred adsorption site; when the Al-end was located downward, the bridge site was the most energetically favorable. Moreover, we investigated some electronic properties such as partial density of states, electron density difference, Mulliken populations, etc., revealing the microscale mechanism for AlN adsorption on Si(111) surface and providing theoretical support for adjusting the processing parameters during AlN or GaN production.

Adsorption and dissociation of oxygen molecules on Si(111)-(7×7) surface

International Nuclear Information System (INIS)

Niu, Chun-Yao; Wang, Jian-Tao

2013-01-01

The adsorption and dissociation of O 2 molecules on Si(111)-(7×7) surface have been studied by first-principles calculations. Our results show that all the O 2 molecular species adsorbed on Si(111)-(7×7) surface are unstable and dissociate into atomic species with a small energy barrier about 0.1 eV. The single O 2 molecule adsorption tends to form an ins×2 or a new metastable ins×2* structure on the Si adatom sites and the further coming O 2 molecules adsorb on those structures to produce an ad-ins×3 structure. The ad-ins×3 structure is indeed highly stable and kinetically limited for diving into the subsurface layer to form the ins×3-tri structure by a large barrier of 1.3 eV. Unlike the previous views, we find that all the ad-ins, ins×2, and ad-ins×3 structures show bright images, while the ins×2*, ins×3, and ins×3-tri structures show dark images. The proposed oxidation pathways and simulated scanning tunneling microscope images account well for the experimental results and resolve the long-standing confusion and issue about the adsorption and reaction of O 2 molecules on Si(111) surface

Surface Modification of Carbon Nanotube Networked Films with Au Nanoclusters for Enhanced NO2 Gas Sensing Applications

Directory of Open Access Journals (Sweden)

M. Penza

2008-01-01

Full Text Available Multiwalled carbon nanotube (MWCNT films have been deposited by using plasma-enhanced chemical vapor deposition (PECVD system onto alumina substrates, provided with 6 nm thick cobalt (Co growth catalyst for remarkably improved NO2 gas sensing, at working temperature in the range of 100–250∘C. Functionalization of the MWCNTs with nanoclusters of gold (Au sputtering has been performed to modify the surface of carbon nanotube networked films for enhanced and specific NO2 gas detection up to sub-ppm level. It is demonstrated that the NO2 gas sensitivity of the MWCNT-based sensors depends on Au-loading used as surface-catalyst. The gas response of MWCNT-based chemiresistor is attributed to p-type conductivity in the Au-modified semiconducting MWCNTs with a very good short-term repeatability and faster recovery. The sensor temperature of maximum NO2 sensitivity of the Au-functionalized MWCNTs is found to decrease with increasing Au-loading on their surface, and continuous gas monitoring at ppb level of NO2 is effectively performed with Au-modified MWCNT chemiresistors.

Unraveling the oxygen vacancy structures at the reduced Ce O2(111 ) surface

Science.gov (United States)

Han, Zhong-Kang; Yang, Yi-Zhou; Zhu, Beien; Ganduglia-Pirovano, M. Verónica; Gao, Yi

2018-03-01

Oxygen vacancies at ceria (Ce O2 ) surfaces play an essential role in catalytic applications. However, during the past decade, the near-surface vacancy structures at Ce O2(111 ) have been questioned due to the contradictory results from experiments and theoretical simulations. Whether surface vacancies agglomerate, and which is the most stable vacancy structure for varying vacancy concentration and temperature, are being heatedly debated. By combining density functional theory calculations and Monte Carlo simulations, we proposed a unified model to explain all conflicting experimental observations and theoretical results. We find a novel trimeric vacancy structure which is more stable than any other one previously reported, which perfectly reproduces the characteristics of the double linear surface oxygen vacancy clusters observed by STM. Monte Carlo simulations show that at low temperature and low vacancy concentrations, vacancies prefer subsurface sites with a local (2 × 2) ordering, whereas mostly linear surface vacancy clusters do form with increased temperature and degree of reduction. These results well explain the disputes about the stable vacancy structure and surface vacancy clustering at Ce O2(111 ) , and provide a foundation for the understanding of the redox and catalytic chemistry of metal oxides.

Unraveling surface enabled magnetic phenomena in low dimensional systems

Science.gov (United States)

Baljozovic, Milos; Girovsky, Jan; Nowakowski, Jan; Ali, Md Ehesan; Rossmann, Harald; Nijs, Thomas; Aeby, Elise; Nowakowska, Sylwia; Siewert, Dorota; Srivastava, Gitika; WäCkerlin, Christian; Dreiser, Jan; Decurtins, Silvio; Liu, Shi-Xia; Oppeneer, Peter M.; Jung, Thomas A.; Ballav, Nirmalya

Molecular spin systems with controllable interactions are of both fundamental and applied importance. These systems help us to better understand the fundamental origins of the interactions involved in low dimensional magnetic systems and to put them in the framework of existing models towards their further development. Following our first observation of exchange induced magnetic ordering in paramagnetic porphyrins adsorbed on ferromagnetic Co surface we showed that magnetic properties of such molecules can be controllably altered upon exposure to chemical and physical stimuli. In our most recent work it was shown that a synthetically programmed co-assembly of Fe and Mn phthalocyanines can also be realized on diamagnetic Au(111) surfaces where it induces long-range 2D ferrimagnetic order, at first glance in conflict with the Mermin-Wagner theory. Here we provide evidence for the first direct observation of such ordering from STM/STS and XMCD data and from DFT +U calculations demonstrating key role of the Au(111) surface states in mediating AFM RKKY coupling of the Kondo underscreened magnetic moments.

Surface-Plasmon-Enhanced Emissions of Phosphors with Au Nanoparticles Embedded in ITO

Energy Technology Data Exchange (ETDEWEB)

Kim, Ja-Yeon [Korea Photonics Technology Institute (KOPTI), Gwangju (Korea, Republic of); Oh, Seung Jong; Park, Hyun-Sun; Kim, Min-Woo; Cho, Yoo-Hyun; Kwon, Min-Ki [Chosun University, Gwangju (Korea, Republic of)

2017-03-15

Au nanoparticles were embedded in a transparent conducting layer of indium tin oxide in order to evaluate the feasibility of applying a surface-plasmon (SP)-enhanced phosphor to light-emitting diodes (LEDs). The efficiency of the phosphor was improved by energy matching between the phosphor and the SP of the Au nanoparticles. After the density of the Au nanoparticles and the thickness of the spacer layer had been optimized, the efficiency of a green phosphor was improved by 64% compared to that of an isolated green phosphor. This work provides a way to fabricate high-efficiency LEDs with high color-rendering indices and wide color gamuts in white LEDs.

Potential dependent adhesion forces on bare and underpotential deposition modified electrode surfaces

Energy Technology Data Exchange (ETDEWEB)

Serafin, J.M.; Hsieh, S.J.; Monahan, J.; Gewirth, A.A. [Univ. of Illinois, Urbana, IL (United States)

1998-12-03

Adhesion force measurements are used to determine the potential dependence of the force of adhesion between a Si{sub 3}N{sub 4} cantilever and a Au(111) surface modified by the underpotential deposition (upd) of Bi or Cu in acid solution or by oxide formation. The measured work of adhesion is near zero for most of the potential region examined in Bi upd but rises after the formation of a full Bi monolayer. The work of adhesion is high at positive potentials for Cu upd but then decreases as the Cu partial and full monolayers are formed. The work of adhesion is low in the oxide region on Au(111) but rises following the sulfate disordering transition at 1.1 V vs NHE. These results are interpreted in terms of the degree of solvent order on the electrode surface.

Magnetism of a Co monolayer on Pt(111) capped by overlayers of 5 d elements: A spin-model study

Science.gov (United States)

Simon, E.; Rózsa, L.; Palotás, K.; Szunyogh, L.

2018-04-01

Using first-principles calculations, we study the magnetic properties of a Co monolayer on a Pt(111) surface with a capping monolayer of selected 5 d elements (Re, Os, Ir, Pt, and Au). First we determine the tensorial exchange interactions and magnetic anisotropies characterizing the Co monolayer for all considered systems. We find a close relationship between the magnetic moment of the Co atoms and the nearest-neighbor isotropic exchange interaction, which is attributed to the electronic hybridization between the Co and the capping layers, in the spirit of the Stoner picture of ferromagnetism. The Dzyaloshinskii-Moriya interaction is decreased for all overlayers compared to the uncapped Co/Pt(111) system, while even the sign of the Dzyaloshinskii-Moriya interaction changes in the case of the Ir overlayer. We conclude that the variation of the Dzyaloshinskii-Moriya interaction is well correlated with the change of the magnetic anisotropy energy and of the orbital moment anisotropy. The unique influence of the Ir overlayer on the Dzyaloshinskii-Moriya interaction is traced by scaling the strength of the spin-orbit coupling of the Ir atoms in Ir/Co/Pt(111) and by changing the Ir concentration in the Au1 -xIrx /Co/Pt(111) system. Our spin dynamics simulations indicate that the magnetic ground state of Re/Co/Pt(111) thin film is a spin spiral with a tilted normal vector, while the other systems are ferromagnetic.

The disclosure of mesoscale behaviour of a 3d-SMM monolayer on Au(111) through a multilevel approach.

Science.gov (United States)

Fernandez Garcia, Guglielmo; Lunghi, Alessandro; Totti, Federico; Sessoli, Roberta

2018-02-22

Here we present a computational study of a full- and a half-monolayer of a Fe 4 single molecule magnet ([Fe 4 (L) 2 (dpm) 6 ], where H 3 L = 2-hydroxymethyl-2-phenylpropane-1,3-diol and Hdpm = dipivaloylmethane, Fe 4 Ph) on an unreconstructed surface of Au(111). This has been possible through the application of an integrated approach, which allows the explicit inclusion of the packing effects in the classical dynamics to be used in a second step in periodic and non-periodic high level DFT calculations. In this way we can obtain access to mesoscale geometrical data and verify how they can influence the magnetic properties of interest of the single Fe 4 molecule. The proposed approach allows to overcome the ab initio state-of-the-art approaches used to study Single Molecule Magnets (SMMs), which are based on the study of one single adsorbed molecule and cannot represent effects on the scale of a monolayer. Indeed, we show here that it is possible to go beyond the computational limitations inherent to the use, for such complex systems, of accurate calculation techniques (e.g. ab initio molecular dynamics) without losing the level of accuracy necessary to gain new detailed insights, hardly reachable at the experimental level. Indeed, long-range and edge effects on the Fe 4 structures and their easy axis of magnetization orientations have been evidenced as their different contributions to the overall macroscopic behavior.

The interaction of deuterium with AgPd/Pd(111) surface alloys

Energy Technology Data Exchange (ETDEWEB)

Diemant, Thomas; Martin, Jan; Behm, R. Juergen [Institute of Surface Chemistry and Catalysis, Ulm University (Germany)

2016-07-01

AgPd/Pd(111) surface alloys, which consist of a reactive and an inert metal, represent an ideal test case for the study of ensemble effects on bimetallic surfaces. In the present contribution, we have studied their deuterium adsorption properties by temperature-programmed desorption (TPD) measurements. The structural properties (surface contents and atom distribution) were determined already earlier by high-resolution scanning tunnelling microscopy (STM), which enables us to correlate the structural properties of these surface alloys to their adsorption behaviour. Most prominently, a steady decrease of the adsorbate coverage with increasing Ag content is observed. The results will be compared to findings on the interaction of CO with these surface alloys.

