Gold Deposition Rate Research Articles

A galvanic exchange process visualized on single silver nanoparticles via dark-field microscopy imaging.

The study of the galvanic exchange (GE) mechanism is beneficial for designing and developing new bimetallic nanocrystal structures with excellent bifunctional catalytic properties. Herein, we have visually demonstrated a GE process by real-time monitoring of the reaction between silver nanoparticles (AgNPs) and Au3+ at the single nanoparticle level using light scattering dark-field microscopy imaging. The localized surface plasmon resonance (LSPR) scattering spectral shifts of the AgNPs which reveal the Ag removal rate and Au deposition rate on the surface of the AgNPs can be observed. Furthermore, a pixel meta three color channel method has been introduced for analyzing the scattering light color changes of plasmonic particles to reveal the kinetics of the atomic deposition process on a single AgNP during GE, thus making the reaction kinetics of the GE process directly observable. Therefore, this study provides an efficient and promising approach for understanding the GE mechanism and exploiting its reaction kinetics.

Room temperature thermally evaporated thin Au film on Si suitable for application of thiol self-assembled monolayers in micro/nano-electro-mechanical-systems sensors

Gold is a standard surface for attachment of thiol-based self-assembled monolayers (SAMs). To achieve uniform defect free SAM coatings, which are essential for bio/chemical sensing applications, the gold surface must have low roughness and be highly orientated. These requirements are normally achieved by either heating during Au deposition or postdeposition Au surface annealing. This paper shows that room temperature deposited gold can afford equivalent gold surfaces, if the gold deposition parameters are carefully controlled. This observation is an important result as heating (or annealing) of the deposited gold can have a detrimental effect on the mechanical properties of the silicon on which the gold is deposited used in microsensors. This paper presents the investigation of the morphology and crystalline structure of Au film prepared by thermal evaporation at room temperature on silicon. The effect of gold deposition rate is studied, and it is shown that by increasing the deposition rate from 0.02 to 0.14 nm s−1 the gold surface root-mean-square roughness decreases, whereas the grain size of the deposited gold is seen to follow a step function decreasing suddenly between 0.06 and 0.10 nm s−1. The x-ray diffraction intensity of the preferentially [111] orientated gold crystallites is also seen to increase as the deposition rate increases up to a deposition rate of 0.14 nm s−1. The formation and characterization of 1-dodecanethiol on these Au coated samples is also studied using the contact angle. It is shown that by increasing the Au deposition rate, the contact angle hysteresis (CAH) decreases until it plateaus, for a deposition rate greater than 0.14 nm s−1, where the CAH is smaller than 9° which is an indication of homogeneous SAM formation, on a smooth surface.

Silicone rubber films functionalized with poly(acrylic acid) nanobrushes for immobilization of gold nanoparticles and photothermal therapy

Prevention and treatment of medical device-related infections demands novel strategies for hindering bacteria adhesion and proliferation. The aim of this work was to immobilize gold nanoparticles onto silicone rubber (SR) and then exploit the plasmon resonance properties for the photothermal killing of adhered bacteria. To obtain a good rate of gold deposition, SR films were grafted with PAAc nanobrushes (SR-g-AAc) using a 60Co gamma source. Effects of absorbed dose, monomer concentration, temperature and reaction time on the grafting percentage, swelling and mechanical properties of the films were first investigated. Gold nanoparticles were immobilized on SR and SR-g-AAc following different strategies. Immersion in gold ions (HAuCl4) solution and subsequent reduction made the films to be uniformly coated by 10–20 nm gold nanoparticles as shown by SEM-EDX and XRD. Photothermal features were evidenced as an increase in 6–7 °C in the first 5 min of irradiation with a 514 nm laser at a power density of 0.5 W/cm2. Finally, SR-g-AAc films were challenged against Staphylococcus aureus and effects of irradiation at 514 nm on bacteria survival evaluated. Overall, the gold-immobilized films were shown to be stable against autoclave sterilization and ultrasounds and exhibited outstanding ability to damage adhered bacteria after laser irradiation.

Understanding the dependence of the ohmic drain-source leakage current on gold deposition rate in top-contact pentacene-based thin film transistors

We studied the influence of the gold deposition rate on the drain-source leakage current of top-contact pentacene-based thin film transistors (TFTs) with different channel lengths. It is demonstrated that the anomalous leakage current which occurs only in short-channel TFTs monotonically increases with increasing the gold deposition rate. For TFTs with channel length of 30μm, we also investigated the dependence of the drain-source leakage current on the pentacene grain size as well as the gold deposition rate. It is shown that the pentacene grain size influences the leakage current only in the case if high gold deposition rate is employed, whereas the anomalous leakage current can be avoided by reducing the gold deposition rate. Finally, due to the observed ohmic character of the anomalous leakage current, we propose that the origin of the current can be attributed to parasitic leakage paths on the surface of the pentacene layers formed by the lateral diffusion of gold clusters from drain/source edges into the channel region during gold deposition. Based on this hypothesis, the observed dependence of the anomalous leakage current on the gold deposition rate can be well explained.

