Nanostructured Aluminum Research Articles

Use of nanostructured alumina thin films in multilayer anti-reflective coatings

A new method for modification of planar multilayer structures to create nanostructured aluminum oxide anti-reflection coatings is reported. The method is non-toxic and low-cost, being based on treatment of the coating with heated de-ionized water after the deposition of aluminum oxide. The results show that the method provides a viable alternative for attaining a low reflectance ARC. In particular, a low average reflectivity of ∼3.3% is demonstrated in a broadband spectrum extending from 400 nm to 2000 nm for ARCs deposited on GaInP solar-cells, the typical material used as top-junction in solar cell tandem architectures. Moreover, the process is compatible with volume manufacturing technologies used in photovoltaics, such as ion beam sputtering and electron beam evaporation.

유한요소법을 이용한 유연소자용 Au 나노구조체의 내구성 평가

In this study, the levels of durability of nanostructures for flexible devices are explored based on tensile force, bending moment, and torsion. First, for application to optical devices, aluminium nanostructures are fabricated using laser interference lithography. The optical characteristics of the fabricated nanopatterns are investigated, and the structure with the highest light transmittance is selected for durability analysis. A structural analysis model using the finite element method is then developed and its reliability is validated through a comparison with the experimental data for both polyethylene terephthalate and Au thin films. Finally, the different levels of durability of the nanostructures are investigated for application based on tensile force, bending moment, and torsion. The structural weakness of each nanostructure is explored and the durability characteristics are highlighted.

Synthesis and characterization of γ-Al2O3 and α-Al2O3 nanoparticles using a facile, inexpensive auto-combustion approach

In the present work, we have developed a facile, inexpensive, auto-combustion method for the synthesis of γ-Al2O3 and α-Al2O3 nanoparticles. This was performed by employing aluminum nitrate as an oxidant and glycine as a fuel. The γ-Al2O3 and α-Al2O3 nanoparticles were obtained by calcination of the combusted products at 800 °C for 2 h and at 1000 °C for 1 h, respectively. The generated alumina nanoparticles were characterized by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field-emission scanning electron microscope (FE-SEM), high-resolution transmission electron microscope (HRTEM), and thermal analyses (TG and DTA). The average crystallite sizes of γ-Al2O3 and α-Al2O3 nanoparticles were estimated to be 5.8 nm and 15 nm, respectively. The TEM results revealed that the prepared alumina nanostructures were of low agglomeration degree. The proposed method exhibited that the phases of the produced alumina nanoparticles could be carefully tuned by the adapted experimental conditions.

Mechanically stable superhydrophobic nanostructured aluminum mesh with reduced water surface friction

Superhydrophobic surfaces demonstrate significant characteristics which make them suitable for a wide variety of applications. In this study, we propose a facile, one-step, and cost-effective anodizing scheme using aluminum nitrate/stearic acid mixture solution to create a superhydrophobic surface on an aluminum mesh. The surface outperforms the surface anodized by the widely used oxalic acid solution in terms of superhydrophobicity and water-surface friction behavior. The proposed surface reduced the friction by 11% on average respective to the surface prepared by oxalic acid. The durability of the introduced superhydrophobic surface has also been investigated. The proposed surface retained its high water contact angle and showed higher hydrophobicity relative to the surface anodized by oxalic acid after ten abrasion cycles. This method and surface may be used for numerous applications due to its ease of fabrication, low cost, and excellent performance in energy-loss reduction.

Oxidative Esterification of 5-Hydroxymethylfurfural into Dimethyl 2,5-Furandicarboxylate Using Gamma Alumina-Supported Gold Nanoparticles.

