Layer Forces Research Articles

Microstructure, phase transformation and photoluminescence of YAG:Ce ceramics by CO2 laser sintering

This study applied laser sintering to transform yttria, alumina, and cerium nitrate powders into Y3Al5O12:Ce (YAG:Ce) phosphor layers. Different hatch distances (0.3 mm–0.7 mm) were performed on the precursors to evaluate their reaction area, depth, and affected zone. Microscopic images and x-ray diffraction results indicated that a hatch distance corresponding to the laser spot size (0.5 mm) is the critical distance between laser scan vectors so as to avoid the residual precursors. Moreover, the grains in YAG:Ce layers presented a texture structure of columns, which are identical to the heat flows during laser sintering. Transmission electron microscopy revealed amorphous boundaries surrounded YAG:Ce single crystals. Photoluminescence of laser-sintered YAG:Ce (0.3 mm hatch distance) by blue excitation was enhanced by around 40% as compared to the solid state reacted one, which should result from rougher surfaces as well as the presence of amorphous boundaries for better light penetration and propagation.

Corrosion Performance of Conversion Treatments for Electrogalvanised Steel Sheet

Fil: Di Sarli, Alejandro Ramon. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Centro de Investigaciones en Tecnologia de Pinturas. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Centro de Investigaciones en Tecnologia de Pinturas; Argentina

Oxidative Layer-By-Layer Multilayers Based on Metal Coordination: Influence of Intervening Graphene Oxide Layers.

Layer-by-layer (LbL) fabricated oxidative multilayers consisting of successive layers of inorganic polyphosphate (PP) and Ce(IV) can electrolessly form thin conducting polymer films on their surface. We describe the effect of substituting every second PP layer in the (PP/Ce) multilayers for graphene oxide (GO) as a means of modifying the structure and mechanical properties of these (GO/Ce/PP/Ce) films and enhancing their growth. Both types of LbL films are based on reversible coordinative bonding between the metal ions and the oxygen-bearing groups in PP and GO, instead of purely electrostatic interactions. The GO incorporation leads to the doubling of the areal mass density and to a dry film thickness close to 300 nm after 4 (GO/Ce/PP/Ce) tetralayers. The film roughness increases significantly with thickness. The (PP/Ce) films are soft materials with approximately equal shear storage and loss moduli, but the incorporation of GO doubles the storage modulus. PP displays a marked terminating layer effect and practically eliminates mechanical losses, making the (GO/Ce/PP/Ce) films almost pure soft elastomers. The smoothness of the (PP/Ce) films and the PP-termination effects are attributed to the reversible coordinative bonding. The (GO/Ce/PP/Ce) films oxidize pyrrole and 3,4-ethylenedioxythiophene (EDOT) and form polypyrrole and PEDOT films on their surfaces. These polymer films are considerably thicker than those formed using the (PP/Ce) multilayers with the same nominal amount of cerium layers. The GO sheets interfere with the polymerization reaction and make its kinetics biphasic. The (GO/Ce) multilayers without PP are brittle and thin.

Two-dimensional metallicity and ferromagnetic ordering in monoatomic-thick Ce layer on Si(111)

Novel properties found in the atom-thick metal overlayed semiconductor systems motivate the studies on the two-dimensional metal films. In this work, the electronic structures of Ce overlayer on a Si substrate have been studied by using first-principles approach. Monoatomic-thick Ce layer on Si(111) surface exhibits metallic behavior and ferromagnetic ordering with weak induced magnetic moments of the Si atoms in the first Si bilayer. Our results reveal the intralayer metallic bonding and the mixed covalent and ionic characteristic of the interfacial bonds in Ce-Si(111). The bonding picture is similar to that of the superconducting monolayer metals on Si(111) surface found in experiments, and elucidates the two-dimensional metallic nature of Ce overlayer with anisotropic band structures in the Ce-Si(111) interfacial systems.