Nanopore formation on Au coated pyramid under electron beam irradiations (plasmonic nanopore on pyramid

Directory of Open Access Journals (Sweden)

Seong Soo Choi

2016-03-01

Full Text Available There have been tremendous interests about the single molecule analysis using a sold-state nanopore. The solid-state nanopore can be fabricated either by drilling technique, or diffusion technique by using electron beam irradiations. The solid-state SiN nanopore device with electrical detection technique recently fabricated, however, the solid-state Au nanopore with optical detection technique can be better utilized as the next generation single molecule sensor. In this report, the nanometer size openings with its size less than 10 nm on the diffused membrane on the 200 nm Au pyramid were fabricated by using field emission scanning electron microscopy (FESEM electron beam irradiations, transmission electron microscopy (TEM, etc. After the sample was being kept under a room environment for several months, several Au (111 clusters with ~6 nm diameter formed via Ostwald ripening are observed using a high resolution TEM imaging. The nanopore with Au nanoclusters on the diffused membrane can be utilized as an optical nanopore device. Keywords: Electron beam irradiation, Surface diffusion, Carbon contamination, Au cluster, Ostwald ripening

Self-assembled Au nanoparticles on heated Corning glass by dc magnetron sputtering: size-dependent surface plasmon resonance tuning

Energy Technology Data Exchange (ETDEWEB)

Grammatikopoulos, S.; Pappas, S. D. [University of Patras, Laboratory of High-Tech Materials, School of Engineering (Greece); Dracopoulos, V. [Hellas-Institute of Chemical Engineering and High Temperature Chemical Processes, (FORTH/ICE-HT), Foundation for Research and Technology (Greece); Poulopoulos, P., E-mail: poulop@upatras.gr [University of Patras, Laboratory of High-Tech Materials, School of Engineering (Greece); Fumagalli, P. [Freie Universitaet Berlin, Institut fuer Experimentalphysik (Germany); Velgakis, M. J.; Politis, C. [University of Patras, Laboratory of High-Tech Materials, School of Engineering (Greece)

2013-02-15

We report on the growth of Au nanoparticles on Corning glass by direct current magnetron sputtering and on the optical absorption of the films. The substrate temperature was kept to relatively high temperatures of 100 or 450 Degree-Sign C. This lead to the growth of Au nanoparticles instead of smooth Au films as the surface energy of Au is much larger than the one of glass. The size of the particles depended on the substrate temperature and deposition time and was shown to follow a logarithmic normal distribution function. Both, the surface plasmon resonance position and bandwidth, were found to depend upon the average particle size. The surface plasmon resonance position showed a 75 nm continuous blue shift from 14 nm down to 2.5 nm average particle size. Thus, we have shown how to tune the nanoparticle size and surface plasmon resonance of Au by varying the substrate temperature and deposition time. The experimental results are reproduced reasonably using a method which is based on the size- and wavelength-dependent complex dielectric function of Au within the framework of the Mie theory for the optical properties of metallic nanospheres.

Facet-controlled phase separation in supersaturated Au-Ni nanoparticles upon shape equilibration

Energy Technology Data Exchange (ETDEWEB)

Herz, A., E-mail: andreas.herz@tu-ilmenau.de, E-mail: dong.wang@tu-ilmenau.de; Rossberg, D.; Hentschel, M.; Theska, F.; Wang, D., E-mail: andreas.herz@tu-ilmenau.de, E-mail: dong.wang@tu-ilmenau.de; Schaaf, P. [Department of Materials for Electronics and Electrical Engineering, Institute of Materials Science and Engineering and Institute of Micro- and Nanotechnologies MacroNano, TU Ilmenau, D-98693 Ilmenau (Germany); Friák, M. [Institute of Physics of Materials, Academy of Sciences of the Czech Republic, v.v.i., Žižkova 22, CZ-616 62 Brno (Czech Republic); Central European Institute of Technology, CEITEC MU, Masaryk University, Kamenice 5, CZ-625 00 Brno (Czech Republic); Holec, D. [Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, A-8700 Leoben (Austria); Šob, M. [Central European Institute of Technology, CEITEC MU, Masaryk University, Kamenice 5, CZ-625 00 Brno (Czech Republic); Institute of Physics of Materials, Academy of Sciences of the Czech Republic, v.v.i., Žižkova 22, CZ-616 62 Brno (Czech Republic); Department of Chemistry, Faculty of Science, Masaryk University, Kotlářská 2, CZ-611 37 Brno (Czech Republic); Schneeweiss, O. [Institute of Physics of Materials, Academy of Sciences of the Czech Republic, v.v.i., Žižkova 22, CZ-616 62 Brno (Czech Republic)

2015-08-17

Solid-state dewetting is used to fabricate supersaturated, submicron-sized Au-Ni solid solution particles out of thin Au/Ni bilayers by means of a rapid thermal annealing technique. Phase separation in such particles is studied with respect to their equilibrium crystal (or Wulff) shape by subsequent annealing at elevated temperature. It is found that (100) faceting planes of the equilibrated particles are enriched with Ni and (111) faces with Au. Both phases are considered by quantum-mechanical calculations in combination with an error-reduction scheme that was developed to compensate for a missing exchange-correlation potential that would reliably describe both Au and Ni. The observed phase configuration is then related to the minimization of strongly anisotropic elastic energies of Au- and Ni-rich phases and results in a rather unique nanoparticle composite state that is characterized by nearly uniform value of elastic response to epitaxial strains all over the faceted surface. The same conclusion is yielded also by evaluating bi-axial elastic moduli when employing interpolated experimental elastic constants. This work demonstrates a useful route for studying features of physical metallurgy at the mesoscale.

Quantum confinement and heavy surface states of Dirac fermions in bismuth (111) films: An analytical approach

Science.gov (United States)

Enaldiev, V. V.; Volkov, V. A.

2018-03-01

Recent high-resolution angle-resolved photoemission spectroscopy experiments have given a reason to believe that pure bismuth is a topologically nontrivial semimetal. We derive an analytic theory of surface and size-quantized states of Dirac fermions in Bi(111) films taking into account the new data. The theory relies on a new phenomenological momentum-dependent boundary condition for the effective Dirac equation. The boundary condition is described by two real parameters that are expressed by a linear combination of the Dresselhaus and Rashba interface spin-orbit interaction parameters. In semi-infinite Bi(111), near the M ¯ point the surface states possess anisotropical parabolic dispersion with very heavy effective mass in the Γ ¯-M ¯ direction order of ten free electron masses and light effective mass in the M ¯-K ¯ direction order of one hundredth of free electron mass. In Bi(111) films with equivalent surfaces, the surface states from top and bottom surfaces are not split. In such a symmetric film with arbitrary thickness, the bottom of the lowest quantum confinement subband in the conduction band coincides with the bottom of the bulk conduction band in the M ¯ point.

Surface-confined fluorescence enhancement of Au nanoclusters anchoring to a two-dimensional ultrathin nanosheet toward bioimaging

Science.gov (United States)

Tian, Rui; Yan, Dongpeng; Li, Chunyang; Xu, Simin; Liang, Ruizheng; Guo, Lingyan; Wei, Min; Evans, David G.; Duan, Xue

2016-05-01

Gold nanoclusters (Au NCs) as ultrasmall fluorescent nanomaterials possess discrete electronic energy and unique physicochemical properties, but suffer from relatively low quantum yield (QY) which severely affects their application in displays and imaging. To solve this conundrum and obtain highly-efficient fluorescent emission, 2D exfoliated layered double hydroxide (ELDH) nanosheets were employed to localize Au NCs with a density as high as 5.44 × 1013 cm-2, by virtue of the surface confinement effect of ELDH. Both experimental studies and computational simulations testify that the excited electrons of Au NCs are strongly confined by MgAl-ELDH nanosheets, which results in a largely promoted QY as well as prolonged fluorescence lifetime (both ~7 times enhancement). In addition, the as-fabricated Au NC/ELDH hybrid material exhibits excellent imaging properties with good stability and biocompatibility in the intracellular environment. Therefore, this work provides a facile strategy to achieve highly luminescent Au NCs via surface-confined emission enhancement imposed by ultrathin inorganic nanosheets, which can be potentially used in bio-imaging and cell labelling.Gold nanoclusters (Au NCs) as ultrasmall fluorescent nanomaterials possess discrete electronic energy and unique physicochemical properties, but suffer from relatively low quantum yield (QY) which severely affects their application in displays and imaging. To solve this conundrum and obtain highly-efficient fluorescent emission, 2D exfoliated layered double hydroxide (ELDH) nanosheets were employed to localize Au NCs with a density as high as 5.44 × 1013 cm-2, by virtue of the surface confinement effect of ELDH. Both experimental studies and computational simulations testify that the excited electrons of Au NCs are strongly confined by MgAl-ELDH nanosheets, which results in a largely promoted QY as well as prolonged fluorescence lifetime (both ~7 times enhancement). In addition, the as-fabricated Au NC

The Role of Surface Passivation in Controlling Ge Nanowire Faceting.

Science.gov (United States)

Gamalski, A D; Tersoff, J; Kodambaka, S; Zakharov, D N; Ross, F M; Stach, E A

2015-12-09

In situ transmission electron microscopy observations of nanowire morphologies indicate that during Au-catalyzed Ge nanowire growth, Ge facets can rapidly form along the nanowire sidewalls when the source gas (here, digermane) flux is decreased or the temperature is increased. This sidewall faceting is accompanied by continuous catalyst loss as Au diffuses from the droplet to the wire surface. We suggest that high digermane flux and low temperatures promote effective surface passivation of Ge nanowires with H or other digermane fragments inhibiting diffusion and attachment of Au and Ge on the sidewalls. These results illustrate the essential roles of the precursor gas and substrate temperature in maintaining nanowire sidewall passivation, necessary to ensure the growth of straight, untapered, ⟨111⟩-oriented nanowires.

Absence of surface stress change during pentacene thin film growth on the Si(111)-(7 x 7) surface: a buried reconstruction interface

International Nuclear Information System (INIS)

Kury, P; Horn von Hoegen, M; Heringdorf, F-J Meyer zu; Roos, K R

2008-01-01

We use high-resolution surface stress measurements to monitor the surface stress during the growth of pentacene (C 22 H 14 ) on the (7x7) reconstructed silicon (111) surface. No significant change in the surface stress is observed during the pentacene growth. Compared to the changes in the surface stress observed for Si and Ge deposition on the Si(111)-(7x7) surface, the insignificant change in the surface stress observed for the pentacene growth suggests that the pentacene molecules of the first adsorbate layer, although forming strong covalent bonds with the Si adatoms, do not alter the structure of the (7x7) reconstruction. The (7x7) reconstruction remains intact and, with subsequent deposition of pentacene, eventually becomes buried under the growing film. This failure of the pentacene to affect the structure of the reconstruction may represent a fundamental difference between the growth of organic thin films and that of inorganic thin films on semiconductor surfaces

Initial stages of Pt(111) electrooxidation: dynamic and structural studies by surface X-ray diffraction

International Nuclear Information System (INIS)

Drnec, Jakub; Ruge, Martin; Reikowski, Finn; Rahn, Björn; Carlà, Francesco; Felici, Roberto; Stettner, Jochim; Magnussen, Olaf M.; Harrington, David A.

2017-01-01

In-situ surface X-ray diffraction is used to characterize the surface oxides on a Pt(111) surface in 0.1 M HClO 4 . Detailed analysis at two potentials confirms that the surface restructuring in the initial oxidation stages is consistent with a place exchange process between Pt and O atoms, and the exchanged Pt atoms are located above their original positions in the Pt(111) lattice. The (1,1,1.5) reflection is used to dynamically study the surface during cyclic voltammetry. The restructuring associated with the place exchange initiates with the CV peak at 1.05 V, even though multiple cycles to 1.17 V lead to no changes in the CV. The restructuring is reversible below a critical coverage of place exchanged Pt atoms, which we estimate to be between 0.07 and 0.15 ML. Extensive cycling to potentials higher or equal to 1.17 V leads to progressive disordering of the surface.

