Polycrystalline Ag Research Articles

Time dependent embrittlement of poly crystalline Ag by liquid Ga

Polycrystalline Ag is embrittled when it is stressed in contact with liquid Ga. This is an example of liquid metal embrittlement. The fracture stress at room temperature is gradually reduced by contacting liquid Ga on the surface. After 48h the fracture stress has reached its minimum and begins to increase again. A reduction of the maximum stress occurs even when a specimen is stressed after removal of liquid Ga from the surface, if the contact time is long enough. The fracture surface is intergranular when the fracture stress is low. From these results, one can conclude that Ga atoms penetrate into the grain boundaries of the polycrystalline Ag, and weaken the grain boundaries. However, Ga atoms can form intermetallic compounds with Ag, leading to a recovery of ductility. Liquid Ga also directly attacks the crack tip. This effect is stronger when the specimen is stressed within several minutes of contact with liquid Ga.

Estimate of the potential difference across metal/water interfaces and across the lipid bilayer moiety of biomimetic membranes: an approach

Mercury is a particularly advantageous support of lipid, thiol and disulfide self-assembled monolayers (SAMs), because it provides them with a perfectly smooth and fluid surface and allows their gradual expansion in aqueous solution with progressive tilt of the adsorbed molecules, without water incorporation. These unique advantageous features permit an estimate of the extrathermodynamic absolute potential difference, ϕ, across the Hg|water interface and of the surface dipole potential of mercury-supported SAMs. Two different models of metal-supported tethered bilayer lipid membranes (tBLMs) incorporating a cation-selective channel predict that the ϕ value at the inflection point of a plot of the in-phase component, Y′, of the electrochemical admittance against the applied potential E is almost coincident with the surface dipole potential, χs, of the hydrophilic spacer moiety of the tBLM. This prediction allows an estimate of the absolute potential difference, ϕ, across the interface between any metal capable of supporting tBLMs and the bulk aqueous phase, provided the χs value of the tBLM is known. Moreover, the potential difference across the lipid bilayer moiety of the tBLM (i.e., the transmembrane potential) is shown to be practically equal to χs at the inflection point of the corresponding Y′ vs.E plot. This approach is applied to polycrystalline Au and Ag(111).

Self-assembling of Z-α-pyridylcinnamic acid molecules over polycrystalline Ag and Au surfaces followed by FT-IR and atomic force microscopies

Self-assembling layers of Z-2(3′-pyridyl)-3-phenyl propenoic acid molecules were built on silver and gold films prepared by pulsed laser deposition. The dip-coating technique was used for depositing the organic material onto the metals. The clean metal surfaces were studied by scanning electron microscopy, and the organic structures formed over the metal surfaces were investigated by FT-IR microspectroscopy and atomic force microscopy. Various surface structures were identified and their rationalisation was attempted.

Elastic properties of polycrystalline Al and Ag films down to 6 mK

The elastic properties of as-deposited high-purity micron-thick polycrystalline Al and Ag films were measured with the double paddle resonator technique down to 6 mK, and important differences from previous measurements were found. The lowest internal frictions $({Q}^{\ensuremath{-}1})$ observed were $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ in Al and $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ in Ag, indicating that these films can contribute substantially to the damping of mechanical resonators, even at very low temperatures. In Al, we also observed agreement between the relative change in sound speed $\ensuremath{\delta}v/{v}_{0}$ and ${Q}^{\ensuremath{-}1}$ and the predictions of the tunneling model for an amorphous superconductor well below ${T}_{c}$. Dislocation kinks tunneling between local minima in a kink-Peierls potential modulated by disorder could form the broad distribution of tunneling states required by the tunneling model. However, previous measurements have shown that the thermal conductivity, heat capacity, and heat release of polycrystalline bulk metal and films are not in agreement with the tunneling model predictions.