Gold nanoparticles (Au NPs) supported on a nanostructured gamma alumina (γ-Al2O3) fiber can exhibit excellent catalytic activity for the conversion of 5-hydroxymethylfurfural to produce its ester derivative, dimethyl 2,5-furandicarboxylate (FDMC). γ-Al2O3 was synthesized using a PEG surfactant to generate oxide fibers that randomly stack together into irregular shapes. The average particle sizes of the Au NPs are 1–6 nm, where the catalytically active Au (111) surface is the exposed facet. This 3D nanocatalyst architecture enhances the 5-hydroxymethylfurfural (HMF) oxidative esterification because HMF reactant molecules can readily diffuse into this fibrous structure and adsorb to active catalytic sites, while ester product molecules can diffuse out. Up to 99% HMF conversion and 90% FDMC selectivity can be obtained at a low reaction temperature of 45 °C, and the catalyst shows excellent recyclability. Increasing the Au content in the catalyst minimizes the requirement of a base for HMF conversion. Thus, the Au NPs supported on γ-Al2O3 can drive HMF esterification to FDMC efficiently with high product selectivity under very mild reaction conditions, omitting the need for an additional esterification step of the HMF acid.

Oxidation resistance, residual strength, and microstructural evolution in Al2O3-MgO–C refractory composites with YAG nanopowder

The decisive role of nanostructured yttrium aluminium garnet (YAG;Y3Al5O12) powder addition on oxidation resistance, residual strength and microstructural evolution were studied in Al2O3-MgO–C refractory composites. Oxidation index and rate constant calculations indicated that the oxidation resistance was almost 70 % improved for the nano-YAG containing refractories oxidized in air at 1600 °C. Residual compressive strength (Rc) estimations showed that there was nearly 75 % strength retained in these oxidized refractories fortified with nano-YAG. Residual bending strength (Rb) estimations based on cyclic thermal shock, exhibited that there was almost 70 % thermal shock resistance enhancement in refractories reinforced with nano-YAG, showed a good agreement between Rb and Rc values. These beneficial properties were attributed to the formation of a well-sintered framework of YAG/Spinel bonding grains throughout the dense oxidized layer microstructure of these new class of refractories. The concept of interfacial toughening and implications of these results to practical applications are discussed.

A Novel Cavity-Enhanced Polyethylene/Nanostructured-Alumina Separator with Long Cycle Life and High Rate Capability for Advanced Lithium-Ion Batteries

Traditional polyolefin separators cannot meet the increasing requirements of lithium-ion batteries (LIBs) for the high power density, high energy density, and high safety that the secondary battery market has expanded to electric vehicles. It is still a great challenge to reduce ion-transport resistance, promote thermal stability, and improve the mechanical properties of polymer-based separators. Herein, a novel composite separator with enhanced conductivity, good mechanical strength, and high thermo-dimensional stability is designed and demonstrated for the application of advanced LIBs. The flexible multiarm structure of nanostructured alumina nanoparticles (NPs) greatly promotes the orientation of high density polyethylene (HDPE) during the polymer processing, significantly enhancing the pore cavity during the separator formation process. The porosity, pore size distribution, thermo-dimensional stability, and mechanical strength of the resultant composite separator are significantly improved, leading to long cycle life and high rate capability. The orientation/crystallization development of HDPE by the introduction of alumina NPs has been examined via microstructure analysis. This demonstration not only shows the high impact on the separator manufacturing of LIBs with a high power density and high safety but also creates a new method in controlling the orientation and cavity design of polyolefin materials.

Broadband asymmetric light transmission interfaces for luminescent solar concentrators.

Luminescent solar concentrators (LSCs) are actively researched to be incorporated into multi-functional building envelope systems. They consist of a plastic matrix with absorbing–emitting media, which guides and concentrates light to edges where solar cells are located. A main drawback of LSCs is escape cone losses at the surface intercepting light. This study investigates trapezoidal nanostructures for creating an interface that enables asymmetric light transmission and reduces these losses. The study employs alumina nanostructures on a PMMA substrate, materials of relevance to LSC applications. The geometry of nanostructures was optimized to maximize asymmetry in the 700–1100 nm wavelength interval, which corresponds to the range best utilized by silicon solar cells. The multiphysics software COMSOL was utilized to simulate forward (air to PMMA) and backward (PMMA to air) transmission. Spectral transmissivity was calculated for this wavelength interval for a variety of incident polar and azimuthal angles. The largest difference between forward and backward light transmission was found at 720 nm, as designed. The forward spectral transmissivity for all polar angles considered was found to be approximately 77% in the 700–1100 nm range at an azimuth angle of zero. The backward spectral directional transmissivity in this range was approximately 37%, resulting in a 40% difference. The difference for the entire wavelength range of 400–1200 nm was approximately 37%. Similar results were obtained when the azimuth angle was varied. All these show that the incorporation of nanostructured interfaces can effectively reduce optical losses in LSCs, which will help increase their efficiency. This will make LSCs a more viable solution for use in zero or net-zero energy buildings.