Reversible and irreversible changes of surface morphology by order-disorder transition in CuAu alloy

International Nuclear Information System (INIS)

Sachl, Jindrich; Sima, Vladimir; Pfeiler, Wolfgang

2004-01-01

The change of symmetry from the disordered fcc structure to tetragonal or orthorhombic structure is accompanied in CuAu alloy by anisotropy of lattice parameters and also by local generation of c-variants of structural antiphase domains. Macroscopic results of these processes can be observed as a dynamic change of the surface morphology. Some surface changes are reversible, on the other hand the internal stresses connected with the order-disorder transformation are also responsible for irreversible surface deformation effects. The domain structure formation can be influenced by external load and a shape memory effect can be observed at special conditions in CuAu. A combination of in-situ microscopic video cinematography and post-mortem 3-D atomic force microscopy (AFM) has been used for the surface study. The AFM images have enabled a detailed analysis of the surface morphology and the cinematography has given an in-situ information dealing with conditions and kinetics of observed surface changes. Measurements on CuAu single- and poly-crystalline samples have been made for a wide variety of experimental conditions (heating/cooling rates, external load, thermal history of the sample)

Reversible and irreversible changes of surface morphology by order-disorder transition in CuAu alloy

Energy Technology Data Exchange (ETDEWEB)

Sachl, Jindrich; Sima, Vladimir; Pfeiler, Wolfgang

2004-09-22

The change of symmetry from the disordered fcc structure to tetragonal or orthorhombic structure is accompanied in CuAu alloy by anisotropy of lattice parameters and also by local generation of c-variants of structural antiphase domains. Macroscopic results of these processes can be observed as a dynamic change of the surface morphology. Some surface changes are reversible, on the other hand the internal stresses connected with the order-disorder transformation are also responsible for irreversible surface deformation effects. The domain structure formation can be influenced by external load and a shape memory effect can be observed at special conditions in CuAu. A combination of in-situ microscopic video cinematography and post-mortem 3-D atomic force microscopy (AFM) has been used for the surface study. The AFM images have enabled a detailed analysis of the surface morphology and the cinematography has given an in-situ information dealing with conditions and kinetics of observed surface changes. Measurements on CuAu single- and poly-crystalline samples have been made for a wide variety of experimental conditions (heating/cooling rates, external load, thermal history of the sample)

Magnetic Fe{sub 3}O{sub 4}-Au core-shell nanostructures for surface enhanced Raman scattering

Energy Technology Data Exchange (ETDEWEB)

Wheeler, D.A.; Adams, S.A.; Zhang, J.Z. [Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, CA 95064 (United States); Lopez-Luke, T. [Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, CA 95064 (United States); Cento de Investigaciones en Optica, A.P. 1-948 Leon, Gto. 37150 (Mexico); Torres-Castro, A. [Universidad Autonoma de Nuevo Leon, A.P. 126-F, Monterrey, NL, 66450 (Mexico)

2012-11-15

The synthesis, structural and optical characterization, and application of superparamagnetic and water-dispersed Fe{sub 3}O{sub 4}-Au core-shell nanoparticles for surface enhanced Raman scattering (SERS) is reported. The structure of the nanoparticles was determined by scanning transmission electron microscopy (STEM) and high-resolution transmission electron microscopy (HRTEM). STEM images of the Fe{sub 3}O{sub 4}-Au core-shell nanoparticles reveal an average diameter of 120 nm and a high degree of surface roughness. The nanoparticles, which display superparamagnetic properties due to the core Fe{sub 3}O{sub 4} material, exhibit a visible surface plasmon resonance (SPR) peaked at 580 nm due to the outer gold shell. The nanoparticles are used as a substrate for surface enhanced Raman scattering (SERS) with rhodamine 6G (R6G) as a Raman reporter molecule. The SERS enhancement factor is estimated to be on the order of 10{sup 6}, which is {proportional_to} 2 times larger than that of conventional gold nanoparticles (AuNPs) under similar conditions. Significantly, magnetically-induced aggregation of the Fe{sub 3}O{sub 4}-Au core-shell nanoparticles substantially enhanced SERS activity compared to non-magnetically-aggregated Fe{sub 3}O{sub 4}-Au nanoparticles. This is attributed to both increased scattering from the aggregates as well as ''hot spots'' due to more junction sites in the magnetically-induced aggregates. The magnetic properties of the Fe{sub 3}O{sub 4} core, coupled with the optical properties of the Au shell, make the Fe{sub 3}O{sub 4}-Au nanoparticles unique for various potential applications including biological sensing and therapy. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

He atom-surface scattering: Surface dynamics of insulators, overlayers and crystal growth

International Nuclear Information System (INIS)

Safron, S.A.; Skofronick, J.G.

1994-01-01

This progress report describes work carried out in the study of surface structure and dynamics of ionic insulators, the microscopic interactions controlling epitaxial growth and the formation of overlayers, and energy exchange in multiphonon surface scattering. The approach used is to employ high resolution helium atom scattering to study the geometry and structural features of the surfaces. Experiments have been carried out on the surface dynamics of RbCl and preliminary studies done on CoO and NiO. Epitaxial growth and overlayer dynamics experiments on the systems NaCl/NaCl(001), KBr/NaCl(001), NaCl/KBr(001) and KBr/RbCl(001) have been performed. They have collaborated with two theoretical groups to explore models of overlayer dynamics with which to compare and to interpret their experimental results. They have carried out extensive experiments on the multiphonon scattering of helium atoms from NaCl and, particularly, LiF. Work has begun on self-assembling organic films on gold and silver surfaces (alkyl thiols/Au(111) and Ag(111))

Ion scattering studies of ordered alloy surfaces: CuAu(1 0 0) and NiAl

International Nuclear Information System (INIS)

Beikler, R.; Taglauer, E.

2000-01-01

The composition and structure of alloy surfaces can differ from the corresponding bulk properties due to segregation and relaxation effects. We studied the (1 0 0) surface of the ordered alloy CuAu and amorphous Ni and Al by low-energy Ne + and Na + ion scattering. The interpretation of the experimental results is supported by numerical simulations using the MARLOWE code. In the CuAu system a certain geometry was found to be very sensitive to Au presence in the 2nd layer. Comparison with MARLOWE results also allows to study variations in the ion yields arising from neutralization effects. By trajectory analysis ion survival probabilities are estimated for Ni and Al

Superstructure of self-aligned hexagonal GaN nanorods formed on nitrided Si(111) surface

Energy Technology Data Exchange (ETDEWEB)

Kumar, Praveen; Tuteja, Mohit; Kesaria, Manoj; Waghmare, U. V.; Shivaprasad, S. M. [Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560 064 (India)

2012-09-24

We present here the spontaneous formation of catalyst-free, self-aligned crystalline (wurtzite) nanorods on Si(111) surfaces modified by surface nitridation. Nanorods grown by molecular beam epitaxy on bare Si(111) and non-stoichiometric silicon nitride interface are found to be single crystalline but disoriented. Those grown on single crystalline Si{sub 3}N{sub 4} intermediate layer are highly dense c-oriented hexagonal shaped nanorods. The morphology and the self-assembly of the nanorods shows an ordered epitaxial hexagonal superstructure, suggesting that they are nucleated at screw dislocations at the interface and grow spirally in the c-direction. The aligned nanorod assembly shows high-quality structural and optical emission properties.

Dynamics of very low energy photoelectrons interacting with image charge of Cs/Cu(111) surface

International Nuclear Information System (INIS)

Hayashi, K.; Arafune, R.; Ueda, S.; Uehara, Y.; Ushioda, S.

2005-01-01

We have measured the very low energy photoelectron spectra of Cs-covered Cu(111) surfaces, and determined the mechanism for the appearance of a spike structure due to the interaction of emitted electron with its image charge. At high Cs coverage of 0.10 and 0.14 monolayers (ML), the spike structure appeared at the vacuum level. No such structure was found at low coverage of 0.06 ML. The vacuum level at high coverage lies in the energy gap at the Γ point in the surface Brillouin zone of the Cu(111) surface, while it lies outside the energy gap at low coverage. These results confirm the validity of our proposed mechanism that the spike structure appears when the vacuum level lies in the energy gap

Chemial Bond and Stability of Adsorption of[Au(AsS3)]2- on the Surface of Kaolinite

Institute of Scientific and Technical Information of China (English)

MIN Xin-min; CHEN Yun; HONG Han-lie

2004-01-01

Density function theory and discrete variation method (DFT-DVM) were used to study the adsorption of [Au(AsS3 ) ]2- on the surface of kaolinite. The correlation among structure, chemical bond and stability was discussed. Several models were selected with [ Au( AsS3 ) ]2- in different directions and sites. The resultsshow that the models with gold on the edge of kaolinite basal layer contain pincerlike bond among gold and severaloxygen atoms and form strong Au - O covalent bond, so these models are more stable than those with gold aboveor under the layer. The models with gold near to [ AlO2(OH)4 ] octahedra are more stable than those with goldnear to the vacancy without aluminium. These two stable tendencies in kaolinite- [ Au( AsS3 ) ]2- are stronger thanthat in kaolinite-Au systems. The interaction between [ Au( AsS3 ) ]2- and kaolinite is stronger than that betweengold and kaolinite, and this interaction is strong enough to form the surface complexes.

Symposium Supramolecular Assemblies on Surface: Nanopatterning, Functionality and Reactivity

Science.gov (United States)

2016-05-19

formed and we relate these observations to recent reports of de- wetting of C60 on alkali halide surfaces. The hBN flakes, which are prepared by... annealing will be discussed while for dicarbonitrile polyphenyl derivatives the adsorption behavior on Au(111) will be compared to the one on graphene

Investigation of reordered (001) Au surfaces by positive ion channeling spectroscopy, LEED and AES

International Nuclear Information System (INIS)

Appleton, B.R.; Noggle, T.S.; Miller, J.W.; Schow, O.E. III; Zehner, D.M.; Jenkins, L.H.; Barrett, J.H.

1974-01-01

As a consequence of the channeling phenomenon of positive ions in single crystals, the yield of ions Rutherford scattered from an oriented single crystal surface is dependent on the density of surface atoms exposed to the incident ion beam. Thus, the positive ion channeling spectroscopy (PICS) technique should provide a useful tool for studying reordered surfaces. This possibility was explored by examining the surfaces of epitaxially grown thin Au single crystals with the combined techniques of LEED-AES and PICS. The LEED and AES investigations showed that when the (001) surface was sputter cleaned in ultra-high vacuum, the normal (1 x 1) symmetry of the (001) surfaces reordered into a structure which gave a complex (5 x 20) LEED pattern. The yield and energy distributions of 1 MeV He ions scattered from the Au surfaces were used to determine the number of effective monolayers contributing to the normal and reordered surfaces. These combined measurements were used to characterize the nature of the reordered surface. The general applicability of the PICS technique for investigations of surface and near surface regions is discussed

Investigation of series resistance and surface states in Au/n - GaP structures

International Nuclear Information System (INIS)

Kiymaz, A.; Onal, B.; Ozer, M.; Acar, S.

