Silver Film Electrodes Research Articles

Unconventional thickness dependence of electrical resistivity of silver film electrodes in substoichiometric oxidation states

The scaling down of metallic electrodes into ultrathin film geometries presents significant challenges in precisely controlling electrical resistivity. This difficulty stems from the rapid variation in resistivity with thickness, particularly near the percolation threshold. Currently, our understanding of the prediction of thickness-dependent resistivity in metallic film electrodes in volatile substoichiometric oxide (suboxide) states is limited. This study offers experimental and numerical evidence demonstrating a marked resistivity fluctuation spanning four to five orders of magnitude during the initial growth stages of suboxidized Ag film electrodes. These stages range from cluster coalescence to reaching the percolation threshold. The unusual resistivity change is attributed to the variation in suboxidation states with thickness, as well as the outward migration of interstitial O ions. These findings offer a crucial framework for controlling the electrical properties of thin metallic oxide films in extreme suboxidation states, extending beyond the conventional understanding applicable to thermodynamically stable metallic oxide phases.

Electrochemical and Optical Analysis of Various Compositions of Au and Ag Layers for Blood Cancer Prognosis

The fabrication of silver (Ag) and gold (Au) thin film electrodes was successfully carried out using the DC sputtering deposition method. These thin film electrodes were able to detect the increase in serum albumin concentration that was used as a prognostic factor for leukemia. The simulation and the optical experimental analysis show that an increase in BSA concentration can increase the absorbance peak observed at a wavelength of 435 nm on hypoalbumin medium and 470 nm on normal concentration of serum albumin medium. The performance of the electrodes was electrochemically tested, in which it was shown that a decrease in oxidation and reduction peaks occurred with respect to an increase in BSA concentration. An oxidation peak was observed at a voltage of 0.5 V for the Ag thin film. For the Au, Au/Ag, and Ag/Au thin films, an oxidation peak was observed at a voltage of 1.0 V. The limits of detection (LODs) of the Ag, Ag/Au, Au, and Au/Ag thin films were 0.56, 0.24, 0.64, and 0.36 g/dL, respectively. Therefore, based on both the electrochemical and optical analysis, the Ag/Au thin film possessed the highest potential for prognosis monitoring of leukemia compared with the other Ag and Au thin films.

Stabilizing Silver Window Electrodes for Organic Photovoltaics Using a Mercaptosilane Monolayer

A single layer of the bifunctional molecule 3-mercaptopropyltrimethoxysilane is shown to be remarkably effective at improving the stability of optically thin silver film electrodes towards spontaneous morphological change and oxidation by airborne sulfur. Inclusion of this layer in the novel transparent electrode; WO3 (30 nm) / silver (13 nm) / sol-gel ZnO (27 nm), at the silver / ZnO interface improves the efficiency of organic photovoltaic devices using this electrode by 20%, such that the power conversion efficiency is very close to that achievable using a conventional indium-tin oxide glass electrode; 9.6 % ± 0.2 % vs 10.0 % ± 0.3 %, with the advantage that the silver electrode has a sheet resistance one third that of the ITO glass (4 Ohms sq-1). The mercaptosilane monolayer is also shown to retard silver diffusion into the ZnO layer whilst imparting a favorable 400 meV reduction in electrode work function. In addition to its utility inside the device, this molecular layer is shown to be useful for improving the stability of the silver film electrodes in top-illuminated semi-transparent photovoltaics, since it can be deposited directly onto a completed device from the vapor phase.

Nitrogen-Mediated Growth of Silver Nanocrystals to Form UltraThin, High-Purity Silver-Film Electrodes with Broad band Transparency for Solar Cells.

Controlling the shape and crystallography of nanocrystals during the early growth stages of a noble metal layer is important because of its correlation with the final layer morphology and optoelectrical features, but this task is unattainable in vapor deposition processes dominated by artificially uncontrollable thermodynamic free energies. We report on experimental evidence for the controllable evolution of Ag nanocrystals as induced by the addition of nitrogen, presumed to be nonresidual in the Ag lattice given its strong float-out behavior. This atypical formation of energetically stable Ag nanocrystals with significantly improved wetting abilities on a chemically heterogeneous substrate promotes the development of an atomically flat, ultrathin, high-purity Ag layer with a thickness of only 5 nm. This facilitates the fabrication of Ag thin-film electrodes exhibiting highly enhanced optical transparency over a broad spectral range in the visible and near-infrared spectral range. An Ag thin-film electrode with a ZnO/Ag/ZnO configuration exhibits an average transmittance of about 95% in the spectral range of 400-800 nm with a maximum transmittance of over 98% at 580 nm, which is comparable with the best transparency values so far reported for transparent electrodes. This degree of optical transparency provides an excellent chance to improve the photon absorption of photovoltaic devices employing an Ag thin film as their window electrode. This is clearly confirmed by the superior performance of a flexible organic solar cell with a power conversion efficiency of 8.0%, which is far superior to that of the same solar cell using a conventional amorphous indium tin oxide electrode (6.4%).

