Silver Vapor Research Articles

Permanent iridium modifier deposited on tungsten and zirconium-treated platforms in electrothermal atomic absorption spectrometry: vaporization of bismuth, silver and tellurium

The stabilizing role of permanent iridium modifier deposited on tungsten-treated (WTP) and zirconium-treated (ZrTP) platforms of transversely heated graphite atomizer (THGA) was studied in detail by electrothermal atomic absorption spectrometry (ETAAS) and different surface techniques in model experiments for Ag, Bi and Te. The comparison of the stabilizing efficiency of permanent Ir modifier on WTP and ZrTP and each of the single components, reveals the better effect of Ir on WTP and Ir itself. The extent of analyte losses during pre-atomization and the strength of analyte association with the modifier were estimated by the plotting of `differential vaporization curves'. The existence of double peaks of Ag, Bi and Te in WTP and Ir on WTP was confirmed and possible reasons for their formation were discussed. The absorbance profiles presented as differential curves reveal an existence of at least two different types of precursors determining processes of atom generation. The observed differences in the behavior of Ir permanent modifier on WTP and ZrTP, respectively, were explained by the different extent of iridium–tungsten and iridium–zirconium interaction and surface distribution. XRF, ESCA and SEM studies reveal non-uniform distribution of the modifier on the graphite substrate and the presence of oxide containing species on the surface.

Production and spectroscopic study of low-temperature silver complexes with mesogenic cyanobiphenyl derivatives

Metal-containing liquid-crystalline systems were obtained by co-condensation of metallic silver vapour with evaporated liquid-crystalline 4-pentyl-4′-cyanobiphenyl (5CB) under conditions of molecular beams. A comprehensive infra-red and ultraviolet-visible spectroscopic study of Ag-5CB film samples of different component ratios at 80 K shows the existence of Ag-5CB complexes owing to interactions of Ag with the π-electrons of the CN bond of cyanobiphenyl molecules.

Ceramic–electrode interaction in PZT and PNN–PZT multilayer piezoelectric ceramics with AG/PD 70/30 inner electrode

Pb(Zr0.53Ti0.47)O3(PZT) and PbNi1/3Nb2/3O3-PZT (PNN–PZT) multilayers with Ag/Pd 70/30 inner electrodes have been studied from the point of view of the ceramic–electrode interaction. PZT multilayers have shown silver free ceramic layers, and no lead has been detected in the electrode after sintering. Silver transport through the ceramic is avoided because of low open porosity–close porosity transition temperature. This transition seems to occur prior to the strong increase of the silver vapour pressure. For PNN–PZT multilayers, similar behaviour to that commonly reported in the literature for PZT is observed. A constant amount of silver, independent of the distance from the electrode, is detected in the ceramic layer. Lead is also detected in the electrode. On the other hand, no interaction between ceramic and electrode has been observed for the other cations.

Cryochemical synthesis of silver organosols in methyl acrylate

Joint condensation of silver vapour and methyl acrylate under vacuum onto a surface cooled with liquid nitrogen, followed by heating of the resulting co-condensate to room temperature, leads to partial polymerisation of the methyl acrylate and formation of highly stable organosols containing up to =0.5 mg ml-1 of silver; the size of the metal particles does not exceed 15 nm.

Modification of catheter materials by coating with polymer layers containing silver

AbstractThe surface of polyurethane based catheter material or of silicon wafers as model surfaces were modified by spin coating of solutions of poly(ethylene oxide) or poly(vinyl alcohol) in water. For the incorporation of silver ions, silver nitrate was added to some of the solutions or the as‐cast surfaces were dipped into AgNO3 solution. Furthermore, samples coated with a thin layer of metallic silver were prepared by deposition of silver vapor in vacuum. The as‐prepared surfaces were studied by atomic force microscopy and X‐ray photoelectron spectroscopy. During the spin coating of the solutions containing AgNO3, clusters of the silver component were formed. They were well dispersed in a poly(vinyl alcohol) matrix but act as nucleation agents in poly(ethylene oxide) where then large spherulites are formed. The surface compositions of coated samples and the depth profiling were carried out by angle dependent X‐ray photoelectron spectroscopy.