Nanostructured Strain-Hardened Aluminum–Magnesium Alloys Modified by C60 Fullerene Obtained by Powder Metallurgy: Part 1. The Effect of the Magnesium Concentration on the Structure and Phase Composition of Powders

This paper provides the first part of a study on the effect of magnesium on the structural phase composition and physical and mechanical properties of nanostructured aluminum–magnesium composite materials with the composition AlxMgy + 0.3 wt % C60 fullerene. Composite powders are obtained by the simultaneous mechanical activation of the initial materials in a planetary ball mill in an argon atmosphere. It is found that the powders have a complex hierarchical structure made up of 50–200 μm aggregates consisting of 5–10 μm strong high-density agglomerates, which in turn are a combination of nanoscale (30–60 nm) crystallites. It is found that the increase in magnesium concentration in the composite up to 18 wt % makes it possible to obtain crystallites with an average size of less than 30 nm during mechanical activation, while the size of aggregates is less than 50 μm. The maximum solubility of magnesium in aluminum with a crystallite size of 30–70 nm during mechanical activation is 15 wt % (17 at %). Using the differential scanning calorimetry method, it is found that nanostructured composites undergo irreversible structural phase transformations during heat treatment in a temperature range of 250–400°C: recrystallization, decomposition of the α-solid solution of magnesium in aluminum, and the formation of intermetallic β-(Al3Mg2), γ-(Al12Mg17) and carbide (Al4C3) phases. In addition, the Raman spectra contain peaks that, according to some sources, correspond to covalent compounds of aluminum with C60 fullerene—aluminum–fullerene complexes. The data that have been obtained will be used in further research to determine the parameters for the thermobaric treatment of nanocomposite powder mixtures in order to obtain and test bulk samples.

Surface roughness and substrate induced symmetry-breaking: influence on the plasmonic properties of aluminum nanostructure arrays.

The surface topography is known to play an important role on the near- and far-field optical properties of metallic nanoparticles. In particular, aluminum (Al) nanoparticles are commonly fabricated through evaporation techniques, therefore exhibiting elevated surface roughness additionally to their native oxide layer. In this study, the mode-dependent influence of surface roughness on the plasmonic properties sustained by Al nanodisks (NDs) is first numerically investigated using a realistic model taking into account the thin native oxide layer. Due to the symmetry-breaking induced by the supporting dielectric substrate to Al ND, it appears that the roughness affects differently the substrate-induced out-of-plane quadrupolar mode (below 300 nm) and the in-plane dipolar mode sustained by the Al ND. By increasing the top surface roughness of the Al ND, the substrate-induced quadrupolar mode is significantly damped especially in the ultraviolet regime, while the dipolar resonance is broadened and redshifted. The explanation of these effects relies in the decoherence and dissipation of the collective electronic oscillations as a result of the top surface roughness to the different near-field distribution of the out-of-plane quadrupolar mode and in-plane dipolar mode. Moreover, the influences of the diameter of Al ND, dielectric substrate with different refractive index, and the oxidation of Al ND on these two modes are also investigated. Particularly, the quadrupolar mode disappears with surface roughness and oxidation, explaining why this mode is very weak and sometimes barely visible on evaporated Al nanostructures reported in the literature. Finally, these results are experimentally confirmed by characterizing the optical properties of periodic Al ND arrays.