Ultrathin Silver Film Electrodes with Ultralow Optical and Electrical Losses for Flexible Organic Photovoltaics.

Improving the wetting ability of Ag on chemically heterogeneous oxides is technically important to fabricate ultrathin, continuous films that would facilitate the minimization of optical and electrical losses to develop qualified transparent Ag film electrodes in the state-of-the-art optoelectronic devices. This goal has yet to be attained, however, because conventional techniques to improve wetting of Ag based on heterogeneous metallic wetting layers are restricted by serious optical losses from wetting layers. Herein, we report on a simple and effective technique based on the partial oxidation of Ag nanoclusters in the early stages of Ag growth. This promotes the rapid evolution of the subsequently deposited pure Ag into a completely continuous layer on the ZnO substrate, as verified by experimental and numerical evidence. The improvement in the Ag wetting ability allows the development of a highly transparent, ultrathin (6 nm) Ag continuous film, exhibiting an average optical transmittance of 94% in the spectral range 400-800 nm and a sheet resistance of 12.5 Ω sq-1, which would be well-suited for application to an efficient front window electrode for flexible solar cell devices fabricated on polymer substrates.

Large actuation and high dielectric strength in metallized dielectric elastomer actuators

Metal films are seldom used as compliant electrodes for dielectric elastomer actuator (DEA) because they tend to restrain deformation of soft dielectrics. This work showed that silver film electrodes formed by electroless deposition (ELD) are indeed stretchable, and the DEA using ELD silver electrodes is able to generate an actuation up to 50% areal strain. Such ELD silver electrodes can self-heal, remain conductive at up to 33% uni-axial strain, and do not stiffen the dielectric layer as much as the sputtered silver electrodes. This metallized DEA can sustain a high breakdown field up to 350 MV/m, which is good for generating a large actuation force.

Preparation of SERS-active silver film electrodes via electrocrystallization of silver

The electrodeposition of a sufficiently large amount of silver on silver films at high over potentials leads to excellent substrates for surface-enhanced Raman scattering (SERS) spectroscopy. The surfaces roughened in this manner show great uniformity across the active area and exhibit SERS enhancement factors which are superior to those of silver surfaces roughened by conventional oxidation–reduction cycles. Since they are excellently reproduced from one sample to another, the prospects for application of this substrate for analytical purposes are very promising. Copyright © 2000 John Wiley & Sons, Ltd.

Adsorption of metal cations precisely quantified by surface resistance of thin epitaxial silver film electrodes

dc-resistance measurements of metal thin films can be used to investigate processes at the solid-vacuum and solid-electrolyte boundary. In electrochemistry this is a new method to determine the quantity of adsorbed species on solid electrodes. We have grown an epitaxial Ag(111) thin film electrode on a Si(111) substrate with stable characteristics under electrochemical conditions [1]. The adsorption and desorption of small quantities of metal cations from aqueous solutions ( eg 1 μM Pb 2+) are detected by changes of the dc-resistance, resulting from a diffuse scattering of conduction electrons by the adsorbates. In contrast to polycrystalline silver films epitaxial Ag(111) thin film electrodes allow us to perform many deposition and stripping cycles of lead—without changing the properties of the thin film.

Surface structural changes of evaporated thin silver film electrodes during the adsorption of chloride ion