The influence of oxygen on the growth of silver on Cu(110)

The influence of the (2 × 1)O reconstruction on the growth of Ag on a Cu(110) surface was studied by scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). On the bare Cu(110) surface, Stranski–Krastanov growth of silver is observed at sample temperatures between 277 K and 500 K: The formation of a Ag wetting layer is followed by the growth of three-dimensional Ag wires. In contrast, on the oxygen-precovered Cu(110) surface, the growth of silver depends heavily on the substrate temperature. Upon Ag deposition at room temperature, a homogeneous, polycrystalline Ag layer is observed, whereas at 500 K, three-dimensional wires separated by (2 × 1)O reconstructed areas are formed. The behavior of a deposited Ag layer upon annealing is also influenced greatly by the presence of oxygen. On the bare surface, annealing does not change the Ag wetting layer and gives rise to Ostwald ripening of the Ag wires. On the oxygen-precovered surface, however, the initial polycrystalline Aglayer first transforms into Ag wires at around 500 K. Above this temperature, the depletion of the (2 × 1)O reconstructed areas due to Ag-induced O desorption is balanced by the formation of a Ag wetting layer. On both, the bare and the oxygen-precovered Cu(110) surface, the deposited silver diffuses into the Cu bulk at temperatures above 700 K.

Preferred heteroepitaxial orientations of ZnO nanorods on Ag

Wurtzite ZnO nanorods were grown from solution onto coarse-grain bulk polycrystalline Ag substrates to explore the nature of preferred heteroepitaxial orientations. ZnO nanorods grow copiously on grains with <111> and <001> surface normals. Two epitaxial orientations were observed: {0001} ZnO ‖ {111} Ag with <20> ZnO ‖ <10> Ag and {0001} ZnO ‖ {001} Ag with <20> ZnO ‖ <10> Ag. Both feature ZnO basal plane growth, and the specific in-plane orientation relationships both feature alignment of close-packed directions in the interface. Nanorod growth was strongly suppressed on Ag grains in most other orientations. Although strain energy minimization is often invoked to explain the {0001} ZnO ‖ {111} Ag with <20> ZnO ‖ <10> Ag orientation, associated with an almost ideal near-coincidence site lattice matching, our data suggests that strain may not be the sole, or even the most important, determinant of the preferred orientations during solution-based epitaxial growth in this system.

Comparison of a Fluorinated Aryl Thiol Self-Assembled Monolayer with Its Hydrogenated Counterpart on Polycrystalline Ag Substrates

The effects of perfluorination of aryl thiols on surface coverage, surface electronic properties, and molecular orientation of self-assembled monolayers of thiophenol (TP) and pentafluorothiophenol (F(5)TP) on polycrystalline Ag were evaluated using linear sweep voltammetry, ultraviolet photoelectron spectroscopy (UPS), and surface Raman spectroscopy, respectively. Electrochemical reductive desorption by linear sweep voltammetry indicates a surface coverage for the TP monolayer of (5.07 +/- 1.29) x 10(-10) mol/cm(2), equating to a molecular area of 32.8 +/- 8.3 A(2), and a surface coverage for the F(5)TP monolayer of (1.95 +/- 0.59) x 10(-10) mol/cm(2), equating to an area of 85.2 +/- 25.8 A(2)/molecule. TP-modified Ag exhibits a change in work function (DeltaPhi) of -0.64 eV relative to bare Ag, whereas F(5)TP-modified Ag exhibits a DeltaPhi of +0.54 eV relative to bare Ag. Quantitative analysis of the UPS and reductive desorption results yields molecular pictures of the proposed interfaces with TP molecules tilted <20 degrees from the surface normal in a herringbone pattern spaced 6.4 A apart and F(5)TP molecules in a more disordered arrangement tilted 67 degrees from the surface normal with an intermolecular distance of 10.4 A. Qualitative surface Raman spectroscopic analysis of in-plane and out-of-plane modes for these systems confirms that TP molecules are oriented more vertical than F(5)TP molecules in these monolayers.

Room Temperature Surfactant Assisted Crystal Growth of Silver Nanoparticles to Nanoribbons

This study presents a simple and systematic growth of Ag nanoparticles (NPs) to nanoribbons by changing the hydrophobicity parameter of a series of cationic Gemini surfactants by using seed-mediated approach in aqueous phase at room temperature. At lowest hydrophobicity of a Gemini surfactant (i.e., dimethylene bis(decyldimethyl-ammonium bromide), 10-2-10), Ostwald ripening process was observed which caused fusion among growing Ag NPs. This process was quite prominent when 0.5 ml of Ag seed solution was used for the growth process but weakened as the amount of seed decreased to 0.125 ml. Similar behavior was demonstrated by Au NPs studied for comparison. The nanostructures were characterized by TEM, XRD, and UV-visible measurements. Further increase in the hydrophobicity of a Gemini surfactant from 10-2-10 to dimethylene bis(tetradecyldimethylammonium bromide) (14-2-14) through dimethylene bis(dodecyldimethylammonium bromide) (12-2-12), resulted in the participation of threads like micelles and liquid crystalline phase as soft-templates towards the nanoribbon formation. Fine polycrystalline Ag nanoribbons were obtained in the presence 14-2-14 and were characterized by the HRTEM and EDX analysis.

