Compact Gold Research Articles

Measurement of 2p-3d absorption in a hot molybdenum plasma

We present measurements of the 2p-3d transition opacity of a hot molybdenum–scandium sample with nearly half-vacant molybdenum M-shell configurations. A plastic-tamped molybdenum–scandium foil sample is radiatively heated to high temperature in a compact D-shaped gold Hohlraum driven by ∼30 kJ laser energy at the SG-100 kJ laser facility. X rays transmitted through the molybdenum and scandium plasmas are diffracted by crystals and finally recorded by image plates. The electron temperatures in the sample in particular spatial and temporal zones are determined by the K-shell absorption of the scandium plasma. A combination of the IRAD3D view factor code and the MULTI hydrodynamic code is used to simulate the spatial distribution and temporal behavior of the sample temperature and density. The inferred temperature in the molybdenum plasma reaches a average of 138 ± 11 eV. A detailed configuration-accounting calculation of the n = 2–3 transition absorption of the molybdenum plasma is compared with experimental measurements and quite good agreement is found. The present measurements provide an opportunity to test opacity models for complicated M-shell configurations.

Self-assembled PVP-gold nanostar films as plasmonic substrates for surface-enhanced spectroscopies: influence of the polymeric coating on the enhancement efficiency.

Colloidal nanoparticles exhibiting anisotropic morphologies are preferred in the structural design of spectroscopically active substrates due to the remarkable optical properties of this type of nano-object. In the particular case of star-like nanoparticles, their sharp tips can act as antennae for capturing and amplifying the incident light, as well as for enhancing the light emitted by nearby fluorophores or the scattering efficiency of Raman active molecules. In the current work, we aimed to implement such star-shaped nanoparticles in the fabrication of nanoparticle films and explore their use as solid plasmonic substrates for surface-enhanced optical spectroscopies. High-density, compact and robust self-assembled gold nanostar films were prepared by directly depositing them from aqueous colloidal suspension on polystyrene plates through convective self-assembly. We investigated the role of the polymeric coating, herein polyvinylpyrrolidone (PVP), in the particle assembly process, the resulting morphology and consequently, the plasmonic response of the obtained films. The efficacy of the plasmonic films as dual-mode surface-enhanced fluorescence (SEF) and surface-enhanced Raman scattering (SERS) substrates was evidenced by testing Nile Blue A (NB) and Rhodamine 800 (Rh800) molecular chromophores under visible (633 nm) versus NIR (785 nm) laser excitation. Steady-state and time-resolved fluorescence investigations highlight the fluorescence intensity and fluorescence lifetime modification effects. The experimental results were corroborated with theoretical modelling by finite-difference time-domain (FDTD) simulations. Furthermore, to prove the extended applicability of the proposed substrates in the detection of biologically relevant molecules, we tested their SERS efficiency for sensing metanephrine, a metabolite currently used for the biochemical diagnosis of neuroendocrine tumors, at concentration levels similar to other catecholamine metabolites.

