Deposition Of Metal Clusters Research Articles

Improved metal cluster deposition on a genetically engineered tobacco mosaic virustemplate

Improved depositions of various metal clusters onto a biomolecular template were achievedusing a genetically engineered tobacco mosaic virus (TMV). Wild-type TMV wasgenetically altered to display multiple solid metal binding sites through the insertion oftwo cysteine residues within the amino-terminus of the virus coat protein. Gold,silver, and palladium clusters synthesized through in situ chemical reductionscould be readily deposited onto the genetically modified template via the exposedcysteine-derived thiol groups. Metal cluster coatings on the cysteine-modifiedtemplate were more densely deposited and stable than similar coatings on theunmodified wild-type template. Combined, these results confirm that the introductionof cysteine residues onto the outer surface of the TMV coat protein enhancesthe usefulness of this virus as a biotemplate for the deposition of metal clusters.

Disordered Carbon Anode for Lithium-Ion Battery: I. An Interfacial Reversible Redox Action and Anomalous Topology Changes

The authors investigated mechanisms for an interfacial reversible surface redox action and a solid electrolyte interphase (SEI) formation based on LiF with surface topology changes for a disordered carbon electrode in . The electrochemical reaction mechanism that delivers a large capacity was found to occur differently in two potential regions, region A (1.4 to 0.4 V) and B (0.4 to 0.0 V). During the reversible process in region A, a lithium alkoxide (C-OLi) is formed on the carbonyl edge planes as solvated lithium complex of the (, 2, or 3). The formation of the lithium alkoxide traps solvents on the edge surfaces preventing further intrusion into stacked graphene sheets, that in turn suppresses a exfoliation and stabilized repeated redox cycles. In region A, a and a LiF are formed as an SEI film by the reduction of solvents and making a smooth surface. region B involves three parallel processes, viz., a lithium intercalation into graphene layers, a lithium metal cluster deposition at nanosized voids or pores, and a formation of LiF by disproportionation of the C-OLi formed at region A. Since the LiF is produced rapidly by a proposed repeated cycle, the electrode surface generates a rough anomalous topology.

Velocity dependence of metal cluster deposition on an insulating surface

We present a detailed study of the deposition of small sodium clusters on a NaCl surface. To that end, we use a microscopic model based on the Time-Dependent Local Density Approximation (TDLDA) for electrons, coupled to classical Molecular Dynamics (MD) for ions. We discuss in particular the deposition mechanism for different initial cluster velocities and demonstrate that extremely slow velocities are necessary to ensure a cluster deposition without damaging the original cluster.

Selective deposition of a gadolinium(III) cluster in a hole opening of single-wall carbon nanohorn.

Selective synthesis of particles of angstrom to nanometer size consisting of one to many metal atoms is instrumental in various applications, but it has been hampered by the tendency of the metal atom to form large clusters. We found, as studied by the state-of-the-art electron microscopic technique, a strategy to produce metal-containing nanoparticles isolated from each other by depositing metal atoms in a hydrophilic hole on or in the interior of a carbon nanotube as demonstrated by the reaction of Gd(OAc)(3) with oxidized single-wall nanohorns. Besides the potential utilities of the deposited metal clusters, the metal deposition protocol provides a method to control permeation of molecules through such openings.

Photoelectron spectroscopy on Pt atoms and clusters deposited on C(0001)

An experimental photoelectron spectroscopy study is presented highlighting several aspects of importance for the study of deposited metal clusters and particles with photoemission. It is shown that the Fermi level is the correct energy reference for the core level binding energies. The choice of different deposition conditions, well within the range of soft landing, has a strong impact on the outcome of the spectroscopic experiments. Single adatoms as well as clusters deposited with some excess energy display relatively narrow core level spectra at much lower binding energies than previously reported, even when atomic mass selection is not performed. In contrast, single sized Pt19 clusters, deposited onto a thin Ar film before being exposed to the graphite surface show spectral broadening and shifts to higher binding energies. We discuss our results in terms of the cluster substrate interaction and the influence of deposition conditions on the metal adsorbate structure.

Cluster beam steering onto silicon surfaces studied by molecular dynamics

The purpose of this study is to investigate the effects of the impact conditions on cluster deposition in silicon and is motivated by recent results obtained using a variable incidence angle during deposition of metallic clusters and atoms. Therefore deposition of silicon clusters with a kinetic energy in the range from 0.5 to 10 eV/atom directed at normal and grazing incidence onto crystalline silicon has been studied using a molecular dynamics simulation method. The influence of other relevant parameters, such as the interatomic forces and the cluster size and shape, has also been investigated. This study shows that the physics of deposition is almost entirely dictated by the nature of the interatomic forces. When using potentials with the four-fold coordination typical of bulk a clear dependence on the size N is observed and the spreading index η decreases with the increase of N for all incidence conditions. The cluster binding strength is perceptibly increased when using a potential accounting for the coordination typical of clusters. In this case η is reduced of almost one order of magnitude with respect to the values calculated with the bulk potentials and its value is independent of N. Also compact clusters, obtained from a quantum mechanical minimization of the total energy, show an enhanced resilience against fragmentation.