Structural Effects on Water Adsorption on Gold Electrodes

We study the molecular properties of the interface formed between aqueous sulfuric acid solutions and gold electrodes by means of surface-enhanced infrared absorption spectroscopy (SEIRAS). The shape of the SEIRAS spectra is observed to be strongly dependent on the deposition rate with which the gold electrodes are prepared. We find that the water molecules coordinating to coadsorbed sulfate anions become invisible in the SEIRAS spectra when the gold films are deposited at 1 A/s, instead of the customary deposition rate of 0.1 A/s employed in previous studies. Atomic force microscopy images of the gold deposits demonstrate that the increase of the gold deposition rate produces a decrease in the size of the nanoparticles composing the gold films. This suggests that water molecules coadsorbed with sulfate anions on small gold nanoparticles are oriented parallel to the surface. On the other hand, the fact that these water molecules are not detected by SEIRAS facilitates the study of the adsorption of hydronium cations, since these SEIRAS bands overlap. It is concluded that the adsorption of sulfate anions does not involve the coadsorption of any hydronium-water complex, since the SEIRAS band of the latter species exhibits a steady decrease with increasing potential

Photoreduction of metallic co-catalysts onto novel semiconducting metal oxides

Abstract Photoreduction of ionic platinum or gold into metallic nanoparticles on the surface of a new type of porous metal oxide material was done from aqueous solutions of the metal salts. The metallization patterns were investigated in an effort to understand the photo activity and electronic properties of new semiconductor materials. In this study, KTiNbO 5 and KNb 3 O 8 were used as starting compounds, and colloids were derived via their chemical exfoliation. The colloids consist of individual lamellar particles that retain their crystallinity from the parent compounds. The colloids were agglomerated into highly porous framework solids. The synthesis provides a low temperature route to stable, porous, polycrystalline materials. Elemental analyses, scanning electron microscopy, and optical absorbance measurements were done to characterize the porous substrates and the metal deposition kinetics. Compared to the gold deposition, the platinum metal nanoparticles were deposited as smaller more widely dispersed islands on the surface of the photocatalysts. The rate of gold deposition was much faster than the platinum and the deposited gold particles were in the 50–400 nm diameter range, with most diameters near 100 nm. The diameters of the particles of platinum varied between 10 and 200 nm, but most were 50 nm or less.

Preparation of Gold Nanoparticles Using Photographic Materials (6): Effect of Thiocyanate Ions

The authors have previously reported a method for preparing gold nanoparticles using silver halide photographic materials and gold deposition development. This process was investigated from the viewpoint of the effect of thiocyanate ion concentration. Gold particles are formed on latent image specks on the exposed silver halide grains by the disproportionation reaction of gold(I) thiocyanate complex ions. The ratio A of gold ions to thiocyanate ions in preparing the gold(I) thiocyanate complex affects gold deposition; that is, the rate of gold deposition increases when the abovementioned ratio A increases from 1:10 to 1:3. Optical measurement, atomic absorption spectroscopy, and electron microscopic observation indicate that the growth rate of gold nanoparticles does not depend on the ratio A, while the total mass of gold atoms increases with an increase in the ratio A. The mass increase is due to the increase not in size but in the number of gold particles. Excess thiocyanate ions inhibit the deposition of gold atoms on latent image specks.

Electroless gold plating from tetrachloroaurate solutions containing hexacyanoferrate(II) ions

A hexacyanoferrate–tetrachloroaurate electroless gold plating solution has been developed for production on Ni–P, Ni–B, Ni–Pd and Cu substrates, giving gold coatings up to 0·25–0·38 μm in thickness. The rate of gold deposition depends on the nature of the substrates and decreases in the series Ni–P>Ni–B>Ni–Pd>Cu. The rate of gold plating on Ni–Pd decreases with the growth of palladium content in the alloy. Gold deposition occurs by mechanisms of cementation (immersion replacement) and gold reduction with hydrazine hydrochloride. The fraction of cementation does not exceed 30–40% with deposition on Ni–P and Ni–B substrates, 10% on copper and diminishes slightly with gold film deposition.

