Polycrystalline Ag Research Articles

Texture and high temperature transport properties of Ag xCa 3− xCo 4O 9 (0 ≤ x ≤ 0.6) compounds

Polycrystalline Ag x Ca 3− x Co 4O 9 ( x = 0–0.6) compound samples were prepared by combining citrate acid sol–gel method with spark plasma sintering and the phase composition, orientation, texture and high temperature transport properties were investigated in detail. The results show that main phase Ag x Ca 3− x Co 4O 9 compounds are formed with a small quantity of silver phase which distributes unevenly in the Ag x Ca 3− x Co 4O 9 matrix and so greatly weakens the orientations of Ag x Ca 3− x Co 4O 9. All samples exhibit semiconductor transport properties except for the x = 0.6 sample which exhibits metallic transport characteristic. The electrical resistivity and the Seebeck coefficient are simultaneously decreased with increasing Ag substitution. The reasons are attributed to hole concentration adjustment and shortcut effect of distributed Ag in Ag x Ca 3− x Co 4O 9 matrix during conduction process. The power factor as a function of Seebeck coefficient and resistivity could be altered with x and it is enhanced at x = 0.3 with its value exceeding 6.8 μW/cm K 2 at 1033 K indicating that the electrical properties could be improved by optimizing the composition and texture in sol–gel process.

Electronic structure investigation of nickel phthalocyanine thin film interfaces with inorganic and organic substrates

AbstractThe interfacial electronic properties of ultra thin films of Nickel Phthalocyanine (NiPc) on inorganic (polycrystalline Au and Ag, sputtered‐ITO) as well as organic (PEDOT:PSS) substrates were compared. The formation of the interfaces was studied by X‐ray and Ultra‐Violet Photoelectron Spectroscopies (XPS, UPS). From the experimental results, information about the interfacial chemistry, band bending in the organic semiconductor and interfacial dipoles was deduced. The valence band structure, the HOMO position and the work function of the NiPc were also determined. The hole injection barrier at the interface was obtained for all substrates and the energy band diagrams were traced in all cases. A Fermi level alignment was found in the interfaces with inorganic substrates, whereas a pinning of the Fermi level was observed with the organic substrate resulting in a significant decrease of the hole injection barrier. All systems investigated divert from the Schottky‐Mott rule and the observed interfacial dipoles appear to increase as the work function value of the substrate increases. The present study shows the importance of the chemical character of the substrate in the electronic properties of the interfaces with an organic semiconductor. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ballistic electron emission spectroscopy on Ag/Si devices

In this work we report on ballistic electron emission spectroscopy (BEES)studies on epitaxial layers of silver grown on silicon surfaces, with either aSi(111)-(7 × 7)or Si(100)-(2 × 1) surface reconstruction. The experiments were done at low temperature and in ultra-high vacuum(UHV). In addition, BEES measurements on polycrystalline Ag films grown on hydrogen-terminatedH:Si(111)-(1 × 1)and H:Si(100)-(2 × 1) surfaces were performed. The Schottky barrier heights were evaluated by BEES. Theresults are compared to the values for the barrier height reported for macroscopic Schottkydiodes. We show that the barrier heights for the epitaxial films substantially differ from thevalues measured on polycrystalline Ag films, suggesting a strong effect of the interface onthe barrier height.

Electrochemical deposition of quaternary Cu2ZnSnS4 thin films as potential solar cell material

Quaternary compound semiconductor Cu2ZnSnS4 (CZTS), which appears to be a promising candidate for the absorber of a thin film type solar cell, was grown on polycrystalline Ag substrates by electrochemical epitaxial method. The elements were deposited in the following sequence: S/Sn/S/Cu/S/Zn/S/Cu… , the order being one cycle of SnS, one cycle of ZnS and two cycles of CuS. Morphology of the deposit has been characterized by field emission scanning electron microscopy (FE-SEM) with an energy dispersive X-ray (EDX) analyzer. X-ray diffraction (XRD) studies showed a (112) preferred orientation for the deposit. X-ray photoelectron spectroscopy (XPS) of the deposit indicated an approximate ratio 2:1:1:4 of Cu, Zn, Sn, and S, the expected stoichiometry for the deposit, and similar results have been obtained from EDX data. Near IR absorption measurements of the deposit at room temperature indicated a direct band gap of 1.5 eV, and open-circuit potential (OCP) studies indicated a good p-type property, both of which were suitable for fabricating a thin film solar cell.

