Formation Of Gold Clusters Research Articles

Gold clusters showing pentagonal atomic arrays revealed by aberration-corrected scanning transmission electron microscopy

In this work we present the analysis by aberration corrected electron microscopy of the formation of gold clusters based on the proton irradiation of larger nanoparticles (NP). Pentagonal arrays have been observed and energetic calculations have been performed in order to prove the stability of these materials.

Nanoclusters of Gold on a High-Area Support: Almost Uniform Nanoclusters Imaged by Scanning Transmission Electron Microscopy

Highly dispersed supported gold offers unprecedented catalytic properties. Determination of the dependence of the catalytic properties on the gold nanocluster size requires the preparation of size-controlled gold nanoclusters on support surfaces with a high degree of uniformity. Starting from site-isolated mononuclear gold complexes on high-area MgO, we demonstrate the preparation of gold clusters consisting of <10 atoms. These samples have been imaged with atomic resolution by aberration-corrected scanning transmission electron microscopy. The images show that treatment of the supported mononuclear complexes at 318 K in flowing helium caused aggregation of the gold into clusters of 2-6 atoms, present with unconverted individual site-isolated mononuclear gold species and in the absence of any larger nanoparticles. Treatment of the sample at a higher temperature (373 K) in flowing helium resulted in the formation of gold clusters with diameters of 0.58 +/- 0.15 nm (containing roughly 10 Au atoms), again in the absence of larger nanoparticles. Upon exposure of the supported nanoclusters to the electron beam, they underwent aggregation to gold clusters approximately 1 nm in average diameter, as shown in consecutive STEM images.

Photoemission study of CF 4 rf-Plasma treated multi-wall carbon nanotubes

Multi-wall carbon nanotubes (MWCNTs) were exposed to a CF 4 rf-plasma. X-ray photoelectron spectroscopy analysis shows that the treatment effectively grafts fluorine atoms onto the MWCNTs. The fluorine atomic concentration and the nature of the C–F bond (semi-ionic or covalent) can be tuned by varying the exposure time. Ultraviolet photoelectron spectroscopy analysis confirms that the valence electronic states are altered by the grafting of fluorine atoms. Characterization with high-resolution transmission electron microscopy reveals that while the plasma treatment does not induce significant etching impact on the CNT-surface, it does increase the number of active sites for gold cluster formation.

Aqueous gold nanosols stabilized by electrostatic protection generated by X-ray irradiation assisted radical reduction

Reductant, stabilizer-free colloidal gold solutions were fabricated by a new room-temperature synchrotron X-ray irradiation method. The influence of process parameters such as the pH value and the exposure time on the structure of gold nanoparticles was investigated. The mechanisms underlying the X-ray-triggered reduction of gold ions and the formation of gold clusters are discussed in detail. The X-ray irradiation derived highly concentrated gold nanoparticles are readily to be re-dispersed and possess suitable colloidal stability within cellular environment. The characterization included a study of the possible cytotoxicity for the EMT-6 tumor cell line: the negative results indicate that the gold clusters produced with our approach are biocompatible.

Gold cluster formation on C 60 surfaces observed with scanning tunneling microscopy: Au-cluster beads and self-organized structures

The growth mechanism of Au-clusters on fullerene layers has been investigated by scanning tunneling microscopy in ultrahigh vacuum at room temperature. The fullerene layers, which serve as substrates, are formed on a graphite surface and exhibit the typical combination of round and fractal shapes, and small sections of the original graphite substrate are exposed. The immobile Au-clusters are concentrated on the C 60 terminated surface section, and the original fullerene island structures are preserved. A preferential nucleation of Au-clusters is observed at the C 60–graphite edges while the C 60–C 60 edges remains undecorated. These Au-clusters are placed directly on the edge and shared by the graphite and fullerene layer. They form bead-like structures, which densely populate this edge, while the first layer C 60 islands are clearly depleted of Au-clusters. A roughness analysis of the fullerene surface indicates the presence of Au atoms (or very small clusters), which are embedded in the fullerene surface, and likely situated in the troughs in between the large molecules. These Au atoms are highly mobile and cannot be individually resolved at room temperature. The analysis of the spatial and size distributions of Au-clusters provides the basis for the development of a qualitative model, which describes the relevant surface processes in the Au–fullerene system. The simultaneous deposition of Au and fullerene on graphite leads to the formation of highly organized structures, in which Au-clusters are embedded in a ring of fullerene molecules with a constant width of about 4 nm. The mechanism for the formation of these structures is highly speculative at present and further experiments will be pursued in the near future. A comprehensive analysis of the Au–C 60 system is presented, which contributes to the advancement in our understanding of the metal–fullerene interaction and furthers the development of composite materials of interest in the synthesis of solar cells and metal contacts to organic materials.

