Pure Ag Layer Research Articles

Influence of thermal annealing on the optical and electrical properties of Ag-Al ultrathin film-based sandwich-like transparent conductor

Heating process is always needed and sometimes inevitable in fabricating high-performance transparent conductors. In this work, the thermal stabilities of the optoelectronic properties of the annealed Ag-Al ultrathin film and the sandwich-like structure of TiO2/Ag-Al/aluminum-doped zinc oxide (AZO) are systematically investigated under different annealing temperatures and durations. After annealing at 200 °C for 20 min, the pure Ag layer dewets into isolated islands completely, but the Ag-Al alloy ultrathin film retains continuous film morphology with low sheet resistance, demonstrating alloying with Al element can effectively improve the thermal stability of the Ag layer. However, increasing the annealing duration further upon Ag-Agl alloy film will lead to serious dewetting, agglomeration, and increased resistance. The TiO2/Ag-Al/AZO sample has a high optical transmittance, which can be maintained after annealing at 200 °C for 60 min. Nevertheless, when annealing at 300 °C its sandwiched structure is destroyed as a result of the agglomeration of the Ag-Al layer. The annealed TiO2/Ag-Al/AZO structure has an average transmittance of about 85.4% in the range of 400–700 nm and a sheet resistance of 12.5 Ω.sq−1, indicating the potential for the high-performance transparent conductor application.

Microstructure evolution and SERS performance of self-formed Ag nanoparticles/Ag-27.9 at% Co-8.9 at% Zr alloy films

Ag-27.9 at% Co-8.9 at% Zr alloy films were deposited on flexible polyimide (PI) by magnetron sputtering and annealed in argon atmosphere. Results show that many fine nanoparticles are formed on the surface of as-deposited Ag–Co–Zr alloy films. Furthermore, the average size of self-formed Ag nanoparticles gradually increases while the number of Ag nanoparticles decreases as alloy film thickness increases. In addition, it is worth noting that flake-like and polyhedral nanoparticles are formed spontaneously on the surface of annealed alloy films and are proved to be single crystal Ag nanoparticles. Moreover, the morphology of flake-like Ag nanoparticles is dependent on annealing temperature. In order to improve “hotspots” activity of the alloy films, a 12 nm pure Ag layer was deposited on the annealed alloy film surface to obtain Ag layer/Ag nanoparticles/Ag–Co–Zr alloy films SERS substrates which can detect 5 × 10−14 M R6G. This paper provides a potential candidate for preparation of SERS substrates with ultra-high sensitivity and stability.

In situ TEM observation of sintered Ag die-attach layer with added tungsten carbide particles while heating to high temperature

We carried out in situ transmission electron microscopy (TEM) on the microstructural change of a sintered Ag die-attach layer heated to 600 °C. It was found that the addition of 2 wt% tungsten carbide (WC) particles to the sintered Ag layer significantly suppressed the microporous structure growth at elevated temperature. In the case of a pure Ag layer without anything added, microporous structure growth started from 450 °C. However, microporous structure growth was hardly observed in the sintered Ag layer with WC added up to 600 °C.

Development of back side technology for light trapping and photon recycling in GaAs solar cells

AbstractIn this work, we propose and realize three different design strategies to implement an optical cavity in GaAs thin film solar cells in order to confine its internal luminescence and hence to exploit photon recycling. The strategies are based on the definition of a highly reflective and very conductive back side, whereas front side light extraction is limited by total internal reflection. We show characterization results on the internal reflectivity of the back reflector and on the contact resistance at the rear side, important quantities for a good functioning of the final solar cell. First, a back side using only metal was optimized with a pure Ag layer leading to an internal reflectivity of 95.2% and a contact resistance of 1.0 × 10−4 Ω for a 1 cm2 device. With a metal‐dielectric stack at the back side and electrical contacts made by metals via point‐contacts, a second approach led to averaged internal reflectivity of 98.0% and contact resistance of 1.8 × 10−4 Ω for a 1 cm2 device. A third strategy in which a transparent conductive oxide in combination with a metal layer was used did not show the expected results in optical and electrical properties. We fabricated and characterized solar cells with the most promising back sides. When comparing with an ordinary reference GaAs solar cell, external radiative efficiency increased by factors of 150% and 90% for the thin film solar cells with pure Ag and with the metal‐dielectric stack at the back side, allowing enhancements of 19 and 13 mV in VOC, respectively.

