Aluminum Films Research Articles

Optical Anisotropy of Nanoporous Alumina Films as the Basis for Creation of Achromatic Phase Plates with a Variable Phase Difference of the Orthogonal Polarized Components of Transmitted Radiation

Optical Anisotropy of Nanoporous Alumina Films as the Basis for Creation of Achromatic Phase Plates with a Variable Phase Difference of the Orthogonal Polarized Components of Transmitted Radiation

Improving bonding strength between Ni/Cu/Ag coatings and MgTiO3 ceramic resonator by alumina thin-film grown by atomic layer deposition

A layer of nano-sized alumina thin-film was grown on MgTiO3 based ceramic resonator using atomic layer deposition (ALD) to improve the bonding between resonator and electroless plated and/or electroplated metal coatings. The hydroxylation of resonator surface ensures the strong bonding between alumina film and ceramic substrate, indicating by the bonding score to 10 from 0. However, it will not result in the degradation of the insertion loss of metalized resonators. The signal insertion loss of metalized ceramic resonator with alumina thin-film intermediate layer is significantly lower than that of resonators treated by traditional HF solution corrosion and/or laser scanning to achieve strong bonding between resonator and metalized coatings. It could be promising to metalize ceramic resonators with highly complex intricate geometric shape.

Exploring the influence of Mott–Schottky acquisition parameters on the semiconduction behaviour of modified native aluminium oxide films

The Mott-Schottky approach was applied to access the semiconduction behaviour of native aluminium oxide films of pure aluminium (99.5 wt%) and Al-7075-T6 (Al-Zn-Mg-Cu) alloy investigating the effect of acquisition parameters and surface treatment. Pristine samples were subjected to Mott-Schottky cycling, showing higher defective donor states for Al-7075-T6. The application of step rates of 50–100 mV resulted in flat M−S plots, implicating the influence of the potential independent Helmholtz layer on the space charge capacitance. Chemical etching reduced the oxide thickness for both specimens, whereas higher defect donor densities were determined for pure Al.

Effect of oxygen potential gradient on mass transfer in polycrystalline alumina film doped with trace elements

The effects of the oxygen potential gradient (dµO) on mass transfer via grain boundaries (GBs) in the thickness direction of polycrystalline alumina films were investigated using an oxygen permeation technique at 1873 K. These trials employed gaseous 18O2 in conjunction with undoped, Y-doped or Hf-doped alumina wafers as models for antioxidative films. The 18O concentration distribution over the entire wafer thickness was evaluated in conjunction with the application of a dµO.The GB diffusion coefficients for oxide ions (DO_gbδ) near the wafer surfaces in the absence of a dµO decreased in the order of undoped, Hf-doped and Y-doped. In the case of the undoped wafer, the diffusivity of oxide ions was inhibited near both surfaces with the application of a dµO. In contrast, that in the Y-doped wafer was not inhibited near either surface when applying a dµO. The results obtained for the Hf-doped wafer were intermediate between those for the undoped and Y-doped wafers, such that the diffusion of oxide ion was not suppressed near the PO2(hi) surface but was suppressed at the PO2(lo) surface.The movement behavior of oxide ions in undoped, Y-doped and Hf-doped alumina wafers under a dµO was investigated in relation to changes in the electrical characteristics toward the thickness direction.

High-performance anti-reflection micro-forests on aluminium alloy fabricated by laser induced competitive vapor deposition.

Surfaces with strong anti-reflection properties have attracted the wide attention of scientists and engineers due to their great application potential in many fields. Traditional laser blackening techniques are limited by the material and surface profile, which are not able to be applied to film and large-scale surfaces. Inspired by the rainforest, a new design for anti-reflection surface structures was proposed by constructing micro-forests. To evaluate this design, we fabricated micro-forests on an Al alloy slab by laser induced competitive vapor deposition. By controlling the deposition of the laser energy, the surface can be fully covered by forest-like micro-nano structures. The porous and hierarchical micro-forests performed a minimum and average reflectance of 1.47% and 2.41%, respectively, in the range of 400-1200 nm. Different from the traditional laser blackening technique, the micro-scaled structures were formed due to the aggregation of the deposited nanoparticles instead of the laser ablation groove. Therefore, this method would lead to little surface damage and can also be applied to the aluminum film with a thickness of 50 µm. The black aluminum film can be used to produce the large-scale anti-reflection shell. Predictably, this design and the LICVD method are simple and efficient, which can broaden the application of the anti-reflection surface in many fields such as visible-light stealth, precision optical sensors, optoelectronic devices, and aerospace radiation heat transfer device.