2009-01-01

The variation in series resistance and surface state density of Au/n - GaP Schottky diodes have been systematically investigated at room temperature by using capacitance-voltage C-V and conductance-voltage G/w-V measurements techniques. The C-V and G/w-V characteristics of these devices were investigated by considering series resistance effects in a wide frequency range. It is shown that the capacitance of the Au/n - GaP Schottky diode decreases with increasing frequency. It is assumed that the surface states were responsible for this behaviour. The distribution profile of Rs-V gives a peak in the depletion region at low frequencies and disappears with increasing frequencies

Improved surface quality of anisotropically etched silicon {111} planes for mm-scale optics

International Nuclear Information System (INIS)

Cotter, J P; Hinds, E A; Zeimpekis, I; Kraft, M

2013-01-01

We have studied the surface quality of millimetre-scale optical mirrors produced by etching CZ and FZ silicon wafers in potassium hydroxide to expose the {111} planes. We find that the FZ surfaces have four times lower noise power at spatial frequencies up to 500 mm −1 . We conclude that mirrors made using FZ wafers have higher optical quality. (technical note)

Direct patterning of negative nanostructures on self-assembled monolayers of 16-mercaptohexadecanoic acid on Au(111) substrate via dip-pen nanolithography

International Nuclear Information System (INIS)

Zheng Zhikun; Yang Menglong; Liu Yaqing; Zhang Bailin

2006-01-01

Both bare and self-assembled monolayer (SAM) protected gold substrate could be etched by allyl bromide according to atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometric (ICPMS) analysis results. With this allyl bromide ink material, negative nanopatterns could be fabricated directly by dip-pen nanolithography (DPN) on SAMs of 16-mercaptohexadecanoic acid (MHA) on Au(111) substrate. A tip-promoted etching mechanism was proposed where the gold-reactive ink could penetrate the MHA resist film through tip-induced defects resulting in local corrosive removal of the gold substrate. The fabrication mechanism was also confirmed by electrochemical characterization, energy dispersive spectroscopy (EDS) analysis and fabrication of positive nanopatterns via a used DPN tip

Direct patterning of negative nanostructures on self-assembled monolayers of 16-mercaptohexadecanoic acid on Au(111) substrate via dip-pen nanolithography

Science.gov (United States)

Zheng, Zhikun; Yang, Menglong; Liu, Yaqing; Zhang, Bailin

2006-11-01

Both bare and self-assembled monolayer (SAM) protected gold substrate could be etched by allyl bromide according to atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometric (ICPMS) analysis results. With this allyl bromide ink material, negative nanopatterns could be fabricated directly by dip-pen nanolithography (DPN) on SAMs of 16-mercaptohexadecanoic acid (MHA) on Au(111) substrate. A tip-promoted etching mechanism was proposed where the gold-reactive ink could penetrate the MHA resist film through tip-induced defects resulting in local corrosive removal of the gold substrate. The fabrication mechanism was also confirmed by electrochemical characterization, energy dispersive spectroscopy (EDS) analysis and fabrication of positive nanopatterns via a used DPN tip.

Growth dynamics of L-cysteine SAMs on single-crystal gold surfaces: a metastable deexcitation spectroscopy study

Science.gov (United States)

Canepa, M.; Lavagnino, L.; Pasquali, L.; Moroni, R.; Bisio, F.; DeRenzi, V.; Terreni, S.; Mattera, L.

2009-07-01

We report on a metastable deexcitation spectroscopy investigation of the growth of L-cysteine layers deposited under UHV conditions on well-defined Au(110)- (1 × 2) and Au(111) surfaces. The interaction of He* with molecular orbitals gave rise to well-defined UPS-like Penning spectra which provided information on the SAM assembly dynamics and adsorption configurations. Penning spectra have been interpreted through comparison with molecular orbital DFT calculations of the free molecule and have been compared with XPS results of previous works. Regarding adsorption of first-layer molecules at room temperature (RT), two different growth regimes were observed. On Au(110), the absence of spectral features related to orbitals associated with SH groups indicated the formation of a compact SAM of thiolate molecules. On Au(111), the data demonstrated the simultaneous presence, since the early stages of growth, of strongly and weakly bound molecules, the latter showing intact SH groups. The different growth mode was tentatively assigned to the added rows of the reconstructed Au(110) surface which behave as extended defects effectively promoting the formation of the S-Au bond. The growth of the second molecular layer was instead observed to proceed similarly for both substrates. Second-layer molecules preferably adopt an adsorption configuration in which the SH group protrudes into the vacuum side.

Growth dynamics of L-cysteine SAMs on single-crystal gold surfaces: a metastable deexcitation spectroscopy study

International Nuclear Information System (INIS)

Canepa, M; Lavagnino, L; Moroni, R; Bisio, F; Terreni, S; Mattera, L; Pasquali, L; De Renzi, V

2009-01-01

We report on a metastable deexcitation spectroscopy investigation of the growth of L-cysteine layers deposited under UHV conditions on well-defined Au(110)- (1 x 2) and Au(111) surfaces. The interaction of He* with molecular orbitals gave rise to well-defined UPS-like Penning spectra which provided information on the SAM assembly dynamics and adsorption configurations. Penning spectra have been interpreted through comparison with molecular orbital DFT calculations of the free molecule and have been compared with XPS results of previous works. Regarding adsorption of first-layer molecules at room temperature (RT), two different growth regimes were observed. On Au(110), the absence of spectral features related to orbitals associated with SH groups indicated the formation of a compact SAM of thiolate molecules. On Au(111), the data demonstrated the simultaneous presence, since the early stages of growth, of strongly and weakly bound molecules, the latter showing intact SH groups. The different growth mode was tentatively assigned to the added rows of the reconstructed Au(110) surface which behave as extended defects effectively promoting the formation of the S-Au bond. The growth of the second molecular layer was instead observed to proceed similarly for both substrates. Second-layer molecules preferably adopt an adsorption configuration in which the SH group protrudes into the vacuum side.

Thin film growth behaviors on strained fcc(111) surface by kinetic Monte Carlo

International Nuclear Information System (INIS)

Doi, Y; Matsunaka, D; Shibutani, Y

2009-01-01

We study Ag islands grown on strained Ag(111) surfaces using kinetic Monte Carlo (KMC) simulations. We employed KMC parameters of activation energy and attempt frequency estimated by nudged elastic band (NEB) method and vibration analyses. We investigate influences of surface strain and substrate temperature on film growth. As the biaxial surface strain increases, the island density increases. As temperature increases, the shape of the island changes from dendric to hexagonal and the island density increases.

In situ study of nitrobenzene grafting on Si(111)-H surfaces by infrared spectroscopic ellipsometry

Energy Technology Data Exchange (ETDEWEB)

Rappich, J. [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Institut fuer Silizium-Photovoltaik, Kekulestr. 5, 12489 Berlin (Germany); Hinrichs, K. [ISAS - Institute for Analytical Sciences, Department Berlin, Albert-Einstein-Str. 9, 12489 Berlin (Germany)

2009-12-15

The binding of nitrobenzene (NB) molecules from a solution of 4-nitrobenzene-diazonium-tetrafluoroborate on a Si(111)-H surface was investigated during the electrochemical processing in diluted sulphuric acid by means of infrared spectroscopic ellipsometry (IR-SE). The grafting was monitored by an increase in specific IR absorption bands due to symmetric and anti-symmetric NO{sub 2} stretching vibrations in the 1400-1700 cm{sup -1} regime. The p- and s-polarized reflectances were recorded within 20 s for each spectrum only. NB molecules were detected when bonded to the Si(111) surface but not in the 2 mM solution itself. Oxide formation on the NB grafted Si surface was observed after drying in inert atmosphere and not during the grafting process in the aqueous solution. (author)

Surface noble metal modified PdM/C (M = Ru, Pt, Au) as anode catalysts for direct ethanol fuel cells

International Nuclear Information System (INIS)

Mao, Han; Huang, Tao; Yu, Aishui

2016-01-01

In this article, we studied the surface noble metal modification on Pd nanoparticles, other than the homogeneous or core-shell structure. The surface modification will lead to the uneven constitution within the nanoparticles and thus more obvious optimization effect toward the catalyst brought by the lattice deformation. The surface of the as-prepared Pd nanoparticles was modified with Ru, Pt or Au by a moderate and green approach, respectively. XPS results confirm the interactive electron effects between Pd and the modified noble metal. Electrochemical measurements show that the surface noble metal modified catalysts not only show higher catalytic activity, but also better stability and durability. The PdM/C catalysts all exhibit good dispersion and very little agglomeration after long-term potential cycles toward ethanol oxidation. With only 10% metallic atomic ratio of Au, PdAu/C catalyst shows extraordinary catalytic activity and stability, the peak current reaches 1700 mA mg"−"1 Pd, about 2.5 times that of Pd/C. Moreover, the PdAu/C maintains 40% of the catalytic activity after 4500 potential cycles. - Highlights: • Pd-based catalysts with complicated exposed facets. • Much enhanced electrocatalytic activity and stability with about 10% noble metal M (M = Ru, Pt, Au) on Pd nanoparticles. • The outstanding electrocatalytic performance of PdAu/C towards ethanol oxidation after the Au modification.

Surface noble metal modified PdM/C (M = Ru, Pt, Au) as anode catalysts for direct ethanol fuel cells

Energy Technology Data Exchange (ETDEWEB)

Mao, Han; Huang, Tao, E-mail: huangt@fudan.edu.cn; Yu, Aishui, E-mail: asyu@fudan.edu.cn

2016-08-15

In this article, we studied the surface noble metal modification on Pd nanoparticles, other than the homogeneous or core-shell structure. The surface modification will lead to the uneven constitution within the nanoparticles and thus more obvious optimization effect toward the catalyst brought by the lattice deformation. The surface of the as-prepared Pd nanoparticles was modified with Ru, Pt or Au by a moderate and green approach, respectively. XPS results confirm the interactive electron effects between Pd and the modified noble metal. Electrochemical measurements show that the surface noble metal modified catalysts not only show higher catalytic activity, but also better stability and durability. The PdM/C catalysts all exhibit good dispersion and very little agglomeration after long-term potential cycles toward ethanol oxidation. With only 10% metallic atomic ratio of Au, PdAu/C catalyst shows extraordinary catalytic activity and stability, the peak current reaches 1700 mA mg{sup −1} Pd, about 2.5 times that of Pd/C. Moreover, the PdAu/C maintains 40% of the catalytic activity after 4500 potential cycles. - Highlights: • Pd-based catalysts with complicated exposed facets. • Much enhanced electrocatalytic activity and stability with about 10% noble metal M (M = Ru, Pt, Au) on Pd nanoparticles. • The outstanding electrocatalytic performance of PdAu/C towards ethanol oxidation after the Au modification.

In Situ Detection of Trace Furfural in Aqueous Solution Based on Au Nanoparticle/Au Film Surface-Enhanced Raman Spectroscopy

Directory of Open Access Journals (Sweden)

Wei Qi

2016-01-01

Full Text Available Furfural is an important chemical solvent and intermediate. Sensitive detection of this compound has attracted great interest in various fields. Surface-enhanced Raman spectroscopy (SERS is a highly sensitive method for material detection because of its optical enhancement effect of plasmonic nanostructures. This study presents a simple and versatile method to synthesize a SERS substrate, where polyaminothiophenol (PATP was used to realize the stable combination of Au nanoparticles (AuNPs and Au film via self-assembly. The near-field electric field distribution was calculated using the finite difference time domain (FDTD simulation to determine the parameters responsible for electric field enhancement. The simulation results show that SERS enhanced factors are sensitive to interparticle spacing and materials for solid support but insensitive to particle size. Moreover, the experimental results show that the optimized substrates with the highest Raman activity were formed by six layers of 60 nm AuNPs decorated on a 30 nm thick Au film, thereby validating the simulation results. The SERS factor of the optimal substrates is approximately 5.57 × 103, and the in situ detection limit is 4.8 ppm. The 3D Raman spectra, relative standard deviation values for major peaks, and changes in signal intensity with time show the good reproducibility and stability of the substrates.

Defect-induced wetting on BaF 2(111) and CaF 2(111) at ambient conditions

Science.gov (United States)

Cardellach, M.; Verdaguer, A.; Fraxedas, J.

2011-12-01

The interaction of water with freshly cleaved (111) surfaces of isostructural BaF2 and CaF2 single crystals at ambient conditions (room temperature and under controlled humidity) has been studied using scanning force microscopy in different operation modes and optical microscopy. Such surfaces exhibit contrasting behaviors for both materials: while on BaF2(111) two-dimensional water layers are formed after accumulation at step edges, CaF2(111) does not promote the formation of such layers. We attribute such opposed behavior to lattice match (mismatch) between hexagonal water ice and the hexagonal (111) surfaces of BaF2(CaF2). Optical microscope images reveal that this behavior also determines the way the surfaces become wetted at a macroscopic level.

Direct inelastic scattering of oriented NO from Ag(111) and Pt(111)

International Nuclear Information System (INIS)

Tenner, M.G.; Kuipers, E.W.; Kleyn, A.W.; Stolte, S.