Dependence of the Magnetization Process on the Thickness of Fe70Pd30 Nanostructured Thin Film.

Fe–Pd magnetic shape-memory alloys are of major importance for microsystem applications due to their magnetically driven large reversible strains under moderate stresses. In this context, we focus on the synthesis of nanostructured Fe70Pd30 shape-memory alloy antidot array thin films with different layer thicknesses in the range from 20 nm to 80 nm, deposited onto nanostructured alumina membranes. A significant change in the magnetization process of nanostructured samples was detected by varying the layer thickness. The in-plane coercivity for the antidot array samples increased with decreasing layer thickness, whereas for non-patterned films the coercive field decreased. Anomalous coercivity dependence with temperature was detected for thinner antidot array samples, observing a critical temperature at which the in-plane coercivity behavior changed. A significant reduction in the Curie temperature for antidot samples with thinner layer thicknesses was observed. We attribute these effects to complex magnetization reversal processes and the three-dimensional magnetization profile induced by the nanoholes. These findings could be of major interest in the development of novel magnetic sensors and thermo-magnetic recording patterned media based on template-assisted deposition techniques.

Development of nanostructured icephobic aluminium oxide surfaces for aeronautic applications

In-flight icing due to the impingement of supercooled water droplets modifies the shape of the aerodynamic surfaces of aircraft, resulting in lower stall speeds and higher fuel consumption. Icephobic coatings help reducing the adhesion strength of ice to a surface and represent a promising technology to support mechanical/thermal ice protection systems. Superhydrophobic surfaces are water-repellent and embody a straightforward solution to tackle icing: nanostructured porous aluminium oxide layers are generated with anodization and superhydrophobicity can be reached by tuning the pores size. However, not much research has been done to verify if such surfaces are generally icephobic in representative icing conditions, or if they need to have additional properties to effectively reduce ice adhesion. In this work, we investigate the ice adhesion strength on cladded Aluminium Alloy 2024 (AA2024), an alloy commonly used for aerospace components, anodized with different process parameters in sulphuric and oxalic acid and hydrophobized by a commercial fluorinated product. Upon the optimization of the two anodization processes, the micro-/nanostructures generated on the surface were effective in reducing the ice adhesion strength. From icing wind tunnel tests, the surfaces anodized in oxalic acid showed superior icephobic (i.e., lower ice adhesion) properties compared to the ones anodized in sulphuric acid because of their larger air-to-solid surface ratio. The proposed anodization process is fast, easy to perform and to implement in existing production lines, low-cost, and operator- and environmentally-friendly.

Comparison of Ordering Characteristics of Anodicformed Nanostructured Aluminum and Titanium Oxides Coatings

This article is concerned with the analysis of ordering the arrays of TiO2 and Al2O3 nanotubes using the correlation-spectral methods. As the tools, the spatial Fourier spectrum and one-dimensional autocorrelation function of SEM-image have served. It was shown that the arrays of the aluminum oxide nanotubes can have a nearly ideal ordering on a small scale at the expense of two-stage anodizing. It this case, the degree of order depends also on the purity of initial aluminum and sample preparation method. The introduced characteristics can serve as the measures of the structure order-disorder sensitive to both type and degree of order as a whole and to configuration of structural elements themselves.

Наноструктуры алюминия на границе двух несмешивающихся жидкостей

Expanding range of nanostructured materials applications based on aluminum initiates the search for new methods for their preparation. A promising method for the synthesis of aluminum nanostructures using the total energy of pulsed plasma and the energy of the interface is proposed in this article. Aluminum nanostructures have been synthesized by dispersing aluminum electrodes in a microemulsion (water-benzene), in benzene and distilled water, using the energy of a pulsed plasma. Obtained nanostructures of aluminum were subjected to X-ray phase and electron microscopic analyzes. Particle sizes are calculated using the Debye-Scherrer formula. The specific surface area (BET method) and porosity (BJH method) of nanostructures synthesized in microemulsion (water-benzene) were determined by the method of physical nitrogen adsorption.

