Aluminum Films Research Articles

Light focusing of Aluminium film-coated capsule-shaped particles with penetrated cylinder

Abstract Microsphere-assisted imaging technology has proven to be a powerful tool for breaking through the Abbe diffraction limit. Appropriate innovation of microsphere structures is of great significance for the design of microlenses. In this paper, a micro-cylinder was added to the center of the microsphere covered with a patchy aluminum film to form a patchy capsule-shaped particle model. The finite difference time domain simulation (FDTD) method was used to simulate the light field. The research model can effectively improve the relevant parameters of focused beams of various structures (photonic nanojet (PNJ), photonic hook (PH), S-shaped photonic hook. In particular, the effective length can be doubled. By changing the position of the patchy aluminum film, the conversion between PNJ, PH and S-shaped PH can be achieved. By changing the height of the central cylinder, a narrower S-shaped PH and more S-shaped PH inflection points can be produced. This work is expected to have potential applications in the fields of nanolithography, super-resolution imaging, light harvesting, micromachining and other fields.

Anodization of Aluminum in a Sodium Hydroxide Solution: Effect of pH on Chemical Dissolution

Abstract The chemical dissolution of anodic alumina film was investigated using the re-anodization technique. The formation of thick oxide films in an alkaline electrolyte is thought to be difficult to achieve due to the high pH value and high solubility of anodic alumina. The dissolution rate of anodic film was found to be strongly affected by the pH of the solution used for chemical dissolution; the film dissolved significantly faster in a sodium hydroxide solution having a high pH of 13.11 than in acidic solutions commonly used for anodization, such as sulfuric acid (pH 0.98) and phosphoric acid (pH 1.54). Nevertheless, the addition of glycerol to the sodium hydroxide solution effectively suppressed the chemical dissolution of the anodic film. The change in solubility of the anodic alumina film in solution was greatly affected by the change in the dissociation of the solute in solution. The results demonstrated that oxide films more than 10 μm thick were produced in an alkaline electrolyte by adding glycerol to the solution. The suppression of the chemical dissolution of alumina by the addition of alcohol has thus been shown to occur not only in acid solutions but also in alkaline solutions.

The aluminum and titanium-doped zinc oxide films with improved blocking effect on copper diffusion

Low-cost transparent conductive oxide films and copper metallization play a crucial role in the advancement of silicon heterojunction technologies (SHJ) to the terawatt level. However, the mechanisms of interfacial diffusion of copper through a zinc-based transparent conductive oxides (TCO) layer into silicon are still not known. In this study, we report that for the aluminum and titanium-doped zinc oxide (ATZO) films prepared by the magnetron sputtering method in the n-Si/110 nm TCOs/50 nm Cu structure, compared with indium tin oxide (ITO) and aluminum-doped zinc oxide (AZO), the blocking effect on copper diffusion can be comparable to that of ITO more than that of AZO. The results show that the measured band gap value of ATZO is 3.64 eV, and in terms of carrier concentration, ATZO has a value of 3.7 × 1020 cm−3, which is much higher than the level of AZO. The sample with an ATZO layer also outperforms AZO in band gap, surface morphology, and conductivity, even after heat treatment up to 600 °C. It is important to note, however, that the high-temperature annealing used in this study may have induced changes in the crystallinity and alloy composition of the TCOs, which are not representative of typical SHJ operating conditions. Further studies with more moderate annealing temperatures are needed to better simulate real-world conditions. Nevertheless, ATZO films show strong potential as effective copper diffusion barriers in low-cost metallized photovoltaic applications, offering performance on par with ITO

Anodic Oxide Films Grown in Dehydrated Phosphate/Glycerol Electrolytes at High Temperatures.

Traditional anodization was generally conducted in aqueous or water-containing solutions at room temperature or even lower temperatures. The two best known examples of the application of traditional anodization in the fabrication of nanostructured oxides are porous anodic alumina and titania nanotube films. In 1998, Melody et al. first observed that anodic oxide films on some valve metals such as tantalum can continue to grow at low anodization voltages in phosphate/glycerol solutions containing less than 0.1% water at elevated temperatures (>150 °C) in a non-thickness-limited (NTL) manner. Clearly, this type of anodization at high temperatures is conceptually different from traditional anodization. This Perspective provides a relatively thorough review of this topic. Particular attention is given to the main features for the NTL growth of anodic oxide films and the mechanism behind this behavior. The anodization behaviors for the NTL growth and typical microscopic morphologies of the resultant films on various metals are discussed. The main applications of the attained anodic films with different nanostructures and anodization in other dehydrated electrolyte systems such as the molten orthophosphoric acid are also involved. Finally, we highlight some unresolved issues for this type of anodization at high temperatures and the potential future directions of this field.