Long Term (4 Years) Performance of Co/Ce Coated 441 for SOFC Interconnect Applications

Ferritic stainless steel interconnectors are widely used in solid oxide fuel cells (SOFC) due to a combination of low cost, compatible thermal expansion properties and ease of manufacturing. However, their viability is hindered by some key technical hurdles. Most stainless steels suggested for SOFC applications rely on the formation of a fairly protective Cr2O3 scale. However, in air side environments Cr species evaporation leads to material failure and insufficient lifetimes. Coatings offer a way to mitigate Cr evaporation and in some cases decrease oxide scale growth. Numerous research papers have investigated different coating compositions and deposition techniques, however, the most commonly suggested material is (Mn,Co)3O4 (MCO). Instead of depositing MCO metallic Co can be applied. During operation Co is converted into Co3O4 and subsequently enriched in Mn from the underlying steel substrate. It has been shown that this type of coating effectively impedes Cr volatilization, even when only very thin layers (600 nm) are applied. Moreover the major advantage of metallic Co coatings are cost savings, since Co can be applied in a large scale roll-to-roll process before stamping the interconnect into its final shape. Furthermore, our previous work has shown that an additional layer of 10 nm Ce in combination with the Co coating results in the aforementioned mitigation of volatilization of Cr species, and also effectively reduces oxide scale growth. Oxide scale growth is detrimental for two reasons. First, a depletion of oxide scale forming element (Cr) can result in the formation of poorly protective iron oxide. Second, even a protective Cr2O3 scale grows with time. Since Cr2O3 is only a moderate electronic conductor this results in an increase of Area Specific Resistance (ASR) as the oxide scale grows in thickness. This eventually creates prohibitively high resistances. Both effects can be mitigated by addition of a thin Ce layer. In the present work Ce/Co (10/600 nm) coated AISI 441 has been exposed for 4 years (35 000 h) at 800 °C. The mass gain of the samples over the course of exposure has been recorded at selected intervals. After 35 000 h a mass gain of 3.76 mg/cm2 has been measured. Over the entire exposure parabolic mass gain kinetics are observed indicating the absence of a poorly protective iron oxide. After 35 000 h the samples were moved to a different setup to measure Cr(VI) evaporation. It was found that despite the fact that the coating was only 600 nm in thickness, it effectively inhibits volatilization of Cr even after 4 years of exposure. Furthermore, samples were removed at selected intervals to measure ASR.

Corrosion protection properties and interfacial adhesion mechanism of an epoxy/polyamide coating applied on the steel surface decorated with cerium oxide nanofilm: Complementary experimental, molecular dynamics (MD) and first principle quantum mechanics (QM) simulation methods

The effect of cerium oxide treatment on the corrosion protection properties and interfacial interaction of steel/epoxy was studied by electrochemical impedance spectroscopy, (EIS) classical molecular dynamics (MD) and first principle quantum mechanics (QM) simulation methods X-ray photoelectron spectroscopy (XPS) was used to verify the chemical composition of the Ce film deposited on the steel. To probe the role of the curing agent in epoxy adsorption, computations were compared for an epoxy, aminoamide and aminoamide modified epoxy. Moreover, to study the influence of water on interfacial interactions the MD simulations were executed for poly (aminoamide)-cured epoxy resin in contact with the different crystallographic cerium dioxide (ceria, CeO2) surfaces including (100), (110), and (111) in the presence of water molecules. It was found that aminoamide-cured epoxy material was strongly adhered to all types of CeO2 substrates, so that binding to ceria surfaces followed the decreasing order CeO2 (111)>CeO2 (100)>CeO2 (110) in both dry and wet environments. Calculation of interaction energies noticed an enhanced adhesion to metal surface due to aminoamide curing of epoxy resin; where facets (100) and (111) revealed electrostatic and Lewis acid-base interactions, while an additional hydrogen bonding interaction was identified for CeO2 (110). Overall, MD simulations suggested decrement of adhesion to CeO2 in wet environment compared to dry conditions. Additionally, contact angle, pull-off test, cathodic delamination and salt spray analyses were used to confirm the simulation results. The experimental results in line with modeling results revealed that Ce layer deposited on steel enhanced substrate surface free energy, work of adhesion, and interfacial adhesion strength of the epoxy coating. Furthermore, decrement of adhesion of epoxy to CeO2 in presence of water was affirmed by experimental results. EIS results revealed remarkable enhancement of the corrosion resistance of epoxy coating applied on the steel specimens treated by cerium oxide.

