Aluminum Films Research Articles

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.

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 () to produce porous anodic alumina (PAA) nanostructures with high porosity. The anodization of Al-0.2Cu in 1 M H2SO4 at 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.

Structural and Hydrophilic Properties of Nanoporous Aluminium Oxide Film as a Function of Voltage Anodization

Abstract The impact of voltage on the formation of nanopores through electrochemical anodization of high-purity aluminum was examined. The electrochemical bath was carefully prepared with oxalic acid electrolyte, while a 99.5% pure aluminum electrode served as the cathode and an aluminum template as the anode. The anodization process was conducted at room temperature, with voltage increments ranging from 20V to 65V, which was made possible by the in-house electrochemical cell. Notably, each incremental increase in voltage yielded a significant surge in current density, accompanied by a marked expansion in nanopore size, growing from approximately 35 nm to 125 nm. X-ray diffractometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Rutherford backscattering spectrometry were used to characterize the films. A slight phase change was observed in the aluminum substrate's FCC structure after the anodization process, transitioning to a monoclinic structure at 39° and 45° for all applied potentials. The stoichiometry of the films was determined through RBS analysis. The nano pores' resulting morphology and phase composition were further examined using SEM and EDS, providing insights into their structural characteristics. Furthermore, the water contact angle of the anodized aluminum oxide samples was measured, revealing a range of approximately 85.16 to 61.01 degrees.

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.

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.

Influence of micro-arc oxidation on the microstructure and dielectric properties of anodic aluminum oxide

To improve the dielectric performance of the anodic alumina film used in aluminum electrolytic capacitors, this study comparatively investigated the microstructure and dielectric properties of anodic aluminum oxide obtained through micro-arc oxidation (MAO) and conventional anodic oxidation (CAO). It is found that from the perspective of microstructure, the internal structure of the MAO treated oxide film has more and larger pores than that of CAO. This was attributed to the generation and overflow of numerous oxygen bubbles from within the oxide film at the locations where plasma sparks occurred during the process, thus forming larger pores. Regarding dielectric properties, the leakage current of the oxide film after MAO treatment was significantly reduced compared to CAO, with reductions of 58%, 56%, 64%, and 74% for the tested electrolytes Y1–Y4, respectively.

Measurements of fluctuation-induced in-plane magneto-conductivity of granular aluminum film

The phenomenon of Berezinskii–Kosterlitz–Thouless (BKT) phase fluctuations and the superconducting fluctuations is investigated in a 40 nm thick granular aluminum film using magneto-transport measurements. The transport measurements suggest the possibility of strong electron–phonon (el–ph) interactions in contrast to a Bardeen–Cooper–Schrieffer superconductor. It shows a BKT transition of 2.304 K and a superconducting mean-field transition at 2.32 K. The presence of the resistive tail even before the BKT transition reflects the abundance of thermally activated free vortices. By analyzing the excess conductivity, Gaussian–Ginzburg–Landau superconducting fluctuations are observed above the superconducting transition, which causes rounding of the transition region even before the superconducting transition. The temperature dependence of the fluctuation conductivity in zero magnetic field exhibits distinct signatures of the two-dimensional direct Aslamazov–Larkin theory, with a significant contribution from the Maki–Thompson (MT) model. Furthermore, the anomalous behavior of the fluctuation conductivity at higher temperatures and perpendicular magnetic fields (up to 700 mT) is explained in terms of the total-energy cutoff (=0.72) in the low-wavelength region of the superconducting fluctuations and a pair-breaking parameter (∼0.031). Further studies on the pair-breaking parameter indicate the presence of the el–ph scattering, which diminishes the MT contribution. Our study carries important bearings on how the BKT phase fluctuations and superconducting amplitude fluctuations control the conductivity of granular superconductor near and above the transition region as non-equilibrium properties of weakly disordered granular superconductors. This research is of significance, offering insights into the fundamental properties of granular superconductivity and aiding in the comprehension of nano-structured thin film devices.

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.

Hydrogen reduction and baking process of Pb-silicate microchannel plate and their performance studies

Microchannel plate (MCP) are honeycomb structures consisting of numerous parallel, hollow micro glass fiber channels renowned for their exceptional secondary electron multiplication. This paper investigates changes in MCP properties under hydrogen reduction temperatures ranging from 300 °C to 500 °C. The findings reveal that higher temperatures reduce surface metal oxides, which then accumulate within and darken the microchannels, affecting electron transport. Bulk resistance decreases before increasing, while gain increases and then decreases. At 350 °C, lead oxide begins to reduce to its conductive state, enhancing electron multiplication. However, increased temperatures cause clustering and roughening of the inner channel walls, which diminishes the efficiency of secondary electron release. These alterations are associated with the reduction dynamics of lead ions and temperature-induced microstructural changes. As the hydrogen reduction temperature increases, internal stresses shift outward, and the uniformity of gain varies, reaching its peak at 400 °C. Additionally, an aluminum oxide film enhances resistance to baking and ensures consistent bulk resistance. This study elucidates the relationship between MCP performance and reduction temperature, providing valuable insights for design improvement.

