Vapor grown silicon dioxide improves transistor base-collector junctions

Vapor grown silicon dioxide layer protects base-collector junction in silicon planar transistors during the emitter diffusion process. This oxide fills in any imperfections that exist in the thermally grown oxide layer and is of greater thickness than that layer. This process is used to deposit protective silicon dioxide coatings on optical surfaces

Coating with overlay metallic-cermet alloy systems

A base layer of an oxide dispersed, metallic alloy (cermet) is arc plasma sprayed onto a substrate, such as a turbine blade, vane, or the like, which is subjected to high temperature use. A top layer of an oxidation, hot corrosion, erosion resistant alloy of nickel, cobalt, or iron is then arc plasma sprayed onto the base layer. A heat treatment is used to improve the bonding. The base layer serves as an inhibitor to interdiffusion between the protective top layer and the substrate. Otherwise, the 10 protective top layer would rapidly interact detrimentally with the substrate and degrade by spalling of the protective oxides formed on the outer surface at elevated temperatures

Three-dimensional low Reynolds number flows near biological filtering and protective layers

Mesoscale filtering and protective layers are replete throughout the natural world. Within the body, arrays of extracellular proteins, microvilli, and cilia can act as both protective layers and mechanosensors. For example, blood flow profiles through the endothelial surface layer determine the amount of shear stress felt by the endothelial cells and may alter the rates at which molecules enter and exit the cells. Characterizing the flow profiles through such layers is therefore critical towards understanding the function of such arrays in cell signaling and molecular filtering. External filtering layers are also important to many animals and plants. Trichomes (the hairs or fine outgrowths on plants) can drastically alter both the average wind speed and profile near the leaf's surface, affecting the rates of nutrient and heat exchange. In this paper, dynamically scaled physical models are used to study the flow profiles outside of arrays of cylinders that represent such filtering and protective layers. In addition, numerical simulations using the Immersed Boundary Method are used to resolve the 3D flows within the layers. The experimental and computational results are compared to analytical results obtained by modeling the layer as a homogeneous porous medium with free flow above the layer. The experimental results show that the bulk flow is well described by simple analytical models. The numerical results show that the spatially averaged flow within the layer is well described by the Brinkman model. The numerical results also demonstrate that the flow can be highly 3D with fluid moving into and out of the layer. These effects are not described by the Brinkman model and may be significant for biologically relevant volume fractions. The results of this paper can be used to understand how variations in density and height of such structures can alter shear stresses and bulk flows.Comment: 28 pages, 10 figure

Effect of hard particle impacts on the atomic oxygen survivability of reflector surfaces with transparent protective overcoats

Silver mirror samples with protective coatings were subjected to a stream of 27 microns alumina particles to induce pinhole defects. The protective coating consisted of a layer of aluminum dioxide over silver followed by a layer of silicon dioxide over the alumina. Samples were prepared on both graphite-epoxy composite and fused quartz substrates. After exposure to the hard particle stream, the samples were exposed to an oxygen plasma environment in a laboratory plasma asher. The effects of both the hard particles and the oxygen plasma were documented by both reflectance measurements and scanning electron microscopy. The results indicated that oxidative damage to the silver reflecting layer continues beyond that of the erosively exposed silver. Oxidative undercutting of the silver layer and graphite-epoxy substrate continues in undamaged areas through adjacent, particle damaged defect sites. This may have implications for the use of such mirrors in a space station solar dynamic power system

Transfer of Graphene with Protective Oxide Layers

Transfer of graphene, grown by Chemical Vapor Deposition (CVD), to a substrate of choice, typically involves deposition of a polymeric layer (typically, poly(methyl methacrylate, PMMA or polydimethylsiloxane, PDMS). These polymers are quite hard to remove without leaving some residues behind. Here we study a transfer of graphene with a protective thin oxide layer. The thin oxide layer is grown by Atomic Deposition Layer (ALD) on the graphene right after the growth stage on Cu foils. One can further aid the oxide-graphene transfer by depositing a very thin polymer layer on top of the composite (much thinner than the usual thickness) following by a more aggressive polymeric removal methods, thus leaving the graphene intact. We report on the nucleation growth process of alumina and hafnia films on the graphene, their resulting strain and on their optical transmission. We suggest that hafnia is a better oxide to coat the graphene than alumina in terms of uniformity and defects.Comment: 13 pgs, 13 figure

Diffusion based degradation mechanisms in giant magnetoresistive spin valves

Spin valve systems based on the giant magnetoresistive (GMR) effect as used for example in hard disks and automotive applications consist of several functional metallic thin film layers. We have identified by secondary ion mass spectrometry (SIMS) two main degradation mechanisms: One is related to oxygen diffusion through a protective cap layer, and the other one is interdiffusion directly at the functional layers of the GMR stack. By choosing a suitable material as cap layer (TaN), the oxidation effect can be suppressed.Comment: 3 pages, 3 figures. to be published in Appl. Phys. Let

An efficient protection of stainless steel against corrosion: Combination of a conversion layer and titanium dioxide deposit

In the present work, a novel process has been developed to improve the corrosion properties of ferritic stainless steels. Titanium oxide coatings have been deposited onto stainless steel by sol–gel process after a pre-functionalization of the substrate in a conversion bath. Gel titania was prepared by hydrolysis of a titanium butoxide through a sol–gel process. Duplex systems "conversion layer/uniform TiO2 coating" have been prepared on stainless steels using a dipping technique and thermal post-treatments at 450 °C. The preparation of sol–gel coatings with specific chemical functions offers tailoring of their structure, texture and thickness and allows the fabrication of large coatings. The morphology and structure of the coatings were analysed using scanning electron microscopy with field effect gun (SEM-FEG), Mass spectroscopy of secondary ions (SIMS) and X-ray diffraction (XRD). The anticorrosion performances and the ageing effects of the coatings have been evaluated in neutral and aggressive media by using several normalized tests. The results show that the conversion layer was not sufficient to protect steel but sol–gel TiO2 coatings, anchored on the metal substrate via the conversion layer, show good adhesion with the substrate and act as a very efficient protective barrier against corrosion. So, duplex layers with TiO2 nanoparticle coatings on steels exhibit an excellent corrosion resistance due to a ceramic protective barrier on metal surface. Analysis of the data indicates that the films act as geometric blocking layers against exposure to the corrosive media and increase drastically the lifetime of the substrate