It is well known that the surface of metal electrodes undergoes structural changes when subjected to different electrochemical treatments (potential cycling, upd reactions, etc) [l-5]. The structural changes of silver in certain electrolytes. particularly chloride. have received much attention because of their connection with the appearance of the SERS effect. The capacitance vs. potential curve of single silver crystals in chloride solutions [6] exhibits a narrow peak in the potential range between -0.5 and 0.0 V (vs. SCE), depending on the crystallographic orientation. Apparently this peak does not appear in polycrystalline silver and evaporated silver thin films [7-91. The peak has been attributed to partial charge transfer and later to a rearrangement of the adsorbed surface layer by Valette et al. [6,10] and to a reconstruction of the silver surface layer by Fleishmann et al. [ll]. Voltammetric studies with polycrystalline [12-141 and single crystal (111) [15] electrodes in chloride-containing electrolytes show, in the potential range mentioned above, the appearance of a small, reversible peak before the massive formation of AgCl, involving a charge smaller than a monolayer of AgCl. This peak has been attributed [13] to the formation of a submonolayer of adsorbed AgCl. It has also been found that the charge and the peak potential depend strongly on the pretreatment of the electrode. Hubbard and co-workers [15] have shown by LEED and Auger spectroscopies that on silver (111) this peak corresponds to a transition from a diffuse (1 X 1) to an ordered Ag (111) structure, (6 X fi)R30”. Valette and Parsons [lo], from the charge dependence of the amount of specifically adsorbed chloride on (110) single silver crystals, have proposed a structure of c(5 X 2) for the adsorbed chloride at the potential of the narrow peak in the C vs. E curve. In this paper we will show that the appearance of this peak is connected with profound changes of the capacitative response of evaporated thin silver film electrodes.

The temperature dependence of electrical conduction in a discontinuous carbon film device between silver film electrodes

The temperature dependence of the d.c. film current and a.c. (1kHz) current- voltage characteristic were measured as the device temperature was raised from 77 to 423 K. It was shown that they differ from each other in the three voltage ranges I(0∼ V T, II( V T∼ V U and III( V U″16V). V T = 2.1 V is the threshold voltage of OFF-ON switching, and V U = 8−9 V is the upper limit of the voltage-controlled negative resistance range. The film currents in a device applied at 6 V started to increase rapidly from 220 K. This increase was caused by the regeneration of conducting paths broken at 77 K. From the analysis of the a.c. characteristics, two possible electrical conduction processes in the formed region were deduced. The first is by a semiconductive carbon filament that is formed between carbon fragments, and the second is by electronic tunnelling through a microslit between the carbon fragments.

The temperature dependence of electron emission from a discontinuous carbon film device between silver film electrodes

Electron emission characteristics are studied by applying an a.c. (1 kHz) bias voltage of 11–16 V to the film device at temperatures of 77–423 K. The emission currents obey the Fowler-Nordheim equation in the lower voltage range but saturate in the higher voltage range. This saturation effect is dominant at high temperatures. It is shown that this can be caused by positive space charges distributed in excess in the cathode metal-insulator interface region of the discontinuous film and an increased space charge density with rising temperature. When the a.c. characteristics are plotted on a semilogarithmic graph, they shift toward higher voltage with increasing amplitude. From this result it is suggested that excess negative space charges are localized in the discontinuous films and increase in quantity as the amplitude increases.

ChemInform Abstract: POTENTIAL DEPENDENCE AND TIME EVOLUTION OF THE DOUBLE LAYER STRUCTURE AND TOPOGRAPHY OF SILVER ELECTRODES. PART I: SMOOTH SILVER FILMS

AbstractAn auf gedampften (l l l)‐Ag‐Filmen wurde die Doppelschicht‐Kapazität in Lösungen mit verschieden stark adsorbierbaren Spezies untersucht (Potentialbereiche der spezifischen Adsorption von Cl′, S2", CN′, SCN‐).

Potential Dependence and Time Evolution of the Double Layer Structure and Topography of Silver Electrodes. Part I: Smooth Silver Films

AbstractDouble layer capacity of evaporated silver film electrodes was studied as a function of potential and of time in solutions containing different strongly adsorbable species. The potential regime of specific adsorption of chloride, cyanide, thiocyanate, and sulfide ions is determined. From the time dependence of the double layer capacitance as well as from electron micrographs, it can be deduced that surface migration takes place which leads to a flattening of the surface. In the case of sulfide and thiocyanate ions an additional process leads to a marked decrease in the capacity, which at the same time becomes nearly potential independent. This observation is attributed to the formation of an adsorbed layer of complexes.

Electrophotography of Internal Discharges in Dielectrics

ELECTROPHOTOGRAPHS of discharges in air inclusions in dielectrics have been used for demonstrating the location and sequence of discharges during the short-time application of alternating and direct voltages1. A photographic film was enclosed between two disks of dielectric carrying silver film electrodes, one disk having a small cylindrical cavity adjacent to the photosensitive surface (Fig. 1). The sample was tested in conjunction with a discharge recorder2. Alternating voltage was applied for 1/25–1/10 sec.