Al Nanostructures Research Articles

TENG-driven single-droplet green electrochemical etching and deposition for chemical sensing applications

Selected area electrochemical etching (EE) and electrochemical deposition (ED) are widely used for fabricating microstructures and devices, but they require complex processes and expensive equipment and generate significant electrolyte waste. This study demonstrates a novel single-droplet electrochemical system using a triboelectric nanogenerator (TENG) for self-powered selected area EE and ED reactions. Utilizing TENG's pulsed power, Al nanostructures were created by EE, while nano-Ag and Cu2O nanocubes were synthesized by ED. The generated nanomaterials were applied to detect trace chemicals through the Surface-Enhanced Raman Scattering effect. The electrochemical reaction area can be controlled by droplet size, and patterns can be created using a needle movement platform. The size and density of nanostructures can be adjusted by the TENG's current, collision frequency, and electrolyte concentration. The deposition gradient from the center to the edge of the droplet is controlled by the distance between the needle and the substrate. COMSOL Multiphysics calculations show that a smaller D creates a larger electric field gradient. However, the varied deposition gradients were attributed to competition of electric field, diffusion effects, and capillary flow. This proposed green technology offers low cost, simplicity, no waste electrolyte, and self-powering capabilities, pioneering new research directions in EE and ED.

Polarization dependent exciton-plasmon coupling in PEA2PbI4/Al and its application to perovskite solar cell.

This paper reports the strong coupling between Al nanostructure and two-dimensional (2D) layered perovskite PEA2PbI4 (PEPI) films. The high exciton binding energy of 118 meV and long carrier lifetime of 216 ps are characterized from the 2D PEA2PbI4 film, which indicates that the excitons in perovskite are robust and can couple to metal plasmons. The ordinary and extraordinary optical dispersions are revealed from the anisotropic 2D perovskite. The transmission spectra of PEA2PbI4/Al nanoparticle arrays are simulated under different polarization excitations, and the typical anti-crossing behaviors originating from exciton-plasmon strong coupling are demonstrated. We found that compared with transverse magnetic (TM) polarization, transverse electric (TE) polarization excitation is more conducive to the realization of exciton-plasmon coupling with a larger Rabi splitting. Furthermore, the PEA2PbI4/Al nanoparticle arrays are proposed, which present polarization-dependent local electrical field enhancement due to the exciton-local surface plasmon polariton coupling. Additionally, it is noticed that the proposed plasmonic structure increases the photo-generation rate inside the active material with improved current density. Therefore, the 2D proposed plasmonic design increases the power conversion efficiency (PCE) with an enhancement of 3.3% and 1.3% relative to the planar structures for TE and TM polarizations, respectively. This study provides a deeper understanding of polarized exciton-plasmon coupling properties, promoting the development of the field of plasmon and providing guidance for the design and preparation of efficient optoelectronic devices.

Neuromorphic devices realised using self-forming hierarchical Al and Ag nanostructures: towards energy-efficient and wide ranging synaptic plasticity.

Closely mimicking the hierarchical structural topology with emerging behavioral functionalities of biological neural networks in neuromorphic devices is considered of prime importance for the realization of energy-efficient intelligent systems. In this article, we report an artificial synaptic network (ASN) comprising of hierarchical structures of isolated Al and Ag micro-nano structures developed via the utilization of a desiccated crack pattern, anisotropic dewetting, and self-formation. The strategically designed ASN, despite having multiple synaptic junctions between electrodes, exhibits a threshold switching (Vth ∼ 1-2 V) with an ultra-low energy requirement of ∼1.3 fJ per synaptic event. Several configurations of the order of hierarchy in the device architecture are studied comprehensively to identify the importance of the individual metallic components in contributing to the threshold switching and energy-minimization. The emerging potentiation behavior of the conductance (G) profile under electrical stimulation and its permanence beyond are realized over a wide current compliance range of 0.25 to 300 μA, broadly classifying the short- and long-term potentiation grounded on the characteristics of filamentary structures. The scale-free correlation of potentiation in the device hosting metallic filaments of diverse shapes and strengths could provide an ideal platform for understanding and replicating the complex behavior of the brain for neuromorphic computing.

Assessing cationic dye adsorption mechanisms on MIL-53 (Al) nanostructured MOF materials using quantum chemical and molecular simulations: Toward environmentally sustainable wastewater treatment

The escalating levels of environmental pollutants, particularly cationic dyes, present a significant ecological threat. Cationic dyes such as rhodamine B (RB) and methylene blue (MB) are extensively used in diverse industrial applications and are known to exert detrimental effects on the environment. The focus of this study revolves around comprehensively examining the adsorption mechanisms associated with the binding of cationic dyes, namely, RB and MB, onto pristine and carboxylic acid (CXA)-modified MIL-53 (Al) nanostructures. By employing quantum mechanics and molecular simulations, this research elucidates the molecular-level behavior of materials and dyes during the adsorption process. The findings demonstrate that incorporating CXA groups enhances MIL-53 (Al)'s adsorption capacity for both RB and MB dyes. Furthermore, the simulations unveil that RB and MB dye adsorption onto the unmodified and modified MIL-53 (Al) materials occurs primarily through electrostatic, van der waals interactions, π-π stacking, and hydrogen bonding. Notably, RB dye exhibits superior reactivity and stability compared to MB dye, owing to its higher adsorption energy. This study provides valuable insights into cationic dye adsorption on nanostructured MIL-53 (Al), emphasizing the suitability of CXA-modified MIL-53 (Al) nanostructures for cationic dye removal from contaminated wastewater. The outcomes of this investigation hold the potential for developing cutting-edge technologies exhibiting superior efficiency and effectiveness for removing cationic dyes, thereby contributing to environmental preservation and public health. Ultimately, this study highlights the prospects of leveraging quantum mechanics and molecular simulations to anticipate the behavior of nanostructured materials and optimize their properties for wastewater treatment.