P-Cadherin is necessary for retinal stem cell behavior in vitro, but not in vivo

Adult retinal stem cells (RSCs) are rare quiescent cells within the ciliary epithelium of the eye, which is made up of non-pigmented N-Cadherin+ve inner and pigmented P-Cadherin+ve outer cell layers. Through FACs and single cell analyses, we have shown that RSCs arise from single cells from within the pigmented CE and express P-Cadherin. However, whether the expression of P-Cadherin is required for maintenance of the stem cell in vivo or in the formation of the clonal stem cell spheres in vitro is not known. Using cadherin functional blocking antibody experiments and a P-Cadherin −/− mouse to test whether the RSC population is affected by the loss of P-Cadherin expression, our experiments demonstrate that the RSCs reside in the pigmented CE layer and express P-Cadherin, which is important to the formation of adherent sphere colonies in vitro, however P-Cadherin is not required for maintenance of RSCs in vivo.

Effect of cerium composition on optical and structural properties of cerium doped ZnO nanowires

Synthesis of cerium (Ce) doped zinc oxide (ZnO) nanowire has been carried out using chemical bath deposition over seed layer. The seed layer of Ce doped ZnO thin film was deposited by spin coating method. Effect of Ce doping on optical and structural properties of nanowire has been explored to optimize the performance of nanowires for their applicability in light emitting devices. High resolution field emission scanning electron microscopy (FESEM) clearly reveals nanowire growth for 15% of Ce in ZnO. Optical band gap of the films was found to increase with an increase in Ce concentration in ZnO. All Ce doped ZnO thin films exhibits more than 90% transparency in the visible region and show absorption sharply in ultra-violet region at approximate 375 nm. Transmittance of the nanowire in visible region is showing an average transmittance of 61%. The photoluminescence (PL) spectra in all samples exhibit a strong ultraviolet emission at the near band edge centered at 389 nm due to free exciton recombination. A broad blue visible emission peak for all the samples located at 467 nm was seen to be originated due to the interstitial position of Zn2+ ions.

Characterization of yttrium-doped ceria with various yttrium concentrations as cathode interlayers of SOFCs

This study focuses on enhancing the efficiency of solid oxide fuel cells (SOFCs) by modulating the thickness of the highly resistive solid solution layer of (Ce,Zr)O2 formed between the yttria-stabilized zirconia (YSZ) electrolyte and the CeO2-based interlayer on the cathode side. The effects of the concentration of dopant in CeO2 on the thickness of the solid solution were analyzed. Yttrium-doped CeO2 (YDC) interlayers were studied, with dopant concentrations in the range of 5–40 mol%. The results revealed that the thickness of the solid solution decreased with increasing dopant concentration up to 20 mol% and then saturated at higher dopant concentrations. In addition, the electrical conductivities of yttrium-doped ceria (YDC) and the solid solution of YSZ and YDC were measured. YDC with a dopant concentration of 20 mol% exhibited the highest conductivity. The conductivities of the YSZ/YDC solid solution decreased compared to those of YDC and YSZ for each dopant concentration, and the extent of the reductions was approximately the same for all dopant concentrations. These results indicate that a dopant concentration of 20 mol% is optimal to minimize the internal resistance of SOFCs when YDC is used as the interlayer material.