Влияние ширины зазора между электродами пьезоэлектрического резонатора с поперечным электрическим полем на его характеристики

The gap width influence between the resonator electrodes with a lateral electric field on its characteristics was experimentally investigated. The resonator represented a plate made of ceramics PZT-19 with shear dimensions of ~ 20×18 mm2. One side of the plate was covered with a film of aluminum with a gap in the center, the width of which was changed wide range. The thickness of the plate was 3.07, 2.38 and 1.9 mm. The frequency dependences of the real and imaginary parts of the electric impedance and admittance were measured, which showed the presence of three resonances in the ranges 63-73 kHz, 75-83 kHz and 91-113 kHz. It is shown that an increase in the gap width leads to an increase in the frequency of parallel and series resonances and to an increase in the maximum value of the real part of the electrical impedance. At the same time, the maximum value of the real part of the electrical admittance decreases for the first and third resonances, and increases for the second one. It was also established that with an increase in the width of the gap, the electromechanical coupling coefficient increases, reaches the maximum and then decreases for the first and third resonances. For the second resonance, the electromechanical coupling coefficient is monotonously increasing with an increase in the gap width.

Selectively Detachable Hydrogel Adhesion Enabled by Stimulus-Specific Cleavable Cross-Linkers.

The development of detachable hydrogel adhesion presents an advancement in the fields of soft electronics and bioengineering as it offers additional functionalities to these applications. However, conventional methods typically rely on a single detachment trigger, so it is unclear whether unintentional detachment might occur in the specific environments of other detachment systems. This makes it difficult to directly introduce two independent detachment triggers directly. In this article, we present a strategy for selective detachable adhesion based on two types of cleavable cross-linkers, N,N'-bis(acryloyl)cystamine (BAC) and N,N'-(1,2-dihydroxyethylene)bis(acrylamide) (DHEBA), each with an independent cleavage trigger. BAC can be cleaved through the reduction of disulfide bonds using reducing agents, while DHEBA can be hydrolyzed through heating. We constructed stitching polymer networks for topological adhesion using two types of cleavable cross-linkers, allowing the networks to be selectively degraded depending on which cross-linker was used. Our findings show that the use of cleavable cross-linkers achieved selectively detachable adhesion in various hydrogels, with adhesion energy that reached up to 1223 J m-2 in polyacrylamide-alginate (PAAm-alginate) tough hydrogel. This strategy also proved versatile as it led to effective adhesion with various substrates, including aluminum, copper, glass, and polyester film (PET). Furthermore, we took advantage of the high programmability of this approach to construct hydrogel-based YES and AND logic gates, whose output changed depending on the applied input triggers. In addition, we designed a selective-release capsule model capable of dual-solution release, which emphasizes the potential of our strategy in creating programmable and responsive soft materials.

Effect of Particle Morphology and Added Gallium on Reactivity of Aluminum Powders

Micron‐sized powders of neat aluminum and aluminum combined with 5 wt% gallium are prepared as flakes and spherical composites by emulsion‐assisted milling. Such powders are of interest as high‐energy‐density fuel additives to solid propellants, explosives, and pyrotechnics. Added gallium does not affect the size or shape of the prepared composites; it also does not change appreciably the oxidation kinetics of the prepared powders. All milled powders ignite readily when coated on an electrically heated filament, unlike the starting aluminum powder. Powders with added gallium ignite at slightly lower temperatures when heated rapidly. The liquid metal embrittlement effect due to added gallium might have caused a smaller microstrain in the refined, milled powders. However, it does not affect the oxidation. Instead, it is proposed that added gallium alters the natural amorphous alumina film, affecting its transition to a crystalline γ‐phase during rapid heating, and thus affecting the powder ignition.

Formulation and Evaluation of Weaning Foods Prepared from Multigrain Flour and Powdered Milk