1991-01-01

A pulsed supersonic and cold oriented beam of NO molecules is incident upon the (111) face of clean Ag and Pt single crystal surfaces. The steric effect in the scattered density distributions is determined by a quadrupole mass spectrometer. It is found that the steric effect in the peak in the distribution of direct inelastically scattered molecules depends linearly on the reflection angle. In all circumstances O-end collisions lead to scattering angles more inclined towards the surface than N-end collisions. For the Pt(111) surface a much stronger steric effect is measured than for the Ag(111) surface. The steric effect seems to scale with the incident normal velocity. These strong steric effects can be explained by the larger trapping probability for the N-end orientation and a leverage effect due to the high trapping probability

Phase diagrams of two dimensional Pd{sub x}Ag{sub 1-x}/Pd(111) and Pt{sub x}Ag{sub 1-x}/Pt(111) surface alloys

Energy Technology Data Exchange (ETDEWEB)

Engstfeld, Albert K.; Roetter, Ralf T.; Bergbreiter, Andreas; Hoster, Harry E.; Behm, R. Juergen [Institute of Surface Chemistry and Catalysis, Ulm University (Germany)

2011-07-01

The distribution of Ag and Pd or Pt in Ag{sub x}Pd{sub 1-x}/Pd(111) and Ag{sub x}Pt{sub 1-x}/Pt(111) surface alloys was studied by high resolution UHV-STM. The alloys were prepared by evaporating Ag on the respective substrate and subsequent annealing to 800 K. From quantitative 2D atom distributions we can show that AgPt tends towards two dimensional clustering and AgPd towards a 'quasi' random distribution, with small deviations for low and high coverages. From effective pair interactions, we are able to calculate the surface mixing energy and determine 2D phase diagrams. Furthermore we will elucidate whether the size mismatch or the differences in the intermetallic bonding are the dominant factor for the respective distribution in the surface alloy.

Three-dimensional nanoporous MoS2 framework decorated with Au nanoparticles for surface-enhanced Raman scattering

Science.gov (United States)

Sheng, Yingqiang; Jiang, Shouzhen; Yang, Cheng; Liu, Mei; Liu, Aihua; Zhang, Chao; Li, Zhen; Huo, Yanyan; Wang, Minghong; Man, Baoyuan

2017-08-01

The three-dimensional (3D) MoS2 decorated with Au nanoparticles (Au NPs) hybrids (3D MoS2-Au NPs) for surface-enhanced Raman scattering (SERS) sensing was demonstrated in this paper. SEM, Raman spectroscopy, TEM, SAED, EDX and XRD were performed to characterize 3D MoS2-Au NPs hybrids. Rhodamine 6G (R6G), fluorescein and gallic acid molecules were used as the probe for the SERS detection of the 3D MoS2-Au NPs hybrids. In addition, we modeled the enhancement of the electric field of MoS2-Au NPs hybrids using Finite-difference time-domain (FDTD) analysis, which can further give assistance to the mechanism understanding of the SERS activity.

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

Energy Technology Data Exchange (ETDEWEB)

Teys, S.A., E-mail: teys@isp.nsc.ru

2017-01-15

Highlights: • Different atomic mechanisms of transition from two-dimensional to three-dimensional-layer growth on Sransky-Krastanov observed. • The transition from 2D–3D Ge growth on Si (111) and (001) is very different. • Various changes in morphology, surface structures and sequence Ge redistribution during the growth shown. • The sequence of appearance of different incorporation places of Ge atoms was shown. - Abstract: 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.

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

International Nuclear Information System (INIS)

Teys, S.A.

2017-01-01

Highlights: • Different atomic mechanisms of transition from two-dimensional to three-dimensional-layer growth on Sransky-Krastanov observed. • The transition from 2D–3D Ge growth on Si (111) and (001) is very different. • Various changes in morphology, surface structures and sequence Ge redistribution during the growth shown. • The sequence of appearance of different incorporation places of Ge atoms was shown. - Abstract: 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.

Surface adhesion and confinement variation of Staphylococcus aurius on SAM surfaces

Science.gov (United States)

Amroski, Alicia; Olsen, Morgan; Calabrese, Joseph; Senevirathne, Reshani; Senevirathne, Indrajith

2012-02-01

Controlled surface adhesion of non - pathogenic gram positive strain, Staphylococcus aureus is interesting as a model system due to possible development of respective biosensors for prevention and detection of the pathogenic strain methicillin resistant Staphylococcus aureus (MRSA) and further as a study for bio-machine interfacing. Self Assembled Monolayers (SAM) with engineered surfaces of linear thiols on Au(111) were used as the substrate. Sub cultured S. aureus were used for the analysis. The SAM layered surfaces were dipped in 2 -- 4 Log/ml S. aureus solution. Subsequent surface adhesion at different bacterial dilutions on surfaces will be discussed, and correlated with quantitative and qualitative adhesion properties of bacteria on the engineered SAM surfaces. The bacteria adhered SAM surfaces were investigated using intermittent contact, noncontact, lateral force and contact modes of Atomic Force Microscopy (AFM).

Ab initio study of atomic disorder on as-rich GaAs(111)A surface

Czech Academy of Sciences Publication Activity Database

Romanyuk, Olexandr; Mutombo, Pingo; Grosse, F.

2015-01-01

Roč. 641, Nov (2015), s. 330-335 ISSN 0039-6028 R&D Projects: GA ČR GPP204/10/P028 Grant - others:AVČR(CZ) M100101201 Institutional support: RVO:68378271 Keywords : GaAs(111) * surface reconstructions * surface kinetics * density functional theory Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.931, year: 2015

Structure and energetics of bimetallic surface confined alloys

Energy Technology Data Exchange (ETDEWEB)

Bergbreiter, Andreas; Roetter, Ralf T.; Engstfeld, Albert K.; Hoster, Harry E.; Behm, R. Juergen [Institute of Surface Chemistry and Catalysis, Ulm University (Germany); Gross, Axel [Institute for Theoretical Chemistry, Ulm University (Germany)

2009-07-01

The atomic distribution in a number of A{sub x}B{sub 1-x}/B type surface alloys was determined by STM imaging with chemical contrast and statistically evaluated. Whereas in the systems Au{sub x}Pt{sub 1-x}/Pt(111), Ag{sub x}Pt{sub 1-x}/Pt(111), and Pd{sub x}Ru{sub 1-x}/Ru(0001) we find preferences for larger homoatomic aggregates, the atom distribution in Pt{sub x}Ru{sub 1-x}/Ru(0001) and Ag{sub x}Pd{sub 1-x}/Pd(111) is very close to a random one[1]. In Ag{sub x}Pd{sub 1-x}/Pd(111), our data show a small tendency towards clustering for x{sub Ag}<0.5, whereas at x{sub Ag}>0.5 this is reversed to a slight preference for heteroatomic neighborhoods. Based on these experimental results, we have derived effective cluster interaction energies for all surface alloys. These allow us to calculate phase diagrams for the surface alloys that we compare to predictions from theoretical work and to the behaviour of the corresponding bulk systems. We also discuss in how far the different atom distributions affect chemical and catalytic properties of the surface alloys.

Initial stages of benzotriazole adsorption on the Cu(111) surface

Science.gov (United States)

Grillo, Federico; Tee, Daniel W.; Francis, Stephen M.; Früchtl, Herbert; Richardson, Neville V.

2013-05-01

Benzotriazole (BTAH) has been used as a copper corrosion inhibitor since the 1950s; however, the molecular level detail of how inhibition occurs remains a matter of debate. The onset of BTAH adsorption on a Cu(111) single crystal was investigated via scanning tunnelling microscopy (STM), vibrational spectroscopy (RAIRS) and supporting DFT modelling. BTAH adsorbs as anionic (BTA-), CuBTA is a minority species, while Cu(BTA)2, the majority of the adsorbed species, form chains, whose sections appear to diffuse in a concerted manner. The copper surface appears to reconstruct in a (2 × 1) fashion.Benzotriazole (BTAH) has been used as a copper corrosion inhibitor since the 1950s; however, the molecular level detail of how inhibition occurs remains a matter of debate. The onset of BTAH adsorption on a Cu(111) single crystal was investigated via scanning tunnelling microscopy (STM), vibrational spectroscopy (RAIRS) and supporting DFT modelling. BTAH adsorbs as anionic (BTA-), CuBTA is a minority species, while Cu(BTA)2, the majority of the adsorbed species, form chains, whose sections appear to diffuse in a concerted manner. The copper surface appears to reconstruct in a (2 × 1) fashion. Electronic supplementary information (ESI) available: Calculated IR spectra, RAIRS assignments, modeling details, statistics on diffusion, experimental details, additional STM images, movie low coverage diffusing species. See DOI: 10.1039/c3nr00724c

Self-diffusion dynamics processes relevant to 2D homoepitaxy growth of Ni adatom on Ni(111) surface

Energy Technology Data Exchange (ETDEWEB)

Liu, Fusheng [College of Metallurgical Engineering, Hunan University of Technology, Zhuzhou 412007 (China); Chen, Yifeng, E-mail: yefengc63@sina.com [College of Metallurgical Engineering, Hunan University of Technology, Zhuzhou 412007 (China); Wang, Yufei, E-mail: yejin802@126.com [College of Metallurgical Engineering, Hunan University of Technology, Zhuzhou 412007 (China); Liu, Zhulin; Hu, Zhongliang [College of Metallurgical Engineering, Hunan University of Technology, Zhuzhou 412007 (China); Yang, Xiyuan [Department of Physics, Hunan University of Arts and Science, Changde 415000 (China); Luo, Wenhua [Department of Physics and Electronic Information Science, Hunan Institute of Science and Technology, Yueyang 414006 (China)

2014-07-01

Using molecular dynamics and modified analytic embedded atom methods, the atomic self-diffusion dynamics behaviors relevant to 2D crystal growth on Ni(111) surface have been studied between 150 and 600 K. On perfect Ni(111) surface, the activation energy and prefactor are 0.058±0.001 eV and 4.2×10{sup −4} cm{sup 2}/s between 150 and 350 K, and 0.082±0.003 eV and 7.8×10{sup −4} cm{sup 2}/s from 400 to 600 K. Ni adatom just hops along the directions of close-packed steps on stepped Ni(111) surface, the corresponding activation energies and prefactors are 0.188±0.002 eV and (3.8–4.4)×10{sup −3} cm{sup 2}/s along the direction of A-type step, 0.140±0.001 eV and (1.1–1.2)×10{sup −3} cm{sup 2}/s along the direction of B-type step, and both fitting lines of Arrhenius law intersect at T{sub c}=420–440 K. Our results show that the atomic growth dynamics under nonequilibrium conditions is gradually dominated by the prefactor with increasing temperature. In addition, the shape-change of the 2D nanometer-size island has been discussed on stepped Ni(111) surface in different temperature range.

High-Resolution Scanning Tunneling Microscopy Studies of Molecular Nanostructures on Surfaces

DEFF Research Database (Denmark)

Song, Xin

. First, to study the role of hydrogen bonding in self-assembly, we investigate the monomolecular self-assembled system of pyrene-4,5,9,10-tetrone and phenanthrene- 9,10-dione molecules on Au(111) and HOPG surface respectively and the binary molecular self-assembled system of stearic acid and guanine...