Formation mechanism of nanopores in dense films of anodic alumina

Constant-current anodization of pure aluminum was carried out in non-corrosive capacitor working electrolytes to study the formation mechanism of nanopores in the anodic oxide films. Through comparative experiments, nanopores are found in the anodic films formed in the electrolytes after high-temperature storage (HTS) at 130 °C for 240 h. A comparison of the voltage−time curves suggests that the formation of nanopores results from the decrease in formation efficiency of anodic oxide films rather than the corrosion of the electrolytes. FT-IR and UV spectra analysis shows that carboxylate and ethylene glycol in electrolytes can easily react by esterification at high temperatures. Combining the electronic current theory and oxygen bubble mold effect, the change in electrolyte composition could increase the electronic current in the anodizing process. The electronic current decreases the formation efficiency of anodic oxide films, and oxygen bubbles accompanying electronic current lead to the formation of nanopores in the dense films. The continuous electronic current and oxygen bubbles are the prerequisites for the formation of porous anodic oxides rather than the traditional field-assisted dissolution model.

The oxide films formed under the low oxygen pressure in a particular system containing competing chromium and aluminium

AbstractIn this paper, pre‐oxidation treatment was carried out at 950 °C under oxygen pressure of 10−16 atm for nickel‐10 % chromium‐x % aluminium‐1 % silicon‐0.5 % yttrium(x=0 wt.–%, 1 wt.–%, 3 wt.–%, 5 wt.–%) alloys. Morphology and structure of oxide layers on the alloys after pre‐oxidation were analyzed by scanning electron microscopy and electron discharge spectroscopy. The results showed that a chromium oxide film was formed on the surface of the alloy without aluminium addition, while the oxide layer on the surface of the alloy with aluminium addition gradually transformed into M2O3 (M=aluminium and chromium) oxide film. The oxidation behavior was analyzed by means of chemical thermodynamics, and it was seen that because the interaction coefficient,εijof aluminium and chromium is a positive value, the increase of aluminium addition will strengthen the interaction and increase the diffusion coefficient,Diof aluminium and chromium. The diffusion of chromium and aluminium in each other therefore promotes their interaction, which is beneficial to the formation of the outer oxide film. Thus, with the increase of aluminium addition, the thickness of the outer oxide film gradually increased, and the aluminium content in M2O3 (M=aluminium and chromium) increased significantly, and with 5 % aluminium added, the aluminium oxide of the outer oxide film became the main body.

Molecular dynamics study of the groove-forming mechanism of mechanically scratched grating multilayer aluminum films

For a long time, the forming quality of large area diffraction gratings is restricted by the one-time coating quality and uniformity of large thickness and large area aluminum films. Large thickness coatings, low accuracy of large depth grooves and diamond tool wear problems were the main reasons for the failure of the test to inscribe large area diffraction gratings. Therefore, the use of layered coating process can effectively ensure the uniformity and consistency of large-area and large-thickness grating blanks coated with aluminum film, and improve the high precision of large depth diffraction grating slot type. In order to reveal the mechanism of the groove-forming process of multilayer aluminum films, the microstructure and mechanical properties of different aluminum films were observed. In this article, the removal behavior and mechanism of nanomechanically scratched multilayer aluminum film materials are investigated using a molecular dynamics approach, and the characteristics of multilayer aluminum films scratched into grooves are analyzed in terms of surface morphology, scratching force, structural evolution, dislocation distribution, von Mises stress and shear strain. The results indicate that in the scratching simulation process, multilayer aluminum film has a higher number of removed atoms and a larger atomic displacement compared to single layer aluminum film, which is conducive to precise shape control of the groove. The average tangential force and normal force of multilayer aluminum film show a decreasing trend compared to single layer aluminum film, which helps to scratch grooves and reduce tool wear. The total length of the dislocation lines of the multilayer aluminum film is large, and the distribution area is large, which improves the precision of scratching the grooves. Therefore, an appropriate increase in the number of aluminum film layers has a precise control effect on the groove shape. This study has certain reference significance for analyzing the complex grooving deformation law of grating aluminum film, improving the diffraction efficiency of grating aluminum film, and further improving the manufacturing process of grating aluminum film.

