SiO2 Protective Layer Research Articles

Oxidation Behavior of ZrB<sub>2</sub>-15vol.%SiC at an Oxygen Partial Pressure of 57 Pa

The oxidation tests of the ZrB2-15vol.%SiC composite were carried out at 1673-1923 K under a low partial pressure of oxygen. Cross sections of the oxidized samples were studied using WDS. The reaction layer consists of ZrO2 and SiO2 at 1673 K. The SiO2 protective layer is formed on the surface. No apparent SiC depleted layer is observed. SiC depletion seems to occur at 1923 K and only the ZrO2 phase exists at the reaction layer. The passive oxidation occurs at 1673 K, whereas the active oxidation at 1923 K. The mass changes are quantitatively discussed by introducing a new emprical equation. The ZrB2-30 vol.%SiC composite is also discussed briefly.

Microstructure and Oxidation Behavior of Molybdenum Disilicide Coating Prepared by Air Plasma Sprayed

Intermetallics molybdenum dislicied has a great potential as a protective coating in aircraft engines and gas turbines in the elevated temperature. The suit for plasma spraying MoSi2 powders were prepared by spray drying process and vacuum sintered. The oxidation behaviors of the coating were determined at 1200 °C. The coatings as sprayed and oxidized were characterized by XRD, SEM and EDS. Results show that the flow ability and loose density of MoSi2 powder by sintered treatment, were 17.1 s/50g and 2.1g/cm3, respectively, ideal for air plasma spraying. During the course of spraying, some of molybdenum disilicide with a tetragonal lattice was converted into molybdenum disilicide with a hexagonal lattice. Also, part of MoSi2 phase oxidized and transformed to Mo5Si3 phase. A relative dense molybdenum disilicide coating was prepared by air plasma spraying. A protective SiO2 layer, seems to be glassy, with a thickness about 10 μm was formed on the surface of MoSi2 coating during MoSi2 coating oxidized at 1200°C for 200 h. The results of the oxidation tests show that MoSi2 coating prepared by air plasma spraying may be provide a protect layer for high temperature structure material.

Transparent nanostructured coatings with UV-shielding and superhydrophobicityproperties

Visible light transparent, UV-shielding and superhydrophobic nanostructured coatingshave been successfully fabricated through a facile layer-by-layer deposition ofTiO2 andSiO2 nanoparticles. The coatings are composed of an underlying UV-shieldingTiO2 layer and a top fullycovered protective SiO2 layer. The resulting coatings can block 100% of UVB and UVC and almost85% of UVA. The fabricated surfaces have contact angles exceeding165° after coating with organic PTES (1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane)molecules. The transparent superhydrophobic surfaces exhibit extremely strongUV stability. All coatings retain the initial UV-shielding and superhydrophobicproperties even after exposure to 275 nm UV light with a light intensity of 75 mW cm − 2 for 12 h.

Development of Si DRIE process allowing simultaneous etching from narrow and wide mask openings

AbstractWe have developed a new Si DRIE process, which allows simultaneous etching of both narrow and wide mask opening patterns. MEMS devices often contain a wide range of mask opening sizes ranging from micrometer to millimeter scale on the same chip. Conventional DRIE process suffered from a trade‐off between minimizing mask‐undercut for narrow grooves and eliminating black Si on an etched bottom surface for large mask apertures. This was caused by nonuniformity in the deposition of the protective polymeric layer during etching in mask aperture areas having different sizes. Our new DRIE process technique, alternating conventional DRIE with O2 plasma irradiation, adds a SiO2 layer onto the polymeric layer. We have ascertained that the new DRIE process can form a SiO2 protective layer of uniform thickness regardless of the mask aperture size. This uniformity is considered a result of equilibrium between surface oxidation and sputtering of oxygen by plasma irradiation. We have demonstrated that our newly developed process allows simultaneous etching of narrow, deep grooves 1 μm wide and 73 μm deep, and wide aperture areas 500 μm square without black Si on the same chip. © 2011 Wiley Periodicals, Inc. Electron Comm Jpn, 94(4): 36–43, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10303