Active surface formation and catalytic activity of phosphorous-promoted electrolytic silver in the selective oxidation of ethylene glycol to glyoxal

Abstract Unpromoted and phosphorus-promoted electrolytic silver catalysts have been investigated in the partial oxidation of ethylene glycol (EG). It was shown that the addition of the phosphorus-containing promoter on the surface of electrolytic Ag catalyst led to 15–20% increase in glyoxal (GO) yield. The formation mechanism of the active P-containing surfaces of silver catalyst as well as polycrystalline Ag foil has been studied by means of X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD) and scanning electron microscopy (SEM) methods. It was shown that silver clusters located nearby the P-containing Ag surface participate in the ethylene glycol oxidation into glyoxal. The rise of glyoxal selectivity is explained by the absence of low temperature peak at 250 °C in TPD spectra of both P-promoted Ag foil and electrolytic Ag catalysts. This peak was assigned to the decomposition of surface oxide-like species (Ag 2 s O) responsible for deep oxidation of ethylene glycol.

Interaction of methanol with amorphous solid water

The interaction of methanol (MeOH) with amorphous solid water (ASW) composed of D2O molecules, prepared at 125 K on a polycrystalline Ag substrate, was studied with metastable-impact-electron spectroscopy, reflection-absorption infrared spectroscopy, and temperature-programmed desorption mass spectroscopy. In connection with the experiments, classical molecular dynamics (MD) simulations have been performed on a single CH3OH molecule adsorbed at the ice surface (T=190 K), providing further insights into the binding and adsorption properties of the molecule at the ice surface. Consistently with the experimental deductions and previous studies, MeOH is found to adsorb with the hydroxyl group pointing toward dangling bonds of the ice surface, the CH3 group being oriented upwards, slightly tilted with respect to the surface normal. It forms the toplayer up to the onset of the simultaneous desorption of D2O and MeOH. At low coverage the adsorption is dominated by the formation of two strong hydrogen bonds as evidenced by the MD results. During the buildup of the first methanol layer on top of an ASW film the MeOH-MeOH interaction via hydrogen-bond formation becomes of importance as well. The interaction of D2O with solid methanol films and the codeposition of MeOH and D2O were also investigated experimentally; these experiments showed that D2O molecules supplied to a solid methanol film become embedded into the film.

Investigation of AG(I) oxide films by combination of it RRDE and photopotential spectroscopy

AbstractThe RRDE multicycle chronoammetry makes it possible to obtain separately the partial currents of silver ionization, anodic oxide formation, and chemical oxide dissolution. In the range of low anodic potentials (0.48–0.51 V), the process of active silver dissolution from the open parts of the surface and through the pores of oxide film prevails; the phase formation current drops fast. At higher potentials (0.52–0.53 V), the phase formation current prevails and noticeably exceeds the rate of the chemical oxide dissolution. The thickness of Ag2O film rapidly increases; and the net phase formation current is close to 100% during the whole period of polarization. Ag(I) oxide is an n‐type semiconductor with an excess of silver atoms. Their concentration in the oxide film formed on monocrystalline Ag(111), Ag(110), and Ag(100) is less than in the film formed on polycrystalline Ag. Copyright © 2008 John Wiley & Sons, Ltd.

ANODIC formation of thin Cu(I) and Ag(I) oxide films on Cu‐Au and Ag—Au alloys

AbstractThe anodic dissolution of Cu, Ag and their alloys with gold under the conditions of the formation of copper or silver oxides was examined by the technique of cyclic voltammetry, chronoammetry and photopotential measurements. The anodic formation and cathodic reduction of Cu(I) oxide on copper and Cu‐Au alloys or Ag(I) oxide on silver and Ag‐Au alloys with XAu≤30 at.% are controlled by migration in the oxide film. The peculiarity of Ag‐Au system is connected with the duplex structure of the oxide film and the initial selective dissolution of silver from Ag15Au and Ag30Au alloys. Ag2O oxide is an n‐type semiconductor with an excess of silver atoms. Oxide layers formed on monocrystalline silver are more stoichiometric than the layer formed on polycrystalline Ag. Copyright © 2008 John Wiley & Sons, Ltd.