Adsorption and diffusion of fluorine on Cr-doped Ni(111) surface: Fluorine-induced initial corrosion of non-passivated Ni-based alloy

Energy Technology Data Exchange (ETDEWEB)

Ren, Cui-Lan, E-mail: rencuilan@sinap.ac.cn [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Key Laboratory of Interfacial Physics and Technology, Chinese Academy of Sciences, Shanghai 201800 (China); Han, Han [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Gong, Wen-Bin [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Shanghai 215123 (China); Wang, Cheng-Bin; Zhang, Wei [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Key Laboratory of Interfacial Physics and Technology, Chinese Academy of Sciences, Shanghai 201800 (China); Cheng, Cheng [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Huai, Ping, E-mail: huaiping@sinap.ac.cn [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Zhu, Zhi-Yuan [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Key Laboratory of Interfacial Physics and Technology, Chinese Academy of Sciences, Shanghai 201800 (China)

2016-09-15

Adsorption and diffusion behaviors of fluorine on Cr-doped Ni(111) surface are investigated by using first-principles simulation. It shows that the Cr in the Cr-doped Ni(111) surface serve a trap site for fluorine with adsorption energy 3.52 eV, which is 1.04 eV higher than that on Ni(111) surface. Moreover, the Cr atom is pulled out the surface for 0.41 Å after the fluorine adsorption, much higher than that on Ni(111) surface. Further diffusion behaviors analysis confirms the conclusion because the fluorine diffusion from neighbored sites onto the Cr top site is an energy barrierless process. Detailed electronic structure analysis shows that a deeper hybrid state of F 2 p-Cr 3 d indicates a strong F−Cr interaction. The Ni−Cr bond is elongated and weakened due to the new formed F−Cr bonding. Our results help to understanding the basic fluorine-induced initial corrosion mechanism for Ni-based alloy in molten salt environment.

TiO2 Films Modified with Au Nanoclusters as Self-Cleaning Surfaces under Visible Light

Directory of Open Access Journals (Sweden)

Ting-Wei Liao

2018-01-01

Full Text Available In this study, we applied cluster beam deposition (CBD as a new approach for fabricating efficient plasmon-based photocatalytic materials. Au nanoclusters (AuNCs produced in the gas phase were deposited on TiO2 P25-coated silicon wafers with coverage ranging from 2 to 8 atomic monolayer (ML equivalents. Scanning Electron Microscopy (SEM images of the AuNCs modified TiO2 P25 films show that the surface is uniformly covered by the AuNCs that remain isolated at low coverage (2 ML, 4 ML and aggregate at higher coverage (8 ML. A clear relationship between AuNCs coverage and photocatalytic activity towards stearic acid photo-oxidation was measured, both under ultraviolet and green light illumination. TiO2 P25 covered with 4 ML AuNCs showed the best stearic acid photo-oxidation performance under green light illumination (Formal Quantum Efficiency 1.6 × 10−6 over a period of 93 h. These results demonstrate the large potential of gas-phase AuNCs beam deposition technology for the fabrication of visible light active plasmonic photocatalysts.

Self-assembled vertically aligned Au nanorod arrays for surface-enhanced Raman scattering (SERS) detection of Cannabinol

Science.gov (United States)

Milliken, Sarah; Fraser, Jeff; Poirier, Shawn; Hulse, John; Tay, Li-Lin

2018-05-01

Self-assembled multi-layered vertically aligned gold nanorod (AuNR) arrays have been fabricated by a simple preparation process that requires a balance between the particle concentration and the ionic strength of the solvent. An experimentally determined critical AuNR concentration of 2.0 nM and 50 mM NaCl produces well-ordered vertically aligned hexagonally close-packed AuNR arrays. We demonstrate surface treatment via UV Ozone cleaning of such samples to allow introduction of analyte molecules (benzenethiol and cannabinol) for effective surface enhanced Raman scattering detection. This is the first demonstration of the SERS analysis of cannabinol. This approach demonstrates a cost-effective, high-yield and simple fabrication route to SERS sensors with application in the screening for the cannabinoids.

Theory of surface enrichment in disordered monophasic binary alloys. Numerical computations for Ag-Au alloys

NARCIS (Netherlands)

Santen, van R.A.; Boersma, M.A.M.

1974-01-01

The regular solution model is used to compute the surface enrichment in the (111)- and (100)-faces of silver-gold alloys. Surface enrichment by silver is predicted to increase if the surface plane becomes less saturated and decreases if one raises the temperature. The possible implications of these

Novel ion-molecular surface reaction to result in CH3 adsorbates on (111) surface of chemical vapor deposition diamond from ethane and surface anionic sites

International Nuclear Information System (INIS)

Komatsu, Shojiro; Okada, Katsuyuki; Shimizu, Yoshiki; Moriyoshi, Yusuke

2001-01-01

The existence of CH 3 adsorbates on (111) surface of chemical vapor deposited diamond, which was observed by scanning tunneling microscopy, was explained by the following S N 2 (bimolecular, substitutional, and nucleophilic) type surface reaction; C(s) - +C 2 H 6 ->C(s)-CH 3 +CH 3 - , where C(s) denotes a surface carbon atom. The activation energy was estimated to be 36.78 kcal/mol and the reaction proved to be exothermic with the enthalpy change of -9.250 kcal/mol, according to ab initio molecular orbital calculations at MP2/3-21+G * //RHF/3-21G * level; this result is consistent with typical substrate temperatures, namely about 900 degree C, for chemical vapor deposition of diamond. Charge transfer from the highest occupied molecular orbital of the surface anionic site to the lowest unoccupied molecular orbital of ethane, that is antibonding at the CH 3 - CH 3 bond, has been clearly visualized. A characteristic configuration of an ethane molecule which is associated with an anionic vacant site C(s) - on hydrogenated (111) surface of diamond was also found. [copyright] 2001 American Institute of Physics

Au-nanoparticles grafted on plasma treated PE

International Nuclear Information System (INIS)

Svorcik, V.; Chaloupka, A.; Rezanka, P.; Slepicka, P.; Kolska, Z.; Kasalkova, N.; Hubacek, T.; Siegel, J.

2010-01-01

Polyethylene (PE) surface was treated with Ar plasma. Activated surface was grafted from methanol solution of 1,2-ethanedithiol. Then the sample was immersed into freshly prepared colloid solution of Au-nanoparticles. Finally Au layer was sputtered on the samples. Properties of the modified PE were studied using various methods: AFM, EPR, RBS and nanoindentation. It was shown that the plasma treatment results in degradation of polymer chain (AFM) and creation of free radicals by EPR. After grafting with dithiol, the concentration of free radicals declines. The presence of Au and S in the surface layer after the coating with Au-nanoparticles was proved by RBS. Plasma treatment changes PE surface morphology and increases surface roughness, too. Another significant change in surface morphology and roughness was observed after deposition of Au-nanoparticles. Nanoindentation measurements show that the grafting with Au-nanoparticles increases adhesion of subsequently sputtered Au layer.

Adsorption energy of iron-phthalocyanine on crystal surfaces

International Nuclear Information System (INIS)

Struzzi, C.; Scardamaglia, M.; Angelucci, M; Massimi, L.; Mariani, C.; Betti, G.

2013-01-01

The adsorption energy of iron-phthalocyanine (FePc) deposited on different crystal surfaces is studied by thermal desorption spectroscopy. A thin film of molecules has been absorbed on highly oriented pyrolytic graphite (HOPG), on graphene epitaxially grown on Ir(111), and on Au(110). Activation energies for the desorption of a molecular thin film and for the FePc single layer are determined at the three surfaces. The desorption temperature measured for the thin films is only slightly dependent on the substrate, since it is mostly dominated by molecule-molecule interactions. A definitely different desorption temperature is found at the single-layer coverage: we find an increasing desorption temperature going from HOPG, to graphene/Ir, to the Au(110) surface. The different adsorption energies of the first FePc layer in contact with the substrate surface are discussed taking into account the interaction and the growth morphology.

Reversible switching in self-assembled monolayers of azobenzene thiolates on Au (111) probed by threshold photoemission

Energy Technology Data Exchange (ETDEWEB)

Heinemann, Nils, E-mail: heinemann@physik.uni-kiel.de [Institut fuer Experimentelle und Angewandte Physik, Christian-Albrechts-Universitaet zu Kiel, Leibnizstr. 19, 24098 Kiel (Germany); Grunau, Jan; Leissner, Till; Andreyev, Oleksiy; Kuhn, Sonja; Jung, Ulrich [Institut fuer Experimentelle und Angewandte Physik, Christian-Albrechts-Universitaet zu Kiel, Leibnizstr. 19, 24098 Kiel (Germany); Zargarani, Dordaneh; Herges, Rainer [Otto-Diels-Institut fuer Organische Chemie, Christian-Albrechts-Universitaet zu Kiel, Otto-Hahn-Platz 4, 24098 Kiel (Germany); Magnussen, Olaf; Bauer, Michael [Institut fuer Experimentelle und Angewandte Physik, Christian-Albrechts-Universitaet zu Kiel, Leibnizstr. 19, 24098 Kiel (Germany)

2012-06-19

Highlights: Black-Right-Pointing-Pointer Photoelectron spectroscopy of liquid phase prepared SAMs of azobenzene derivative. Black-Right-Pointing-Pointer Photo-induced reversible switching in densely packed SAM is monitored. Black-Right-Pointing-Pointer Maximum density of switched molecules in SAM is derived from photoemission data. Black-Right-Pointing-Pointer Switching reaction only enabled at defects sites within the molecular layer. - Abstract: The reversible photo- and thermally activated isomerization of the molecular switch 3-(4-(4-Hexyl-phenylazo)-phenoxy)-propane-1-thiol (ABT, short for AzoBenzeneThiol) deposited by self-assembly from solution on Au (111) was studied using laser-based photoelectron spectroscopy. Differences in the molecular dipole moment characteristic for the trans and the cis isomer of ABT were monitored via changes in the sample work function, accessible by detection of the threshold energy for photoemission. A quantitative analysis of our data shows that the fraction of molecules within the densely packed monolayer that undergoes a switching process is of the order of 1%. This result indicates the relevance of substrate and film defects required to overcome the steric or electronic hindrance of the isomerization reaction in a densely packed monolayer.

A recyclable Au(I) catalyst for selective homocoupling of arylboronic acids: significant enhancement of nano-surface binding for stability and catalytic activity.

Science.gov (United States)

Zhang, Xin; Zhao, Haitao; Wang, Jianhui

2010-08-01

Au nanoparticles stabilized by polystyrene-co-polymethacrylic acid microspheres (PS-co-PMAA) were prepared and characterized via X-ray diffraction (XRD), and transmission electron microscope (TEM). The Au nanoparticles supported on the microspheres showed highly selective catalytic activity for homo-coupling reactions of arylboronic acids in a system of aryl-halides and arylboronic acids. X-ray photoelectron spectroscopy (XPS) spectra of the catalyst shows large amounts of Au(I) complexes band to the surface of the Au nanoparticles, which contributes to the selective homocoupling of the arylboronic acids. More importantly, this supported Au complex is a highly recyclable catalyst. The supported Au catalyst can be recycled and reused at least 6 times for a phenylboronic acid reactant, whereas the parent complex shows very low catalytic activity for this compound. The high catalytic activity of this material is attributed to: (1) the high surface to volume ratio which leads to more active sites being exposed to reactants; (2) the strong surface binding of the Au nanoparticle to the Au(I) complexes, which enhances both the stability and the catalytic activity of these complexes.

Extra metal adatom surface diffusion simulation on 1/3 ML Si(111) √3×√3 metal-induced surfaces

International Nuclear Information System (INIS)

Luniakov, Yu V

2013-01-01

A first-principle simulation of the surface diffusion of an extra metal (Me) adatom has been performed on the corresponding 1/3 monolayer (ML) Si(111) √3×√3 Me-induced surfaces. Using the nudged elastic band (NEB) optimization method, the minimum energy paths and the activation energy barrier profiles for all known Me-inducing √3×√3 reconstruction on an Si(111) surface at the 1/3 ML coverage have been obtained and compared with the available experimental data. The activation barrier is shown to depend on the atomic size of the diffusing adatom: the barrier has the highest value for the largest Me adatom, Pb (0.44 eV); lower values for the smaller Me adatoms, Sn (0.36 eV), In (0.22 eV) and Ga (0.13 eV); and the lowest value for the smallest Me adatom, Al (0.08 eV). The Arrhenius pre-exponential factors that were obtained in the harmonic approximation are as large as ∼10 11−13 Hz for all of the investigated surfaces, which supports the single-adatom diffusion model considered here. (paper)

Distinction of heterogeneity on Au nanostructured surface based on phase contrast imaging of atomic force microscopy

International Nuclear Information System (INIS)

Jung, Mi; Choi, Jeong-Woo

2010-01-01

The discrimination of the heterogeneity of different materials on nanostructured surfaces has attracted a great deal of interest in biotechnology as well as nanotechnology. Phase imaging through tapping mode of atomic force microscopy (TMAFM) can be used to distinguish the heterogeneity on a nanostructured surface. Nanostructures were fabricated using anodic aluminum oxide (AAO). An 11-mercaptoundecanoic acid (11-MUA) layer adsorbed onto the Au nanodots through self-assembly to improve the bio-compatibility. The Au nanostructures that were modified with 11-MUA and the concave surfaces were investigated using the TMAFM phase images to compare the heterogeneous and homogeneous nanostructured surfaces. Although the topography and phase images were taken simultaneously, the images were different. Therefore, the contrast in the TMAFM phase images revealed the different compositional materials on the heterogeneous nanostructure surface.