Kinetics of Silver Photodiffusion Into Amorphous Ge20S80 Films: Case of Pre‐Reaction

Silver photodiffusion into amorphous chalcogenide has attracted much attention because of its potential applications for example in memory devices. For its development, it is important to know how Ag ions diffuse in chalcogenide layers upon light exposure. In this paper, the photo‐induced effect on “pre‐reacted” films before light exposure, originating from Ag/Ge20S80/Si substrate and Ge20S80/Ag/Si substrate is investigated, using neutron reflectivity, X‐ray reflectivity, and X‐ray diffraction. Two types of “pre‐reacted” films according to the original stacking order are obtained. In both cases, a pure Ag layer almost disappeared, and there is a small amount of monoclinic Ag2S. The reaction time for the photodiffusion is shorter, in both cases, than that in Ag/Ge20S80 with a pure Ag layer, indicating a different reaction process. After prolonged light exposure, a uniform amorphous reaction layer is produced in the films originating from the Ag/Ge20S80/Si substrate, while both an amorphous reaction product and the Ag2S fragments exist in the films originating from Ge20S80/Ag/Si substrate. The mechanism of the specific photo‐reaction is discussed in terms of the role of the Ag2S fragments.

Thermal durability of AZO/Ag(Al)/AZO transparent conductive films

Effects of Al doping on surface morphology, sheet resistance, optical transmission spectra, and thermal durability of a thin Ag layer and AZO/Ag/AZO dielectric/metal/dielectric (DMD) transparent conductive films (TCFs) were investigated. The 1.7 at. % Al doping suppressed the initial island growth of a thin Ag layer and the plasmon resonant absorption dip in the optical transmission spectra. The threshold thickness of percolation conductivity was reduced from 9–10 (pure Al layer) to 5–6 nm (1.7 at. % Al-doped Ag layer). Al doping in the Ag layer improved the thermal durability of AZO/Ag/AZO-DMD TCFs. The threshold temperature for Ag void formation increased from 400 °C (DMD with pure Ag layer) to 600 °C (DMD with a 10.5 at. % Al-doped Ag layer). The optimum annealing temperature increased from 300 °C (DMD with a pure Ag layer) to 500 °C (DMD with a 10.5 at. % Al-doped Ag layer). Maximum figures of merit (FOM) were 0.5 × 10−2 and 1.1 × 10−2 Ω−1 for the DMD with a pure Ag layer and that with a 10.5 at. % Al-doped Ag layer, respectively.

Effect of Al doping in the Ag layer of MgZnO/Ag/MgZnO dielectric/metal/dielectric UV–visible transparent conductive films

AbstractTransparent conductive films (TCFs) with dielectric/metal/dielectric (DMD) structure covering the UVA (λ = 315–380 nm) and visible wavelength region (380–780 nm) were fabricated using Al‐doped Mg0.4Zn0.6O (AMZO) dielectric and 1.7 at% Al‐doped Ag (Ag(Al)) metal layers. The AMZO/Ag(Al)/AMZO‐DMD film with a 7 nm thick Ag(Al) layer after annealing in vacuum at 400 °C showed superior performance as a TCF, i.e., average transmittance from UVA to visible region (315–780 nm) of 88.2% and sheet resistance of 7.6 Ω/sq. The effect of Al doping on optical transmission, sheet resistance, surface morphology, and thermal durability of the AMZO/Ag(Al)/AMZO‐DMD films were also investigated. The 1.7 at% Al doping suppressed the initial island growth of the thin Ag layer and the plasmon resonance absorption dipped in the optical transmission spectra. Al doping in the Ag layer also improved the thermal durability of AMZO/Ag/AMZO‐DMD films. The threshold temperature for Ag void formation caused by metal segregation increased from 300 °C (DMD with a pure Ag layer) to 400 °C (DMD with an Al‐doped Ag layer). (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Sub-surface laser nanostructuring in stratified metal/dielectric media: a versatile platform towards flexible, durable and large-scale plasmonic writing

Laser nanostructuring of pure ultrathin metal layers or ceramic/metal composite thin films has emerged as a promising route for the fabrication of plasmonic patterns with applications in information storage, cryptography, and security tagging. However, the environmental sensitivity of pure Ag layers and the complexity of ceramic/metal composite film growth hinder the implementation of this technology to large-scale production, as well as its combination with flexible substrates. In the present work we investigate an alternative pathway, namely, starting from non-plasmonic multilayer metal/dielectric layers, whose growth is compatible with large scale production such as in-line sputtering and roll-to-roll deposition, which are then transformed into plasmonic templates by single-shot UV-laser annealing (LA). This entirely cold, large-scale process leads to a subsurface nanoconstruction involving plasmonic Ag nanoparticles (NPs) embedded in a hard and inert dielectric matrix on top of both rigid and flexible substrates. The subsurface encapsulation of Ag NPs provides durability and long-term stability, while the cold character of LA suits the use of sensitive flexible substrates. The morphology of the final composite film depends primarily on the nanocrystalline character of the dielectric host and its thermal conductivity. We demonstrate the emergence of a localized surface plasmon resonance, and its tunability depending on the applied fluence and environmental pressure. The results are well explained by theoretical photothermal modeling. Overall, our findings qualify the proposed process as an excellent candidate for versatile, large-scale optical encoding applications.