OXYGEN REDUCTION ON THE SURFACE OF Fe3O4&Au NANOCOMPOSITES

Functional materials based on ferromagnetics and noble metals are attractive due to their unique optical, catalytic and magnetic properties. Nowadays these materials find their application in various fields of science and technology: medicine, biotechnology, chemistry, physics and energy sector. The aim of the present work is to study the electrochemical characteristics of the oxygen reduction on the surface of Fe3O4&Au nanocomposites. The formation of the composite particles took place on the surface of a rotating steel disk which was in contact with HAuCl4 aqueous solution and air. Initial gold concentration was varied from 0.2 to 10.0 mg/l. Oxygen reduction was studied on a floating gas diffusion electrode (pressed carbon black P803 + 30 % PTFE) with surface, modified by prepared Fe3O4&Au nanocomposites, in 1 M KOH solution at 20 ºC. Electrochemical measurements were carried out using a PI-50-1.1 potentiostat.
 Tafel slopes of the stationary polarization curves ∂E/∂lgj of oxygen reduction on the electrode modified by composites formed at с(Au3+) from 0.2 to 5.0 mg/l lay in the ranges: b1 = 0.048 – 0.060 V, b2 = 0.119 – 0.131 V. When nanocomposites were obtained at с(Au3+) from 7.0 to 10 mg/l these values were: b1 = 0.042 –0.061 V, b2 = 0.079 – 0.105 V. It was concluded that oxygen reduction mechanism is multistep and includes formation of the hydrogen peroxide as intermediate. Obtained b1 and b2 values indicate that electrode process me-chanism changes when current density grows.
 The largest exchange current (8.51∙10–3 A/g) was achieved when electrode was modified by composite formed at с(Au3+) = 1.0 mg/l, whereas when the composite formed at с(Au3+) = 10.0 mg/l was used, the j0 value was smallest. Perhaps, the increase in the initial Au3+ concentration during nanocomposite formation led to an increase in the number of separate gold clusters on the surface of Fe3O4 nanoparticles and to raise of composite catalytic activity. But when с(Au3+) exceeded 1.0 mg/l the core-shell Fe3O4&Au composites with compact gold shell were formed. Such coreshall composites had lower catalytic activity in the oxygen reduction than composites with separate gold clusters on the surface of Fe3O4 particles.

Comparison study of gold coatings prepared by traditional and modified galvanic replacement deposition for corrosion prevention of copper

Gold coating is one of the choices to prevent copper circuit in PCBs from corrosion. Although galvanic replacement deposition is supposed to be a convenient method to prepare gold coating on copper circuit, compact gold coating is hard to be obtained through traditional galvanic replacement deposition. In this work, gold coatings were prepared on copper substrates through traditional and modified galvanic replacement deposition. According to the SEM, EDS, XPS and XRD tests, the gold coating prepared by traditional galvanic replacement deposition had lots of micropores and nanopores, and Cu-Au solid solution phase was generated on copper substrate other than the gold phase. Therefore, the gold coating prepared by traditional galvanic replacement deposition could not prevent copper substrate from corrosion, but slightly increased the corrosion current density of copper substrate in 3.5 wt% NaCl solution owing to the galvanic corrosion. However, compact gold coating could be obtained through modified galvanic replacement deposition, in which aluminum foil was contacted to the copper substrate to form galvanic couple and donated the electrons for the deposition of gold instead of the copper substrate. The SEM, EDS, XPS and XRD tests demonstrated the gold coating prepared by modified galvanic replacement deposition was compact and mainly composed of pure gold phase. The gold coating prepared by modified galvanic replacement deposition obviously enhanced the corrosion resistance of copper substrate, and it reduced the corrosion current density of copper substrate in 3.5 wt% NaCl solution to 1.773 μA·cm−2 from 87.40 μA·cm−2 with the corrosion inhibition efficiency of 98.0%.

Calculation of water equivalent ratios for various materials at proton energies ranging 10–500 MeV using MCNP, FLUKA, and GEANT4 Monte Carlo codes

Dosimetry of proton beams is generally evaluated in liquid water, or alternatively in solid phantoms via water equivalent ratios (WER). WER is defined as the ratio of proton range in liquid water to that in a phantom of certain material. Presently, WER is not available in the literature neither for a wide range of energies nor for variety of relevant materials. Thus, the goal of this study is to provide such data through Monte Carlo simulations. WER is calculated for 10–500 MeV energies for compact bone, adipose tissue, polymethyl methacrylate (PMMA), PTFE (teflon), graphite (C), aluminum (Al), copper (Cu), titanium (Ti), and gold (Au) using MCNPX.2.70, GEANT4, and FLUKA Monte Carlo (MC) codes. The MCNPX code was considered as the reference to which other codes were compared. The mean values of WER obtained through the MCNPX simulations for Au, Cu, Ti, Al, PTFE, graphite, PMMA, bone, and adipose tissue were 8.83, 5.40, 3.18, 2.03, 1.87, 1.52, 1.13, 1.71, and 0.96, respectively, for 10–500 MeV energy range. The maximum deviations of WER values between MCNPX and GEANT4 results were about 6.85% for adipose tissue at energies <20 MeV, whereas they were about 7.74%, 7.74% between MCNPX and FLUKA, for adipose and Al, respectively. This inter-code uncertainties are mainly due to different physic models and stopping powers in each code. Comparing the results to that in the literature, the range of discrepancy was found to be 0–8% with greatest discrepancy for Au. Based on the materials evaluated, the PMMA remained the closest to water, for a non-tissue solid material, with an average WER of 1.13, for proton energy ranging 10–500 MeV.