Modeling of Chemical Membrane Degradation Mitigation and Performance Tradeoffs in Ceria-Supported Fuel Cells

Ceria supported membranes have been proposed to mitigate chemical membrane degradation in polymer electrolyte fuel cells. It was confirmed that ceria as a radical scavenger protects the membrane under open circuit voltage (OCV) or ex-situ Fenton’s durability conditions [1-7]. However, its effectiveness has not been examined for cell voltages below OCV, which are necessary conditions for field operation of fuel cells. On the other hand, ceria membrane additive can be considered as a cation contamination since it is dissolved in the membrane [8]. Performance tradeoffs have been observed experimentally with the use of ceria membrane additive, and the tradeoffs are more significant at lower cell voltages [9]. Therefore, a comprehensive investigation on chemical membrane mitigation and performance tradeoffs in ceria-supported fuel cells is required. In the present work, a transient in-situ chemical degradation model for simulating the transport and reaction of cerium redox couples in the membrane electrode assembly (MEA) is developed and integrated with the chemical membrane degradation models in which the effects of iron redox couples on membrane degradation and detailed ionomer degradation processes are included [10-11].The developed model is then applied to investigate the mitigation effectiveness of cerium redox couples and the fundamental mechanisms for the performance tradeoffs under different cell voltage conditions. The modeling results reveal that abundant Ce(III) ions are available in the membrane to quench hydroxyl radicals at high cell voltages. Since the hydroxyl radical is the dominant reactive species to attack the membrane ionomer, the modeling results demonstrate the primary mechanism for the significant mitigation observed in ceria supported MEAs at OCV conditions. However, this type of mitigation is found to be suppressed at low cell voltages, where electromigration drives Ce(III) ions into the cathode catalyst layer and reduces the available Ce(III) ion in the membrane. Ce(III) ion is the dominant species for hydroxyl radical quenching, and inadequate amount of Ce(III) ion in the membrane leads to a ten-fold reduction in the mitigation effectiveness at cell voltages below 0.7 V. The simulated Ce(III) ion migration to the cathode catalyst layer is found to be responsible for the performance losses observed in ceria supported MEAs. The modeling results reveal that proton starvation can occur in the cathode catalyst layer due to the local Ce(III) ion accumulation. Without the adequate supply of protons in the ionomer of the cathode catalyst layer, proton conductivity and oxygen reduction kinetics are reduced. Significant performance tradeoffs in the form of combined ohmic and kinetic voltage losses are therefore evident and shown to increase with current density. Overall membrane durability and fuel cell performance management is shown to be possible at high cell voltages with the use of ceria membrane additive, where cerium migration and the associated performance loss are insignificant. Unfortunately, at low cell voltages additional steps must be taken to address proton starvation in the cathode catalyst layer and inadequate amount of Ce(III) ion in the membrane in order to achieve a durable membrane without compromising fuel cell performance. Acknowledgement: This research was supported by Ballard Power Systems and the Natural Sciences and Engineering Research Council of Canada through an Automotive Partnership Canada (APC) grant. The authors wish to thank their colleagues at SFU FCReL and Ballard for providing valuable comments and advices.

Preparation and performance of solid oxide fuel cells with YSZ/SDC bilayer electrolyte

YSZ (Y2O3-stabilized ZrO2)/SDC (Sm-doped CeO2) bilayer electrolyte film was successfully fabricated on NiO/YSZ anode substrate using stepwise sintering processing by screen-printing technique. OCVs (open-circuit voltages) of 1.06V, 1.05V and 0.88V were achieved at 750°C for single cells with bilayer electrolyte of 12μm-SDC/8μm-YSZ, 12μm-SDC/5μm-YSZ, and 12μm-SDC/2μm-YSZ, respectively. Interdiffusion of ions at YSZ/SDC interface and formation of YSZ–SDC solid solution after sintering at 1400°C for 2h was investigated. The EDX result suggested that the region for the interdiffusion in a YSZ/SDC bilayer structure was 2.0μm from the YSZ/SDC interface into the YSZ layer for Sm and Ce, and 0.5μm into the SDC layer for Zr and Y. The YSZ–SDC solid solution exhibited a low electrical conductivity, which negatively affected the performance of single cell. After two thermal cycles, the maximum power density of the single cell exhibited a significant decrease. The destruction of YSZ/SDC bilayer electrolyte structure was not observed during the thermal cycles.