Copper surface enrichment of AgCu alloys

AbstractWe summarise the X‐ray electron spectroscopy (XPS) study of changing surface composition of polycrystalline Ag–2.2 mass% Cu and Ag–5.1 mass% Cu alloys during in situ annealing at chosen temperatures ranging from 300 to 600 °C. The results show obvious surface enrichment by copper, which is different for individual alloys. The contradiction of this result to general knowledge on preferential silver segregation can be explained on basis of attractive interaction of copper with oxygen and of accelerated diffusion of copper to the surface resulting in final copper surface enrichment. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Thermoelectric properties of rapid hot pressed polycrystalline Ag1−xPb18SbTe20 synthesized from doping PbTe nanocrystals

AbstractPolycrystalline thermoelectric (TE) materials of n‐type and with compositions of Ag1−xPb18SbTe20 (x = 0, 0.1, 0.2) were prepared by rapid hot pressing from alloy powders, which were obtained by ball milling crystalline ingots. The ingots were synthesized from PbTe nanoparticles, made by solvothermal reactions, and Ag, Sb and Te powders via vacuum‐sealed melting in quartz ampoules. Through rapid hot pressing at 748 K for 15 min under 80 MPa, the polycrystalline samples possessed 95% relative densities with the average grain size of 5 µm. The electrical resistivity, Seebeck coefficient and thermal conductivity of the Ag1−xPb18SbTe20 (x = 0, 0.1, 0.2) samples were measured in the range from room temperature (RT) to 673 K. The thermal conductivity was dramatically decreased, caused by scattering of phonons from grain boundaries and interfaces. By optimizing the values of carrier concentration and carrier transference, the Ag1−xPb18SbTe20 (x = 0.2) sample achieved a maximum ZT value of 1.019 at 673 K.

The influence of the conditions of the anodic formation and the thickness of Ag(I) oxide nanofilm on its semiconductor properties

The anodic formation of Ag(I) oxide nanofilms on polycrystalline silver and Ag–Au alloys as well as on low-index single crystals of silver in 0.1 М KOH was examined. By the methods of photocurrent i ph and photopotential E ph measurements, the n-type conductivity of Ag2O film was established. Since the film (6–120 nm) is thinner than the space charge region, the dependence of photocurrent and photopotential appears on the film thickness L: i ph ~L and E ph ~L 2. The transition from polycrystalline silver to single crystals as well as the addition of a small amount of gold (X Au ≤ 4 at.%) into the silver lattice decreases the degree of deviation from the stoichiometric composition Ag2O. The parameters of Ag2O film (optical absorption coefficient α, donor defects concentration N D, space charge region W, and Debye’s length of screening L D) depend on the index of a crystal face of silver, volume concentration of gold X Au in the alloy, and film-formation potential E. At Е = 0.52 V, the sequences of variation of these parameters correlate with the reticular density sequence. The growth of the potential disturbs these sequences. The band gap in Ag2O formed on Agpoly, Aghkl, and Ag–Au is 2.32, 2.23, and 2.19 eV. Flat band potential in Ag(I) oxide, formed on Agpoly in 0.5 M KOH is 0.37 V. The appearance of the clear dependence between the state of the oxide/metal interface and the structure-sensitive parameters of semiconductor Ag(I) oxide phase allows considering the anodic formation of Ag2O on Ag as a result of the primary direct electrochemical reaction, not of the precipitation from the near-electrode layer.

