Thin Alumina Layer Research Articles

Fabrication of dense alumina layer on Ti alloy hybrid by cold metal transfer and micro-arc oxidation methods

Abstract

Transmittance in a thin aluminum layer at nanosecond pulsed laser ablation

AbstractSince the beginning of the 1960s and up to the present time, laser ablation from metal surfaces under the action of short light pulses has been the topic of many researches. One of the first objects in the early ablation experiments presented thin metal films evaporated by radiation, which were used in lasers with nanosecond pulses as optical gates for Q-switching in resonators or for decoupling in amplifiers. Bleaching of the gates based on metal layers with a time constant τt ≈ 10−8 s observed in a number of experiments, was usually considered as a result of a simple evaporation of matter. We analyze the data of the experiments with a mylar tape [≈0.05 µm aluminum (Al) layer on ≈20 µm lavsan substrate] used as a gate for optical isolation in one of the first Nd: glass laser facilities with a power of ≈1 GW. That gate was irradiated by pulses of Q-switched oscillators: pulse duration 10−7–10−8 s, intensity 107–108 W/cm2. A jump in the transmittance of the expanding Al layer was registered (from ≈0.1 to 50% at τt ≈ 10−9 s). The present study shows that one should consider the metal–insulator phase transition in a superheated liquid metal layer as the mechanism of the fast (up to 10–10–10–11 s) increase in the transmittance of the Al film gate at nanosecond-pulsed laser ablation.

Tuning the nanoscale morphology and optical properties of porous gold nanoparticles by surface passivation and annealing

We synthesized the arrays of porous gold nanoparticles attached to a fused silica and SiO2/Si substrates employing a combination of thin film solid state dewetting and dealloying methods. We demonstrated that the surface of porous gold nanoparticles can be passivated with a thin and conformal alumina layer produced by the plasma-enhanced atomic layer deposition method. This passivation results in significant improvement of the thermal stability of the nanoporous morphology. Whereas as–produced porous gold nanoparticles start to coarsen at the temperature as low as 160 °C, their passivated counterparts are thermally stable up to 800 °C. At higher temperatures, the solid gold nanoparticles are formed on the outer surfaces of the passivated porous gold nanoparticles, leaving behind partially emptied alumina shells. We correlated the optical absorbance spectra of the as-produced and annealed particles with their morphology and microstructure. A broad absorption peak in the infrared region was associated with thin gold ligaments of 10–15 nm in diameter, and coarsening of these ligaments in the unpassivated particles has led to the attenuation of the peak. The passivated particles demonstrated the stability of the infrared absorption intensity up to the formation of solid gold nanoparticles at 900 °C, and the red shift of the visible-range plasmon resonance peak above 600 °C. We conclude that surface passivation and heat treatments represent efficient tools for tuning surface plasmon resonance properties of porous gold nanoparticles.

Failure assessment of thin-walled FML profiles during buckling and postbuckling response

Abstract The paper discusses nonlinear buckling and failure analysis of FML thin-walled structures under axial compression. Study was carried out on Fibre Metal Laminates (FMLs) made of alternating thin layers of aluminium and glass fibre-reinforced unidirectional prepreg. Various 3/2 symmetrical lay-ups were investigated and depending on fibres alignment 7 stacking sequences of FML were considered when subjected to axial compression in laboratory buckling tests. The behaviour of thin walled compression members was investigated with main focus on buckling and post-buckling response and various failure mechanisms. Experimental procedures included macroscopic and microscopic examination performed by means of stereoscopic, optical and scanning electron microscope (SEM). The results of experimental investigations were compared with finite element simulations wherein Tsai-Wu, Hashin and Puck failure criteria were applied. Failure assessment by FEM included also an attempt to estimate particular regions of laminate's fracture within buckling and post-buckling state.

Experimental Investigation of Static & Dynamic Loading Conditions for Glare Material

Now a day’s weight plays a very important role in aircraft industries. The reason behind this is efficient & effective working of aircraft. It also needs the high strength to weight ratio. This requirement is fulfilled by the composites. In this research, GLARE is a hybrid composite consisting of thin aluminum, glass fiber & epoxy layer. GLARE materials have been using over 36 years for wide range of advance aerospace structural applications. GLARE laminates offer a distinctive amalgamation of properties such as outstanding fatigue resistance, high specific static properties, exceptional impact resistance, good flame resistance, corrosion resistance and ease of manufacture and repair. But the delaminating occurs in the sheets of aluminum and similarly aluminum wire mesh is used. Solicitation of GLARE materials for the skin or the outer parts here presented the need of GLARE materials in supportive structural members; the present work focuses on the fabrication various structural cross sections of glare material. For fabrication purpose, selected method is hand lay-up. Static & dynamic analysis of these glare material cross sections was carried out; it follows a comparative study with the aluminum cross sections gives that the glare has a better performance.

