Inhibition effect of self-assembled films formed by gold nanoparticles on iron surface

The self-assembled (SA) films formed by gold nanoparticles on iron surface had been proved to have inhibition effect for the substrate in 0.5 M H₂SO₄ solutions. The inhibition action was investigated using electrochemical impedance spectroscopy (EIS). The SA films formed by gold nanoparticles protected with sodium oleate had better corrosion protection to the iron substrate than only by sodium oleate. Scanning electron microscopy (SEM) was used to observe the imagines of the SA films. In addition, it was found that the gold nanoparticles could influence the nickel electroless plating films on the iron substrate. The structure and composition of the plating films were test by electron probe microanalyzer (EPMA). The mechanisms of the formation of the SA films and the nickel electroless plating reaction were also discussed.     

Formation of gold nanoparticles in heat-treated reactive co-sputtered Au-SiO2 thin films

In this work, formation of gold nanoparticles in radio frequency (RF) reactive magnetron co-sputtered Au-SiO₂ thin films post annealed at different temperatures in Ar + H₂ atmosphere has been investigated. Optical, surface topography, chemical state and crystalline properties of the prepared films were analyzed by using UV-visible spectrophotometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and X-ray diffractometry (XRD) techniques, respectively. Optical absorption spectrum of the Au-SiO₂ thin films annealed at 800 °C showed one surface plasmon resonance (SPR) absorption peak located at 520 nm relating to gold nanoparticles. According to XPS analysis, it was found that the gold nanoparticles had a tendency to accumulate on surface of the heat-treated films in the metallic state. AFM images showed that the nanoparticles were uniformly distributed on the film surface with grain size of about 30 nm. Using XRD analysis average crystalline size of the Au particles was estimated to about 20 nm.     

Model for UV induced formation of gold nanoparticles in solid polymeric matrices

UV irradiation of polymeric PMMA films containing HAuCl₄ followed by annealing at 60-80 °C forms gold nanoparticles directly within the bulk material. The kinetics of nanoparticle formation was traced by extinction spectra of nanocomposite film changes vs annealing time. We propose that UV irradiation causes HAuCl₄ dissociation and thus provides a polymeric matrix with atomic gold. The presence of an oversaturated solid solution of atomic gold in the polymeric matrix leads to Au nanoparticle formation during annealing. This process can be understood as a phase transition of the first order. In this paper we apply several common kinetic models of the phase transition for describing Au nanoparticle formation inside the solid polymer matrix. We compare predictions of these models with the experimental data and show that these models cannot describe the process. We propose that the stabilization effect of the matrix on the growing gold nanoparticles is important. The simplest model introducing some probability for the transition from growing nanoparticle to the non-growing, stabilized form is suggested. It is shown that this model satisfactorily describes the experimentally observed evolution of the extinction spectrum of Au nanoparticles forming in a polymer matrix.     

Hybrid Nanoparticle Film Material

A new hybrid material consisting of a nanoparticle film on a flexible, porous substrate is formed. The hybrid nanoparticle films are non-redispersable in solvents, yet remain porous and flexible. Visually, the hybrid films are highly reflective and metallic gold in appearance. However, the electronic properties of the films are characteristic for materials made from separate, non-sintered nanoparticles. Films of large area (several tens of cm²) and several microns in thickness can be formed. The method of formation is based on cross-linking gold nanoparticles using alkane-dithiols followed by filtration onto nanoporous supports. The films were characterized by transmission electron microscopy, atomic force microscopy and resistance measurements. The effect of the ratio of alkane-dithiol cross-linker to gold nanoparticles on the resistance of the nanoparticle films was also studied.     

Plasma-activated core-shell gold nanoparticle films with enhanced catalytic properties

Catalytically active gold nanoparticle films have been prepared from core-shell nanoparticles by plasma-activation and characterized by high-resolution transmission electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Methane can be selectively oxidized into formic acid with an O₂–H₂ mixture in a catalytic wall reactor functionalized with plasma-activated gold nanoparticle films containing well-defined Au particles of about 3.5 nm in diameter. No catalytic activity was recorded over gold nanoparticle films prepared by thermal decomposition of core-shell nanoparticles due to particle agglomeration.     

Gold-Containing Nanocomposition Materials on the Basis of Homo- and Copolymers of Methylmethacrylate

Films of polymethyl methacrylate and methyl methacrylate copolymers with ethylhexyl acrylate doped with HAuCl₄ were subjected to UV irradiation followed by thermal treatment at various temperatures. The films were studied by absorption spectroscopy and small-angle X-ray scattering. The photolysis of HAuCl₄ was found to result in the formation of gold nanoparticles, whose size depended on the structure of the polymeric matrix. An increase in the free volume of polymers caused the formation of larger particles.     