Comparative study of the interaction of pyridine with polycrystalline Ag and amorphous solid water

The interaction of pyridine (C5H5N) with polycrystalline Ag and amorphous solid water (D2O) is compared. Metastable impact electron spectroscopy (MIES) and reflection-absorption infrared spectroscopy (RAIRS) were utilized to obtain information on the structure of the pyridine-Ag and pyridine-water interfaces. On polycrystalline Ag, C5H5N adsorbs with its molecular axis perpendicular to the surface whereby a work function decrease of 1.5 eV takes place during the build up of the first layer. In the second layer the molecular axis is tilted with respect to the surface normal. On amorphous solid water, C5H5N is initially adsorbed on top with its ring plane oriented preferentially near parallel with respect to the surface, reflecting the contribution of two different interactions to the bonding, the formation of a pi-hydrogen bond, and competitive bonding via the nitrogen lone pair. Coverage-driven reorientation takes place during the completion of the first monolayer and increases the average tilt angle. We have followed the growth of pyridine films up to the third layer which, according to RAIRS, shows clear signs of condensation. No embedding of pyridine species into the underlying water film can be noticed when heating up to desorption. The exposure of a pyridine film at 124 K to D2O molecules does not lead to on top adsorption. Instead, D2O becomes initially embedded into the pyridine film, and RAIRS indicates solvation of the pyridine species.

Interaction of benzene with amorphous solid water adsorbed on polycrystalline Ag

The interaction of benzene with polycrystalline Ag and amorphous solid water (D(2)O) deposited thereupon at 124 K was investigated. Metastable impact electron spectroscopy, Reflection-absorption infrared spectroscopy, and temperature programmed desorption were utilized to obtain information on the electronic structure and the relative contribution to the bonding properties of the aromatic molecules among themselves and with D(2)O. On Ag, the benzene molecular plane is oriented parallel to the surface in the first layer. The second layer is tilted with respect to the first one. A total work function decrease of 0.8 eV takes place during the buildup of the first two layers. On amorphous solid water, the orientational distribution of the benzene molecular planes is initially peaked at an angle parallel to the water surface. During the completion of the first adlayer a coverage-induced reorientation takes place, inducing a tilt of the benzene molecules of the first adlayer. Still larger benzene exposures appear to lead to the formation of three-dimensional benzene clusters. Films produced by codepositing benzene and D(2)O or by postdepositing D(2)O layers on benzene films display "volcano like" benzene desorption during ice crystallization.

Structural characterization of polycrystalline Ag–In–Se thin films deposited by e-beam technique

The Ag–In–Se thin films were deposited by e-beam evaporation of the Ag 3 In 5 Se 9 single crystal powder under high vacuum without intentional doping. Energy dispersive X-ray analysis (EDXA) showed the decreasing behavior of Se and Ag in the structure depending on the annealing. X-ray diffraction (XRD) analysis showed that as-grown films have amorphous structure while annealing the films under nitrogen environment at 200 °C transformed from the amorphous to polycrystalline structure. The crystallinity of the films improved as annealing temperature increases up to 400 °C by 100 °C-step. The polycrystalline films show mixed binary and ternary crystalline phases. Each phase was determined by comparing XRD patterns with complete data cards as Ag 3In 5Se 9, AgInSe 2, In 4Se 3, In 2Se 3, InSe, Se 6 and Se. The existence of Se segregation was supported by the formation of Se aggregates in crystalline phases of Se 6 and Se. The X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analysis have been carried out in order to obtain detailed information about the atomic composition, chemical states and morphology of the thin film surface. The decomposition of In 4d, Se 3d and Ag 3d photoelectron peaks revealed the existence of In–In, In–Se, In–Ag, Se–Se and Ag–Ag bondings in as-grown thin films. After annealing the thin films at different temperatures, the concentration of In–Se and In–Ag bonds decreases significantly, which results in an In-rich, but Ag- and Se-deficient thin film structure. The roughness of the film surface as a result of application of post-annealing in between 200 and 400 °C monitored by AFM technique was observed to change from 1.81 to 22.89 nm.

