SiO2 Overcoat Research Articles

Resistivity and surface scattering of (0001) single crystal ruthenium thin films

The resistivity size effect in nanoscale metals is of both scientific and technological interest, the latter due to its importance to interconnects between transistors in integrated circuits. In this work, the authors report the variation of resistivity with film thickness and with changes in surface scattering of ex situ annealed single crystal Ru thin films grown on sapphire substrates by sputter deposition. The room temperature deposition of SiO2 on the Ru sample surface was observed to increase the resistivity of films that had previously been subjected to annealing in a reducing gas ambient. These overcoated samples were also found to increase in resistivity as a result of an oxidizing anneal and reduce in resistivity as a result of a subsequent reducing gas (Ar + H2) anneal. To a large extent, the surface structure and electron scattering characteristics were found to be reversible between oxidizing and reducing gas anneals. The chemistry and structure of the Ru upper surface was characterized by low energy electron diffraction (prior to the SiO2 overcoat deposition), x-ray reflectivity, x-ray photoelectron spectroscopy, and resistivity measurements. The changes in surface structure and chemistry were related to the changes in the specularity of the Ru surface for electron scattering in the context of the Fuchs–Sondheimer semiclassical model of the resistivity size effect, and in this context a mostly specular metal/dielectric interface is reported.

Influence of deposition temperature and SiO2 overcoat layer on laser resistance of 532-nm high-reflection coating

In this work, 532-nm high-reflection (HR) coatings have been deposited at different deposition temperatures by electron-beam evaporation technology. The spectral performance, e-field distribution, surface roughness, stoichiometry, as well as the laser resistance of the prepared 532-nm HR coatings are investigated. Experimental results indicate that the LIDT of the 532-nm HR coatings can be greatly influenced by deposition temperature. A relatively high deposition temperature benefits the crystallization and oxidation, and improves the LIDT of the 532-nm HR coatings. In addition, the SiO2 overcoat layer is also demonstrated to be effective in suppressing the delamination damage morphology and improving the LIDT of the 532-nm HR coatings.

New separator with hydrophilic surface treatment for flooded-type lead-acid battery

By using organic non-woven fabrics, which are less costly than inorganic ones, we have studied the effect of the fabrics attached to a conventional polyethylene (PE)-based separator on sedimentation of sulfuric acid to prevent stratification in flood-type lead-acid batteries. The effect of surface treatment for the fabrics on the diffusion of sulfate ions has also been studied to reduce the electric resistance. The results of model experiments showed that the organic non-woven fabrics suppressed the sedimentation of sulfuric acid. In addition, by clarifying the relationship between surface tension of non-woven fabrics and diffusion coefficients of sulfate ions, we found that hydrophilic non-woven fabric with a SiO2 overcoat film was the most effective for improving the diffusion of sulfate ions.

Role of SiC substrate surface on local tarnishing of deposited silver mirror stacks

The role of the SiC substrate surface on the resistance to the local initiation of tarnishing of thin-layered silver stacks for demanding space mirror applications was studied by combined surface and interface analysis on model stack samples deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous H2S. It is shown that suppressing the surface pores resulting from the bulk SiC material production process by surface pretreatment eliminates the high aspect ratio surface sites that are imperfectly protected by the SiO2 overcoat after the deposition of silver. The formation of channels connecting the silver layer to its environment through the failing protection layer at the surface pores and locally enabling H2S entry and Ag2S growth as columns until emergence at the stack surface is suppressed, which markedly delays tarnishing initiation and thereby preserves the optical performance. The results revealed that residual tarnishing initiation proceeds by a mechanism essentially identical in nature but involving different pathways short circuiting the protection layer and enabling H2S ingress until the silver layer. These permeation pathways are suggested to be of microstructural origin and could correspond to the incompletely coalesced intergranular boundaries of the SiO2 layer.

Local Degradation Mechanisms by Tarnishing of Protected Silver Mirror Layers Studied by Combined Surface Analysis.