Formation of Transparent SiO2 Protective Layer on Polycarbonate by 157 nm F2 Laser for Lightweight Automobile Window

A transparent, hard silica glass (SiO2) layer was formed on a conventional protective coat made of silicone ([SiO(CH3)2]n) on a polycarbonate plate by the 157 nm F2 laser-induced photochemical modification of silicone into SiO2. An optimum laser irradiation time of the F2 laser was found to form a crack-free SiO2 layer. The high optical transparency of the samples in the visible light region remained unchanged after the F2 laser irradiation. In the Taber abrasion test, the SiO2 layer markedly reduced the number of scratches, resulting in a low haze value. The haze values of the samples also depend on the thickness of the silicone protective coat underneath the SiO2 protective layer. As a result, the difference of haze value (δHz) was successfully reduced to 3.6%, compared with these of the nonirradiated sample and a bare polycarbonate plate of approximately 11.3 and 41.3%, respectively, which is comparable to the case of a bare silica glass of approximately 1.6%. In addition, the thickness of the SiO2 protective layer was estimated to be approximately 0.44 µm for the 30-s laser irradiation by immersing the samples in 1 wt % hydrogen fluoride aqueous solution and measuring the depth using a surface profilometer.

Improved Hydrogen Gas Generation Rate of n-GaN Photoelectrode with SiO2 Protection Layer on the Ohmic Contacts from the Electrolyte

Direct photoelectrolysis of water to generate hydrogen was performed using n-type GaN films with ohmic contacts to serve as working electrodes. To enhance the efficiency of electron collection in the GaN working electrode, meshed contacts with a protection layer were immersed in the NaCl electrolyte. With an external bias of , the typical photocurrent densities (gas generation rate) of the n-GaN working electrodes with and without the immersed ohmic contact layer were approximately 19.6 (9.4) and , respectively, which corresponded to an enhancement in the photocurrent density (gas generation rate) of around 98% (160%). The marked enhancement in the gas generation rate could be attributed to the fact that the distance between the neighbor ohmic contacts is small enough to reduce the recombination probability of photogenerated electrons with holes or charged defects in the GaN layer before the electrons reach the ohmic contacts. In other words, the photogenerated electrons can be effectively collected by the ohmic contacts and thereby reach the Pt counter electrode to lead the generation of hydrogen.

Application of Si-N Insulating Layer to CPP-GMR Device

Tb-Fe-Co, an RE-TM alloy, is a promising material for perpendicular magnetic CPP-GMR devices. Because the spontaneous magnetization of RE-TM alloy can be controlled by its composition, the magnetic field generated from the pinned layer can be reduced by using a Tb-Fe-Co alloy film for the pinned layer. However, Tb-Fe-Co oxidizes easily. In this study, we applied a Si-N insulating layer to a CPP-GMR device in place of a SiO2 protective layer and successfully improved the magnetic characteristics of the Tb-Fe-Co pinned layer.

Influence of methacryl polyhedral oligomeric silsesquioxane on the thermal and mechanical properties of methylsilicone resin

AbstractA methacryl polyhedral oligomeric silsesquioxane (POSS)‐reinforced methylsilicone resin was prepared in this work. The structures of the obtained products were confirmed with Fourier transform infrared and atomic force microscopy. The influence of methacryl‐POSS on the thermal behavior of the methylsilicone resin was studied by thermogravimetric analysis and isothermal thermogravimetric analysis. The results showed that the thermal stability of the methylsilicone resin was improved, and the degree of thermooxidative degradation was lowered; this was due to the retardation of polymer chain motion and the formation of a protective layer of SiO2. The interlaminar shear strength and flexural strength of quartz fiber/methylsilicone resin composites were tested to determine the effects of methacryl‐POSS on the mechanical properties of methylsilicone resin. The results revealed that the mechanical properties of the methylsilicone composites also increased obviously after the incorporation of methacryl‐POSS because of the increase in the cure degree and rigidity of the resin. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Influence of metastable tetragonal ZrO2-reinforcements on the properties of MoSi2-composites