Electrochemical Behavior of Aromatic Compounds on Nanoporous Gold Electrode

This study aimed at investigating the electrochemical behavior of benzene and its substituted derivatives on nanoporous gold and assessing the possibility of utilizing this electrode as a platform for simultaneous detection of different aromatic compounds. Cyclic voltammetric studies were performed with benzene, hydroquinone, catechol, phenol, 2-aminophenol, 2-chlorophenol as well as their mixtures on the nanoporous gold prepared from dealloying of AuxSi1-x films. The nanoporous structure was found to provide enhanced electro-oxidation of hydroquinone, catechol, phenol, 2-aminophenol and 2-chlorophenol and remarkable fouling resistance in the electro-oxidation of phenol and 2-aminophenol compared to the compact and flat gold electrode. Interestingly, oxidation potentials of these aromatics appear to be affected significantly by the attachment of functional groups to the benzene ring. Based on the onset oxidation potentials, the easiness of oxidation at nanoporous gold was found to follow the order: hydroquinone > catechol > 2-aminophenol > 2-chlorophenol, phenol > benzene. Moreover, nanoporous gold was found to be advantageous over nanoporous platinum for potential application in simultaneous analysis employing voltammetric techniques as it could offer discernable peak potential separation in the electro-oxidation of the different aromatics.

Approach to Fabricating a Compact Gold Nanoparticle Film with the Assistance of a Surfactant.

We report a facile method to fabricate a compact Au nanoparticle film with the assistance of surfactants. First, the dodecanethiol-coated Au nanoparticles were floated on the surface of the toluene/acetonitrile solvent mixture and adjusted to an expanded dispersion by changing the mixture ratio. Silicone oil was then added as a surfactant to compress the floating nanoparticles from the original loose status to a closely packed arrangement that produced a compact nanoparticle film. The relationship of the compressed film area to the silicone oil concentration was plotted and compared to the surface tension curve of silicone oil. The results were quite consistent, suggesting that the surface location of the surfactant induced the nanoparticles' compression. The resulting nanoparticle film was uniform and sufficiently robust to be transferred to the solid substrate. Moreover, it could be applied to catalyze the reduction of 4-nitrophenol. Our study indicated that the utilization of surfactants to compress the well-dispersed nanoparticles on the liquid surface is a simple, fast, and adaptable method of fabricateing compact nanoparticle films with great promise for future applications.

Hollow Gold Cages and Their Topological Relationship to Dual Fullerenes.

Golden fullerenes have recently been identified by photoelectron spectra by Bulusu et al. [S. Bulusu, X. Li, L.-S. Wang, X. C. Zeng, PNAS 2006, 103, 8326-8330]. These unique triangulations of a sphere are related to fullerene duals having exactly 12 vertices of degree five, and the icosahedral hollow gold cages previously postulated are related to the Goldberg-Coxeter transforms of C20 starting from a triangulated surface (hexagonal lattice, dual of a graphene sheet). This also relates topologically the (chiral) gold nanowires observed to the (chiral) carbon nanotubes. In fact, the Mackay icosahedra well known in gold cluster chemistry are related topologically to the dual halma transforms of the smallest possible fullerene C20 . The basic building block here is the (111) fcc sheet of bulk gold which is dual to graphene. Because of this interesting one-to-one relationship through Euler's polyhedral formula, there are as many golden fullerene isomers as there are fullerene isomers, with the number of isomers Niso increasing polynomially as O(Niso9 ). For the recently observed Au16- , Au17- , and Au18- we present simulated photoelectron spectra including all isomers. We also predict the photoelectron spectrum of Au32- . The stability of the golden fullerenes is discussed in relation with the more compact structures for the neutral and negatively charged Au12 to Au20 and Au32 clusters. As for the compact gold clusters we observe a clear trend in stability of the hollow gold cages towards the (111) fcc sheet. The high stability of the (111) fcc sheet of gold compared to the bulk 3D structure explains the unusual stability of these hollow gold cages.