Molecular dynamics simulation of structural characteristics in metal cluster deposition on surfaces

The deposition of small metal clusters (Cu, Au and Al) on f.c.c. metals (Cu, Au and Ni) has been studied by molecular dynamics simulation using Finnis–Sinclair (FS) potential. The impact energy varied from 0.01 to 10 eV/atom. First, the deposition of single cluster was simulated. We observed that, even at much lower energy, a small cluster with ( I h) icosahedral symmetry was reconstructed to match the substrate structure (f.c.c.) after deposition. Next, clusters were modeled to drop, one after the other, on the surface. The nanostructure was found by soft landing of Au clusters on Cu with increasing coverage, where interfacial energy dominates. While at relatively higher deposition energy (a few eV), the ordered f.c.c.-like structure was observed in the first adlayer of the film formed by Al clusters depositing on Ni substrate. This characteristic is mainly attributive to the ballistic collision. Our results indicate that the surface morphology synthesized by cluster deposition could be controlled by experimental parameters, which will be helpful for controlled design of nanostructure.

Electrochemical deposition of copper in polyaniline films — number density and spatial distribution of deposited metal clusters

The electrochemical deposition of copper in reduced polyaniline (PAN) films is studied at different polymer layer thicknesses. A saturation in the number density, n 0, of active sites for metal deposition is found at 0.5 μm PAN thickness ( n 0=10 8 cm −2). The surface spatial distribution of the deposited copper crystals is analysed in two cases. It is found that nucleation exclusion zones play an appreciable role in the course of the deposition process in thin PAN films. In contrast, a random distribution and a larger number of deposited crystals are obtained in thicker PAN layers.

Molecular dynamics study of cluster impact on the [formula omitted] and [formula omitted] surfaces of fcc metals

Molecular dynamics simulations of the impact deposition of metal clusters on fcc metal surfaces are presented. Two-dimensional elongated islands are formed when the incident cluster travels parallel to the surface. For perpendicular incidence the results of the impact event are very sensitive to the relative cohesive properties of the cluster and substrate atoms.

Metal–oxide interaction for metal clusters on a metal-supported thin alumina film

The interaction between deposited metal clusters and a thin model alumina film grown on NiAl(110) have been studied using X-ray absorption spectroscopy (XAS) and core and valence photoelectron spectroscopy. A lower limit for the fundamental gap of the supported alumina film is determined, and found to be slightly lower than that of alumina surfaces. O 1s XAS shows that new states appear in the fundamental gap upon metal deposition. Al 2p X-ray photoelectron spectra from the alumina film are also sensitive to metal deposition, whereas spectra from Al atoms at the substrate–oxide interface appear unaffected. The present data demonstrate the existence of gap states in the pristine film, and we discuss the effects of these states for the properties of this film as a model oxide substrate.

Electron field emission from phase pure nanotube films grown in a methane/hydrogen plasma

Phase pure nanotube films were grown on silicon substrates by a microwave plasma under conditions which normally are used for the growth of chemical vapor deposited diamond films. However, instead of using any pretreatment leading to diamond nucleation we deposited metal clusters on the silicon substrate. The resulting films contain only nanotubes and also onion-like structures. However, no other carbon allotropes like graphite or amorphous clustered material could be found. The nanotubes adhere very well to the substrates and do not need any further purification step. Electron field emission was observed at fields above 1.5 V/μm and we observed an emission site density up to 104/cm2 at 3 V/μm. Alternatively, we have grown nanotube films by the hot filament technique, which allows to uniformly cover a two inch wafer.

Etching fabrication of silicon nanostructures using deposited metal clusters as formation nuclei

Clusters of Au and Ag deposited on Si substrates were used as nuclei for self-formation of etching masks during electron cyclotron resonance plasma etching with SF 6 gas. As a result, Si pillars ~0.1 μm high were formed with a uniform diameter. The formation mechanism is concluded to be condensation of the reaction product of the etching gas S x F y , preferentially around the deposited clusters, forming etching masks when the substrate temperature was kept at − 130 °C, Au clusters yielded the average pillar diameter of 9 nm, while Ag clusters yielded a 16 nm diameter, indicating that the reactivity of the clusters with the reaction products plays a decisive role in the mask formation. In contrast, experiments using the deposition of size-selected Ag cluster ions indicate that the pillar diameter is almost independent of the cluster size. This feature is particularly advantageous in that equal size pillars can be fabricated without the need for an accurate control of the cluster size.

Preparation of model catalysts by laser interference nanolithography followed by metal cluster deposition

Metal clusters arranged on nanostructured oxidized silicon wafers are presented as new model catalyst systems. A photoresist layer spun on top of a wafer was patterned by laser interference exposure. The grid obtained after removing the exposed parts of the resist is used as an etching mask. Hollows with diameters of 300 nm and depths between 50 and 60 nm were etched into the oxide layer using wet chemical methods. Two methods were applied to deposit metal clusters (Pd or Cu) in a defined way within the hollows. The particles ranged from 10 to 50 nm in height and from 80 to 200 nm in diameter. The model catalyst systems were characterized by atomic force microscopy and X-ray photoelectron spectroscopy. The method presented here allows us to produce 4 inch wafers that are covered completely by nanometer-sized structures in a reasonable period of time.