Role of electrode temperature in anodic growth of sulfuric acid alumina films

Role of electrode temperature in anodic growth of sulfuric acid alumina films

Nanometer-thick molecular beam epitaxy Al films capped with in situ deposited Al2O3—High-crystallinity, morphology, and superconductivity

Achieving high material perfection in aluminum (Al) films and their associated Al/AlOx heterostructures is essential for enhancing the coherence time in superconducting quantum circuits. We grew Al films with thicknesses ranging from 3 to 30 nanometers (nm) epitaxially on sapphire substrates using molecular beam epitaxy (MBE). An integral aspect of our work involved electron-beam (e-beam) evaporation to directly deposit aluminum oxide (Al2O3) films on the freshly grown ultrathin epitaxial Al films in an ultra-high-vacuum (UHV) environment. This in situ oxide deposition is critical for preventing the oxidation of parts of the Al films, avoiding the formation of undesired native oxides, and thereby preserving the nm-thick Al films in their pristine conditions. The thicknesses of our Al films in the study were accurately determined; for example, coherence lengths of 3.0 and 20.2 nm were measured in the nominal 3.0 and 20 nm thick Al films, respectively. These Al films were epitaxially grown on sapphire substrates, showing an orientational relationship, denoted as Al(111)⟨21¯1¯⟩∥sapphire(0001)[21¯1¯0]. The Al/sapphire interface was atomically ordered without any interfacial layers, as confirmed by in situ reflection high-energy electron diffraction (RHEED) and cross-sectional scanning transmission electron microscopy (STEM). All sample surfaces exhibited smoothness with a roughness in the range of 0.1–0.2 nm. The Al films are superconducting with critical temperatures ranging from 1.23 to around 2 K, depending on the film thickness.

On the Occurrence of Domain Boundaries and Defects in Self-Organized Ordered Porous Anodic Alumina Systems.

The formation of domains and defects is a part of every self-organized structure without prepatterning which evolves from the electrochemical oxidation of valve metals like Ti, Al or Ta. Defects and domains, especially in highly ordered porous alumina films (PAOX), are one of the most studied phenomena in the current literature. The focus is on understanding their formation in order to find parameters to minimize their amount for applications that require the most highly organized structures. In this letter we give a solution to this problem by showing that the occurrence of defects and domains is an unavoidable consequence of the underlying self-organized process due to the simultaneous impact of the minimum (MINEP) and maximum (MAXEP) entropy production principle. As a consequence, experimental procedures to manufacture defect-free PAOX-films from a self-organization process face a fundamental limitation.

Mitigation of interfacial dielectric loss in aluminum-on-silicon superconducting qubits

We demonstrate aluminum-on-silicon planar transmon qubits with time-averaged T1 energy relaxation times of up to 270 μs, corresponding to Q = 5 million, and a highest observed value of 501 μs. Through materials analysis techniques and numerical simulations we investigate the dominant source of energy loss, and devise and demonstrate a strategy toward its mitigation. Growing aluminum films thicker than 300 nm reduces the presence of oxide, a known host of defects, near the substrate-metal interface, as confirmed by time-of-flight secondary ion mass spectrometry. A loss analysis of coplanar waveguide resonators shows that this results in a reduction of dielectric loss due to two-level system defects. The correlation between the enhanced performance of our devices and the film thickness is due to the aluminum growth in columnar structures of parallel grain boundaries: transmission electron microscopy shows larger grains in the thicker film, and consequently fewer grain boundaries containing oxide near the substrate-metal interface.

The surface chemistry of the atomic layer deposition of ruthenium on aluminum and tantalum oxide surfaces

The surface chemistry of Ru atomic layer deposition (ALD) processes based on the use of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)ruthenium(III) (Ru(tmhd)3) and either molecular oxygen or atomic hydrogen on aluminum oxide films was characterized by a combination of surface-sensitive techniques. The thermal decomposition of the Ru metalorganic precursor was determined, by using a combination of reflection-absorption infrared spectroscopy (RAIRS), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS), to start below 400 K and to take place in a stepwise fashion over a wide range of temperatures. Gas-phase products from this chemistry include 2,2,6,6-tetramethyl-3,5-heptanedione (the protonated ligand, Htmhd; in a TPD peak at 520 K), isobutene (540 K; indicating the fragmentation of the organic ligands), and other products from isomerization and/or aldol condensation (650 and 730 K). This chemistry is accompanied by the reduction of the Ru3+ ions in two stages, involving the loss of some of their ligands and their direct bonding to the substrate first (between 500 and 600 K) and a full reduction to a metallic state later on (600–700 K). ALD cycles using either molecular oxygen or atomic hydrogen resulted in the slow build-up of Ru on the surface, but the co-deposition of carbon could not be avoided, at least in the initial cycles, while the alumina surface was still exposed. With O2, the Ru atoms alternate between partially-oxidized (after the O2 exposures) and zero-valent (after the Ru(tmhd)3 doses) states, and some Ru loss in the form of the volatile RuO4 oxide was seen after the second half of the ALD cycles; neither the Ru oxidation state alternation nor the elimination of some Ru from the surface were observed when using H·. The deposited Ru was determined, by combining results from angle-resolved XPS (ARXPS) and low-energy ion scattering (LEIS) experiments, to grow as 3D nanoparticles rather than as a layer-by-layer 2D film, presumably because the Ru precursor preferentially adsorbs (and decomposes more cleanly) on the metal surface. A discussion is provided of the implications of these results for the design of ALD processes.