Rapid Fabrication of Gold Nanoflowers Tuned by pH: Insights Into the Growth Mechanism.

We reported a one-pot, no added seeding and green method to synthesize gold nanoflowers, in which HAuC4 and H2O2 were added one by one into the alkaline protocatechuic aldehyde solution at room temperature. Au(III) was partially reduced by protocatechuic aldehyde to produce primary Au nanocrystals, and then Au nanocrystals agglomerated into loose flower-like nanoparticles as seeds, which catalyzed H2O2 reduction of the residual Au(III), thus accelerating the formation of compact 3D gold nanoflowers. The key synthesis strategy was to use protocatechuic aldehyde as a structure-induced agent to influence the growth of gold nanoflowers. The pH value of growth solution could tune the size and/or morphology of gold nanoflowers through its influence on the adhesion force of protocatechuic aldehyde on gold surfaces and the species type of Au(III) complexes. When the pH value of growth solution was above 7.26 (the pKa of protocatechuic aldehyde), the flower-like of gold nanostructural architectures with different sizes could be fabricated. The obtained gold nanoflowers had a large dimension of 198 and 157 nm at the pH of 7.6 and 8, respectively. Size control of gold nanoflowers can be accomplished in the growth solutions of pH 9.4-12.0 with a similar diameter around 60 nm. The as-synthesized gold nanoflowers exhibited good stability and have the prospects for surface-enhanced Raman scattering enhancement.

Preparation and characterization of magnetic gold shells using different sizes of gold nanoseeds and their corresponding effects on catalysis

The effect of gold nanoseeds with different sizes on the gold shell was investigated. Gold nanoparticles of two different sizes (∼3 nm and ∼15 nm) were prepared and attached to the surface of amine functionalized silica coated iron oxide nanoparticles. The gold nanoparticles assembled on the surface were used as seeds for further gold shell formation. It was observed that the amount of Au attached to iron oxide nanoparticles is higher for bigger gold nanoseeds as compared to smaller gold nanoseeds. Similarly, after the formation of gold shell, a higher amount of Au was found for larger gold nanoparticles. However, both transmission electron microscopy (TEM) and scanning electron microscopy (SEM) results show that a complete, uniform, and compact gold shell was formed in the case of using small gold nanoseeds, but for larger gold nanoseeds the shell formed was discontinuous and was not uniform, while most of the gold nanoparticles were found to be aggregated on the surface. The nanocomposites showed high efficiency in catalysis for the reduction of 4-nirophenol, among which Nanocomp-2, with a thin stable gold shell showed excellent catalytic activity and reusability. All of the nanocomposites have high magnetization values and can be easily separated from the reaction mixture using a magnet and can be reused.

Nucleated crystallization of isotactic polypropylene in multilayered sandwich nanocomposites with gold particles

AbstractNucleation of isotactic polypropylene (PP) crystallization by gold particles with various sizes and shapes was studied. The morphology of gold particles ranged from microcrystals with well‐developed crystal facets (AuMC) to vacuum‐sputtered 5 nm gold nanoparticles (AuNP), 30 nm gold nanoislands (AuNI), and compact gold nanolayer (AuNL). To minimize agglomeration of Au particles in molten PP, the nucleated crystallization was studied by means of the improved sandwich method, which consisted in the controlled deposition of a homogeneous nucleant layer between ∼ 100 μm PP films, followed by the careful thermal treatment and the evaluation of the nucleation activity by three independent methods: polarized‐light microscopy, two‐dimensional wide‐angle X‐ray scattering, and differential scanning calorimetry. It was demonstrated that the nucleating activity of gold strongly depended on its morphology: The nucleation effect of microcrystalline AuMC resulted in a transcrystallization comparable to that caused by a strong commercial α‐nucleant (Hyperform HPN‐68), whereas the effect of vacuum‐sputtered layers of nanocrystalline AuNL, AuNI, and AuNP was extremely weak. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Synthesis of Core-Shell Gold Nanoparticles with Maltose-Modified Poly(Ethyleneimine)