Self-breaking in planar few-atom Au constrictions for nanometer-spaced electrodes

The authors present results on electromigrated Au nanojunctions broken near the conductance quantum of 77.5μS. At room temperature it is found that wires, initially narrowed by an actively-controlled electromigration technique down to a few conductance quanta, continue to narrow after removing the applied voltage. Separate electrodes form as mobile gold atoms continuously reconfigure the constriction. They find, from results obtained on over 300 samples, no evidence for gold cluster formation in junctions broken without an applied voltage, implying that gold clusters may be avoided by using this self-breaking technique.

The Effect of pH-adjusted Gold Colloids on the Formation of Gold Clusters over APTMS-coated Silica Cores

An electrostatic interaction is responsible for the attachment of gold seeds of 1-3 nm onto APTMS (3-aminopropyl trimethoxysilane)-coated silica cores in the formation of gold clusters. A surface plasmon resonance and morphology of gold clusters were significantly affected by the pH of gold colloids prepared by THPC reducing agent. Gold colloids of alkaline pH induced the heterogeneous deposition of gold seeds onto the silica nanoparticles, probably due to the continuous reduction of residual gold ions during the attachment process. Gold colloids of acidic pH induced the monodisperse deposition of gold seeds, consequently leading to the formation of smooth gold layer on the silica nanoparticles surface. The gold nanoshells (core radius = 80 nm) prepared by gold colloids of pH 3.1 exhibited the more red-shift and relatively stronger intensity of plasmon absorption bands, compared with gold nanoshells prepared by alkaline gold colloids of pH 9.7.

RETRACTED: Studies on interactions of thionine with gold nanoparticles

The interactions of thionine with gold nanoparticles have been studied by using UV-vis absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. With addition of small amounts of gold nanoparticles, the absorption peak intensity of monomers of thionine decreases significantly, whereas that of H-type dimers of thionine increases. With further addition of gold nanoparticles, both the absorption peak intensities of the monomers and dimers of thionine increase, and the increasing magnitude of the peak intensity of the dimers is larger than that of monomers. The addition of gold nanoparticles makes the equilibrium between the monomer and H-type dimer forms of thionine move toward the dimer forms. Due to the binding between thionine and gold nanoparticles, the fluorescence quenching of thionine by gold nanoparticles is enhanced with increasing amounts of gold nanoparticles, and the quenching is both static and dynamic. TEM images show that the addition of thionine results in the formation of gold clusters, and further support the spectral results. Infrared spectroscopic studies show that the nitrogen atoms of both the NH 2 moieties of thionine strongly bind to the gold nanoparticle surfaces through the electrostatic interaction of thionine with gold nanoparticles. For 3-6 nm particles, the number of adsorbed thionine molecules per gold particle is about 1.21 x 10 3 . Thionine molecules can not only bind to a particle to form a compact monolayer via both the NH 2 moieties of thionine, but also bind to two particles via their two NH 2 moieties, respectively.

Gold cluster formation on a fullerene surface

The growth of Au clusters on a fullerene thin film was investigated by in situ photoelectron spectroscopy in the ultraviolet (UPS) and x-ray (XPS) regime. Due to its highly corrugated surface fullerene films provide a wide range of bonding sites which could be exploited as molecular templates and serve to create a cluster superstructure. To gain insight into the fullerene-Au interaction two types of experiments were performed: (i) the deposition of Au on a fullerene surface, and (ii) the deposition of fullerenes on a Au surface. In both experiments an island growth mode is observed. The deposition of submonolayer amounts of C60 onto a gold film showed that the main interaction of the two species is due to chemisorption of the first C60 monolayer. In addition a constant band bending in the fullerene film is detected, but the UPS valence-band spectra show that there is no charge transfer from the Au to the C60 lowest unoccupied molecular orbital. In the reverse experiment, the cluster growth of Au on the corrugated C60 surface, the analysis of the Au core level does not reveal a specific bonding or nucleation site for Au atoms and clusters. This is in contrast to observations with Si clusters, which prefer to reside in the troughs between the fullerene molecules. The Au clusters grow continually from a size of about 55 atoms for the early stages of growth up to 150 atoms for the deposition of a nominal coverage of 1.5 nm. These data are derived from an analysis of the d-band splitting and the Au 4f core-level shift due to delayed photohole relaxation. The thermal stability of the Au-clusters-covered fullerene film was investigated by annealing in situ up to temperatures of 650 degrees C. For temperatures up to 450 degrees C a continuous growth of the clusters is detected, which is accompanied by a slight drop in Au concentration in the range of XPS for annealing temperatures higher than 350 degrees C. This may be due to a ripening of the clusters. The presence of Au apparently delays fullerene sublimation. The film shows a very good thermal stability and even after annealing at 650 degrees C there is still a fullerene film detectable in the photoelectron spectroscopy spectra.