In this work, we addressed the local degradation mechanisms limiting the prelaunch environmental durability of thin-layered silver stacks for demanding space mirror applications. Local initiation and propagation of tarnishing were studied by combined surface and interface analysis on model stack samples consisting of thin silver layers supported on lightweight SiC substrates and protected by thin SiO2 overcoats, deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous H2S. The results show that tarnishing is locally initiated by the formation of Ag2S columns erupting above the stack surface. Ag2S growth is promoted at high aspect ratio defects (surface pores) of the SiC substrate as a result of an imperfect protection by the SiO2 overcoat. Channels most likely connect the silver layer to its environment through the protection layer, which enables local H2S entry and Ag2S growth. The silver sulfide columns grow in number and size eventually leading to coalescence with increasing H2S exposure. In more advanced stages, tarnishing slows down owing to saturation of all pre-existing imperfectly protected sites of preferential sulfidation. However, it progresses radially at the basis of the Ag2S columns underneath the protection layer, consuming the metallic silver layer and deteriorating the protecting overcoat.

Investigation of the effects of AR layers on the structure and properties of transparent conductive oxide thin films

Abstract Antireflective (AR) layers, i.e., a SiO2 overcoat and an Al2O3 undercoat were added to an ITO film to improve its visible transmittance. The microstructure and optical, electrical, and mechanical properties of the ITO films with and without AR coatings were systematically investigated. It is found that: 1) while the SiO2 overcoat has little impact on the microstructure of the ITO layer, the Al2O3 undercoat decreases the lattice parameter and grain size of the ITO layer; 2) while the carrier mobility for the ITO films with and without AR coatings is quite similar, the carrier concentration for the ITO film is little affected by the SiO2 overcoat, and it is increased by 31% with the Al2O3 undercoat; 3) the ITO film with AR layers shows significant improvement in scratch resistance, which is attributable mainly to the increased value of H/E and H3/E2 (where H and E are the hardness and elastic modulus respectively) and decreased residual stress; 4) the increased ratio H/E for the ITO film sandwiched structure over the ITO single layer indicates that there is a possibility to tailor the mechanical properties of a material by making multilayer composite.

Influence of SiO2 overcoat layer and electric field distribution on laser damage threshold and damage morphology of transport mirror coatings

Four mirror coatings were designed for transporting 1064nm light, and prepared under the same process parameters. The laser induced damage threshold (LIDT), electric field distribution, as well as the damage morphology of the prepared transport mirror coating was investigated. The results indicate that the SiO2 overcoat layer and electric field distribution have a great impact on the LIDT and damage morphology of the transport mirror coating. A thicker SiO2 overcoat layer can suppress the delamination damage morphology, and significantly increase the LIDT. For the designs with similar SiO2 overcoat layer thickness, the nano-absorbing defects can survive at higher laser fluence in the design with lower electric field intensity. In addition, the HfO2 over SiO2 interface has a better interfacial strength and less “invisible” nano-absorbing defects than the SiO2 over HfO2 interface, suggesting that improving the SiO2 over HfO2 interfacial quality will be an effective way to enhance the laser damage performance of the transport mirror coating.

Optical properties of Ag/dielectric-material multilayers

Abstract The optical properties of the silver/dielectric-material multilayers have been investigated and it was found that the absorption exists at the silver/dielectric-material interfaces and is caused by the excitation of the surface plasmons of silver generated in the vicinity of the interface. In order to analyze the silver/dielectric-material interface, we prepared the silver layers overcoated with thin dielectric-material, whose thicknesses are less than the escaping depth of photoelectrons. X-ray photoelectron spectroscopy surface analysis on this two-layer stacks makes it possible to observe the oxidation state of silver and the surface plasmon of silver around the interface between the silver and the dielectric layer. The plasmon loss peaks of silver were observed to shift, depending on the dielectric constant of overcoating layers, TiO2, SiNx, ZnO and SiO2; these peaks shift largely with TiO2 overcoat and shift less with SiNx or ZnO overcoat. SiO2 overcoat makes almost no peak shift. Namely, the resonance energy of surface plasmons decreases and reaches to visible region with the increase of the dielectric constant of overcoating layer. These results are consistent with the fact that a larger absorption is observed in the stacks overcoated with a layer having a higher dielectric constant.