Theoretical Investigation of Small Transition-Metal Clusters Supported on the CeO2(111) Surface

We have performed a systematic investigation of 4-atom transition-metal (TM) clusters (TM = Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au) supported on the unreduced CeO2(111) surface using density functional theory calculations within the Perdew–Burke–Ernzerhof functional and on-site Coulomb interactions for the Ce f-states. We found two structure TM4 patterns on CeO2(111), namely, two-dimensional (2D) arrays with zigzag orientation for Ru, Rh, Os, and Ir and tetrahedral three-dimensional (3D) configurations for Cu, Pd, Ag, Pt, and Au. Our analyses indicate that the occupation of the antibonding d-states and the hybridization of the TM d-states with O p-states play a crucial role in the magnitude of the TM–TM and TM–O interactions and determine the formation of the 2D and 3D configurations on CeO2(111). The interaction of TM4 with the CeO2(111) surface changes the nature of the occupied Ce f-states from itinerant (CeIV in the clean surface) to localized (CeIII) states; hence, it increases the atomic size of CeIII compared with CeIV by 4.4%, which plays a crucial role in building in a lateral tensile strain in the topmost Ce layer in the surface. Furthermore, we found an enhancement of the electron localization of the TM d-states upon the adsorption of TM4 on CeO2(111). We found that the number of Ce atoms in the CeIII oxidation state depends on the TM element and structure. For Ru, Rh, Os, and Ir on CeO2(111), all the Ce atoms in the topmost Ce layer change the oxidation state from IV to III (i.e., 100%), while for (Pd, Pt) and (Cu, Ag, Au) on CeO2(111), only 25% and 50% of Ce atoms, respectively, convert the oxidation state from IV to III.

Studying Rare Earth Surface Treatment for Magnesium Using Scanning Electrochemical Microscopy

Rapid dissolution of magnesium alloys in biological solutions limits its successful application as a biodegradable implant where a controlled dissolution/corrosion of magnesium along with healing of tissue is required. Treatment of magnesium surface with rare earth conversion layers has been subject of several studies 1–4 revealing its potential as a passivating layer. Given the biocompatibility properties of such surface treatments, two type of rare earth conversion layers based on Ce(NO3)3 and Pr(NO3)3 have been studied in this present work as surface treatment for AZ80X in simulated biological (buffered) solution. Conversion layers were formed by acid etching the Mg samples in 15mM HCl followed by immersion in 0.05 M Pr(NO3)3 or Ce(NO3)3solutions. Morphology and elemental composition of the conversion layers were characterized by SEM-EDXS.Scanning electrochemical microscope (SECM) was used to investigate protective properties and degradation behaviour of Ce and Pr conversion layers on a local scale. Surface generation/tip collection (SG/TC) mode was used to study the hydrogen evolution rate and localization while AC mode was used to resolve the resistive/capacitive behaviour of conversion layer. Figure 1 represents the schematic SG/TC mode for probing the local hydrogen evolution. Self-healing properties of the conversion layer in presence of Ce3+ and Pr3+was also studied using SECM. Electrochemical impedance spectroscopy (EIS) was used to look at the changes in charge transfer and diffusion phenomena due to the formation of conversion layer and its degradation in the long term. Preliminary results have shown that Ce and Pr conversion layers improve corrosion resistance in the short term by producing an electrochemically stable surface. In the long term, however, conversion layer shows instability in simulated biological fluid and tends to degrade locally exposing the magnesium substrate to corrosive media.1. A. Rudd, C. Breslin, and F. Mansfeld, Corrosion Science, 42, 275-288 (2000).2. M. F. Montemor, a. M. Simões, and M. J. Carmezim, Applied Surface Science, 253, 6922-6931 (2007).3. K. Brunelli, M. Dabalà, I. Calliari, and M. Magrini, Corrosion Science, 47, 989-1000 (2005).4. M. Dabalà, K. Brunelli, E. Napolitani, and M. Magrini, Surface and Coatings Technology, 172, 227-232 (2003).Figure 1 Schematic representation of SG/TC mode SECM for probing hydrogen evolution