Blood Compatibility of Multilayered Polyelectrolyte Films Containing Immobilized Gold Nanoparticles

Surface material functionalization including layer‐by‐layer (LbL) polyelectrolyte films with incorporated nanoparticles is a growing field with a wide range of biomedical applications: drug reservoirs, medical devices, or tissue engineering. In parallel, gold nanoparticles (AuNPs) can be grafted by drugs and sensitive molecules using simple protocols. This study shows that AuNP behavior is modified when they are entrapped into three partner LbL films in comparison to the colloidal solution. A polycationic (polyallylamine hydrochloride (PAH)) and a polyanionic (polyacrylic acid (PAA)) polymer is used to build films based on three cycles ((PAH/AuNP/PAA)₃). To investigate the interaction with biomolecules and cells, three different films are developed changing the outer layer (either PAH or AuNP or PAA) with the same number of AuNP deposit. The best biocompatibility is observed with a polyacrylic acid outer layer. Due to the high capacity of drug grafting on gold nanoparticles, the results seem promising for the development of nanostructured biomedical devices.     

Interaction of Gaseous Reagents on Gold and Nickel Nanoparticles

The adsorption and interaction of hydrogen, carbon monoxide, and oxygen with gold and nickel nanoparticles is studied by scanning tunneling microscopy and spectroscopy. It is established that the HCO radical is formed on gold nanoparticles by the reaction between adsorbed H₂ and CO, which is subsequently oxidized by oxygen to water and CO₂. At the same time, after exposure to H₂ and CO, nickel nanoparticles coated with oxide are reduced. The formation of adsorbed HCO on such nanoparticles is not observed.     

Stable multilayer thin films composed of gold nanoparticles and lysozyme

It needs appropriately attractive forces to construct multilayer thin films by layer-by-layer (LBL) assembly technique. It is feasible to prepare multilayer thin films on glass slides with negatively charged gold nanoparticles and positively charged lysozyme through the electrostatic LBL assembly technique. The gold nanoparticles/lysozyme multilayer thin films are highly stable; immersion in 0.1 M HCl, NaOH, and surfactant sodium dodecyl sulfate aqueous solutions cannot destroy the films. The highly stable gold nanoparticles/lysozyme multilayer thin films have potential application in long-term antibacterial coating.     

Analysis of gold films used in microcircuit chip-attachment

ESCA and SEM were used to evaluate various gold deposition methods and different backside die preparations on the adhesion of backside gold films. Results indicate that poor die-attachment yield is most likely caused by an intermediate SiO₂ film which forms between the silicon die and gold film. Data indicate that sputtered gold films are much better than vacuum evaporated films at preventing the formation of this intermediate oxide. Formation of the gold-silicon eutectic using a RTA immediately after the gold deposition allows vacuum evaporated films to perform as reliably as sputtered films.     

Size control synthesis of starch capped-gold nanoparticles

Metallic gold nanoparticles have been synthesized by the reduction of chloroaurate anions [AuCl₄]⁻ solution with hydrazine in the aqueous starch and ethylene glycol solution at room temperature and at atmospheric pressure. The characterization of synthesized gold nanoparticles by UV–vis spectroscopy, high resolution transmission electron microscopy (HRTEM), electron diffraction analysis, X-ray diffraction (XRD), and X-rays photoelectron spectroscopy (XPS) indicate that average size of pure gold nanoparticles is 3.5 nm, they are spherical in shape and are pure metallic gold. The concentration effects of [AuCl₄]⁻ anions, starch, ethylene glycol, and hydrazine, on particle size, were investigated, and the stabilization mechanism of Au nanoparticles by starch polymer molecules was also studied by FT-IR and thermogravimetric analysis (TGA). FT-IR and TGA analysis shows that hydroxyl groups of starch are responsible of capping and stabilizing gold nanoparticles. The UV–vis spectrum of these samples shows that there is blue shift in surface plasmon resonance peak with decrease in particle size due to the quantum confinement effect, a supporting evidence of formation of gold nanoparticles and this shift remains stable even after 3 months.     

Effect of nanoparticle dispersion on glass transition in thin films of polymer nanocomposites

We present spectroscopic ellipsometry measurements on thin films of polymer nanocomposites consisting of gold nanoparticles embedded in poly(styrene). The temperature dependence of thickness variation is used to estimate the glass transition temperature, T _g . In these thin films we find a significant dependence of T _g on the nature of dispersion of the embedded nanoparticles. Our work thus highlights the crucial role played by the particle polymer interface morphology in determining the glass transition in particular and thermo-mechanical properties of such nanocomposite films.     