Kinetic peculiarities of anodic dissolution of silver and Ag–Au alloys under the conditions of oxide formation

The kinetics of anodic dissolution of silver and Ag–Au alloys ( X Au = 0.1–30 at.% Au) in aqueous alkaline solution under the conditions of the formation of silver oxides has been examined. The techniques of cyclic voltammetry, chronoammetry, and photopotential measurements have been used. It was established that the anodic formation and cathodic reduction of Ag 2O on silver and alloys are controlled by migration in the oxide layer. Ag 2O oxide is an n-type semiconductor with an excess of silver atoms. Oxide layers formed on monocrystalline Ag(1 1 1) and Ag(1 1 0) are more stoichiometric than the layer formed on polycrystalline Ag.

Room-temperature magnetoresistance effects of Ag-added Fe 3O 4 films with single-domain grains

Polycrystalline Ag x (Fe 3O 4) 1− x films ( x = 0 , 0.1, 0.2 and 0.3) have been prepared by the sol–gel method in combination of the spin-coating technique with a precursor solution containing polyvinyl alcohol (PVA) on fused quartz substrates. XRD analysis and SEM images indicate that the Fe 3O 4 grains are nearly spherical single-domain particles. The coercivities of the films are about 290 Oe for x = 0.1 and 360 Oe for x = 0.3 , respectively, which are nearly the same as the magnetocrystalline anisotropic effective field H K of Fe 3O 4. At 300 K, the x = 0.1 film has a maximal magnetoresistance of −8.7% at a magnetic field of 50 kOe and −3.5% at 8.8 kOe, while the pure Fe 3O 4 film is only −2.2% at 8.8 kOe. This enhancement of the MR can be attributed to the contribution from the spin-dependent scattering at the Ag–Fe 3O 4 interfaces as well as the spin-polarized tunneling at boundaries of Fe 3O 4 grains of the spin-polarized electrons. In addition, different MR behaviors for Ag-added Fe 3O 4 bulk polycrystalline samples and polycrystalline films are discussed.

Microstructure and mechanical properties of polycrystalline-Ag/amorphous-CoZrNb multilayers

Ag/CoZrNb multilayers were prepared by direct current magnetron sputtering. Their microstructure, hardness, elastic modulus and plastic deformation were investigated by X-ray diffraction, high-resolution transmission electron microscopy, X-ray absorption near-edge structure, field emission scanning electron microscopy and nanoindentation technique. The results show that the multilayers have well modulated structure. For all the multilayers, Ag layer is polycrystalline structure, while CoZrNb layer is amorphous structure. With the decrease of modulation periodicity the elastic modulus decreases due to the compliant interface. The polycrystalline Ag layer not only makes the hardness enhanced with the decrease of modulation periodicity, but also restricts the propagation of shear bands and promotes the nucleation of new shear bands, which may be of help for the plasticity enhancement of amorphous CoZrNb layer.

Preparation of visible-light-active Ag and In-doped ZnS thin film photoelectrodes by reactive magnetron co-sputtering

Ag and In-doped ZnS thin films were prepared by direct current and radio frequency reactive co-sputtering of a zinc target and an indium target covered by Ag wires in gas mixtures of argon and hydrogen sulfide. The influences of the various deposition parameters on the structural, optical and electrical performances of thin films as visible-light-active photoelectrodes have been investigated. The X-ray diffraction data revealed that the polycrystalline (Ag, In, Zn)S thin films contain mixed structures of AgIn 5S 8 and ZnS. The images from an atomic force microscopy showed that the surface roughness was significantly increased with incremental increases of plasma power, resulting in increases of the refractive index and the reduction in photocurrent. The film deposited in the optimal deposition parameters, DC and RF powers at 50 W using a hydrogen sulfide ratio of 0.40 with a substrate temperature of 300 °C, exhibits the smallest refractive index, highest donor density, and the highest photocurrent density under illumination with a solar simulator (AM 1.5) at + 1.00 V vs. Ag/AgCl. The band-gap energies of as-prepared films are found to be in the range of 2.28 to 2.39 eV and flat-band potentials determined by application of the Mott–Schottky equation vary from − 0.55 to − 0.68 V versus normal hydrogen electrode.

The STM view of the initial stages of polycrystalline Ag film formation

The growth of Ag thin films deposited at 300 K on amorphised Si surfaces under ultra high vacuum conditions is investigated by in situ scanning tunnelling microscopy. The analysis of film morphology as a function of film thickness together with additional annealing experiments allow a quite complete picture of the film formation processes to be obtained.