Suppression of zinc anode corrosion for printed flexible zinc‐air battery

AbstractSelf‐discharge caused by hydrogen evolution reaction (HER) coinciding with corrosion of the zinc anode is a major drawback of printed zinc‐air batteries. Thus, this work aims at suppressing self‐discharge of flexible printed zinc‐air batteries by coating thin layer of aluminum oxide () onto the surface of zinc particles. The coating layer was directly synthesized onto the zinc particles by a low‐cost and facile sol–gel method. The coating effectively mitigated HER of the zinc particles, and delayed the corrosion of the zinc anode. Further, the effects of the thickness of layer on corrosion behavior of the zinc anode in 9 M potassium hydroxide as well as performance of the batteries were investigated. With a proper thickness of coating, corrosion of the battery was considerably suppressed without sacrificing the battery performance.(a) Photographic image of the fabricated battery, (b) transmission electron microscopic image of zinc particle coated with .

Compositional highly porous thermal insulation with effective porosity parameters

In this work, thermal insulation material which consists of the fireproof wool covered by a thin aluminum layer and the aluminum foil was investigated. The objective was to determine effective porosity parameters for composite heat insulation by which a minimum thermal conductivity will be obtained. According to the objective, following tasks were formulated: make the empirical research with different porosity parameters; find regression equation of dependence of the material thermal conductivity on the geometric dimensions; analyze and verify the importance of factors; obtain the optimal porosity parameters for composite heat insulation material. To improve the thermal properties of the composite material, in the wool were made cells with paraboloid shape and then surface was covered by thin layer of aluminum. Cells were made by pressing method. The total width of the experimental samples was 5 mm. The depth of the cell was 4 mm, thickness of the aluminum foil was 0,2 mm. The thermal conductivity of the material was measured using a thermal conductivity meter IT-λ-400. The optimal geometric values of the cell in composite material were obtained by the regulatory simplex algorithm (cell length 7,6074 mm, cell thickness 12,534 mm). At the optimal geometric values, the following thermal conductivity coefficient was achieved – 0,226 W/(m∙K). Set tasks were completed in full The obtained results can be introduced into existing production technologies of composite sandwich panels, for example in the sandwich panels by Rockwool company. Also it can be serve as a basis for the development of more modern materials. Composite materials with such cell structure will be more effective in comparison with usual non cell materials.

Photo‐Electrical Characterization of Silicon Micropillar Arrays with Radial p/n Junctions Containing Passivation and Anti‐Reflection Coatings

In order to assess the contributions of anti‐reflective and passivation effects in microstructured silicon‐based solar light harvesting devices, thin layers of aluminum oxide (Al2O3), silicon dioxide (SiO2), silicon‐rich silicon nitride (SiNx), and indium tin oxide (ITO), with a thickness ranging from 45 to 155 nm, are deposited onto regularly packed arrays of silicon micropillars with radial p/n junctions. Atomic layer deposition of Al2O3 yields the best conformal coating over the micropillars. The fact that layers made by low‐pressure chemical vapor deposition (SiO2 and SiNx) are not conformally deposited on the sidewalls of the Si micropillars do not influence the photoelectrical efficiency. For ITO, a change in composition along the micropillar height is measured, which leads to poor performance. For Al2O3, deconvolution of the contributions of passivation and anti‐reflection to the overall efficiency gain exhibits the importance of passivation in micro/nano‐structured Si devices. Al2O3‐coated samples perform the best, for both n/p and p/n configured pillars, yielding (relative) increases of 116% and 37% in efficiency of coated versus non‐coated samples for p‐type and n‐type base micropillar arrays, respectively.