Application of the Kelvin equation to vaporization of silver and gold in electrothermal atomic absorption spectrometry

In order to obtain additional insight into the release mechanism of the metals in electrothermal atomization atomic absorption spectrometry, a quantitative relation between the heat of vaporization and the size of the released particles is proposed on the basis of the Kelvin equation. The applicability of the equation for the investigation of silver and gold vaporization is demonstrated and the limits in which the model is valid are determined. According to the present considerations the activation energy could be equal to the heat of vaporization of the silver and gold droplets. An explanation of the observed dependence of activation energy on analyte mass is given. The proposed relation provides a possibility for definition and evaluation of an “effective” radius/size of the droplets on the basis of their heat of vaporization. A correlation between the mass of the injected sample and the “effective” radius of the droplets, obtained at higher temperature is found. The minimum and maximum “effective” radii of the droplets, following the proposed equation are calculated for Ag on pyrolytic graphite coated electrographite (PGC) and Au on PGC, uncoated electrographite (EG) and glassy carbon (GC) tubes. The results obtained are indirect evidence for the island structure of precursor metal layer and for the existence of silver and gold microdroplets on the graphite support.

Application of a QMG-420 mass spectrometer for high temperature studies

A quadruple QMG-420 mass spectrometer was modified for the high temperature Knudsen effusion method. Features of the vaporizer design such as graphite furnace, position of the effusion cell and the thermocouple are considered. The vapour mass spectra over NaCl and B 2O 3 obtained in the present study and available in the literature are compared. It is shown that the results of the determination of partial pressures of vapour species over NaCl, CsCl, B 2O 3 and Ag and enthalpy of vaporization of silver are in good agreement with the data available. Advantages of the Quadstar ™ program for high temperature thermodynamic measurements are illustrated.

A Wall Stabilized Nitrogen Arc Model at Different Concentration of Silver Vapour and Current Intensity

This paper presents theoretical results for a nitrogen arc contaminated with silver vapours emitted from arc electrode in a range from 0 to 10% and current intensity between 5 to 50 A. By solving the equation of conservation of energy, the effect of these vapours on the arc plasma characteristics are studied. In particular it was seen that the presence of 10-4% Ag in the arc column decreases strongly the axial temperature while the presence of 10-1% Ag has an explicit decreases in the electric field at current near 20 A.

Intercalation of vacuum deposited silver into 1T-TaS2 and its influence on charge density waves

It is shown that silver vapour deposited onto (00.1) faces of 1T-TaS2 crystals at 300–500 K starts to intercalate into van der Waals gaps of the host crystal already during the deposition process, even at room temperature deposition. This is demonstrated by superstructure reflections in electron diffraction patterns. The intercalated silver also lowers the transition temperatures among various 1T-TaS2 CDW phases. These effects show that the octahedral coordination of Ta atoms changes into the trigonal prismatic one. In crystals with silver deposited above 500 K, where the transformation of 1T-TaS2 into the stable 2Ha form takes place, the observed superstructures are in agreement with the literature results for electrochemically silver intercalated 2Ha-TaS2 crystals.

Kinetics of clustering processes in expanding vapor

An analysis of the cluster growth process is given within the framework of the liquid drop model for clusters. The processes of atom attachment to a cluster, evaporation of atoms from the cluster surface, and also the coagulation processes are taken into account. Calculations are made for conditions of the Hagena experiments for silver vapor expanding after a nozzle. The results are compared with the Hagena scaling laws. From this it follows that the coagulation processes are essential for the cluster growth. The character of collision of two clusters is analyzed.

Laser induced fluorescence and radiative lifetimes of the low-lying electronic states of gaseous AgF

At the fringes of the visible region, two low-lying 1 (Ω=1) electronic states A′Ω1 and aΩ1 of gaseous AgF located ∼4300 cm−1 below the previously known lowest excited A0+ state have been excited for the first time in a silver vapor–fluorine reaction system. The A′Ω1–X 1Σ+ and a Ω1–X 1Σ+ band systems (also observed in chemiluminescence) have been excited and studied using pulsed laser induced fluorescence spectroscopy. The band system associated with the A′Ω1–X 1Σ+ transition has been rotationally analyzed. The UV fluorescence of the A0+ and B0+–X 1Σ+ transitions has also been excited. The radiative lifetimes of these four low-lying electronic states have been measured as 7.1 μs (A′Ω1), 9.1 μs (aΩ1), 240 ns (A0+), and 21 ns (B0+), respectively, revealing that the two Ω=1 states are of triplet character, while the two 0+ states are of singlet character. The observed low-lying states of AgF appear to dissociate adiabatically to neutral atoms in contrast to the apparent dissociation of the low-lying electronic states in CuF to ion pairs. The observation of the low-lying 1 states of AgF also indicates the existence of similar stable 1 states for the remaining silver halides, all of which should absorb visible photons. Major molecular constants of the newly observed A′Ω1 state of 107AgF are Te=24 950.71(10) cm−1, ΔG1/2=506.74(8) cm−1, Be=0.281 32(15) cm−1, De=0.116(60)×10−6 cm−1, and re=1.927 Å.