Abstract In this work, MoSi2 – ZrO2-composites with different volume fractions (15-, 25-, 35 vol.% ZrO2) were examined. Zirconium oxide was successfully tetragonal stabilised (metastable state) through a high temperature isostatic pressure process, where the tetragonal – monoclinic phase transformation is inhibited by the pressure of the MoSi2-matrix. Stabilisers, e. g. Y2O3 were not used. Increasing ZrO2 content enhances strength and fracture toughness at room temperature. For temperatures above 900°C up to 1500°C no influence of the volume fraction of ZrO2 was observed with respect to the compression tests. Wear of pre-oxidised samples (20 min at 1000°C) is higher for the 25 and 35 vol.% than non-oxidised material. Oxidation resistance is observed to be poor and decreases with increasing ZrO2 content in the composite. Early crack initiation leads to poor creep behaviour and thermo-shock behaviour. This is probably due to the oxygen diffusing through the ZrO2-particles. Consequently no continuous protective SiO2-layer can be built as known from pure MoSi2-materials. In general the investigated material is not suitable for high temperature applications because of the poor oxidation behaviour.

SiO2保护层和退火对Ta2O5薄膜激光损伤阈值影响的对比研究

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition. The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated. The results show that SiO2 protective layers exert little influence on the electric field intensity (EFI) distribution, microstructure and microdefect density but increase the absorption slightly. Annealing is effective on decreasing the microdefect density and the absorption of the films. Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT. Moreover, the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.

真空紫外光学薄膜及薄膜材料

The research and development of vaccum ultraviolet(VUV) optical coatings and film materials are outlined. The Al film attracts much attention for its high reflectivity until 80 nm. With a protective layer, its reflectivity is up to 90% at 157 nm under high vacuum and at 30 nm/s deposition rate. Oxide films have small mechanical stress, and better environmental stability than fluoride films, which is widely applied at 193 nm. Fluoride films have wide bandwidth and low absorption. With a dense SiO2 protective layer, the highly reflective fluoride stacks can provide a reflectivity of nearly 99% in the center wavelength of 180 nm, and the stability as well as the laser damage threshold has been greatly enhanced. Anti-fluoride films can obtain a reflectivity below 0.1% at 157 nm. So far, the resistance evaporation process is the best deposition technology for fluoride films.

シリコンのＤＲＩＥにおける大小開口混在パターン一括加工技術の開発

We have developed a new Si DRIE process, which allows simultaneous etching of both narrow and wide mask opening patterns. MEMS devices often contain a wide range of mask opening sizes ranging from micrometer to millimeter scale on the same chip. Conventional DRIE process suffered from a trade-off between minimizing mask-undercut for narrow grooves and eliminating black Si on an etched bottom surface for large mask apertures. This was caused by nonuniformity in the deposition of the protective polymeric layer during etching in mask aperture areas having different sizes. Our new DRIE process technique, alternating conventional DRIE with O2 plasma irradiation, adds a SiO2 layer onto the polymeric layer. We have ascertained that the new DRIE process can form a SiO2 protective layer of uniform thickness regardless of the mask aperture size. This uniformity is considered a result of equilibrium between surface oxidation and sputtering of oxygen by plasma irradiation. We have demonstrated that our newly developed process allows simultaneous etching of narrow, deep grooves 1 μm wide and 73 μm deep, and wide aperture areas 500 μm square without black Si on the same chip. © 2011 Wiley Periodicals, Inc. Electron Comm Jpn, 94(4): 36–43, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10303

Influences of MonoSilanolIsobutyl-POSS on thermal stability of polymethylsilxoane