Temperature measurement and control system for transtibial prostheses: Functional evaluation

ABSTRACTThe accumulation of heat inside the prosthetic socket increases skin temperature and fosters perspiration, which consequently leads to high tissue stress, friction blister, discomfort, unpleasant odor, and decreased prosthesis suspension and use. In the present study, the prototype of a temperature measurement and control (TM&C) system was designed, fabricated, and functionally evaluated in a phantom model of the transtibial prosthetic socket. The TM&C system was comprised of 12 thermistors divided equally into two groups that arranged internal and external to a prosthetic silicone liner. Its control system was programmed to select the required heating or cooling function of a thermal pump to provide thermal equilibrium based on the amount of temperature difference from a defined set temperature, or the amount of difference between the mean temperature recorded by inside and outside thermistors. A thin layer of aluminum was used for thermal conduction between the thermal pump and different sites around the silicone liner. The results showed functionality of the TM&C system for thermoregulation inside the prosthetic socket. However, enhancing the structure of this TM&C system, increasing its thermal power, and decreasing its weight and cost are main priorities before further development.

Preparation of Aluminum Oxide-Coated Glass Slides for Glycan Microarrays.

In this study, we report the fabrication of aluminum oxide-coated glass (ACG) slides for the preparation of glycan microarrays. Pure aluminum (Al, 300 nm) was coated on glass slides via electron-beam vapor deposition polymerization (VDP), followed by anodization to form a thin layer (50–65 nm) of aluminum oxide (Al-oxide) on the surface. The ACG slides prepared this way provide a smooth surface for arraying sugars covalently via phosphonate formation with controlled density and spatial distance. To evaluate this array system, a mannose derivative of α-5-pentylphosphonic acid was used as a model for the optimization of covalent arraying based on the fluorescence response of the surface mannose interacting with concanavalin A (ConA) tagged with the fluorescence probe A488. The ACG slide was characterized using scanning electron microscopy, atomic force microscopy (AFM), and ellipsometry, and the sugar loading capacity, uniformity, and structural conformation were also characterized using AFM, a GenePix scanner, and a confocal microscope. This study has demonstrated that the glycan array prepared from the ACG slide is more homogeneous with better spatial control compared with the commonly used glycan array prepared from the N-hydroxysuccinimide-activated glass slide.

Light transmission coefficients by subwavelength aluminum gratings with dielectric layers

Spectral positions of plasmon resonances related to boundaries between a thin aluminum layer and dielectrics (air, glass, VDF–TrFE 65/35 ferroelectric copolymer, and indium tin oxide (ITO)) have been determined in the transmission spectra of aluminum gratings of three types with 30 × 30 μm2 dimensions and 350-, 400-, and 450-nm line periods. Experimental results agree well with spectral positions of plasmon resonances calculated for the normal incidence of TM-polarized light. In addition, maximum values of transmission coefficients in the region of λ ≈ 900–950 nm have been determined for glass–Al–copolymer and glass–ITO–Al–copolymer structures. These values are close to 100%, which shows that the effective optical aperture is two times greater than the geometric areas of slits.

Enhanced Optoelectronic Properties of PFO/Fluorol 7GA Hybrid Light Emitting Diodes via Additions of TiO₂ Nanoparticles.

The effect of TiO2 nanoparticle (NP) content on the improvement of poly(9,9′-di-n-octylfluorenyl-2,7-diyl) (PFO)/Fluorol 7GA organic light emitting diode (OLED) performance is demonstrated here. The PFO/Fluorol 7GA blend with specific ratios of TiO2 NPs was prepared via a solution blending method before being spin-coated onto an indium tin oxide (ITO) substrate to act as an emissive layer in OLEDs. A thin aluminum layer as top electrode was deposited onto the emissive layer using the electron beam chamber. Improvement electron injection from the cathode was achieved upon incorporation of TiO2 NPs into the PFO/Fluorol 7GA blend, thus producing devices with intense luminance and lower turn-on voltage. The ITO/(PFO/Fluorol 7GA/TiO2)/Al OLED device exhibited maximum electroluminescence intensity and luminance at 25 wt % of TiO2 NPs, while maximum luminance efficiency was achieved with 15 wt % TiO2 NP content. In addition, this work proved that the performance of the devices was strongly affected by the surface morphology, which in turn depended on the TiO2 NP content.