Deposition of metallic clusters on a metallic surface at zero initial kinetic energy: Evidence for implantation and site exchanges

We have investigated the deposition at zero impact kinetic energy of the Ag atom and clusters $({\mathrm{Ag}}_{7}{,\mathrm{A}\mathrm{g}}_{19})$ on the (100) and (111) surfaces of Pd by molecular-dynamics simulations performed within the embedded-atom-method scheme. Our results elucidate the role played by the adsorption energy in determining the final morphology of the cluster/substrate system when ideal nondestructive deposition conditions are implemented. While implantation of the atom is not observed, we find a finite probability of site Ag-Pd exchanges in the case of clusters. Deposition-assisted mixing occurring at the topmost surface layer appears to be correlated to the size of the cluster and the orientation of the substrate, being higher for ${\mathrm{Ag}}_{7}/\mathrm{P}\mathrm{d}(100)$ and lower for ${\mathrm{Ag}}_{19}/\mathrm{P}\mathrm{d}(111).$ Total-energy calculations, combined with an analysis of the atomic motion, indicate that the structural transformation accompanying the deposition of the cluster provides the needed activation energy to induce the observed Ag-Pd atomic exchanges.

Chemical reactivity of size-selected supported clusters: An experimental setup

We describe an experimental setup for the investigation of the chemical reactivity of size-selected, supported clusters. The clusters are generated by a high frequency laser vaporization source. After mass selection and energy control the clusters are deposited under ultrahigh-vacuum conditions and with low kinetic energy onto thin oxide films grown on metal single crystals. Such films are ideal in their function as supports for size-selected deposited metal clusters. Measured currents of mass-selected niobium cluster ions were of the order of 1 nA and are high enough for fast deposition rates. Adsorbed molecules used on the one hand as probes to characterize the supported clusters and on the other hand for studying chemical reactions on these clusters are investigated in situ by Fourier transform infrared spectroscopy, temperature desorption spectroscopy, and Auger electron spectroscopy. The performance of these analytical tools is illustrated with CO adsorbed on Ni atoms supported on thin MgO(100) films grown on a Mo(100) single crystal.

Application and Progress in the Scanning Probe Microscopy. High Density Information Storage Using Langmuir-Blodgett Film and Atomic Force Microscopy.

A nanometer-scale structure of metal/Langmuir-Blodgett (LB) film/metal is realized using an atomic force microscope (AFM) with an electrically conducting probe. In this configuration, increase in conductance can be induced at any point in the LB film by application of a voltage pulse. Clear spots are observed in the current image at the points where voltage pulses are applied, while no specific feature such as protrusions or holes is observed in the AFM image obtained simultaneously. These results show that the conductance of the LB film changes without pit formation in the LB film or metal cluster deposition from the tip of the probe. The transition takes place within 1 μs, and the transition can be induced at several thousand points, at least, without tip degradation. These facts demonstrate the feasibility of constructing information storage devices with high density.

Nanometer scale conductance change in a Langmuir-Blodgett film with the atomic force microscope

A nanometer scale metal/Langmuir-Blodgett (LB) film/metal structure is realized with an atomic force microscope combined with scanning tunneling microscope (AFM/STM). Even in this nanometer scale configuration, increase in conductance can be induced at any point in the LB film by application of a voltage pulse. The AFM/STM observation shows little surface modification has occurred by the voltage application, which shows that the conductance of the LB film changes without pit formation in the LB film or metal cluster deposition from the tip of the probe.

The deposition of metallic clusters on surfaces

It is shown how the rate of deposition of ionized clusters with a given energy range (from a cluster source) is dependent on the impact area, the energy spread in the beam and the source emittance. A novel technique, SLED (soft landing by electrostatic dispersion), is described for reducing the impact energies whilst still depositing a significant fraction of the total beam.

A novel technique for the preparation of metal clusters in dielectric matrices

Metal clusters trapped in solid‐state matrices can be produced in various wayas. The new method presented here relies on the simultaneous plasma polymerization of a vinyltrimethylsilane monomer and deposition of metal clusters (e.g., Au, Ag, Pd) by an inert gas evaporation technique. The characterization by TEM, XPS, and UV‐vis and FTIR spectroscopy of amonorphous plasma‐polymer films containing gold clusters is described, which revelas that the clusters areunigorm in size and crystalline.

Valence band photoemission from deposited metal clusters: Case studies

Metal clusters (PbN,AuN) grow in a pulsed arc cluster ion source (PACIS). After supersonic expansion in the helium carrier gas the resulting beam is soft-landed under UHV conditions on either cold poly-cristalline silver,Si(111) or naturalSiO2. Photoemission measurements with light from the synchrotron BESSY serve to investigate the electronic structure of the clusters. In this communication, valence band photoemission is presented forPbN onAg, PbN onSi/SiO2 andAuN onAg. After lead deposition, the valence band region exhibits only low, weakly structured intensity, whereas deposited gold clusters lead to the formation of a resolved narrow peak at 3.52 eV below eF, which we attribute toAu 5d5/2.