アスコルビン酸を還元剤とする無電解金めっき浴の電気化学的挙動

A novel electroless (autocatalytic) gold plating bath containing sodium L-ascorbate as the reducing agent has been developed. A suitable bath composition was formulated based on the results of an electrochemical study in which were determined at a gold electrode the anodic polarization curves of various reducing agents and the cathodic polarization curves of sodium tetrachloroaurate (III) dissolved in solutions of sodium sulfite and/or sodium thiosulfate.A typical bath containing 0.0125mol/dm3 sodium tetrachloroaurate (III), 0.1mol/dm3 sodium sulfite, 0.1 mol/dm3 sodium thiosulfate, and 0.25mol/dm3 sodium L-ascorbate, was operated under moderate conditions, typically at a pH of 6.0 and 333K. The rate of gold deposition obtained with this bath was in the same range or greater than that obtained with the classical cyanide-borohydride bath. The deposition rate of the new bath depended on both the ascorbate and gold concentrations, and the gravimetrically determined deposition rate was found to correspond well with the rate estimated from electrochemical polarization measurements.

In-Situ X-Ray Reflectivity Study on Growth Dynamics of Sputter Deposited Gold on Silicon

ABSTRACTWe performed in-situ x-ray reflectivity measurements to study the growth dynamics of gold sputter deposited onto silicon using an x-ray scattering chamber equipped with a faced magnetron source where the substrate is held at a right angle relative to the sputtering guns. By operating the guns at low power (1 watt) and under 20 mTorr Ar, we could control the gold deposition rate to less than 1Å/sec. The observed x-ray reflectivity for gold deposited onto a silicon substrate at 300 K and 400 K is consistent with nucleated island growth for average gold particle sizes less than 50 Å. Above 50 Å, the reflectivity data indicates that the gold film uniformly covers the silicon surface, and that as the film thickness is increased the gold-vacuum interface gets progressively rougher. Detailed analysis of room temperature data is in progress, as is the temperature dependence on the roughness of the gold vacuum interface.

Electrodeposition of Gold: Depolarization Effects Induced by Heavy Metal Ions

Addition of trace quantities (ppm) of heavy metal ions such as Pb(II) or Tl(I) to soft gold electroplating baths induces a marked cathode depolarization that extends the current density range in which bright, fine‐grained deposits can be obtained and produces uniform coverage of irregularly shaped substrates. In this study it is shown that the trace foreign metal additives which are most effective as depolarizers are those which tend to deposit uniformly on a gold surface to form an adsorbed monolayer at electrode potentials positive to those where their cathodic deposition as bulk metals begins,i.e., at underpotentials. Of the series of Group B elements (As, Bi, Cd, Cu, Ga, Hg, Pb, Sb, Sn, Tl, and Zn) investigated for depolarization action in alkaline phosphate solutions (pH 8, 70°C), only Pb, Tl, Bi, and Hg were found to induce significant effects. The latter two metals have not previously been reported to act as depolarizers in gold electrodeposition processes. The kinetics of the potential relaxation effects induced by these species under galvanostatic conditions were found to be strongly dependent on mass transport rate, gold deposition rate (i.e., plating current density), and temperature. In addition, it was found that Pb, Bi, Hg, and particularly Tl enhance the anodic dissolution of gold in cyanide‐containing solutions. The ranges of underpotential deposition of the metals Pb, Tl, Bi, and Hg from very dilute (∼5 μM) solutions of their ions in pure phosphate supporting electrolyte at 70°C were determined under steady‐state mass transport conditions at a rotating gold disk electrode. By varying the disk rotational speed and the potential scan rate, it was shown that a significant amount of Pb(II) [the equivalent of ∼20% of a close‐packed monolayer of Pb(0)] is specifically adsorbed in the ionic double layer at the gold surface and is not desorbed even at high anodic potentials. A similar phenomenon was observed for the Bi(III) species. The depolarization induced by the trace heavy metal ions is examined in terms of electrocrystallization and electrocatalytic mechanisms. From the magnitude of the potential relaxation (∼0.2V), its temperature dependence, and the ability of Hg to alloy with Au, it is concluded that screw dislocation generation is not responsible for this effect. Failure of Cs+ ions to enhance the rate of electroreduction of anions and also the ability of Pb(II) to catalyze the electroreduction of indicates that electrostatic repulsion effects are of minor importance. It is concluded that the depolarization phenomenon is caused by an enhancement of nucleation rate produced by the strongly adsorbed foreign metal atoms. In addition, catalytic electrochemical displacement reactions are made possible by the fact that the exchange current densities of the various Mz+/M depolarizer couples are much greater than that of the couple and by the specific adsorption of the Mz+species. In the case of Hg, displacement is made thermodynamically possible by the complexation of Hg2+ by CN− ions released during the electroreduction of .