Silver surface segregation in Ag-DLC nanocomposite coatings

AgDLC coatings were deposited by magnetron sputtering in order to evaluate: i) the Ag nanoparticle size distribution along the coatings thickness and ii) the silver stability in DLC coatings. Four different coatings were deposited, two AgDLC nanocomposite coatings containing 20at.% of Ag, with thicknesses of 250nm and 1000nm, a 250nm AgDLC nanocomposite coating with carbon barrier layer of 75nm and a multilayer coating, consisting of a pure Ag layer with a carbon barrier layer of 75nm. The coatings were characterized with respect to their structure (by means of X-ray diffraction (XRD)), morphology (by scanning electron microscopy (SEM)) and Ag distribution in depth (by glow discharge optical emission spectroscopy (GDOES)). The AgDLC nanocomposite coatings are composed of Ag nanograins (with a size of about 3nm) dispersed in an amorphous carbon matrix. The SEM results suggest a bimodal size distribution along the coatings thickness, it was found that Ag forms nanoparticles and aggregates with sizes ranging from 14nm up to 52nm on the coating's surface, whereas in bulk, no Ag nanoparticles were visible by SEM. The monitoring of the Ag stability at room temperature conditions during a period of 6months showed that Ag segregates to the coatings surface, in the AgDLC nanocomposite coating with 1000nm forming Ag nanofibers, while the thinner AgDLC (250nm) as well as the multilayer (Ag+DLC and AgDLC+DLC) coatings were stable over time.

Characteristic difference between ITO/ZrCu and ITO/Ag bi-layer films as transparent electrodes deposited on PET substrate

The metallic-glass film of ZrCu layer deposited by co-sputtering was utilized as the metallic layer in the bi-layer structure transparent conductive electrode of ITO/ZrCu (IZC) deposited on the PET substrate using magnetron sputtering at room temperature. In addition, the pure Ag metal layer was applied in the same structure of transparent conductive film, ITO/Ag, in comparison with the IZC film. The ZrCu layer could form a continuous and smooth film in thickness lower than 6 nm, compared with the island structure of pure Ag layer of the same thickness. The 30 nm ITO/3 nm ZrCu films could show the optical transmittance of 73% at 550 nm wavelength. The 30 nm ITO/12 nm ZrCu films could show the better sheet resistance of 20 Ω/sq, but it was still worse than that of the ITO/Ag films. It was suggested that an alloy system with lower resistivity and negative mixing heat between atoms might be another way to form a continuous layer in thickness lower than 6 nm for metal film.

Exudation of Ag and Cu in internally oxidized Ag–Sn–In–(Cu) alloys

Growth and structure of pure Ag layers are investigated on the surface and at grain boundaries of Ag alloys that have been internally oxidized. Two Ag–Sn–In and an Ag–Sn–In–Cu alloy were studied by ion polishing, field emission scanning electron microscopy and optical microscopy. As already known from previous studies Ag atoms diffuse towards the surface. In the present study it is shown that grain boundaries can act as a sink for diffusing Ag atoms in competition with the surface. In the quaternary alloy Ag and Cu diffuse towards the surface simultaneously. The Cu diffusion is confined by the nucleation of CuO particles. The progress of the internal oxidation front is discussed in conjunction with the nucleation of pure Ag crystallites and CuO particles at grain boundaries.

Manufacture of (Bi,Pb)2Sr2Ca2Cu3O10-based tapes with a composite sheath

(Bi,Pb)2Sr2Ca2Cu3O10-based single-filament tapes were prepared using a pure Ag protective sheath in contact with the ceramic core and an external sheath consisting of Ni. The influence of the composite sheath geometry on the (Bi,Pb)2Sr2Ca2Cu3O10 phase formation kinetics was studied by in-situ synchrotron x-ray diffraction in a 8.5% O2 – 91.5% N2 gas mixture and was found to depend strongly on the sheath architecture as a consequence of differences in the oxygen supply between the ceramic core and the outer atmosphere. Owing to the efficient protection of the pure Ag layer against Ni diffusion, the critical temperature of the (Bi,Pb)2Sr2Ca2Cu3O10 phase is unaffected. Critical current densities as high as 35 kA/cm2 (77K, self field) were obtained in a single heat treatment when a slow cooling rate was used. The ceramic density was significantly improved in comparison with that of tapes prepared using only pure Ag as sheath material and heat treated once. This effect can be attributed to the higher mechanical strength of the composite sheath at elevated temperatures, which prevents the development of an otherwise significant porosity during the growth of the superconducting crystallites.