UV-radiation-induced formation of gold nanoparticles in a three-dimensional polymer matrix

The possibility of generation of a surface plasmon resonance by gold nanoparticles in a 3D network polymer matrix upon irradiation of a liquid acrylic composition containing a dissolved Au³⁺ salt is demonstrated for the first time. UV-irradiation of the solution simultaneously causes gold photoreduction to Au⁰ and acrylate photopolymerization. The possibility of preparing transparent colorless films that, when heated or exposed to light, give rise to a visible-spectrum absorption band belonging to a plasmon resonance of metal nanoparticles is demonstrated. The intensity and position of the plasmon resonance band depend on the parameters of the 3D polymer network, chemical structure of the oligomer, type of the support, and conditions of formation of Au⁰ particles. The formation of reduced gold nanoparticles responsible for the plasmon resonance band occurs more effectively in low-density networks with a large interchain length and containing oligomer block capable of complexation with the metal. The formation of nanoparticles is affected by the chlorine-containing products of the reduction of the gold salt.     

Au nanoparticles in PMMA matrix: In situ synthesis and the effect of Au nanoparticles on PMMA conductivity

Thin PMMA films with and without gold nanoparticles were subjected to ±10 V d.c. and a.c. (square wave) excitations in various frequencies while recording their XPS spectra, and the resulting differences due to charging were examined. Both pure PMMA films and films containing gold nanoparticles showed charging shifts, but those of pure PMMA were more extensive than of PMMA containing gold nanoparticles, suggesting enhanced conductivity, induced by the incorporated gold nanoparticles. Non-charging behavior for these films was also observed with the increase of gold nanoparticle concentration. Gold nanoparticles were in situ synthesized and photo-patterned within the polymer films by UV irradiation.     

Step-addition Method for Enhancing the Yield of Gold Nanoparticles in Block Copolymer Solution

Triblock copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) has been used to synthesize gold nanoparticles from hydrogen tetrachloroaureate (III) hydrate (HAuCl₄·3H₂O) salt in aqueous solution at room temperature. Measurements were performed using the triblock copolymer Pluronic P85 (EO₂₆PO₃₉EO₂₆) at a fixed concentration (1 wt%) mixed with varying HAuCl₄·3H₂O concentration in the range of 0.001 to 0.1 wt%. The surface plasmon resonance (SPR) band in UV-visible absorption spectra confirmed the formation of the gold nanoparticles. The maximum yield of the nanoparticles was found at 0.005 wt% of the salt solution. Small-angle neutron scattering (SANS) does not show any significant change in the scattering profile in these suspensions of the nanoparticles. A similar behavior was also observed in dynamic light scattering (DLS) experiments where autocorrelation function was found to be independent of the salt concentration. This can be understood since a high-block copolymer-to-gold ion ratio (r ～ 22) is required in the reduction reaction to produce gold particles. As a result, a very small fraction of the block copolymers were associated with the gold nanoparticles, and hence lead to a very low yield. Both SANS and DLS basically see the micelles of most of these block copolymers, which are not associated with nanoparticles. Based on this explanation, a step-addition method was used to enhance the yield of gold nanoparticles by manifold, where the gold salt is added in small steps to maintain higher value of r (>22), and therefore continuous formation of nanoparticles.     

Enhancement of activity of platinum towards oxidation of ethanol by supporting on titanium dioxide containing phosphomolybdate-modified gold nanoparticles

A new concept of utilization of titanium dioxide matrix in electrocatalysis by admixing it with polyoxometallate modified gold nanoparticles is described here. The approach utilizes Keggin-type phosphododecamolybdate (PMo₁₂O₄₀³⁻) adsorbates capable of modifying, activating and stabilizing Au nanoparticles of the sizes of 30-40 nm. Ultra-thin films of phosphomolybdates on nanostructured gold are characterized by well-defined fast (reversible) multi-electron electrochemical reactions. By dispersing platinum black over the Au-containing TiO₂, the electrocatalytic activity of Pt nanoparticles towards oxidation of ethanol has been enhanced. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account improvement of overall conductivity (due to the presence of nanostructured gold) at the electrocatalytic interface (including TiO₂-support), as well as and possibility of specific Pt-TiO₂ or Pt-Au electronic interactions and existence of active hydroxyl groups (on titanium dioxide or polyoxometallate surfaces) in the vicinity of catalytic Pt sites.     