An introduction to triboelectric nanogenerators

Today, there is a continuous rise in the requirement for upgraded healthcare systems that are self-driven, dynamic and very low in maintenance. With a steep rise in the evolution of devices and their applications, such as sensors, there is an increment in the supply of sustainable energy without the replacement and recharging of the installed charge storage devices. Among the various energy scavengers, triboelectric nanogenerators (TENGs) have garnered huge attention as they have a high instantaneous output power and can be developed from a broad selection of available materials, like aluminium (Al) and copper (Cu) metal films, fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE) and green materials like cellulose-based materials. TENGs have a great ability to convert extracted mechanical energies into electrical energies very effectively due to the coupling effects of contact electrification and electrostatic induction. They have tremendous potential in a diverse range of applications, such as medical therapies that include biomedical applications, energy scavenging and active sensing. TENGs are devices made of self-energizing materials that are non-polluting, long-lasting and small sized. They can be developed through inexpensive fabrication processes and are environmentally friendly. In this paper, the mechanism by which the triboelectric nanogenerators perform their applications and how strategies are being developed to improve their performance have been discussed. We have also discussed the future research directions that are being undertaken to advance development in this field. So far, TENGs have mainly been used as mechanical and chemical stimuli to detect sensors and as an electrical source for electronic equipment and devices. Most of the studies found in the literature have reported that TENGs are primarily focused on optimization of systems and circuit designs or on the application of TENGs. A thorough review of the fundamentals of TENGs has been presented here.

Influence of heat treatment process on leakage current of anodic aluminum oxide films

Influence of heat treatment process on leakage current of anodic aluminum oxide films

Aerosol deposition of alumina films on microstructured silicon substrates

Aerosol deposition (AD) is a room-temperature ceramic coating method, which has been used for many applications. Various substrates, such as metals and ceramics, have been used depending on the application, but it is not clear how the substrate microstructure affects the deposition processes and film quality. In this study, AD alumina films deposited on silicon substrates with microstructures consisting of line and space patterns were systematically investigated. The films were formed along the microstructure on the substrate when the linewidth was much larger than the grain size of the raw powder. Conversely, on narrow-linewidth substrates, the films were supported by the lines and the spaces were sealed. The effect of the substrate microstructure was analyzed in terms of the residual stress of the films.

Effect of high temperature exposure on microstructure, mechanical and tribological properties of cold sprayed NiCoCrAlTaY coatings

NiCoCrAlTaY coating is widely used in high temperature oxidation resistance, gas erosion protection and gas path sealing of hot-end parts of aeroengines and gas turbines. In this study, NiCoCrAlTaY coatings were prepared on cobalt-based superalloy substrates by high pressure cold spray technology. The microstructure, mechanical property and tribological behaviors of the coatings before and after thermal exposure at 1050 °C were systemically studied. The results showed that NiCoCrAlTaY coatings with very dense structure could be obtained by high-pressure cold spraying with nitrogen as carrier gas. The coating remained completely intimate with the substrate without any cracking and spalling after thermal exposure at 1050 °C for 500 h. Due to elemental diffusion at high temperatures, the coating formed a four-layer structure, including alumina film on the surface, β-NiAl phase depletion layer near the surface, intermediate layer containing β-NiAl phase and β-NiAl phase depletion layer near the substrate. With the prolongation of thermal exposure at 1050 °C, the thicknesses of β-NiAl phase depletion layers both near the surface and the substrate increased. The thickness and content of the intermediate β-NiAl phase layer decreased gradually during thermal exposure. Besides, the average hardness values of the coating rapidly decreased by about 30 % after thermal exposure at 1050 °C for 5 h. In particular, the hardness of the β-NiAl phase depletion layer near the surface substrate was lower than that of the intermediate area containing β-NiAl phase. Due to the microstructure and hardness evolution, the wear resistance of the coating decreased significantly after thermal exposure. The friction coefficient of the coating increased from 0.2 to 0.5, and the volume wear rate of the thermally exposed coating was about 4.5 times higher than that of the as-sprayed coating. The results of this study provide guidance for design and application of high-performance MCrAlY coatings.