First principles calculations for the cleaved and annealed Ge(111) surfaces

International Nuclear Information System (INIS)

Takeuchi, N.; Tosatti, E.; Selloni, A.

1992-11-01

We use ab initio Molecular Dynamics to study the structural and electronic properties of cleaved and annealed Ge(111) surfaces. New features emerge for both structures. For the (2x1) it is found that even though the stable state has a π-bonded chain structure, there are two isomers with the tilt angle of the chain in opposite directions. For the c(2x8) we find an asymmetry in the surface unit cell, in agreement with LEED experiments that show weak quarter-order spots. This inequivalence also produces a splitting of the rest atom and adatom dangling bond, which explains recent STM experiments. (author). 15 refs, 3 figs

New pathway to prepare gold nanoparticles and their applications in catalysis and surface-enhanced Raman scattering.

Science.gov (United States)

Chang, Chun-Chao; Yang, Kuang-Hsuan; Liu, Yu-Chuan; Hsu, Ting-Chu

2012-05-01

As shown in the literature, additional energies are necessary for the reduction of positively charged noble metal ions to prepare metal nanoparticles (NPs). In this work, we report a new green pathway to prepare Au NPs in neutral 0.1M NaCl aqueous solutions from bulk Au substrates without addition of any stabilizer and reductant just via aid of natural chitosan (Ch) at room temperature. Au- and Ch-containing complexes in aqueous solution were electrochemically prepared. The role of Ch is just an intermediate to perform electron transfer with Au NPs. The stability of these prepared Au NPs is well maintained by Au NPs themselves with slightly positively charged Au remained on the surface of Au NPs. The particle size of prepared spherical Au (111) NPs is ca. 15 nm in diameter. Moreover, increasing the pH of preparation solutions can be contributive to preparing concentrated Au NPs in solutions. The prepared Au NPs are surface-enhanced Raman scattering (SERS)-active for probe molecules of Rhodamine 6G. They also demonstrate significantly catalytic activity for decomposition of acetaldehyde in rice wine. Copyright © 2012 Elsevier B.V. All rights reserved.

Zinc (hydr)oxide/graphite oxide/AuNPs composites: role of surface features in H₂S reactive adsorption.

Science.gov (United States)

Giannakoudakis, Dimitrios A; Bandosz, Teresa J

2014-12-15

Zinc hydroxide/graphite oxide/AuNPs composites with various levels of complexity were synthesized using an in situ precipitation method. Then they were used as H2S adsorbents in visible light. The materials' surfaces were characterized before and after H2S adsorption by various physical and chemical methods (XRD, FTIR, thermal analysis, potentiometric titration, adsorption of nitrogen and SEM/EDX). Significant differences in surface features and synergistic effects were found depending on the materials' composition. Addition of graphite oxide and the deposition of gold nanoparticles resulted in a marked increase in the adsorption capacity in comparison with that on the zinc hydroxide and zinc hydroxide/AuNP. Addition of AuNPs to zinc hydroxide led to a crystalline ZnO/AuNP composite while the zinc hydroxide/graphite oxide/AuNP composite was amorphous. The ZnOH/GO/AuNPs composite exhibited the greatest H2S adsorption capacity due to the increased number of OH terminal groups and the conductive properties of GO that facilitated the electron transfer and consequently the formation of superoxide ions promoting oxidation of hydrogen sulfide. AuNPs present in the composite increased the conductivity, helped with electron transfer to oxygen, and prevented the fast recombination of the electrons and holes. Copyright © 2014 Elsevier Inc. All rights reserved.

Dynamics of Pseudomonas aeruginosa azurin and its Cys3Ser mutant at single crystal gold surfaces investigated by cyclic voltammetry and atomic force microscopy

DEFF Research Database (Denmark)

Friis, Esben P.; Andersen, Jens Enevold Thaulov; Madsen, Lars Lithen

1997-01-01

Cyclic voltammetry of Pseudomonas aeruginosa azurin on polycrystalline gold is reversible (E0=360mV vs she;50mM ammonium acetate) but the voltammetric signals decay with time constants of about 3x10-3 s-1. No signal is observed for monocrystalline Au(111). Cys3Ser azurin is electrochemically inac...... into the solution, recovering the free Au(111) surface. The cyclic voltammetry and AFM data are consistent with time dependent adsorption of the azurins on gold via the disulphide bridge (wild-type) or free thiol group (Cys3Ser mutant).......Cyclic voltammetry of Pseudomonas aeruginosa azurin on polycrystalline gold is reversible (E0=360mV vs she;50mM ammonium acetate) but the voltammetric signals decay with time constants of about 3x10-3 s-1. No signal is observed for monocrystalline Au(111). Cys3Ser azurin is electrochemically...... inactive on either type of gold electrode but shows a reversible although decaying peak (362mV, 50mM ammonium acetate; decay time constant ~ 2x10-3 s-1) on edge-plane pyrolytic graphite.Ex situ and in situ atomic force microscopy (AFM) of the azurins on Au(111) show initially arrays of protein structures...

Rare-Earth Surface Alloying: A New Phase for GdAu2

International Nuclear Information System (INIS)

Corso, M.; Schiller, F.; Fernandez, L.; Verstraete, M. J.; Ormaza, M.; Greber, T.; Torrent, M.; Rubio, A.; Ortega, J. E.

2010-01-01

Surface alloying is a powerful way of varying physical and chemical properties of metals, for a number of applications from catalysis to nuclear and green technologies. Surfaces offer many degrees of freedom, giving rise to new phases that do not have a bulk counterpart. However, the atomic characterization of distinct surface compounds is a major task, which demands powerful experimental and theoretical tools. Here we illustrate the process for the case of a GdAu 2 surface phase of extraordinary crystallinity. The combined use of surface-sensitive techniques and state-of-the-art ab initio calculations disentangles its atomic and electronic properties. In particular, the stacking of the surface layers allows for gadolinium's natural ferromagnetic state, at variance with the bulk phase, where frustration leads to antiferromagnetic interlayer coupling.

Probing Surface-Adlayer Conjugation on Organic-Modified Si(111) Surfaces with Microscopy, Scattering, Spectroscopy, and Density Functional Theory

International Nuclear Information System (INIS)

Kellar, Joshua A.; Lin, Jui-Ching; Kim, Jun-Hyun; Yoder, Nathan L.; Bevan, Kirk H.; Stokes, Grace Y.; Geiger, Franz M.; Nguyen, SonBinh T.; Bedzyk, Michael J.; Hersam, Mark C.

2009-01-01

Highly conjugated molecules bound to silicon are promising candidates for organosilicon electronic devices and sensors. In this study, 1-bromo-4-ethynylbenzene was synthesized and reacted with a hydrogen-passivated Si(111) surface via ultraviolet irradiation. Through an array of characterization and modeling tools, the binding configuration and morphology of the reacted molecule were thoroughly analyzed. Atomic force microscopy confirmed an atomically flat surface morphology following reaction, while X-ray photoelectron spectroscopy verified reaction to the surface via the terminal alkyne moiety. In addition, synchrotron X-ray characterization, including X-ray reflectivity, X-ray fluorescence, and X-ray standing wave measurements, enabled sub-angstrom determination of the position of the bromine atom with respect to the silicon lattice. This structural characterization was quantitatively compared with density functional theory (DFT) calculations, thus enabling the π-conjugation of the terminal carbon atoms to be deduced. The X-ray and DFT results were additionally corroborated with the vibrational spectrum of the organic adlayer, which was measured with sum frequency generation. Overall, these results illustrate that the terminal carbon atoms in 1-bromo-4-ethynylbenzene adlayers on Si(111) retain π-conjugation, thus revealing alkyne molecules as promising candidates for organosilicon electronics and sensing.

Density functional theory studies of the adsorption of ethylene and oxygen on Pt(111) and Pt3Sn(111)

DEFF Research Database (Denmark)

Watwe, R.M.; Cortright, R.D.; Mavrikakis, Manos

2001-01-01

Density functional theory, employing periodic slab calculations, was used to investigate the interactions of ethylene and oxygen with Pt(111) and Pt3Sn(111). The predicted energetics and structures of adsorbed species on Pt(111) are in good agreement with experimental data. The binding energies...... more than adsorption on two-fold and one-fold sites. Oxygen atoms bond as strongly on Pt3Sn(111) as on Pt(111), and these atoms prefer to adsorb near Sn atoms on the surface. The addition of Sn to Pt(111) leads to a surface heterogeneity, wherein ethylidyne species prefer to adsorb away from Sn atoms...

Activation and dissociation of CO2 on the (001), (011), and (111) surfaces of mackinawite (FeS): A dispersion-corrected DFT study.

Science.gov (United States)

Dzade, N Y; Roldan, A; de Leeuw, N H

2015-09-07

Iron sulfide minerals, including mackinawite (FeS), are relevant in origin of life theories, due to their potential catalytic activity towards the reduction and conversion of carbon dioxide (CO2) to organic molecules, which may be applicable to the production of liquid fuels and commodity chemicals. However, the fundamental understanding of CO2 adsorption, activation, and dissociation on FeS surfaces remains incomplete. Here, we have used density functional theory calculations, corrected for long-range dispersion interactions (DFT-D2), to explore various adsorption sites and configurations for CO2 on the low-index mackinawite (001), (110), and (111) surfaces. We found that the CO2 molecule physisorbs weakly on the energetically most stable (001) surface but adsorbs relatively strongly on the (011) and (111) FeS surfaces, preferentially at Fe sites. The adsorption of the CO2 on the (011) and (111) surfaces is shown to be characterized by significant charge transfer from surface Fe species to the CO2 molecule, which causes a large structural transformation in the molecule (i.e., forming a negatively charged bent CO2 (-δ) species, with weaker C-O confirmed via vibrational frequency analyses). We have also analyzed the pathways for CO2 reduction to CO and O on the mackinawite (011) and (111) surfaces. CO2 dissociation is calculated to be slightly endothermic relative to the associatively adsorbed states, with relatively large activation energy barriers of 1.25 eV and 0.72 eV on the (011) and (111) surfaces, respectively.

Adsorption of metal-phthalocyanine molecules onto the Si(111) surface passivated by δ doping: Ab initio calculations

Science.gov (United States)

Veiga, R. G. A.; Miwa, R. H.; McLean, A. B.

2016-03-01

We report first-principles calculations of the energetic stability and electronic properties of metal-phthalocyanine (MPc) molecules (M = Cr, Mn, Fe, Co, Ni, Cu, and Zn) adsorbed on the δ -doped Si(111)-B (√{3 }×√{3 }) reconstructed surface. (i) It can be seen that CrPc, MnPc, FePc, and CoPc are chemically anchored to the topmost Si atom. (ii) Contrastingly, the binding of the NiPc, CuPc, and ZnPc molecules to the Si (111 ) -B (√{3 }×√{3 }) surface is exclusively ruled by van der Waals interactions, the main implication being that these molecules may diffuse and rearrange to form clusters and/or self-organized structures on this surface. The electronic structure calculations reveal that in point (i), owing to the formation of the metal-Si covalent bond, the net magnetic moment of the molecule is quenched by 1 μB , remaining unchanged in point (ii). In particular, the magnetic moment of CuPc (1 μB ) is preserved after adsorption. Finally, we verify that the formation of ZnPc, CuPc, and NiPc molecular (self-assembled) arrangements on the Si(111)-B (√{3 }×√{3 } ) surface is energetically favorable, in good agreement with recent experimental findings.