Dissolution–recrystallization mechanism for the conversion of silver nanospheres to triangular nanoplates

A solution chemistry method for transforming polycrystalline Ag spherical particles into single crystalline triangular Ag nanoplates has been developed. The synthesis consists of three consecutive steps: (1) the synthesis of Ag nanospheres by NaBH 4 reduction of AgNO 3 in the presence of sodium citrate; (2) the conversion of citrate-stabilized Ag nanospheres into SDS (sodium dodecyl sulfate)-stabilized Ag nanospheres, and (3) the aging of the SDS-stabilized Ag nanospheres in 0.01 M NaCl solution. Our study indicates that the shape evolved through a Ag nanoparticle dissolution- and re-deposition process; and demonstrated the critical role of SDS in the process: SDS regulates the dynamics in the dissolved O 2/Cl − etching of the Ag nanospheres and the reduction of the released Ag + by citrate ions in the same solution. SDS also functions as a shape-directing agent to assimilate the Ag 0 atoms into single crystalline triangular Ag nanoplates. A model for the shape conversion is also proposed which provides the clue for the synthesis of anisotropic Ag nanoparticles with other shapes (rods, wires, cubes, etc.).

Laser-Induced Microstructural Modification of Polycrystalline Cu and Ag Films Encapsulated in SiO2

ABSTRACTExcimer-laser-induced rapid lateral solidification was used to produce large grain microstructures in copper and silver thin films. These were multilayer thin film structures consisting of sputter deposited copper and silver thin films encapsulated by silica (SiO2/metal/SiO2/Si substrate). In this process, a single excimer laser pulse and projection imaging optics were used to melt a 60 micron wide line in the metal film. The resolidification of the melted lines is found to occur laterally in the plane of the film, resulting in grains greater than 20 um in length and 1 um wide. Electron diffraction analysis allowed identification of a strong <001> texture in the growth direction along the major axis of the elongated grains as well as similar texture parallel to the film surface. Various dislocation and faulted defect structures are identified and examined in the context of the rapid solidification and potential application to interconnects.

Electronic properties of Ag nanoparticle arrays. A Kelvin probe and high resolution XPS study

The electronic properties of citrate stabilised Ag nanoparticles with sizes ranging from 4 to 35 nm were investigated by the Kelvin probe method and high resolution XPS. Two and three dimensional assemblies of the particles were prepared by electrostatic adsorption from aqueous solution onto poly-l-lysine modified surfaces. The work function of the Ag particles increased from 5.29 +/- 0.05 to 5.53 +/- 0.05 eV as the particle size decreased. These values are approximately 0.8 eV higher than for clean polycrystalline Ag surfaces. The origin of these remarkable high work functions cannot be explained in terms of either citrate induced changes in the surface dipole or image forces in the confined metallic domains. High resolution XPS spectra of the Ag 3d(5/2) core level were characterised by broad bands and a 0.4 eV shift towards lower binding energies for the smallest particles. Comparisons with reported studies on extended Ag surfaces indicate that as-grown particles exhibit partially oxidised surfaces. The behaviour of the work function further suggests that the strength of the Ag-O bonding increases with decreasing particle sizes. These findings are highly relevant to the interpretation of the catalytic properties of Ag nanoparticles.

In Situ Investigation of the Silver-CTAB System

AbstractRecent research has shown that biologically inspired approaches to materials synthesis and self-assembly, hold promise of unprecedented atomic level control of structure and interfaces. In particular, the use of organic molecules to control the production of inorganic technological materials has the potential for controlling grain structure to enhance material strength; controlling facet expression for enhanced catalytic activity; and controlling the shape of nanostructured materials to optimize optical, electrical and magnetic properties. In this work, we use organic molecules to modify silver crystal shapes towards understanding the metal-organic interactions that lead to nanoparticle shape control.Using in situ electrochemical AFM (EC-AFM) as an in situ probe, we study the influence of a cationic surfactant cetyltrimethylamminobromide (CTAB) on Ag growth during electrochemical deposition on Ag(100). The results show that the organic surfactant leads to a unique crystal growth habit. With CTAB present in the growth solution, Ag islands grow in a truncated pyramidal shape. To understand the shape evolution of the Ag islands, we utilize electron backscatter diffraction (EBSD) in conjunction with microscopic ellipsometry to characterize the facet-specific binding of the organic molecules to large-grained polycrystalline Ag substrates.