Composite p-Si/Al2O3/Ni Photoelectrode for Hydrogen Evolution Reaction.

A photoelectrode for hydrogen evolution reaction (HER) is proposed, which is based on p-type silicon (p-Si) passivated with an ultrathin (10 nm) alumina (Al2O3) layer and modified with microformations of a nickel catalyst. The Al2O3 layer was formed using atomic layer deposition (ALD), while the nickel was deposited photoelectrochemically. The alumina film improved the electronic properties of the substrate and, at the same time, protected the surface from corrosion and enabled the deposition of nickel microformations. The Ni catalyst increased the HER rate up to one order of magnitude, which was comparable with the rate measured on a hydrogen-terminated electrode. Properties of the alumina film on silicon were comprehensively studied. Grazing incidence X-ray diffraction (GI-XRD) identified the amorphous structure of the ALD oxide layer. Optical profilometry and spectroscopic ellipsometry (SE) showed stability of the film in an acid electrolyte. Resistivity measurements showed that annealing of the film increases its electric resistance by four times.

Tuning of the plasmon resonance location in Au nanostructures coated with a ultrathin film of Al2O3 – Optical measurements and FDTD simulations

The Au nanostructures have been coated with an ultra-thin films of amorphous aluminium oxide. Optical absorption spectra show the influence of the thickness of Al2O3 on plasmon resonance wavelength. The observed red-shift of the resonance location with the increase of the thickness of the Al2O3 film, can be explained by the change in the dielectric function of this film. It allows control of the optical spectra of the coated particles. In this paper we present a two ways for determinaton of optical paramaters of aluminium oxide ultra-thin films. The first one is based on a ellipsometry method, while in second approach a shift of plasmon resonance is used for computer simulations of films. The experimental data are in agreement with the results of the FDTD calculations, showing the possibility of both determining such a function for ultra-thin layers by the computer simulation method, as well as predicting the value of the dielectric constant depending on the thickness of the layer. The experimental data needed for the simulation was obtained in studies such as XRD, XPS, SEM and HR TEM. The proposed models can help to adjust the coating thickness to the desired plasmon resonance position.

Preliminary study on Hot Isostatic Pressing diffusion bonding of Fe–Cr–Al and CLF–1 steel for preparation of tritium permeation barrier

In the internal cooling channel forming of the blanket component for fusion reactor, the combination of Fe-Cr-Al ferritic steel with RAFM steel (reduced activation ferritic/martensitic steel) can form alumina film and then be served as tritium permeation barrier (TPB), which can inhibit the penetration of tritium into structural materials. To realize reliable joining between the two materials, Hot Isostatic Pressing (HIP) diffusion bonding, which is considered as the most promising fabrication technique for blanket component was used. The microstructure and mechanical properties of the joints were analyzed, and the results showed that Fe-Cr-Al/CLF-1 steel interfaces generated some large-size AlN, and the interfacial microvoids are not totally eliminated. While adding Ni interlayer between Fe-Cr-Al/CLF-1 steel could significantly reduce the size of AlN and promote interfacial microvoids closure. Fine NiAl and Ni3Al phases, as the strengthening phases in Nickel-based superalloys, were formed due to atom interdiffusion across the interfaces. Fe-Cr-Al/Ni/CLF-1 joints exhibited average tensile strength of 636 and 529 MPa, and elongation rate of 3% and 15% when tested at 25 and 300 °C, respectively. Microhardness test demonstrated Fe-Cr-Al/Ni/CLF-1 steel joints could be enhanced by precipitation-hardening of NixAly phases. These preliminary studies have laid a foundation for the preparation of TPB in the cooling channel of blanket components.