Fabrication of dense α-alumina layer on Ti-6Al-4V alloy hybrid for bearing surfaces of artificial hip joint

Recent advances in hip replacements are focused towards producing reliable bearing surfaces to enhance their longevity. In this perspective, progressive attempts have been made to improve the wear resistance of polyethylene to eliminate osteolysis and mechanical reliability of brittle alumina ceramics, but in vain. It is proposed that both high wear resistance and mechanical reliability can be retained if a thin layer of dense alumina is formed onto high toughness Ti-6Al-4V alloy. For this purpose, we devised a unique methodology in which a layer of Al metal was deposited onto the Ti alloy substrate by cold spraying (CS), followed by a heat treatment to form Al3Ti reaction layer at their interface to improve adhesion and subsequent micro-arc oxidation (MAO) treatment to transform Al to alumina layer. An optimal MAO treatment of cold sprayed Al formed an adherent and dense α-alumina layer with high Vickers hardness matching with that of sintered alumina used as a femoral head. Structure-phase-property relationships in dense α-alumina layer have been revealed and discussed in the light of our research findings. The designed alumina/Ti alloy hybrid might be a potential candidate for reliable bearing surfaces of artificial hip joint.

Investigations of fml profile buckling and post-buckling behaviour under axial compression

The buckling and post-buckling behaviour of thin-walled Fibre Metal Laminate (FML) profiles subjected to axial loading is discussed. Study concerns open cross-section profiles which consist of alternating thin layers of aluminium and fibre-reinforced unidirectional prepreg. Laboratory tested specimens were manufactured by autoclaving technique. Depending on fibres alignment, various 3/2-layer stacking were considered and subjected to axial compression in buckling tests. Carrying out an experiment allowed one to determine buckling load and equilibrium paths in buckling and post-buckling state. The results of substantial experimental investigations were compared with FML panel/columns modelling in FEA and with analytically examined based on Koiter's asymptotic theory. In conducted experiments the careful design of simply support boundary conditions of loaded edges of thin-walled columns is examined and discussed. Detailed analysis was also performed to assess the influence of the various fibres alignment on the specimen buckling and post-buckling response.

Insulator-protected mechanically controlled break junctions for measuring single-molecule conductance in aqueous environments

We present a method to fabricate insulated gold mechanically controlled break junctions (MCBJ) by coating the metal with a thin layer of aluminum oxide using plasma enhanced atomic layer deposition. The Al2O3 thickness deposited on the MCBJ devices was varied from 2 to 15 nm to test the suppression of leakage currents in deionized water and phosphate buffered saline. Junctions coated with a 15 nm thick oxide layer yielded atomically sharp electrodes and negligible conductance counts in the range of 1 to 10−4 G0 (1 G0 = 77 μS), where single-molecule conductances are commonly observed. The insulated devices were used to measure the conductance of an amphiphilic oligophenylene ethynylene derivative in deionized water.

Pt Nanoparticle Sintering and Redispersion on a Heterogeneous Nanostructured Support

Understanding how nanostructure and atomic-scale defects of the support affect metal catalyst nanoparticle sintering is of crucial importance to minimize thermal deactivation, as well as to understand the origin of widely observed but still unexplained phenomena, such as transient multimodal particle size distributions and nanoparticle redispersion. To shed light on these issues, we present a generic experimental approach that relies on nanofabrication to introduce controlled structural heterogeneity in a chemically homogeneous model catalyst support. This is achieved by fabricating arrays of nanocone structures separated by flat areas, where both are homogeneously sputter-coated with a thin amorphous alumina layer. Using ex situ aberration-corrected scanning transmission electron microscopy (STEM) to analyze Pt model catalyst nanoparticles on such nanostructured supports prior and after exposure to 4% O2 in Ar carrier gas at 600 °C, we find that the initial particle size distributions and their time evol...

A Research Tool to Evaluate Safety Response of Lithium Batteries to Internal Short Ciurcuit

Safety of Li batteries is a major concern for many applications. One of major safety concerns is thermal runaway due internal short circuits created because of dormant internal defects. New processes, designs, and materials are being investigated to improve safety of batteries, particularly to prevent thermal runaway due to internal short circuits (ISC). The challenge is how to evaluate these improvements as existing methods using external triggers, such as nail or blunt rod penetration, crush, and heating, are widely known to be deficient. In response to this challenge, we have developed a very thin and small “thermal switch” to be implanted in a Li-ion cell for triggering ISC on demand to see if the cell goes to thermal runaway. This “thermal switch” or “ISC emulator device” consists of very thin layers of copper, wax, aluminum, and separator that are all compatible with the Li-Ion chemistries. The ISC device is inactive when is placed anywhere in a cell during its fabrication; the cell could be cycles many times without any performance issues. ISC device is activated by applying heat to raise the temperature of the thermal switch to tunable 45°C-60°C to melt the thin layer of wax and create a current path between positive and negative electrode and or current collectors. The ISC device can create any of 4 types of internal short circuit: +ve current collector to –ve current collector, anode active to +ve current collector, cathode active to –ve current collector, and anode active to cathode active. The ISC device can work in any li-ion cell format (cylindrical can and prismatic pouch/can). With support from DOE’s Vehicle Technologies Office, we have demonstrated that more than ISC devices are triggered in a cell creating ISC. In laboratory testing, the activated device can handle currents in excess of 300 A to simulate hard shorts (< 2 mohms). Phase change melting has been 100% successful during trigger tests to go from non-conducting to conducting. Experiments have shown that the creating ISC in cells can lead to thermal runaway depending on the type of internal short circuit is created, the safety measures in the cell, and the chemistry. We have provided more than 300 ISC devices to several cylindrical and pouch cell manufacture to implant them into their cell for evaluation of their safety supplying them to their clients for evaluation. The ISC device has been able to initiate thermal runaway in portion of the cells tested. In this paper, we provide details of the ISC device and the results of triggering the device. We believe that the ISC device a useful research tool for evaluating the safety of lithium ion batteries in response to inherent internal defects. Figure 1