Luminescent and dosimetric properties of transition phases of nanostructured aluminum oxide

The luminescent and dosimetric properties of nanostructured aluminum oxide which contains a mixture of metastable transition Θ, δ, and κ-phases were investigated. To vary the phase composition of the samples, they were annealed in air at 850–1200 оС. It was found that annealing the samples at Т = 850–1100 оС in air results in a change in the percentages of κ- and δ-phases with a slight variation in the Θ-phase concentration. Alpha-phase begins to form in the samples at Т = 1100 оС, its concentration reaches 100% at Т = 1200 оС. The PCL spectra featured bands associated with F- and F2-type centers, the intensity of which decreased with increasing annealing temperature due to thermal destruction of centers. Kinetic TL parameters of the samples irradiated with a pulsed electron beam (130 keV) were found by deconvoluting TL curves into elementary peaks of general order kinetics. These parameters change insignificantly when the annealing temperature increases up to 1000 оС and they change greatly when the temperature grows further and α-phase is formed in the samples. The presence of sublinear sections of the TL dose response at doses of 1.5–45 kGy shows that the use of nanostructured aluminum oxide which contains transition phases for high-dose TL dosimetry of pulsed electron beams is promising.

High-speed galvanostatic anodizing without oxide burning using a nanodimpled aluminum surface for nanoporous alumina fabrication

Rapid formation of a porous alumina film without oxide burning was achieved by anodizing in etidronic acid at large current densities using a nanodimpled aluminum surface. After the electropolished aluminum specimens were galvanostatically anodized in a 0.3 M etidronic acid solution at 293 K, a uniform porous alumina film without oxide burning was formed at relatively low current densities of up to 20 Am−2. After the first anodizing process, an array of dimples was fabricated on the aluminum surface by oxide film removal in a chromic acid/phosphoric acid solution. After the nanostructured aluminum specimen was galvanostatically anodized once again under the same conditions, the possible applied current density without burning increased with the size of the nanodimples, and the current density during the high-speed anodizing process of the dimpled aluminum specimen increased by five times. Many pores grew on the whole surface of the aluminum dimples from the initial anodizing stage; then, pores that grew from the bottom of the dimples survived the anodizing process, and a clear porous alumina film was formed as the voltage reached the maximum value.

Antiviral Nanostructured Surfaces Reduce the Viability of SARS-CoV-2.

In this letter, we report the ability of the nanostructured aluminum Al 6063 alloy surfaces to inactivate the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). There was no recoverable viable virus after 6 h of exposure to the nanostructured surface, elucidating a 5-log reduction compared to a flat Al 6063 surface. The nanostructured surfaces were fabricated using wet-etching techniques which generated nanotextured, randomly aligned ridges approximately 23 nm wide on the Al 6063 alloy surfaces. In addition to the excellent mechanical resilience properties previously shown, the etched surfaces have also demonstrated superior corrosion resistance compared to the control surfaces. Such nanostructured surfaces have the potential to be used in healthcare environment such as hospitals and public spaces to reduce the surface transmission of SARS-CoV-2 and combat COVID-19.

Inhibition Effectiveness of Laser-Cleaned Nanostructured Aluminum Alloys to Sulfate-reducing Bacteria Based on Superwetting and Ultraslippery Surfaces.