Behaviour Aspects of an EB-PVD Alumina (Al2O3) Film with an Interlayer (NiCrAlY) Deposited on AISI 316L Steel Investigated in Liquid Lead

The use of lead as a primary coolant is one of the most attractive options for next-generation lead-cooled fast reactor systems (LFR). Despite many favourable features, liquid Pb is a harsh environment that induces many problems on metallic components. Therefore, candidate materials for LFR must be qualified, and the solutions to improve their properties must be found. This paper’s objective is to present the results obtained from the tensile tests of AISI 316L steel in liquid lead at 400 °C, 450 °C, and 500 °C, and the short-term corrosion tests performed on coated and uncoated AISI 316L steel at 550 °C. The coating was made of Al2O3 with a CrNiAlY interlayer using the electron beam-physical vapor deposition (EB-PVD) technique. Both the mechanical and corrosion tests were performed in stagnant lead saturated with oxygen. After testing, the specimens were characterised by several analyses, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), optical microscopy (OM), scratching test, and Vickers micro-hardness test. The tensile test results highlight the ductile behaviour of the material, and in the case of the corrosion tests, the coatings prove to be effective in protecting the substrate from the harsh environment.

Measurement of alumina film induced ablation of internal insulator in solid rocket environment

This study investigates the ablation of internal insulation induced by the deposition of an alumina film with different lateral film speeds. A sub-scale test solid rocket motor (SRM) was designed in an impinging jet configuration to form an alumina film on the sample and to encourage the lateral movement of the film by a high-speed wall jet. Fifteen static fire tests of the test SRM were conducted with six different jet velocities (Vjet = 100 m/s, 150 m/s, 200 m/s, 268 m/s, 330 m/s, and 450 m/s) that indirectly affected the velocity of the wall jet and the deposition rate of alumina droplets. The ablation velocity was deduced from the difference in the sample thickness after a test using a coordinate measuring machine. The droplet deposition mass flux and wall jet velocity were obtained via two-phase flow simulation with the same jet velocity and effective pressure. As a result, the characteristics of alumina-induced ablation and the changes in ablation with jet velocities were obtained. The area within 0.8 × jet diameter was focused upon, where the ratio of ablation velocity to incoming alumina mass was constant for each jet velocity, and showed a similarity in jet structure. When the ablation velocity was increased from 2.05 to 9.98 mm/s with increasing jet velocity, the ratio of the ablation velocity and alumina mass flux decreased from 1.07×10−4 to 0.49×10−4 m3/kg as Al2O3–C reactions became less efficient with a reduced residence time of the film. Because the decrease in residence time by the wall jet is more pronounced for slow reactions involved in Al2O3–C reactions, fast reactions in Al2O3–C reactions are less affected and result in a convergence of the volumetric rate of ablation per unit mass of alumina.

A thin film force sensor on AISI 5140 steel surface with multilayer SI3N4/AL2O3 film as insulation structure

To develop a thin film force sensor on AISI 5140 steel surface, alternating stack thin films of silicon nitride and alumina were sputtered on the 5140 steel surface as the insulating structure before NiCr thin film electrodes were deposited. The insulation was investigated by measuring the resistance between different electrodes. The sample cross-section was examined and a nano-scratch test was carried out. Finally, a Ni80Cr20 thin film strain gauge was formed on the surface of a well-insulated sample with a hard masque, and its force (0 ∼ 250 kN and 0 ∼ 500 N) and temperature (25 °C ∼ 200 °C) responses were investigated. The results show that the alternating four-layer Si3N4/Al2O3 thin film structure can provide insulation close to 1.2 GΩ with a thickness of 2360 nm. The insulation layers have fine adhesion to 5140 steel, and there is no significant inter-layer diffusion which indicates the integrity of the multi-layer structure. The resistance strain coefficient of the sensor is 1.57 ∼ 1.67, and the resistance temperature coefficient is 190.3 ppm/ °C.

Dielectric and thermal properties of rubidium nitrate embedded into porous aluminum oxide films

The results of studying the dielectric permittivity, the third harmonic coefficient, and the DTA signal for Al2O3 nanoporous matrices filled with rubidium nitrate are presented. A shift of the phase transition T c ≈ 437 K by 3 K to the low-temperature region and an increase in the temperature hysteresis of the phase transition from 14 K for polycrystalline RbNO3 to 33 K for RbNO3 in the pores of the Al2O3 oxide film were found.