Ion beam induced modification of gold thin films deposited over polymers

In the present work we report on significant modifications of the surface structure of Au thin films deposited over polymers induced by heavy ion beam irradiation. Under 2 MeV Au + ion beam irradiation, performed with the target at 200 °C, the combination of RBS and AFM analysis demonstrates the formation of gold clusters with nanometric dimensions of about 115 nm size and 40 nm high. These clusters have irregular shapes and are randomly distributed over a heavy damaged polymer layer, with first neighboring distance of about 150 nm. Annealed material, at the same temperature and time, do not show the formation of these clusters. This fact gives support that an ion beam radiation process takes place.

Polyaniline-Gold Nanocomposite System

Nanostructured composite materials of polyaniline (PANI) with gold clusters of different sizes and amounts have been produced. PANI films of the same thickness were grown electrochemically on platinum substrates. Then nucleation of gold clusters in the PANI film was initiated by chemical reduction of tetrabromoaurate ion in acidic solution. The spontaneous process of gold cluster formation was evaluated using UV-vis spectroscopy, scanning electron microscopy, and the Kelvin probe. It was found that the amount and size distribution of gold clusters vary with immersion time. The measured work function of the PANI/Au composite changes its magnitude according to the changes in composition of the materials. Despite the fact that the preparation method makes the gold cluster growth difficult to control in size and in distribution, it is of interest to applications for solid-state potentiometric sensors, batteries, supercapacitors, or catalysis since it modifies the electron affinity of the synthesized conducting polymer/gold composite. © 2003 The Electrochemical Society. All rights reserved.

Amphipolar Core−Shell Cylindrical Brushes as Templates for the Formation of Gold Clusters and Nanowires

Methacryloyl end-functionalized block copolymers consisting of styrene and vinyl-2-pyridine were polymerized to poly(block co-macromonomer)s with a much higher main chain than side chain degree of ...

Can a thin film to be pinned at the surface by hollows?

Glass slices with a low roughness (∼0.2 nm) irradiated with swift heavy ions were studied by atomic force microscopy (AFM). Ion impacts are materialized by the formation of hollow structures having a maximal depth of ∼3 nm. In order to investigate the role played by such modifications on the surface properties, thin gold films of ∼2 nm thickness were deposited on both virgin and pre-irradiated samples. After annealing at 150 °C, a red shift is observed in the optical absorption of virgin samples indicating a gold cluster formation, whereas no significant modifications were observed in samples pre-irradiated with energetic Kr ions. By combining AFM observations with optical absorption spectroscopy we discuss in this paper the role played by topographic modifications on both the surface diffusion and the film wetting phenomena.

Electrochemical and Chemical Oxidation of Gold(I) Thiolate Phosphine Complexes: Formation of Gold Clusters and Disulfide

Electrochemical and Chemical Oxidation of Gold(I) Thiolate Phosphine Complexes: Formation of Gold Clusters and Disulfide

Gold cluster formation at the interface of a gold/Langmuir-Blodgett film/gold microsandwich resulting in Coulomb charging phenomena

Structural analysis of the cross section of gold/Langmuir-Blodgett (LB) polymer film/gold sandwich structures was performed using transmission electron microscopy (TEM), and the obtained results were complemented by electron transport investigations of the sandwich structures. The polymer film consisted of four to ten LB monolayers of a nonconducting polymer. TEM analysis of the sandwich cross section revealed a number of gold particles, 2–5 nm in size, formed during the fabrication process within the LB film close to the top electrode. Low temperature dc-transport measurements showed current-voltage (I-V) characteristics with equidistant steps that are not expected if the polymer film is thought to form a single laterally extended tunneling barrier between the metal electrodes. This feature can be understood, however, on the basis of the Coulomb blockade model applied to cluster-like metallic inclusions acting as an island separated from both Au electrodes by tunneling barriers.