Performance of a hypersonic impactor with silver particles in the 2 nm range

The performance of a hypersonic impactor is studied in the diameter range down to 2 nm with condensation particles from silver vapors. Particles of a single mobility are selected with a differential mobility analyzer, and sized from the measured mobility on the assumption that the usual size-mobility relations hold in the nanometer range. The inferred “aerodynamic density“ is between 2 and 3 times smaller than that of crystalline Ag, so that the particles are either non-spherical or non-pure crystalline Ag, or the usual size-mobility relations fail in this size range. Yet, this aerosol provides a source for the smallest particles yet analyzed aerodynamically. New results are that: (a) the resolving power of the instrument does not diminish at decreasing particle size, at least down to 2 nm; (b) the minimum capture efficiency η min observed below the critical Stokes number (6.5–8%) is nearly independent of particle diameter in all the range above 2 nm and (c) the characteristic response curves of the impactor do not improve upon sheathing a core aerosol flow with clean air. A provisional conclusion is that the origine of η min is probably turbulent diffusion.

Nanometer patterning of InP using aerosol and plasma etching techniques

By the application of aerosol techniques for the deposition of well-defined particles of silver in combination with methane-based electron cyclotron resonance plasma etching, we have been able to fabricate nanometer sized columns of InP. Silver particles are produced via homogeneous nucleation out of silver vapor saturated nitrogen gas from a tube furnace at around 1100 °C and, after size selection, deposited on the surface of InP. Scanning electron microscope images show that equally sized particles of silver, with an effective diameter in the range 20–40 nm, can be generated and deposited on the semiconductor. In a dry etching process applied subsequently we transfer vertically the feature of the particles into the InP material underneath producing free-standing columns of InP with diameters as small as 50 nm.

An investigation of cluster formation in an ionized cluster beam deposition source

We have investigated the concentration of Agn clusters (25<n<1600) in a vapor of Ag expanding from the nozzle of a crucible heated to temperature as high as 1950 K (which corresponds to a silver vapor pressure of about 30 Torr). The goal of the experiment was to determine whether there were enough of these clusters present to have a significant effect on the ion-enhanced deposition of Ag films, as postulated for ion cluster beam (ICB) deposition. Time-of-flight mass spectra were obtained by using an excimer laser at 248 nm (KrF) or 193 nm (ArF) to photoionize a fraction of the vapor. The ions were extracted normal to the direction of average velocity of the neutral species and detected with a Faraday plate after a 20 cm field-free flight path. At the level of experimental uncertainty, no convincing evidence for the presence of large clusters was found for Ag vapor pressures in the 2–30 Torr range (typical for ICB). We conclude that under the conditions of our experiment, not more than one atom in 5000 is contained in a cluster with between 25 and 1600 atoms.

Nucleation and growth of condensate clusters on solid surfaces

The nucleation and growth of the condensate clusters during the early stages of the vapour deposition process were studied by depositing silver vapour on silicon, glass, mica, NaCl and KBr in a small coater. It was observed that the formation of the condensate film can be divided into four stages and the condensate clusters exhibit liquid-like behaviour during their early stage of growth. The mode of cluster growth is affected by the interfacial properties between the condensate and the substrate. The effect of surface roughness on the cluster growth is relatively insignificant and the experimental reproducibility is usually poor because of unavoidable contamination.

Vibronic spectroscopy of Ag 2-Ar

The weakly bound complex Ag 2-Ar is produced using laser vaporization of solid silver in a pulsed supersonic molecular beam. Resonant two-photon photoionization yields a vibrationally-resolved electronic spectrum with an origin at 35329 cm −1. This origin is red-shifted 480 cm −1 from that of the uncomplexed silver dimer. Progressions are observed for the solvated Ag 2 stretch (156 cm −1), the van der Waals stretch (74 cm −1) and the bending mode (28 cm −1). Excited state (755 cm −1) and ground state (275 cm −1) binding energies are obtained.