Influence of preparation time on chemical bath deposited alumina (Al2O3) thin films

The alumina (Al2O3) thin films exhibit superior characteristics over the other oxide materials. In the present work, the alumina thin films were deposited by the low-cost chemical bath deposition (CBD) technique on glass substrates. The structural, optical and electrical properties of the films have been investigated as a function of preparation time. The XRD patterns of the films have shown polycrystalline nature with an improvement in crystallinity. The optical properties of the films were analyzed by a UV–Visible spectrophotometer. The absorbance of the film was found in the ultraviolet region, and the bandgap was obtained as 3.5 eV. The electrical properties of the alumina films have been improved with preparation time.

Plasmon-Enhanced Fluorescence of Single Quantum Dots Immobilized in Optically Coupled Aluminum Nanoholes.

Fluorescence-based optical sensing techniques have continually been explored for single-molecule detection targeting myriad biomedical applications. Improving signal-to-noise ratio remains a prioritized effort to enable unambiguous detection at single-molecule level. Here, we report a systematic simulation-assisted optimization of plasmon-enhanced fluorescence of single quantum dots based on nanohole arrays in ultrathin aluminum films. The simulation is first calibrated by referring to the measured transmittance in nanohole arrays and subsequently used for guiding their design. With an optimized combination of nanohole diameter and depth, the variation of the square of simulated average volumetric electric field enhancement agrees excellently with that of experimental photoluminescence enhancement over a large range of nanohole periods. A maximum 5-fold photoluminescence enhancement is statistically achieved experimentally for the single quantum dots immobilized at the bottom of simulation-optimized nanoholes in comparison to those cast-deposited on bare glass substrate. Hence, boosting photoluminescence with optimized nanohole arrays holds promises for single-fluorophore-based biosensing.

Density-of-States Matching-Induced Ultrahigh Current Density and High-Humidity Resistance in a SimplyStructured Triboelectric Nanogenerator.

Triboelectric nanogenerators (TENGs) can covert mechanical energy into electricity in a clean and sustainable manner. However, traditional TENGs are mainly limited by the lowoutput current, and thus their practical applications are still limited. Herein, a new type of TENG is developed by using conductive materials as the triboelectric layers and electrodes simultaneously. Because of the matched density of states between the two triboelectric layers, this simplystructured device reaches an open-circuit voltage of 1400V and an ultrahigh current density of 1333mA m-2 when poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film and copper (Cu) or aluminum (Al) foil are used as the triboelectric pair. The current density increases by nearly three orders of magnitude compared with traditional TENGs. More importantly, this device can work stably in high-humidity environments, which is always a big challenge for traditional TENGs. Surprisingly, this TENG can even perform well in the presence of water droplets. This work provides a new and effective strategy for constructing high-performance TENGs, which can be used in many practical applications in the near future.

Comprehensive Study of the Chemical, Physical, and Structural Evolution of Molecular Layer Deposited Alucone Films during Thermal Processing

Thermal processing of molecular layer deposited (MLD) hybrid inorganic–organic alucone thin films produced porous and low-k materials. Alucone films were deposited by MLD using trimethyl aluminum and ethylene glycol at 120 °C. Changes in the film density and thickness during annealing were monitored using in-situ X-ray reflectivity and were compared to atomic layer deposited (ALD) alumina films. The chemical evolution of the as-deposited and annealed alucone films during post-deposition heating with and without UV was probed using infrared spectroscopy, Rutherford backscattering, nuclear reaction analysis, and 15N spectroscopy, providing a detailed understanding of the induced changes. The concentration of OH groups decreased after depositing 1 nm of alumina capping layer as a barrier to moisture uptake, which also decreased the etch rate in CF4/O2 plasma. The lowest dielectric constant of the processed alucone films (kmin = 4.75) was 25% lower than the lowest values measured in ALD alumina counterparts (kmin = 6.7). Large thickness decreases for alucone films were observed at ∼200 °C of anneal temperatures. Removal of retained organic components by thermal processing of MLD films is demonstrated to be a promising and versatile route to porous thin films for a wide range of applications including low dielectric constant materials.