Temperature dependence of EXAFS cumulants of Ag nanoparticles in glass

Ag nanoparticles of 1.5 to 7 nm size were produced by ion exchange of soda-lime glass for various duration. Information on local order and thermal vibrations were available by means of X-ray absorption spectroscopy using experiments at the Ag K-edge (25.514 keV). Ratio method and EXAFS fitting procedure were successfully applied to reveal the temperature dependence using the cumulant-expansion method up to third order ones. The temperature dependence of the nearest neighbor Ag-Ag distance appears different from that of polycrystalline Ag foil below 400 K. This effect can be explained by a thermoelastic model describing the mismatch of thermal expansion coefficients of Ag particles and the glass matrix. In addition, the parameter of Ag-Ag bond length of 1.5 nm particles is governed by precursor formation for crystalline Ag nanoparticles. The data of the second cumulant, the Debye-Waller factor (DWF), represent a higher static disorder, especially for nanoparticles of 1.5 – 3.5 nm size, caused by the increasing portion of surface or interface atoms. From the temperature dependent part of DWF we estimated a slightly increased Einstein temperature.

Velocity dependence of the energy loss of very slow proton and deuteron beams in Cu and Ag

We present energy loss measurements of protons and deuterons down to velocities of 0.1 a.u. in very thin polycrystalline Cu and Ag foils, using the transmission technique. As in previous experiments in Au, a transition between two energy loss regimes is observed, i.e., from a stopping due to the excitation of only the free conduction band electrons at the lowest velocities, to a slowing down with the participation of both the free electrons and the loosely bound $d$ electrons. This transition causes a change of the slope in the energy loss versus ion velocity curve at a characteristic threshold velocity related to the binding energy of the $d$ electrons. As shown by model calculations these threshold velocities for Cu and Ag are shifted according to their density of states distributions.

Angle-dependent ultraviolet photoelectron spectroscopy of sputter cleaned polycrystalline noble metals

Polycrystalline noble metal films are commonly used in practical applications across a variety of different fields. However, the surface electronic structure of the noble metals has primarily only been studied on single crystal substrates. In addition, sputter cleaned polycrystalline noble metal films are commonly used substrates in ultraviolet photoelectron spectroscopy (UPS) studies, but have yet to be systematically studied in terms of their photoemission anisotropy. The angle-dependence of the valence band spectra of sputter cleaned polycrystalline Au, Ag and Cu were studied using angle-resolved UPS. It is found that the photoemission is anisotropic with respect to photoelectron take-off angle. The results for Ag and Cu are in good agreement with previous reports of surface d-band narrowing in polycrystalline noble metal films. However, significant anisotropies in the d-band, s-band and Fermi edge of sputter cleaned Au are observed, which cannot be attributed to surface d-band narrowing alone. The unusual results for Au are attributed to drastic changes in the film morphology near the surface as a result of sputter cleaning.

Diffusion induced grain boundary migration in the Ag–Zn system

Diffusion induced grain boundary migration (DIGM) has been studied in the Ag–Zn system by exposing polycrystalline Ag to Zn vapor with a Ag-25 wt.% Zn alloy as the source of Zn. The time and temperature dependence of the migration distance has been studied in the temperature range 660 to 810 K. The composition profile was obtained on the sheet cross-section along a line perpendicular to the edge to determine D b δ at each temperature. Similarly, the Zn concentration profile was obtained from the region swept by the migrating grain boundary. The coherency strain energy, the total chemical free energy change and the effective free energy change were calculated. The regular solution model was used for calculating the free energy change. It has been observed that a fraction of the total free energy has been used for volume diffusion in front of the migrating grain boundary. The instantaneous rate of migration has been observed to be directly proportional to the chemical free energy change and the coherency strain energy. The instantaneous rate of migration versus the composition graph has indicated that the driving force for DIGM in the Ag–Zn system is the coherency strain energy. The fine-grained layer formed at the surface follows a parabolic growth behavior. The diffusion coefficients calculated from the composition profile as well as from the rate of growth of the fine-grained layer are of the same order of magnitude. The diffusivity values are four to six orders of magnitude higher than the volume diffusion coefficients. From the activation energy and the diffusivities it is clear that DIGM in the Ag–Zn system occurs by the diffusion of Zn along the grain boundaries of polycrystalline Ag.