Silver-Indium-Cadmium Control Rod Behavior in Severe Reactor Accidents

Silver-indium-cadmium (Ag-In-Cd) control rod behavior in severe reactor accidents is examined with a goal of improving the methodology used to estimate reactor accident source terms. Control rod behavior in both in-pile and out-of-pile experiments is reviewed. A mechanistic model named VAPOR is developed that calculates the downward relocation and simultaneous vaporization behavior of the Ag-In-Cd alloy expected after control rod failure in a severe reactor accident. VAPOR is used to predict the release of silver, indium, and cadmium vapors expected in the Power Burst Facility (PBF) severe fuel damage (SFD) 1-4 experiment. In addition, a sensitivity study is performed to examine the effects of system pressure and flow rate on control rod vapor release. Although cadmium is found to be the most volatile constituent of the alloy, all of the calculations predict that the rapid relocation of the alloy down to cooler portions of the core results in a limited release for all three control rod alloy vapors. Results of the control rod and aerosol behavior in PBF test SFD 1-4 are presented. VAPOR calculations are found to compare much better with the control rod material release in test SFD 1-4 than empirical models that do not consider relocation of the alloy away from the hotter portions of the core. The timing and magnitude of control rod material release and the potential for control rod aerosol/fission product interactions during the early phase of a severe accident are dependent on the system pressure. A better understanding of control rod material behavior during the later in-vessel phase of the accident is needed to define more accurately both the magnitude of the aerosol source and the initial composition of molten material exiting the vessel in the event of lower vessel head failure.

High-intensity ionized cluster beams of large metal clusters

Generation and partial ionization of cesium cluster beams from pure vapor expansions with mean cluster sizes of up to several thousand atoms per cluster are described. The ionized cluster portion yields a deposition rate of the order of 4 nm/s at 15 cm distance from the nozzle while the total mass flux is estimated to correspond to an at least one order of magnitude higher deposition rate. Silver vapor expansions are found to contain silver microdroplets of up to some hundred micrometer diameter. The droplets do not freeze before impact on a room temperature substrate.

Formation of large metal clusters by surface nucleation

The formation of metal clusters with hundreds of atoms in and near vapor ejection nozzles is analyzed. A previously discussed model, cluster generation by homogeneous nucleation and collisional growth in the vapor phase, is found to be untenable because it cannot account for the large number of collisions required to remove the latent heat of condensation, freed during cluster growth. An alternative mechanism that involves heterogeneous nucleation (i.e., cluster formation on surfaces) is proposed and evaluated. To determine the applicability of this mechanism, the following process steps are considered: formation of an adequate supply of critical embryos on nozzle and adjacent crucible walls, growth of embryos into large clusters, and cluster ejection into the surrounding vapor atmosphere. The conclusion is that, with nonwetting vapor and surface material combinations, substantial quantities of large clusters can be formed and ejected. Specifically, predictions for silver vapor at a few Torr pressure, passing through a graphite nozzle at about 1600 K, are cluster generation rates of 1013–1014 clusters/cm2 s, and cluster sizes up to about 600 atoms. Available experimental observations support these predictions qualitatively.

Control of cluster size in nozzle jet expansion

Recent reports showed that ultrasmall metal and semiconductor clusters (up to 1000 atoms per cluster) can be produced during the jet expansion of hot vapor through a small nozzle without the use of carrier gas. Cluster beams are potentially useful in very large-scale integrated (VLSI) thin film processing. In this report, the kinetics of the nonsteady state, stepwise cluster growth in a jet beam with metal vapor is solved quantitatively based on the classical liquid–drop theory. In our calculation for the jet expansion of silver vapor, we found that cluster size up to more than 100 atoms can be formed. This result is consistent with the notion that the nucleation barrier for metal and semiconductor cluster formation can still be small despite their high surface tension. We found that the cluster size distribution depends very much on the stagnation pressure (P0) before the expansion and the nozzle geometry, particularly the expansion angle (θ). For sufficiently large P0 (several Torr) and small θ (<30°), the cluster size distribution is peaked at a value which increases exponentially with the terminal Mach number Mt —the parameter characterizing the expansion conditions.