SERS study of surface plasmon resonance induced carrier movement in Au@Cu2O core-shell nanoparticles

Science.gov (United States)

Chen, Lei; Zhang, Fan; Deng, Xin-Yu; Xue, Xiangxin; Wang, Li; Sun, Yantao; Feng, Jing-Dong; Zhang, Yongjun; Wang, Yaxin; Jung, Young Mee

2018-01-01

A plasmon induced carrier movement enhanced mechanism of surface-enhanced Raman scattering (SERS) was investigated using a charge-transfer (CT) enhancement mechanism. Here, we designed a strategy to study SERS in Au@Cu2O nanoshell nanoparticles with different shell thicknesses. Among the plasmonically coupled nanostructures, Au spheres with Cu2O shells have been of special interest due to their ultrastrong electromagnetic fields and controllable carrier transfer properties, which are useful for SERS. Au@Cu2O nanoshell nanoparticles (NPs) with shell thicknesses of 48-56 nm are synthesized that exhibit high SERS activity. This high activity originates from plasmonic-induced carrier transfer from Au@Cu2O to 4-mercaptobenzoic acid (MBA). The CT transition from the valence band (VB) of Cu2O to the second excited π-π* transition of MBA, and is of b2 electronic symmetry, which was enhanced significantly. The Herzberg-Teller selection rules were employed to predict the observed enhanced b2 symmetry modes. The system constructed in this study combines the long-range electromagnetic effect of Au NPs, localized surface plasmon resonance (LSPR) of the Au@Cu2O nanoshell, and the CT contribution to assist in understanding the SERS mechanism based on LSPR-induced carrier movement in metal/semiconductor nanocomposites.

Growth kinetics of metastable (331) nanofacet on Au and Pt(110) surfaces

International Nuclear Information System (INIS)

Ndongmouo, U.T.; Houngninou, E.; Hontinfinde, F.

2006-12-01

A theoretical epitaxial growth model with realistic barriers for surface diffusion is investigated by means of kinetic Monte Carlo simulations to study the growth modes of metastable (331) nanofacets on Au and Pt(110) surfaces. The results show that under experimental atomic fluxes, the (331) nanofacets grow by 2D nucleation at low temperature in the submonolayer regime. A metastable growth phase diagram that can be useful to experimentalists is presented and looks similar to the one found for the stationary growth of the bcc(001) surface in the kinetic 6-vertex model. (author)

Stability of Ta-encapsulating Si clusters on Si(111)-(7x7) surfaces

CERN Document Server

Uchida, N; Miyazaki, T; Kanayama, T

2003-01-01

Tantalum containing Si cluster ions TaSi sub 1 sub 0 sub - sub 1 sub 3 H sub x sup + were synthesized in an ion trap and deposited onto Si(111)-(7x7) surfaces with a kinetic energy of 18 eV. Scanning tunnelling microscope observations revealed that the clusters adsorbed on the surface without decomposition, consistent with ab initio calculation results, that predicted the clusters would have stable Si-cage structures with a Ta atom at the centre. (rapid communication)

Ab initio hybrid DFT calculations of BaTiO{sub 3}, PbTiO{sub 3}, SrZrO{sub 3} and PbZrO{sub 3} (111) surfaces

Energy Technology Data Exchange (ETDEWEB)

Eglitis, Roberts I., E-mail: rieglitis@gmail.com

2015-12-15

Highlights: • Surface energies for AO{sub 3}-term (111) surfaces are larger than for Ti (Zr)-term surfaces. • A increase of Ti−O (Zr−O) bond covalency near the ABO{sub 3} (111) surface relative to the bulk is observed. • The ABO{sub 3} (111) surface energy is larger than the earlier calculated (001) surface energy. • Band gap for PbTiO{sub 3}, SrZrO{sub 3} and PbZrO{sub 3} (111) surfaces becomes smaller, but for BaTiO{sub 3} (111) larger with respect to the bulk . - Abstract: The results of ab initio calculations for polar BaTiO{sub 3}, PbTiO{sub 3}, SrZrO{sub 3} and PbZrO{sub 3} (111) surfaces using the CRYSTAL code are presented. By means of the hybrid B3LYP approach, the surface relaxation has been calculated for two possible B (B = Ti or Zr) or AO{sub 3} (A = Ba, Pb or Sr) BaTiO{sub 3}, PbTiO{sub 3}, SrZrO{sub 3} and PbZrO{sub 3} (111) surface terminations. According to performed B3LYP calculations, all atoms of the first surface layer, for both terminations, relax inwards. The only exception is a small outward relaxation of the PbO{sub 3}-terminated PbTiO{sub 3} (111) surface upper layer Pb atom. B3LYP calculated surface energies for BaO{sub 3}, PbO{sub 3}, SrO{sub 3} and PbO{sub 3}-terminated BaTiO{sub 3}, PbTiO{sub 3}, SrZrO{sub 3} and PbZrO{sub 3} (111) surfaces are considerably larger than the surface energies for Ti (Zr)-terminated (111) surfaces. Performed B3LYP calculations indicate a considerable increase of Ti−O (Zr−O) chemical bond covalency near the BaTiO{sub 3}, PbTiO{sub 3}, SrZrO{sub 3} and PbZrO{sub 3} (111) surface relative to the BaTiO{sub 3}, PbTiO{sub 3}, SrZrO{sub 3} and PbZrO{sub 3} bulk. Calculated band gaps at the Γ-point near the PbTiO{sub 3}, SrZrO{sub 3} and PbZrO{sub 3} (111) surfaces are reduced, but near BaTiO{sub 3} (111) surfaces increased, with respect to the BaTiO{sub 3}, PbTiO{sub 3}, SrZrO{sub 3} and PbZrO{sub 3} bulk band gap at the Γ-point values.

Manipulation of surface plasmon resonance of a graphene-based Au aperture antenna in visible and near-infrared regions

Science.gov (United States)

Wan, Yuan; An, Yashuai; Tao, Zhi; Deng, Luogen

2018-03-01

Behaviors of surface plasmon resonance (SPR) of a graphene-based Au aperture antenna are investigated in visible and near-infrared (vis-NIR) regions. Compared with the SPR wavelength of a traditional Au aperture antenna, the SPR wavelength of the graphene-based Au aperture antenna shows a remarkable blue shift due to the redistribution of the electric field in the proposed structure. The electric field of the graphene-based Au aperture antenna is highly localized on the surface of the graphene in the aperture and redistributed to be a standing wave. Moreover, the SPR of a graphene-based Au aperture antenna is sensitive to the thickness and the refractive index of the dielectric layer, the graphene Fermi energy, the refractive index of the environment and the polarization direction of the incident light. Finally, we find the wavelength, intensity and phase of the reflected light of the graphene-based Au aperture antenna array can be actively modulated by varying the graphene Fermi energy. The proposed structure provides a promising platform for realizing a tunable optical filter, a highly sensitive refractive index sensor, and other actively tunable optical and optoelectronic devices.

Determination of the bonding of alkyl monolayers to the Si(111) surface using chemical-shift, scanned-energy photoelectron diffraction

Energy Technology Data Exchange (ETDEWEB)

Terry, J.; Linford, M.R.; Wigren, C.; Cao, R.; Pianetta, P.; Chidsey, C.E. [Stanford University, Stanford, California 94309 (United States)

1997-08-01

The bonding of alkyl monolayers to Si(111) surfaces has been studied by conventional x-ray photoelectron spectroscopy (XPS) and chemical-shift, scanned-energy photoelectron diffraction (PED) using synchrotron radiation. Two very different wet-chemical methods have been used to prepare the alkyl monolayers: (i) olefin insertion into the H{endash}Si bond on the H{endash}Si(111) surface, and (ii) replacement of Cl on the Cl{endash}Si(111) surface by an alkyl group from an alkyllithium reagent. In both cases, XPS has revealed a C 1s signal chemically shifted to lower binding energy, which we have assigned to carbon bonded to silicon. PED has shown that both preparative methods result in carbon bonded in an atop site with the expected C{endash}Si bond length of 1.85{plus_minus}0.05{Angstrom}. Chemical-shift, scanned-energy photoelectron diffraction is a particularly valuable probe of local structure at surfaces that contain the same element in multiple, chemically distinct environments. {copyright} {ital 1997 American Institute of Physics.}

Determination of the bonding of alkyl monolayers to the Si(111) surface using chemical-shift, scanned-energy photoelectron diffraction

International Nuclear Information System (INIS)

Terry, J.; Linford, M.R.; Wigren, C.; Cao, R.; Pianetta, P.; Chidsey, C.E.

1997-01-01

The bonding of alkyl monolayers to Si(111) surfaces has been studied by conventional x-ray photoelectron spectroscopy (XPS) and chemical-shift, scanned-energy photoelectron diffraction (PED) using synchrotron radiation. Two very different wet-chemical methods have been used to prepare the alkyl monolayers: (i) olefin insertion into the H endash Si bond on the H endash Si(111) surface, and (ii) replacement of Cl on the Cl endash Si(111) surface by an alkyl group from an alkyllithium reagent. In both cases, XPS has revealed a C 1s signal chemically shifted to lower binding energy, which we have assigned to carbon bonded to silicon. PED has shown that both preparative methods result in carbon bonded in an atop site with the expected C endash Si bond length of 1.85±0.05 Angstrom. Chemical-shift, scanned-energy photoelectron diffraction is a particularly valuable probe of local structure at surfaces that contain the same element in multiple, chemically distinct environments. copyright 1997 American Institute of Physics

A density functional theory study on the conversion of ethylene to carbon monomer on PdAu(1 0 0) surface

Energy Technology Data Exchange (ETDEWEB)

Zhang, Minhua; Yang, Bing [Key Laboratory for Green Chemical Technology of Ministry of Education, R& D Center for Petrochemical Technology, Tianjin University, Tianjin 300072 (China); Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072 (China); Yu, Yingzhe, E-mail: yzhyu@tju.edu.cn [Key Laboratory for Green Chemical Technology of Ministry of Education, R& D Center for Petrochemical Technology, Tianjin University, Tianjin 300072 (China); Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072 (China)

2015-11-30

Graphical abstract: - Highlights: • The successive decomposition of ethylene on PdAu(1 0 0) was studied with DFT method. • The C−H, C−C bond scission and a hydrogen-shift process were investigated. • The alloying of Au with Pd affects the studied reactions on PdAu(1 0 0) greatly. - Abstract: Calculations based on the first-principles density functional theory (DFT) were performed to study the possible transformation pathways of ethylene on PdAu(1 0 0) surface to investigate the effect of Au atom alloying with Pd on the formation of CHx (x = 0–2), which may eventually form carbon monomer and lead to the deactivation of catalysts. The energetic properties of reactions including the scission of the C−H, C−C bond and a hydrogen-shift process were determined. The C−H bond scission is confirmed to be prone to happen on the studied surface, while it is difficult for the C−C bond scission to occur due to relatively high barriers, the values of which are as high as 2.72–4.62 eV. The activation barriers for all related reactions except for the dehydrogenation of vinyl, vinylidene and acetenyl demonstrate that it is harder for the conversion of ethylene to occur on PdAu(1 0 0) surface than on Pd(1 0 0) surface, especially for the C−C bond scission. All the results indicate that the alloying of Au atom with pure Pd catalyst can prevent the formation of carbon monomer, which may notably affect properties of catalysts.

Global structural optimizations of surface systems with a genetic algorithm

International Nuclear Information System (INIS)

Chuang, Feng-Chuan