The synthesis of ultrafine gold nanoparticles in presence of maltose-modified hyperbranched poly(ethyleneimines) (PEI) is described. The polymer acted as both a reducing and stabilising agent in the particle formation process. The nanoparticles were characterized by means of dynamic light scattering (DLS), transmission electron microscopy (TEM), analytical ultracentrifugation (AUC), small-angle x-ray scattering (SAXS), and small-angle neutron scattering (SANS). The mechanism of nanoparticle formation can be described in two steps. The reduction process of the Au3+ ions located in the inner coil region of the hyperbranched PEI led to the formation of a compact gold core, and is accompanied by a collapse of the polymer coil. Therefore, in the subsequent reduction process a gold-polymer hybrid shell is formed. By using the PEI of higher molar mass, core-shell gold nanoparticles of about 3.6 nm size with a more narrow size distribution and special fluorescence behavior could be synthesized.

DMH镀金体系在ICF空腔靶中的应用

Gold plating using DMH as complexing agent has been applied to hohlraum target. The effects of bath compositions and operating conditions on gold plating quality were investigated by scanning electron microscopy and coulometric measurement. The results show that the gold plating bath is stable. Uniform and compact gold deposits are formed in the bath containing 8 g/L gold salt and 80 g/L DMH at the cathode current density of 1.5 A/dm2, pH level of 9-10 and bath temperature of 45 ℃.

Corrosion under mixed flowing gas conditions of various connector coatings

AbstractThis paper presents an investigation on the corrosion performance of Ni/Au, NiP/Au, Ni/NiP/Au and Ni/NiPd/Au electrical connector coating systems. The coating systems were exposed to 10 days Class III mixed flowing gas and were subsequently examined by X‐ray diffraction, focused ion beam microscopy, scanning electron microscopy and energy dispersive spectroscopy to evaluate the performance of each coating system. The Ni/Au coating system showed the worst performance followed by NiP/Au and Ni/NiP/Au. The Ni/NiPd/Au coated connector materials exhibited the least surface corrosion and this was attributed to a number of factors including a thicker coating system, more compact gold layer with fewer defects and a reduction in the electrochemical potential difference between layers reducing the local cell effect.

Aggregation of polymer-grafted nanoparticles in good solvents: A hierarchical modeling method

Brownian dynamics simulations are carried out to study the aggregation behavior of polymer-grafted nanoparticles (NPs) in good solvents by using the coarse-grained model derived from the all-atom force field, according to the hierarchical modeling strategy, and here PEG-grafted gold nanoparticles (GNPs) were taken as an example. Generally, grafting PEG to the surface of GNPs is to protect them from aggregation in the solution. However, our results reveal that PEG-grafted GNPs may also aggregate when concentration increases. Our simulations indicate that there exists a critical aggregating concentration (CAC), beyond which the PEG-grafted GNPs will aggregate. We further check the effects of grafting density and the length of grafted chains on the aggregation behavior of the grafted GNPs, and find that there exists an optimized length of grafted chain, at which the system has the maximal CAC. Furthermore, the aggregate size of self-assembled mesostructures formed by the grafted GNPs increases with the concentration. Interestingly, it is observed that the aggregation favors to form linear gold nanowires rather than compact gold nanoclusters, and the corresponding mechanism is also addressed. It is expected that this work would provide useful information for the fabrication of metal nanowires and the surface modification of metal nanoparticles.