Sputtering of neutral clusters from silver–gold alloys

Polycrystalline Ag, Ag 20Au 80, Ag 40Au 60, Ag 80Au 20 and Au samples were bombarded with 15 keV Ar + at 60° incidence and the resulting secondary neutral yield distribution was studied by non-resonant laser postionisation mass spectrometry. Neutral clusters containing up to 21 atoms were observed for the targets. The yield of neutral clusters, Ag m Au n− m , containing n atoms, Y n , was found to follow a power in n, i.e. Y n ∝ n − δ , where the exponent δ varied from 3.2 to 4.0. For a fixed n, the cluster yields showed a variation with number of gold atoms similar to that expected for a binomial distribution. In addition, the cluster compositions from the sputtered alloys were indicative of sputtering from a gold rich surface.

Preferential growth and orientation relationship of Ag3Sn grains formed between molten Sn and (001) Ag single crystal

The current study shows that there is a preferred orientation relationship between Ag3Sn and Ag in reaction between molten Sn and Ag. Due to the preferred orientation relationship, the morphology of Ag3Sn grains formed on (001) Ag single crystal is different from those formed on (011), (358) single crystal Ag, and polycrystalline Ag Facet scallop-type Ag3Sn grains formed irregularly on (011), (358) single crystal Ag, and polycrystalline Ag; whereas the regular Ag3Sn grains with parallel edges grew on (001) Ag single crystal, and they were elongated along two perpendicular directions. The orientation relationship between Ag3Sn grains and (001) Ag single crystal was determined using electron backscattered diffraction. The preferential growth of regular Ag3Sn grains with parallel edges formed on (001) Ag single crystal can be attributed to their minimum misfit.

Synthesis and high temperature thermoelectric properties of Ba xAg yCa 3− x− yCo 4O 9 compounds

Polycrystalline Ba x Ag y Ca 3− x− y Co 4O 9 bulk samples were prepared by citrate acid sol–gel and spark plasma sintering method. The grain orientation, microstructure and high temperature thermoelectric properties of the bulk samples were systematically studied. Small quantities of the secondary phase Ag precipitated within the x ≤ y compound sample matrices, the grain orientation and microstructure of Ca 3Co 4O 9 could be optimized. The electrical resistivity was decreased and the thermal conductivity was increased by increasing y/ x ratio. The x = y = 0.1 sample exhibited lowest electrical resistivity (7.2 mΩ cm at 973 K) and thermal conductivity (1.41 W/mK at 973 K) simultaneously with high Seebeck coefficient (172 μV/K at 973 K), the dimensionless figure of merit could reach 0.29 at 973 K.

High-Pressure Raman Spectroscopy of Molecular Monolayers Adsorbed on a Metal Surface

The effects of high pressure up to 10 GPa on organic molecules in the form of a solid or a self-assembled monolayer (SAM) on a metal surface are investigated by Raman spectroscopy. The SAMs studied are benzenethiol (BT) and benzenemethylthiol (BMT) on polycrystalline Ag(111). Raman spectra of the SAMs are obtained using a periodically nanostructured Ag surface that provides surface-enhanced Raman scattering (SERS). All the vibrational modes studied show a pressure-dependent blue-shift. These blue-shifts are remarkably similar for the SAMs and solids. There are some minor differences between the SAM and solid-state spectra in the ν18a symmetric in-plane CH-bend and in the νCS CS-stretch. The ν18a mode in BT blue-shifts more in the SAM than in the solid, but in BMT it blue-shifts less in the SAM than in the solid. The greater blue-shift for the BT SAM is attributed to the much lower surface coverage of BT, causing greater compressibility. In the SAM, νCS blue-shifts slower in BT than in the solid, but in BM...

Electrochemical properties of gas-generated silver nanoparticles in the presence of cyano- and chloride-containing compounds

The electrochemistry of gas-generated naked Ag nanoparticles deposited on indium-tin oxide covered glass plates is compared to bulk polycrystalline Ag. The nano-specific electrochemistry has been identified and includes the preferential formation of beta-oxides. In 100 mM KOH supporting electrolyte, disruption of beta-oxide formation is exploited to test for the presence of diethyl cyanophosphonate. While in 8.0 M KOH, beta-oxide formation is enhanced leading to testing capabilities for 2-chloroethyl ethyl sulfide. These non-redox active compounds are effective simulants for the chemical warfare agents Tabun nerve agent and sulfur mustard, respectively.