Semiclassical electronic transport calculations in multilayered granular alloys

We have calculated the electrical conductivity in the current-in-plane geometry of multilayered granular alloys composed of Co clusters embedded in Ag alternating with pure Ag layers. In particular, we have paid attention to the conductivity behavior as a function of Ag layer thickness, Co clusters’ size, and degree of percolation. The electronic structure is self-consistently calculated within the unrestricted Hartree–Fock approximation using a parametrized tight binding Hamiltonian which includes a Hubbard-like term. The conductivity tensor is obtained by using the semiclassical Boltzmann equation in the anisotropic relaxation time approximation. We have used a s−d Mott-like scattering model for the electronic mean free path taking into account the Sondheimer’s picture for electronic transport in thin films. We find that the experimental conductivity behavior at coalescence can be explained through the electronic band contribution. The conductivity behavior of continuous multilayers is already attained in the very early stage of percolation, as in the experiments.

Effect of alloying and cladding on the failure of silver metallization under high temperature and current stressing

Pure Ag layers were cladded with thin alloy (Ag with 3 at. % aluminum) layers to form a [Ag(Al)∕Ag∕Ag(Al)] structure on SiO2. The effective resistivity of the cladded Ag metallization is slightly greater than pure silver and less than the Ag(Al) alloy metallization. The clad structures showed a nearly 38 times enhancement in electromigration resistance when compared to pure Ag and seven times greater than the Ag(Al) alloy. The enhancement in lifetime of the clad structure was attributed to enhanced thermal stability due to segregation of Al2O3 at the Ag grain boundaries leading to reduced grain size and changes in thermodynamic properties and also reduced atomic mobility because of the topmost layer acting as a passivation layer.

イオンビームスパッタリング法により形成したＡｇ‐Ｃｕ合金薄膜を用いたＴｉの接合

A novel bonding process, which is a kind of diffusion bonding with cleaning the bonding surface followed by deposition of Ag-28mass% Cu alloy thin layer using ion beam sputtering, was applied to joining of commercial pure titanium (CPTi) under atmospheric pressure. The deposition of the Ag-Cu layer after removing the oxide film of the bonding surface successfully improve bondability of CPTi. The joint strengths depend on the thickness of the Ag-Cu deposited layer. A maximum joint strength close to the base metal strength is obtained using the optimum thickness of Ag-Cu deposited layer, 0.3μm, under the conditions of a bonding temperature of 1153K and bonding time of 300s or more. The thicker Ag-Cu deposited layer of 1.0μm in thickness results in a hardened microstructure including Ti2 (Cu, Ag) intermetallic precipitates and thereby lower strength and lower ductility after bonding at 1153K for 1800s. The joint with the thinner Ag-Cu deposited layer of 0.1μm in thickness is not bonded at all.The Ag-Cu deposited layers having 0.3μm or more in thickness become enriched in Ag during heating in the bonding process because of a greater diffusion coefficient of Cu than that of Ag in titanium. As a result a almost pure Ag layer is formed on the bonding surface after heating above 973K. The bonding is, therefore, considered to proceed via solid state diffusion bonding between the surface layers enriched in Ag and be completed after homogenization of the solute elements of Ag and Cu.

Highly Supersaturated, Highly Strained Sputtered Ag-Co and Ag-Ni Layers

ABSTRACTThin Ag-Ni and Ag-Co layers with compositions of 0, 15, 22 to 28 at% Ni or Co were made by magnetron sputtering. TEM experiments revealed that the layers exhibited a {111} fiber texture with a high density of twins, always with the twinning plane parallel to the layer surface. X-ray diffraction and TEM results indicate that all Ni or Co is dissolved in the Ag, although some compositional inhomogeneity occurs: the layers are highly supersaturated with Ni or Co. Unlike the pure Ag layer, the Ag-Ni and Ag-Co layers exhibited high strains in the as prepared state.Upon annealing Ni or Co precipitated. The Ni precipitates were small, spherical particles oriented parallel to the surrounding Ag. The strains in the Ag-Ni and Ag-Co layers after annealing were less than the calculated thermal strains, but they were larger than the strain in the pure Ag layer after an equal annealing treatment.

Preliminary results on Cu diffusion through grain boundaries of thin ion-plated AgSn films

The diffusion process of copper through grain boundaries of 500 nm thick ion-plated Ag-12at%Sn films was studied in the temperature range 100–250°C. The method is based on the determination of the time of first appearance of Cu on the AgSn surface using Auger electron spectroscopy for determining trace amounts of Cu. An activation energy of E a = 0.53 eV and a diffusivity of D′ o = 1.3 × 10 −7cm 2s −1 was obtained. For comparison, diffusion studies of Cu through ion-plated pure Ag layers have been performed. In this case an activation energy of E a = 0.68 eV and a diffusivity of D′ o = 2.3 × 10 −5cm 2s −1 have been found.