Incorporation of polyhedral oligomeric silsesquioxane (POSS) molecules into polymer matrix resulted in increased used and decomposition temperatures. Polymethylsiloxane (PMS)/MonoSilanolIsobutyl-POSS hybrid copolymers containing various proportions of MonoSilanolIsobutyl-POSS were prepared. The structures and thermal properties of the obtained products were characterized with Gel Permeation Chromatography (GPC), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), differential thermogravimetric analysis (DTG) and X-ray photoelectron spectroscopy (XPS). The GPC and FTIR spectra suggested successful bonding of MonoSilanolIsobutyl-POSS and PMS. TGA, DTG and XPS analysis revealed that MonoSilanoIsobutyl-POSS reinforced PMS are thermally more stable than the original PMS, primarily by the elimination of SiOH effects, the nanoreinforcement effect of POSS, the retardation of polymer chain motion and the formation of SiO2 protective layer.

Effect of SiO2 protective layer on the femtosecond laser-induced damage of HfO2/SiO2 multilayer high-reflective coatings

Two kinds of HfO2/SiO2 800nm high-reflective (HR) coatings, with and without SiO2 protective layer were deposited by electron beam evaporation. Laser-induced damage thresholds (LIDT) were measured for all samples with femtosecond laser pulses. The surface morphologies and the depth information of all samples were observed by Leica optical microscopy and WYKO surface profiler, respectively. It is found that SiO2 protective layer had no positive effect on improving the LIDT of HR coating. A simple model including the conduction band electron production via multiphoton ionization and impact ionization is used to explain this phenomenon. Theoretical calculations show that the damage occurs first in the SiO2 protective layer for HfO2/SiO2 HR coating with SiO2 protective layer. The relation of LIDT for two kinds of HfO2/SiO2 HR coatings in calculation agrees with the experiment result.

Mechanism of Properties of Noble ZnS–SiO2 Protection Layer for Phase Change Optical Disk Media

A ZnS–SiO2 composite dielectric is widely used in the optical stack designs of rewritable optical recording media as an index-matching medium and as a protection layer for the high-index chalcogenide (compound with sixth group element of S, Se, Te) phase change material used in these media. The addition of Si and O to ZnS is primarily intended to stabilize against crystalline grain growth of ZnS with high numbers of direct overwriting cycles. In this study, we carry out infrared (IR) spectroscopy to clarify the role of Si in this stabilization process. IR spectroscopy is performed on sputter as-deposited and annealed ZnS–SiO2 dielectric protection layers. We find that Si exists not in the SiO2 oxide phase but as [SiS4-nOn] tetrahedrons. Moreover, zinc and sulfur do not exist as ZnS, but in highly chemically disordered ZnS:O crystallites. The highly directional and rigid covalent bonds in the [SiS4-nOn] tetrahedrons are key to establishing thermal stability against the coalescence of ZnS. The importance of the Si–S bond also extends into a more thorough understanding of the low thermal conductivity of the ZnS–SiO2 material. The consideration of elastic implications allows us to predict an average phonon velocity less than 50% compared to that in SiO2. With this, we predict a thermal conductivity of 0.0067 W cm-1 K-1 for this material, which is in complete agreement with measured values.

Suppression of Pt Sintering on MFI Zeolite by Modification with Tetramethoxysilane

Platinum sintering on zeolite catalyst is successfully suppressed by modification using tetramethoxysilane. Modification in this manner produces a protective layer of SiO2 over each Pt particle. High-temperature (1000 °C) aging tests in air confirm the superior durability of the modified catalyst compared to a conventional γ-alumina-supported catalyst.

Processing and interfacial bonding strength of 2014 Al matrix composites reinforced with oxidized SiC particles

The SiC powder with a SiO2 protective layer is used as the reinforcements for 2014Al/SiCp composites to suppress the reaction between the Al matrix and the SiC particle. 2014Al/SiCp composites were fabricated by vacuum hot pressing (VHP) and subsequent extrusion using 2014Al powders and the SiC particles covered with a SiO2 layer. The interfacial product was found to be Mg spinel (MgAl2O4) formed mainly by the chemical reactions of the SiO2 layer covered on SiC particles with the Mg, Al in the 2014Al alloy matrix. Also the interfacial bonding strength of the composites was investigated using push-out tests of SiC rods with the SiO2 oxidation layer, which were processed within 2014Al alloy.