This paper is a continued study on laser cleaning removal of marine microbiofouling from Al alloy surfaces. According to our previous study, it is noted that the antifouling functions of the generated laser-cleaned metallic surfaces must be highlighted. In this work, the inhibition effectiveness of the laser-cleaned Al alloy surfaces was evaluated using a type of vital marine microorganism, sulfate-reducing bacteria (SRB) Desulfovibrio desulfuricans subsp. desulfuricans, in a dynamic bacterial solution. Before the immersion tests, the laser-cleaned surfaces with nanostructures were chemically processed into superhydrophilic, superhydrophobic, and ultraslippery surfaces. SRB attachment behaviors as well as inhibition mechanisms of the three surfaces to the SRB settlement were characterized and revealed. The SRB adhering to the above surfaces presented three different morphologies, i.e., broken, dented, and plump cells. Superhydrophilic surfaces unexpectedly showed a not inferior antibacterial ability. A piercing effect of the nanostructures caused nontoxic mechanical damage to the cell membranes. The antiadhesion property of superhydrophobic solid-air hybrid surfaces was unreliable due to the loss of air bubbles. The morphology of the last surviving SRB cells left on the ultraslippery surfaces was basically plump. The stable repellent function of the surfaces was responsible for the vigorous prevention of the adhesion of the SRB. The research results offer an insight into the antibacterial/antiadhesion properties of the laser-cleaned surfaces and a practical value for the periodic service of marine high-end equipment.

Application of nanostructured aluminium titanate (Al2TiO5) photocatalyst for removal of organic pollutants from water: Influencing factors and kinetic study

In this study, aluminum titanate (Al2TiO5)-based nanostructure with the outstanding photocatalytic performance was prepared via the simple citrate sol-gel method. The effects of thee operational variables such as pH, temperature, catalyst dosage, and initial dye concentration on the photodegradation efficiency of methylene blue (MB) were explored in some details. The results showed that compared to TiO2, AT benefits a superior photocatalytic activity due to its narrow band gap (2.88 eV) and low recombination rate of charge carriers. Increasing the wastewater temperature from 25 to 60 °C can improve the degradation percent from 22.15 to 52%. Based on the thermokinetic calculations, the Arrhenius activation energy, ΔH, and ΔS values were also estimated as +24.69 kJ mol−1, 21.78 J mol−1, and 222.48 J K−1.mole−1, respectively. According to the Langmuir-Hinshelwood kinetic model, the photocatalyst follows a first-order equation in a wide range of temperatures. In addition, escalating the pH value from 4 to 9.5 may noticeably enhance the photodegradation efficiency from 7.1 to 46.6%. The enhanced photocatalytic activity at alkaline media was mainly attributed to the excessive generation of hydroxyl ions, improved adsorption of cationic dye on the catalyst surfaces, and effective separation of involved charge carriers. The maximum performance was obtained for the AT dosage of 20 mg/lit and MB concentration of 2.5 mg/lit. Finally, the recycling experiments after 6 runs verified the high stability of the photocatalyst.

Understanding the role of Ca segregation on thermal stability, electrical resistivity and mechanical strength of nanostructured aluminum

Achieving a combination of high mechanical strength and high electrical conductivity in low-weight Al alloys requires a full understanding of the relationships between nanoscaled features and physical properties. Grain boundary strengthening through grain size reduction offers some interesting possibilities but is limited by thermal stability issues. Zener pinning by stable nanoscaled particles or grain boundary segregation are well-known strategies for stabilizing grain boundaries. In this study, the Al–Ca system has been selected to investigate the way segregation affects the combination of mechanical strength and electrical resistivity. For this purpose, an Al–Ca composite material was severely deformed by high-pressure torsion to achieve a nanoscaled structure with a mean grain size of only 25 nm. X-ray diffraction, transmission electron microscopy and atom probe tomography data revealed that the fcc Ca phase was dissolved for large levels of plastic deformation leading mainly to Ca segregations along crystalline defects. The resulting microhardness of about 300 HV is much higher than predictions based on Hall and Petch Law and is attributed to limited grain boundary mediated plasticity due to Ca segregation. The electrical resistivity is also much higher than that expected for nanostructured Al. The main contribution comes from Ca segregations that lead to a fraction of electrons reflected or trapped by grain boundaries twice larger than in pure Al. The two-phase state was investigated by in-situ and ex-situ microscopy after annealing at 200 °C for 30 min, where precipitation of nanoscaled Al4Ca particles occurred and the mean grain size reached 35 nm. Annealing also significantly decreased electrical resistivity, but it remained much higher than that of nanostructured pure Al, due to Al/Al4Ca interfaces that reflect or trap more than 85% of electrons.