Facile Synthesis of Gold Nanoflowers in a Polyvinyl Pyrrolidone Alkaline Aqueous Solution

Three-dimensional (3D) gold nanoflowers of 60-80 nm in diameter were successfully synthesized using polyvinyl pyrrolidone (PVP) as both a protecting agent and a reducing agent in alkaline aqueous solutions. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images revealed that many antennae of 10-15 nm existed on their surfaces. X-ray diffraction (XRD) pattern suggested face-centered cubic (fcc) structures for these gold nanoflowers. The selected area electron diffraction (SAED) pattern of a single gold nanoflower indicated polycrystal characteristics. We found that there were three key stages in the growth of the gold nanoflowers: primary nanocrystals agglomerated to form multipod-like nanoparticles, and then the multipod-like nanoparticles aggregated into loose flower-like nanoparticles that ultimately grew into compact gold nanoflowers through Ostwald ripening. During the synthesis of gold nanoflowers, the molar ratios of PVP/HAuCl4 at fixed HAuCl4 and NaOH concentrations mostly influenced the morphologies of the final products. Therefore, a proper molar ratio of PVP/HAuCl4 and a suitable NaOH concentration were essential for the synthesis of typical gold nanoflowers with controlled sizes and antenna architectures.

Electrodeposition of bright gold—a green path using hypoxanthine as a complexing agent

A simple, low cost, stable and environmentally friendly gold plating electrolyte containing hypoxanthine as a complexing agent is introduced. Bright and compact gold deposits could be obtained by using PEI-1800 and SUNO (a compound that contains the element sulfur) as additives for electrodepositing gold on a nickel substrate.

Optimization of layer structure supporting long range surface plasmons for surface plasmon-enhanced fluorescence spectroscopy biosensors

Long range surface plasmons (LRSPs) are optical waves that propagate along thin metallic films with up to orders of magnitude lower damping compared to regular surface plasmons. Therefore, LRSPs attracted a great deal of attention for development of ultrasensitive biosensors based on surface plasmon resonance and surface plasmon-enhanced fluorescence spectroscopy (SPFS). In this article, the authors investigate the excitation of LRSPs on a biosensor-compatible layer structure consisting of a Cytop fluoropolymer, thin gold film modified by thiol self-assembled monolayer for coupling of receptor biomolecules, and an aqueous sample on its top. The morphology, and optical and electrical properties of the layer structure are determined and related to the performance of a SPFS biosensor. Through increasing the surface energy of Cytop fluoropolymer by O2 plasma, more compact gold films that exhibit lower roughness were prepared which resulted in a higher binding capacity, decreased nonspecific adsorption of biomolecules to the biosensor surface, and in a larger enhancement of electromagnetic field intensity accompanied with the excitation of LRSPs. The authors show that by improving the quality of a gold film supporting LRSPs, the fluorescence signal can be enhanced up to sixfold with respect to regular SPFS biosensors.

The role of dimensionality on the quenching of spin-orbit effects in the optics of gold nanostructures

By first-principles time-dependent density-functional calculations, we show the relevance of relativistic effects to shape the photoabsorption cross section of small gold clusters (Au(n), n < or = 8, and n = 20) and small nanowires (n < or = 7). The relativistic effects not only dictate the stabilization of planar geometries (as it has already been shown by treating the core electrons relativistically): The spin-orbit coupling also has a strong impact in the absorption spectra (resonances and oscillator strengths). This is especially true for nanowires, where the effect of spin orbit is large and not substantially reduced with the chain length, in contrast to more compact gold clusters where this spin-orbit effect tends to be quenched. These results have far reaching consequences in fields such as electronic transport, where gold nanowires are often used, but where spin-orbit effects are generally disregarded.

Ion formation by high velocity impacts on porous metal targets

In impact ionization studies the target normally consists of a metal surface of compact solid density. In the present experiments, we investigate the use of a layer of a highly porous structure of nanometre-sized grains, sometimes also called “metal black”, as an alternative target. In our comparative experiments, spherical iron particles (0.1< d p<1.5 μm) were shot with velocities 2–30 km/s onto both a compact solid silver plate and a silver metal black layer of about 7 μm thickness (grain size 20–40 nm, mean density ≈1 g/cm 3), deposited on a compact solid gold plate. Impact generated ions were analysed by means of time-of-flight mass spectrometry. The results reveal important advantages of the porous black layer, such as better mass resolution and a larger amount of ions from the impacting particle. Therefore metal blacks may be very suitable targets for the purposes of identification and characterisation of the impacting particle's composition. An attempt is made to give a physical explanation of the results in the frame of existing empirical ionization models. The study is part of a programme to improve devices for in-situ analysis of fast moving cosmic dust particles.