Gold cluster formation using an atomic force microscope and its applications to GaAs whisker growth

Au clusters were formed on the GaAs(111)B substrate by the field evaporation of Au atoms using an atomic force microscope (AFM). The obtained clusters appeared as mounds with typical diameters of 100–150 nm and heights of 1.5 nm. Furthermore, GaAs whiskers were grown after annealing by using these clusters as seeds. However, the sites of whiskers did not correspond to the sites of the Au clusters existing before annealing and growth. These results indicate that Au cluster formation by the AFM method did some damage to the substrate and permitted Au to diffuse into the substrate at relatively low temperatures.

Radiation-induced and chemical formation of gold clusters

The kinetics of the γ-radiolytical or chemical reduction of AuIII Cl4-, or of the combination of both methods, is followed as a function of the experimental conditions through the time evolution of the surface plasmon spectrum of the gold nanoparticles formed or of their sizes as observed by AFM imaging. It appears from the discussion on the mechanism that even with the strongly reducing radiolytic radicals, the low valency AuI ions are somewhat protected by the more concentrated AuIII ions from reduction, up to a ratio of AuI/AuIII=1, and are stabilized for hours, unless clusters or 2-propanol (or PVA, but more slowly) catalyze their disproportionation. The cluster concentration increases correlatively with the dose.2-Propanol or PVA are mild reducing agents and are unable to reduce AuIII directly except at the surface of clusters, previously formed, for instance, by partial radiolytic reduction. In this case, the cluster concentration remains the same but the size obtained after reduction by the alcohol increases slowly with time up to 100–500 nm, as in a development process. In order to avoid the relative extent of this development, associated with chemical reduction and even with the direct γ-reduction of AuIII, in particular the AuI disproportionation and reduction steps, high dose rate radiolysis has been used up to total reduction of the same solutions. The mechanism of reduction and growth, step-by-step, is discussed.

Reduction of Gold in Concentrated LiCl

Reduction of gold from concentrated solutions of LiCl containing low gold concentration was investigated using electrochemical and microscopic techniques. Cyclic voltammetric measurements in solutions containing 0.5 mM Au in 6 M LiCl show two reduction peaks on both platinum and HOPG electrodes, indicating that the reduction of gold occurs in two steps. Chronocoulometric measurements on platinum electrodes give evidence of a two‐electron reaction in the region of the first reduction peak, whereas in the region of second peak a three‐electron reaction is approached. The morphology of deposited gold on highly oriented pyrolytic graphite (HOPG) substrates from solutions containing in 6 M LiCl was characterized using in situ scanning tunneling microscopy (STM). In situ STM images in the potential range of the first reduction peak show the formation of gold clusters weakly bound to the HOPG substrate. In the region of the second reduction peak an increase in the z‐range of the STM images was observed due to the formation of the three‐dimensional gold bulk phase. However no stable gold clusters could be imaged in situ in this potential range due to reproportionation of freshly deposited gold and Au(III) from the electrolyte to form Au(I).

Preparation and decomposition of gold(I) hydrazido complexes: gold cluster formation

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPreparation and decomposition of gold(I) hydrazido complexes: gold cluster formationVisalakshi Ramamoorthy, Zhidan Wu, Yang Yi, and Paul R. SharpCite this: J. Am. Chem. Soc. 1992, 114, 4, 1526–1527Publication Date (Print):February 1, 1992Publication History Published online1 May 2002Published inissue 1 February 1992https://doi.org/10.1021/ja00030a084RIGHTS & PERMISSIONSArticle Views382Altmetric-Citations38LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Formation of gold clusters in the ionized clusterbeam deposition technique

The unique aspect of the ionized cluster beam (ICB) thin film depositionmethod is that material is deposited from a beam of atom clusters, a fraction of which are ionized and accelerated to the substrate. A large number of different material films have been deposited to research the ICB method and advantages in film formation have been claimed. However, because methods for measuring cluster size distribution in film deposition instruments have been under development, the presence of clusters in the depositing beam normally has been inferred from theory rather than measured directly. Thus it is not yet clear whether interesting ICB film effects were due to clusters or other factors. A new measurement method which overcomes many of the difficulties of previous methods is developed in this work. Gold clusters up to an average of 3 gold atoms per ionized cluster have been formed and detected. Cluster size increased with crucible pressure and attempts to achieve larger clusters are underway.