Surface plasmons in porous gold films

The surface plasmon resonance effects in porous gold (por-Au) films—nanocomposite porous films containing an ensemble of disordered gold nanoparticles—have been investigated by modulation-polarization spectroscopy. Por-Au films have been obtained by pulsed laser deposition (using a direct particle flow from an erosion torch formed by a YAG:Nd³⁺ laser in argon). The spectral and angular dependences of the polarization difference ρ(λ, θ) of internal-reflection coefficients of s- and p-polarized radiation in the Kretschmann geometry and the spectral dependences of isotropic reflection angles at ρ(θ) = 0 are measured. Two types of surface plasmon resonance are found: one occurs on isolated nanoparticles (dipole and multipole modes), and the other is due to the dipole–dipole interaction of neighboring nanoparticles. The frequency of electron plasma oscillations for the nanoparticle ensemble and the frequencies and decay parameters of resonances are determined. Dispersion relations for the radiative and nonradiative modes are presented. The negative sign of the dispersion branch of nonradiative modes of dipole–dipole interaction is explained by the spatial dispersion of permittivity. The relationships between the formation conditions of the films, their structure, and established resonance parameters (determining the resonant-optical properties of films) are discussed.     

Synthesis and characterization of uncoated and gold-coated magnetite nanoparticles

We report on the synthesis and characterization of uncoated and gold coated magnetite nanoparticles. Structural characterizations, carried out using X-ray diffraction, confirm the formation of magnetite phase with a mean size of ~7 and ~8 nm for the uncoated and gold covered magnetite nanoparticles, respectively. The value of the gold coated Fe₃O₄ nanoparticles is consistent with the mean physical size determined from transmission electron microscopy images. Mössbauer spectra at room temperature are consistent with the thermal relaxation of magnetic moments mediated by particle-particle interactions. The 77 K Mössbauer spectra are modeled with four sextets. Those sextets are assigned to the signal of iron ions occupying the tetrahedral and octahedral sites in the core and shell parts of the particle. The room-temperature saturation magnetization value determined for the uncoated Fe₃O₄ nanoparticles is roughly ~60 emu/g and suggests the occurrence of surface effects such as magnetic disorder or the partial surface oxidation. These surface effects are reduced in the gold-coated Fe₃O₄ nanoparticles. Zero-field–cooled and field-cooled curves of both samples show irreversibilities which are consistent with a superparamagnetic behavior of interacting nanoparticles.     

Metal nanocluster formation in silica films prepared by rf-sputtering: an experimental study

Composite silica films containing metal nanoclusters were prepared by the rf- sputtering technique, in which SiO₂ was co-deposited with gold+copper, gold+silver, or copper+silver. The formation of either pure or alloy clusters was studied by extended X-ray absorption fine structure spectroscopy and transmission electron microscopy. For all systems, the presence of alloy aggregates was evidenced. Moreover, small amounts of pure metal aggregates as well as dispersed or oxidized dopants were observed. 61.46.+w Nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals – 61.10.Ht X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc. – 81.05.Pj Glass-based composites, vitroceramics Received 29 June 2001     

Influence of colloidal-gold films on the luminescence of Eu(TTFA)3 in PMMA

The effects of colloidal-gold layers on the luminescent properties of thin films of Eu(TTFA)₃(TTFA=thenoyltrifluoroacetonate) in PMMA (PMMA=poly(methyl methacrylate)) were investigated. Layers of spherical gold nanoparticles (12 nm) were formed by self-assembly on the surface of amino-derivatized glass slides. Eu(TTFA)₃-PMMA films were then spin-coated either directly onto the Au metal surfaces or onto spacer layers covering the gold. The luminescence properties were characterized both as a function of the density of Au particles in the colloidal layer, and as a function of the distance between the Au layer and the luminescent film. The distance between the metal and luminescent layers was controlled using polyelectrolyte spacer layers deposited on the colloidal-gold films by a spin-assisted, layer-by-layer (SA-LBL) method. It was found that the colloidal gold layer has a net quenching effect on Eu(TTFA)₃ luminescence under all conditions considered in this study. The luminescence intensities and lifetimes decrease with increasing density of Au nanoparticles and with decreasing separation (d) between the luminescent film and the gold layer. The measured luminescence intensity drops more quickly with decreasing distance than one would predict based solely on lifetime data, if one assumes a constant radiative relaxation rate. Fits of the luminescence decay kinetics to a model for non-radiative energy-transfer from Eu(TTFA)₃ to the gold layer yields a 1/d² dependence, where d is the distance from the gold layer to the nearest face of the luminescent film. It is suggested that there is no reasonable physical interpretation of this result within the constraints of the model and, therefore, the interaction between the luminescent and gold layer cannot be explained solely in terms of non-radiative energy transfer.