Precoated AISI441 for SOFC Interconnectors Studied by TEM Methods

Precoated AISI441 (EN 1.4509) for SOFC interconnectors were investigated using energy-filtered transmission electron microscopy (EFTEM) and electron energy-loss spectroscopy (EELS) looking at the diffusion processes in the initial stage of the oxidation. The PVD coating contained Ce and Co/Mn-alloy in two layers with at total thickness of 800nm. The samples were exposed up to 168 hours at 800°C then characterized by TEM. In parallel cyclic oxidation and chromium volatilization studies have been performed. The studies have revealed that the Ce retard the outward migration of Cr though the scale and that the discrete Ce layer transforms to isolated nanoparticles during initial oxidation.

Lanthanoid Oxide Layers on Rhodium-Loaded (Ga1–xZnx)(N1–xOx) Photocatalyst as a Modifier for Overall Water Splitting under Visible-Light Irradiation

Lanthanoid oxide modifier layers were applied to Rh metal nanoparticles on (Ga1–xZnx)(N1–xOx) photocatalyst for overall water splitting under visible-light irradiation. Structural analysis by transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy revealed that lanthanoid(III) oxide layers coated the Rh nanoparticles on (Ga1–xZnx)(N1–xOx), although they were also deposited directly on the (Ga1–xZnx)(N1–xOx) surface. Certain lanthanoid oxide layers (La, Pr, Sm, Gd, and Dy) functioned as modifiers for Rh-metal/(Ga1–xZnx)(N1–xOx) to produce H2 and O2 gases, although the Rh-metal/(Ga1–xZnx)(N1–xOx) photocatalyst exhibited little activity for overall water splitting due to rapid water formation from H2 and O2 on Rh. Ce and Eu oxide layers showed no photocatalytic activity, most likely due to their ability to capture photoexcited electrons from Rh-metal/(Ga1–xZnx)(N1–xOx). The enhancement of photocatalytic activity by lanthanoid oxide loading was shown to be dependent on the formation of redox-inactive lanthanoid(III) oxide layers on the Rh nanoparticles, which effectively suppresses the backward water formation reaction to enable H2 evolution on Rh.

有機強誘電体を用いた磁性半導体 Si:Ce 薄膜の電界効果

Field effect transistor (FET) was fabricated using MBE grown Si:Ce magnetic semiconductor films. To suppress the inter-diffusion between ferroelectric and Si:Ce layer, organic ferroelectric film, P(VDF-TeFE) which can be grown below 200℃ was used. By improving the surface roughness by optimizing the spin coat process condition, P(VDF-TeFE) films with ferroelectric behavior and high insulation property were successfully fabricated on Si:Ce thin films. Eventually, ferroelectric type C-V hysteresis was observed. High frequency C-V measurement shows a decrease of capacitance suggesting a formation of depletion layer in a negative bias region. Low frequency C-V measurement reveals an increase of capacitance suggesting a formation of inversion layer.