Aims: Children after 6 months need to shift from breast milk to weaning food. The present study aims to develop low cost nutritious weaning foods to fulfil the increased nutritional requirements during this phase of growth. Study Design: The present study involved development of three different samples of low cost weaning foods prepared with multigrain flour (combination of rice flour, wheat flour and gram flour in the ratio of 2:1:0.5) mixed with milk powder (5%, 7.5% and 10% of the total flour mixture). Sensory, physicochemical and cost analyses were performed for the samples. Place and Duration of Study: University Polytechnic (Boys), Aligarh Muslim University, Aligarh, Uttar Pradesh, between January 2016 and July 2016. Methodology: Sensory evaluation was done on a 9 point hedonic scale after preparing the samples for consumption by adding either water or milk. Physicochemical properties of the developed samples such as moisture content, ash content and protein content were assessed during storage at room temperature (25-32˚C) for 2 months in airtight laminated aluminium film packing material. Results: In sensory of samples prepared with water, sample 3 was found to be the most preferred sample while in case of samples prepared with milk, sample 1 was found to be the best in sensory quality. All the developed weaning food samples were found to be stable during 50 days of storage. Moisture content, Protein content and Ash content of the samples ranged from 4.84 to 10.38%, 13.23 and 16.29% and 1.22 to 1.54% respectively. Samples with more milk powder showed higher protein content and fat content. Conclusion: The prepared weaning food samples had comparable physicochemical and sensory characteristics and lower cost than the commercially available weaning foods. They will be helpful in fulfilling the nutritional requirement of the vulnerable sections of society including middle-income groups (MIG) and low-income groups (LIG) consumers and overcoming malnutrition.

On the Effect of Randomly Oriented Grain Growth on the Structure of Aluminum Thin Films Deposited via Magnetron Sputtering

The microstructure of aluminum thin films, including the grain morphology and surface roughness, are key parameters for improving the thermal or electrical properties and optical reflectance of films. The first step in optimizing these parameters is a thorough understanding of the grain growth mechanisms and film structure. To investigate these issues, thin aluminum films with thicknesses ranging from 25 to 280 nm were coated on SiOx/Si substrates at ambient temperature under high-vacuum conditions and a low argon pressure of 3 × 10−3 mbar (0.3 Pa) using the radio frequency magnetron sputtering method. Quantitative analyses of the surface roughness and nanograin characteristics were conducted using atomic force microscopy (AFM), transmission electron microscopy (TEM), and X-ray diffraction. Changes in specular reflectance were measured using ultraviolet–visible and near-infrared spectroscopy. The low roughness values obtained from the AFM images resulted in high film reflectivity, even for thicker films. TEM and AFM results indicate monomodal, randomly oriented grain growth without a distinct columnar or spherical morphology. Using TEM cross-sectional images and the dependence of the grain size on the film thickness, we propose a grain growth mechanism based on the diffusion mobility of aluminum atoms through grain boundaries.

Biocompatibility and antibacterial properties of medical stainless steel and titanium modified by alumina and hafnia films prepared by atomic layer deposition

New methods for producing surfaces with suitable biocompatible properties are desirable due to increasing demands for biomedical devices. Stainless steel 316 L and cp- titanium specimens were coated with thin films of alumina and hafnia deposited using the atomic layer deposition method at two temperatures, 180 and 260 °C. The morphology of the films was analysed using scanning electron microscopy, and their surface energies were determined based on drop contact angle measurements. Biocompatibility assays performed using mesenchymal stem cells were evaluated by incubating the specimens and then exposing their extracts to the cells or directly seeding cells on the specimen surfaces. No detrimental effect was noticed for any of the specimens. Antibacterial properties were tested by directly incubating the specimens with the bacteria Staphylococcus aureus. Overall, our data show that all prepared films were biocompatible. Alumina films deposited on cp-titanium at 260 °C outperform the other prepared and tested surfaces regarding antiadhesive properties, which could be related to their low surface energy.

Multiple shock and acceleration processes of high-velocity flyers driven by the HEAVEN-I laser facility

The experiments of high-velocity flyer acceleration were performed on the HEAVEN-I KrF laser facility with a long-pulse duration (∼ 28 ns). Double-layered flyers consisting of polystyrene and aluminum films can be accelerated to more than 10 km/s measured by VISAR. The polystyrene layer is used as the ablative material, insulation layer, and shock wave regulator. Multiple shock and acceleration processes were observed by adjusting the thickness of the polystyrene layer. We simulated and analyzed the multiple shock processes driven by the long laser pulses and square pressure pulses. The results indicate that the reverberation processes can be induced by the alternating shock and rarefaction waves due to the wave–interface interactions. The reverberations in the Al layer can modulate the pressure evolution and the fine structure of flyer acceleration history. Similar processes in the polystyrene layer can lead to a secondary or multiple shock loading process when the driving pulse duration is several times longer than the shock round trip time in the double-layered flyer. Multiple accelerations can effectively enhance the final velocities in the experimental and simulation results. However, multiple accelerations involve more complex shock loading and unloading processes, and flyers are more prone to breakup compared with single acceleration.