In situ instrumentation for localized wear studies of magnetic thin-film disks

An experimental set-up and a procedure to make in situ localized measurements of various wear processes on magnetic thin-film disks are developed. The coefficient of friction, acoustic emission and optical reflectance are monitored simultaneously. Results are analysed to determine ‘precursors to failure’ and to compare the effects of lubricant, surface roughness, overcoat and normal load on disk wear. Disk wear is observed to follow a pattern of lubricant depletion followed by head slider-overcoat asperity contact. Wear tracks are formed after asperity contact. Lubricant extends disk wear life, as does a polished surface texture, and an SiO2 overcoat wears more slowly than a diamond-like carbon overcoat. The experimental methodology developed in this study should be of interest in studying precursors to failure of any moving interface.

Characterization of SiO2-Overcoated Silver-Island Films as Substrates for Surface-Enhanced Raman Scattering

Vapor deposition of a 45-Å layer of silver and a subsequent 50−65-Å layer of SiO2 onto a glass slide is shown to be a viable substrate for surface-enhanced Raman spectroscopy (SERS) and a model of the silica surface suitable for adsorption kinetic studies. The chemistry of the silica is characterized by UV absorption and contact angle measurements. The physical structure is probed by atomic force microscopy to compare the surface roughness of the silver-island film and its SiO2 overcoat. Auger electron spectroscopy and X-ray photoelectron spectroscopy are used to probe the silica layer for exposure of silver through gaps in the overcoat. Comparison of SERS of dibenzyl disulfide bound to a silver-island film versus that of a silver film protected by the SiO2 overlayer tests the continuity of the SiO2 film and its ability to block access of adsorbates to the underlying silver surface. The model silica surface is used to detect the Raman spectrum of adsorbed pyridine and its adsorption isotherm; the adsorbate vibrational frequencies are consistent with previous reports of pyridine on silica.

Effect of preannealing on the kinetics of the reorientation of the field-induced anisotropy in CoZr thin films (abstract)

In this paper, we will analyze the changes in the kinetics of the induced anisotropy due to preannealing in 300-Å and 1-μm-thick Co94Zr6 amorphous films. Samples were prepared by a dc sputtering method. A silicon wafer with SiO2 overcoat was used as a substrate material, and a field of 200 Oe was applied during the deposition to induce uniaxial anisotropy. Based on x-ray data and resistivity measurements, the films were considered amorphous. The samples were annealed in a magnetic field at temperatures up to 500 °C, and the annealing time was varied from 0.5 to 400 h. As previously reported, the anisotropy, Ku, in as-deposited samples is a function of sample thickness and varied from 1.6×104 ergs/cm3 for 300-Å film to ∼1×104 ergs/cm3 for 1-μm films [T. Jagielinski, J. Appl. Phys. 61, 3237 (1987)]. It was found that the Ku in thick films is reversible, and the kinetics can be fully explained by the anelasticity model [T. Egami, Rep. Prog. Phys. 47, 1601 (1984)]. The mean value of the activation energy is ∼2 eV for samples preanneled at 375 °C. However, in the case of thin films, an additional irreversible component of anisotropy, always along the direction of the field applied during the deposition, is observed. The magnitude is a growing function of annealing temperature, and is as large as 3×104 ergs/cm3 for a 300-Å sample preanneled at 400 °C. The origin of the irreversible component of the anisotropy is not well understood. Based on x-ray data, we concluded that this effect is not related to crystallization. However, since anisotropy is thickness dependent, the structure of the film-substrate interface seems to be responsible for the irreversible part. The reversible parts of anisotoropy behave similarly in both thin and thick films and are 1.6×104 ergs/cm3 and 8×103 ergs/cm3 for 300-Å and 1-μm films, respectively.