Wideband Absorbers in the Visible with Ultrathin Plasmonic-Phase Change Material Nanogratings

The narrowband surface plasmon resonance of metallic nanostructures was once thought to limit the bandwidth of absorptance, yet recent demonstrations show that it can be harnessed using mechanisms such as multiple resonances, impedance matching, and slow-light modes to create broadband absorptance. However, in the visible spectrum, realization of absorbers based on patterned plasmonic nanostructures is challenging due to strict fabrication tolerances. Here we experimentally compare two different candidates for visible light broadband high absorptance. The first candidate is planar thin film dual layers of Ge2Sb2Te5 and aluminum (Al), while the second structure employs ultrathin Al grating/Ge2Sb2Te5 dual layers. In both cases, the absorbers yield a measured absorptance greater than 78% in the visible. A remarkably high-absorptance bandwidth of 120 nm was measured and associated with the large imaginary part of Ge2Sb2Te5 dielectric function. We find that the simple dual-layer planar structure is an effectiv...

Extending nanoscale spectroscopy with titanium nitride probes

We present a means of controlling the stoichiometry of titanium nitride (TiN) coatings on probes for tip‐enhanced Raman spectroscopy measurements made using sputtering so that outstanding enhancements can be obtained. This provides a more robust alternative to gold‐coated tips that also has potential for tuning the plasmon resonance and working in new environments. Proof of concept measurements on poly(3,4‐ethylenedioxythiophene)/poly(styrenesulfonate) thin films demonstrate increases in the observed intensity with contrast values up to 3.1. TiN is mechanically, chemically, and thermally robust. When deposited under appropriate conditions it has optical properties, including a plasmon resonance, very similar to those of gold. However, the spontaneous formation of a surface TiNxOy layer with relatively high values of y has prevented attaining enhancements in tip‐enhanced Raman spectroscopy beyond that provided by the lightning rod effect. Depositing a thin layer of aluminum to form a passivating Al2O3 layer over the TiN plasmonic structure allows the stoichiometry achieved in the vacuum deposition to be maintained. Copyright © 2016 John Wiley &amp; Sons, Ltd.

A mechanism for the growth of a plasma electrolytic oxide coating on Al

The growth of a plasma electrolytic oxide (PEO) coating on Al was widely considered as an ejection of molten alumina on the surface, induced by a localized breakdown of the solid coating. However, evidences presented here indicated no breakdown of the insulating coating in the PEO process, based on the X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive spectrometry investigations. There are abundant channels in the coating layer from surface to substrate. However, the SEM observes indicating that the channels in the outer layer with a low-density distribution and a micron-sized diameter, the channels extending into the internal layer with a high-density distribution and a nano-sized diameter. In addition, a continuous thin amorphous alumina layer (AAL) was found between coating and substrate. An intermediate state of the AAL before transition to crystalline, with unusually thick character (∼2.7μm), is reported for the first time, which presented a typical cross-sectional characteristic of the ionic migration processes. Based on these microstructure observations, a growth mechanism is proposed here to explain the structural features, in which the discharge ignited in the gas-filled channels passing through both the outer layer and the internal layer. The main voltage drop of applying the hole sample loaded on the AAL at a magnitude of ∼1V·nm-1 due to excellent conductivity of discharge plasmas in the channels. Under a high electrical field, the AAL was thickening, ultimately squeezing the coating expanding outward. Abundant moving micro-discharges and localized expansions could result in the growth of the whole coating.