Optimization of the deposited Al2O3 thin film process by RS-ALD and edge passivation applications for half-solar cells

Al2O3 film process experiments were conducted utilizing atomic layer deposition (ALD) technology to optimize the process conditions for rotating-space type ALD Al2O3 thin films, which were then applied to edge passivation of tunneling oxide (TOPCon) solar cells. The composition of the films was characterised using XPS, the thickness and refractive index were measured using ellipsometry, the surface morphology was examined using AFM, and the passivation impact of the alumina films was assessed using a minority carrier lifetime meter. High-quality Al2O3 films were formed on silicon wafers at a temperature of 200 °C and a rotational speed of 60 rpm utilizing trimethylaluminum (TMA) and water as precursors. In this setting, the Al2O3 film deposition rate was 0.12 nm/s, surface roughness was 0.883 nm, and minority carrier lifetime was 189.6μs. And, under these conditions, edge passivation of solar cells resulted in the greatest enhancement, with a 0.123 % increase in cell efficiency and a 3.78W increase in module power.

Synthesis, characterization, and optical sensing of hydrophilic anodic alumina films

Herein, the anodization of 2.6 μm Al-0.2 at. % Cu (Al-0.2Cu) films on TiN/p-type Si substrate were performed using common acidic mediums at different ranges of anodization voltage (Va) to produce porous anodic alumina (PAA) nanostructures with high porosity. The anodization of Al-0.2Cu in 1 M H2SO4 at Va range of 10–30 V produced a higher oxide thickness, and hence, a higher volume expansion factor, compared to the anodization in 0.75 M H3PO4 at Va range of 100–140 V. The increase in Va, as expected, increases the inter-pore distance, pore size, and porosity of the PAA and improves the anodization rate. The optical sensing performance of the synthesized PAA under different conditions was investigated. The maximum surface wettability was attained for PAA anodized in 1 M H2SO4 at 20 and 30 V. Moreover, the Vickers hardness (HV) of PAA was improved by forming a thin alumina layer on the Al-0.2Cu surface, and the anodized Al-0.2Cu in 0.3 M C2H2O4 revealed the highest HV compared to other acids. The synthesized PAA was tested as an optical sensor for some liquids by monitoring the refractive index. The synthesized PAA structure demonstrated a sensitivity of 180 nm/RIU. The anodization of Al-0.2Cu films using a one-step anodization process in different acidic mediums, and the resulting multifunctional properties (improved hardness, tunable wettability, and competitive sensitivity) existing a novel and potentially impactful approach.

Morphology and Magnetic Properties of Ni Nanowires in Thin Film Anodic Alumina Templates

The features of the morphology and magnetic properties of Ni nanowire arrays have been studied. Aluminum oxide matrices are used as a template for electrolytic deposition of nanowires. The matrices are obtained by anodizing the aluminum films with a thickness of 2 μm that are formed on glass substrates by high frequency ion sputtering. Electrochemical deposition of the metal is carried out using direct and alternating currents. Morphology and microstructure studies show that the nanowire arrays are polycrystalline and have a branched dendritic structure due to the morphological features of aluminum oxide matrices. A relationship between the magnetization reversal patterns and the modes of electrodeposition of Ni nanowire arrays is established. The process of magnetization reversal of an array of this kind of structures is simulated.

Flexible Asymmetrically Transparent Conductive Metamaterial Electrode Based on Photonic Nanojet Arrays

AbstractFlexible transparent electrodes, encompassing the combination of optical transparency and electrical conductivity, empower numerous optoelectronic applications. While the main efforts nowadays concentrate on developing wire meshes and conductive oxides, those technologies are still in a quest to find a balance between price, performance, and versatility. Here we propose a new platform, encompassing the advantages of nanophotonic design and roll‐to‐roll large‐scale lithography fabrication tools, granting an ultimate balance between optical, electrical, and mechanical properties. The design is based on an array of silica microspheres deposited on a patterned thin aluminum film attached to a flexible polymer matrix. Microspheres are designed to squeeze 80% light through nanoscale apertures with the aid of the photonic nanojet effect given the light impinges the structure from the top. The photonic structure blocks the transmission for the backpropagation direction thus granting the device with the high 5‐fold level of asymmetry. The patterned layer demonstrates a remarkable 2.8 Ω sq−1 sheet resistance comparable to that of a continuous metal layer. The high conductivity is shown to be maintained after a repeatable application of strain on the flexible electrode. Such remarkable optical, mechanical and electrical properties, makes the demonstrated device an essential component for applications, where such attributes are critically required.

Superhydrophobic Modification of Atomic Layer Deposition Antireflection Aluminum Oxide Film: A Simple Evaporative Coating Technique.