White Light Emitting Transparent Double Layer Stack of Al2O3 :Eu3+, Tb3+, and Ce3+ Films Deposited by Spray Pyrolysis

Aluminum oxide films doped with Tb, Ce and Eu have been deposited by spray pyrolysis using acetylacetonates as precursors. The photoluminescence emission for these films and for double layer stacks is reported. Eu and Tb doped films present the emissions associated with the radiative transitions among the electronic energy states of the triple ionized atom, being dominant the 5D0 to 7F2 at ∼ 612.5 nm for the Eu+3 ion, and the 5D4 to 7F5 at ∼547.5 nm for the Tb+3 ion. In the case of Ce doped films, there are two broad bands associated also with the 5d to 4f transitions of this ion at∼400 and 510 nm. These films have low surface roughness lower than 3 nm, and thickness between 50 to 260 nm. The double layer stacks involved an initial Eu doped layer and a second Ce and Tb co-doped layer with different thicknesses. The films are transparent with an optical bandgap of approximately 5.63 eV, the photoluminescence of these stacks presented an overlap of the emissions corresponding to all the dopants when excited with 300 nm light, resulting in a white light emission.

Atomistic observation of electron irradiation-induced defects in CeO2

ABSTRACTWe have investigated the atomistic structure of radiation-induced defects in CeO2 formed under 200 keV electron irradiation. Dislocation loops on {111} habit planes are observed, and they grow accompanying strong strain-field. Atomic resolution scanning transmission electron microscopy (STEM) observations with high angle annular dark-field (HAADF) and annular bright-field (ABF) imaging techniques showed that no additional Ce layers are inserted at the position of the dislocation loop, and that strong distortion and expansion is induced around the dislocation loops. These results are discussed that dislocation loops formed under electron irradiation are non-stoichiometric defects consist of oxygen interstitials.

The Effect of Water Vapour on the Corrosion of Sandvik Sanergy HT Under Dual Atmosphere Conditions

Interconnects of PCFC and SOFC are exposed to dual atmosphere conditions; fuel (e.g. H2) on the anode side and air on the cathode side. Sandvik Sanergy HT has been investigated under simulated fuel cell conditions at high temperatures. The microstructure and composition of the oxide scales formed at the cathode side (air) were significantly influenced by dual atmosphere conditions. The main effect was a substantial increase of Fe in the oxide scales by the formation of Fe rich nodules accompanied by localized metal loss. The size and number of the nodules increased when introducing water vapour on the air side of the samples. It is suggested that the preferred localization of nodule formation is given by the surface finish as a result of fabrication (e.g. grooves and scratches). By increasing the reaction temperature or duration of the exposures, the effect of dual atmosphere conditions became less pronounced. Alterations to the oxidation mechanism as a consequence of dual atmosphere environments are discussed with basis in the effect of hydrogen permeation through the interconnect alloy. Samples PVD coated with a double layer of metallic Ce and Co were also tested under single and dual atmosphere conditions. No significant change was found in the oxidation behaviour by dual atmosphere exposures.

Enhanced absorption and emission of Y_3Al_5O_12:Ce^3+ thin layers prepared by epoxide-catalyzed sol-gel method

We have developed a method for fabricating thin layers of Ce3+ doped yttrium aluminium garnet, Y3Al5O12 (YAG:Ce) based on a sol-gel approach with propylene oxide as a gelation initiator. A single spin-coating process followed by a sequence of heat treatments allows the fabrication of polycrystalline YAG:Ce thin layers with a thickness of a few hundreds of nanometers. Surface morphology, crystallite size, and quantum efficiency are examined as a function of heat treatment temperature. The optical quality of the layer is further investigated by measuring the enhanced absorption of light coupled into the layer. We fabricate a three-layered slab waveguide system consisting of a fused silica glass substrate, a YAG:Ce layer and a SiO2 upper layer, and excite the system by illumination through a prism. The incident light couples to the fundamental waveguide mode in the YAG:Ce layer where it is eventually absorbed, resulting in an enhancement of absorption by a factor of 30. In correspondence, we observe a similar increase in emission intensity of photoluminescence caused by the enhanced absorption.