Optical recording characteristics of WO3 films grown by pulsed laser deposition method

W O 3 films were deposited on the glass substrate (Corning No. 7059 with an area of 26×38mm) by the pulsed laser deposition method using an ArF excimer laser. It was found that after annealing at 500°C for 10min, the film thickness became 1.8 times compared with that (approximately 40nm) in the as deposited state. At this time, the difference in the transmittance, ΔT, between the annealed state and the as deposited state was about 40% at the wavelength of 400nm. From x-ray diffraction spectra and x-ray photoelectron spectroscopy spectra, it was considered that the ratio of the peak values of W6+ 4f5∕2 (tungsten oxide) versus W 4f5∕2 (metal tungsten) increased steeply after the annealing process. From this, it was considered that oxygen was absorbed into the WO3 films through the annealing process. From the revolution test for the sample without the protection layer in which the WO3 films were deposited upon the digital versatile disk disk substrate, a write peak-power dependence of carrier to noise ratio (CNR) (at λ=406nm, NA=0.65) of 3T signal (58.5MHz) was measured at a linear velocity of 5m∕s and a read power of 0.6mW. It was confirmed that the values of CNR obtained at the write peak-power 5–6mW were near 50dB (the region A) and the ones obtained at the write power 7–10mW were more than 60dB (the region B). From scanning electron microscopy observation, it was recognized that bits with 0.16–0.25μm size, having the fine-shaped dots with clear-cut edge, were made in the region A. This corresponded to the maximal storage capacity of 25GB in the “Blu-ray disk” specification. However, it was also identified that holes were formed in the region B and the film materials were scattered by receiving a train of high write power impulses. Next, it was found that the write power corresponding to region A for the structures with the WO3 layer sandwiched between a Al2O3 or ZnS–SiO2 protection layer increased or decreased, respectively. Larger values of the CNR will be obtained if the film thickness of each layer including the active layer were optimized.

Oxidation of SiOC Composite Having Dispersoids of Mo<sub>4.8</sub>Si<sub>3</sub>C<sub>0.6</sub> and MoSi<sub>2</sub>

New ceramic composites that consist of the amorphous SiOC matrix having dispersoids of Mo4.8Si3C0.6 and some MoSi2 were synthesized, and their oxidation characteristics were investigated between 450 and 1050oC in air. The SiOC matrix was obtained by converting polymethylsiloxane via pyrolysis. The good oxidation resistance of the prepared composites originated from a thin, protective SiO2 layer formed on the surface. But the outermost oxide surface was porous, owing to the formation of the highly volatile MoO3, which was formed together with SiO2.

Surface-Plasmon-Coupled Emission of Quantum Dots

We studied surface plasmon-coupled emission (SPCE) of semiconductor quantum dots (QDs). These QDs are water-soluble ZnS-capped CdSe nanoparticles stabilized using lysine cross-linked mercaptoundecanoic acid. The QDs were spin-coated from 0.75% PVA solution on a glass slide covered with 50 nm of silver and a 5-nm protective SiO(2) layer. Excited QDs induced surface plasmons in a thin silver layer. Surface plasmons emitted a hollow cone of radiation into an attached hemispherical glass prism at a narrow angle of 48.5 degrees. This directional radiation (SPCE) preserves the spectral properties of QD emission and is highly p-polarized irrespective of the excitation polarization. The SPCE spectrum depends on the observation angle because of the intrinsic dispersive properties of SPCE phenomenon. The remarkable photostability can make QDs superior to organic fluorophores when long exposure to the intense excitation is needed. The nanosize QDs also introduce a roughness near the metal layer, which results in a many-fold increase of the coupling of the incident light to the surface plasmons. This scattered incident illumination transformed into directional, polarized radiation can be used simultaneously with SPCE to develop devices based on both quantum dot emission and light scattered from surface plasmons on a rough surface.