The antireflective transmittance-enhancing films have important applications in solar cells and other applications due to their self-cleaning and high light transmittance. However, obtaining high transmittance, highly durable, and superhydrophobic surfaces in a simple and easily accessible way is still a challenge. A simple evaporative coating technique has been proposed that can be used to prepare antireflective superhydrophobic aluminum oxide films using 1H,1H,2H,2H-perfluoroalkyltriethoxysilanes. The results show that the contact angle of grass-like alumina increased from 99.5° to 155°. The surface energy of grass-like alumina decreased from 17.96 to 1.93 mN/m. The maximum value of light transmittance is close to 98%, and the average transmittance is above 95%. The films have excellent ultraviolet resistance and thermal stability along with relative mechanical and chemical stability. Meanwhile, this method has an excellent capacity for shape preservation. The relationships between the evaporation temperature and time and the light transmittance and hydrophobic angle of the films were also investigated together. This approach has the potential to be extended to large-scale industrial production.

Optical parameter inversion of thin films based on angular reflectance spectroscopy

This article proposes a method for obtaining the refractive index and thickness of thin films based on reflectivity at different angles combined with optimization algorithms. This method has high computational accuracy for both high absorption films (such as aluminum films, gold films, etc.) and low absorption films (such as MgF2 films). Since this study did not adopt the inversion scheme of refractive index dispersion equation fitting, it can be used for optical constant inversion in the case of unknown composition of coating materials. The results indicate that this method can simultaneously obtain high-precision information on the complex refractive index and film thickness of the coating material on the substrate. The calculation example achieved a thickness inversion error of 0.165 % for a 2nm metal aluminum film layer and 0.3303 % for a 150 nm MgF2 transparent film layer. Therefore, this study may provide further guidance for high absorption and measurement of the complex refractive index and thickness of transparent films.

Enhancing corrosion resistance of T91 F/M steel in liquid lead-bismuth (LBE) by slurry FeAl coating

A FeAl coating was fabricated on T91 steel via slurry aluminizing. The corrosion behavior of coated and uncoated samples was assessed in static LBE (lead-bismuth eutectic) with two both high and low dissolved oxygen concentrations at 550 °C. The coating was mostly intact and exhibited great corrosion resistance compared to the uncoated specimens regardless of the oxygen concentration. That is because the coating can form a protective alumina film on the surface at extremely low dissolved oxygen level. This coating is of significant engineering value in enhancing the corrosion resistance of Fe base alloy in LBE.

Laser Control of Specular and Diffuse Reflectance of Thin Aluminum Film-Isolator-Metal Structures for Anti-Counterfeiting and Plasmonic Color Applications

Plasmonic structural color originates from the scattering and absorption of visible light by metallic nanostructures. Stacks consisting of thin, disordered semicontinuous metal films are attractive plasmonic color media, as they can be mass-produced using industry-proven physical vapor deposition techniques. These films are comprised of random nano-island structures of various sizes and shapes resonating at different wavelengths. When irradiated with short-pulse lasers, the nanostructures are locally restructured, and their optical response is altered in a spectrally selective manner. Therefore, various colors are obtained. We demonstrate the generation of structural plasmonic colors through femtosecond laser modification of a thin aluminum film–isolator–metal mirror (TAFIM) structure. Laser-induced structuring of TAFIM’s top aluminum film significantly alters the sample’s specular and diffuse reflectance depending on the fluence value and the number of times a region is scanned. A “negative image” effect is possible, where a dark field observation mode image is a negative of a bright field mode image. This effect is visible using an optical microscope, the naked eye, and a digital camera. The use of self-passivating aluminum results in a long-lasting, non-fading coloration effect. The reported technique could be used in anti-counterfeiting and security applications, as well as in plasmonic color printing and macroscopic and microscopic marking for personalized fine arts and aesthetic products such as jewelry.

Fabrication-related impurity study of thin superconducting Al films using x-ray absorption spectroscopy

Superconducting aluminum thin films are integral to many astrophysics detector applications. Using x-ray absorption spectroscopy (XAS), we have studied the residues and adsorbates created during various standard lithography and etch steps, which are commonly used to pattern thin aluminum films into device structures. We have observed the formation of aluminum oxide as α-Al2O3 and aluminum fluoride as β-AlF3. We have observed correlations between these XAS signatures and the Al film’s microwave loss due to two-level systems. This study, which guides the way for future device optimization, further explores the chemical impact of different process steps, including standard silicon substrate wafer cleaning processes, sulfur-hexa-fluoride plasma etching, passivation with a fluorocarbon, and exposure to photoresist adhesion promoters during the lithography process with the help of control samples.