Functional properties of transparent Al, Mg-doped and Al-Mg co-doped ZnO nanostructures grown by electrochemical and chemical bath deposition: a comparative study

Functional properties of transparent Al, Mg-doped and Al-Mg co-doped ZnO nanostructures grown by electrochemical and chemical bath deposition: a comparative study

MIL-53 (Al) nanostructure for non-steroidal anti-inflammatory drug adsorption in wastewater treatment: Molecular simulation and experimental insights

Pharmaceuticals are prevalent in the environment, especially the nanostructures of non-steroidal anti-inflammatory drugs (NSAIDs) in water, which can harm human health and the environment. Adsorption processes are effective and energy efficient for removing contaminants. In this study, a new adsorbent, MIL-53 (Al), was used to remove pharmaceutical pollutants, including diclofenac (DIC), ketoprofen (KET), indomethacin (IND), and mefenamic acid (MFA), from wastewater. This study employed a combination of quantum mechanical (QM) calculations, Monte Carlo (MC) simulations, and molecular dynamics (MD) simulations to understand the adsorption behaviors of these contaminants. This study first analyzed the structures of the contaminants and the adsorbent using various techniques, such as electrostatic potential, reduced density gradients, and Hirshfeld surfaces. Then, we investigated the adsorption affinity of pharmaceutical pollutants on MIL-53 (Al) using the COSMO sigma profile and HOMO–LUMO energies. The simulation results revealed that HBs, electrostatic interactions, and π–π stacking primarily contribute to the adsorption mechanism. Laboratory tests confirmed the synthesis of MIL-53 using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and wide-angle X-ray diffraction (WAXD). Ultraviolet-visible (UV–Vis) spectroscopy was performed to analyze the adsorption of the targeted drugs, and the experimental results agreed well with the modeling results. This study concluded that MIL-53 (Al) has the potential to serve as an effective adsorbent for the removal of pharmaceutical pollutants from wastewater because of its strong adsorption properties.

Quantum hydrodynamic model for noble metal nanoplasmonics

The quantum hydrodynamic model (QHDM) has become a versatile and efficient tool for plasmonics at nanometer and even subnanometer length scales, but the theory is principally applicable only to simple metals. For the most common plasmonic materials, i.e., noble metals, QHDM has not been duly justified to describe their optical responses. In particular, when noble metal structures interface with dielectric materials, electron spillover plays an important role. Although a background optical permittivity is usually invoked in Amp\`ere's law to encompass the $d$-band electrons' effect on optical responses in a direct manner, their indirect effects, e.g., acting via conduction electrons, still remain elusive. Here we identify these indirect effects and develop a near-field potential ${U}_{\mathrm{aff}}$ refined QHDM (U-QHDM), in which the $d$-band electrons' effects on the conduction electrons are recognized and the electrostatic properties of dielectric are incorporated. We report the detailed procedures of calibrating U-QHDM. Material-independent model parameters are fitted with density functional theory (DFT) calculations for simple metals. Last, the calibrated U-QHDM is benchmarked against DFT and time-dependent DFT within stabilized jellium model for Ag, Au, and Al nanostructures interfacing with dielectrics. We expect U-QHDM will be a valuable asset for the rapidly developing field of extreme nanophotonics.

Surface group directed low-temperature synthesis and self-assembly of Al nanostructures for lithium storage

Surface group directed low-temperature synthesis and self-assembly of Al nanostructures for lithium storage

Corrosion protection and mechanical properties of the electroless Ni-P-MOF nanocomposite coating on AM60B magnesium alloy

Al-based MIL-53 MOF nanostructure was synthesized hydrothermally and then co-deposited in the electroless nickel coating on AM60B magnesium alloy using Zr pretreatment as an eco-friendly underlayer. The MIL-53(Al) nanostructure was synthesized in the form of layered semi-cube crystals with the surface area and mean pore diameter of 985.72 m 2 g −1 and 2.00 nm, respectively. The SEM images captured with two various zooming scales from the surface of the plain and MOF containing electroless layers showed cauliflower-like morphology with even distribution of nodule size. Also, the sub-grains of the plain coating disappeared after incorporation of the MOF. Although, both the normal and nanostructure-containing electroless layers have crystalline-amorphous structure, but the nanocomposite coating showed less crystallinity. The average surface roughness of the plain electroless coating was about 309 nm, which decreased to about 222 nm after incorporation of the MOF. The XRD patterns showed that the characteristic peak of Ni broadened after incorporation of the MOF, probably due to the decreasing of the crystallinity. For the heat-treated normal and MOF containing coatings at 200 °C no phase transition takes place, but new peaks appeared for heat-treated coatings at 400 °C due to the crystallization and second-phase precipitation. The results of the EIS tests showed an increase in the amount of the charge transfer resistance (from 19 to 29 kΩ cm 2 ) after addition of the MOF, which means an improvement in the corrosion resistance. Also, low J corr of the composite coating represents its higher corrosion resistance with respect to the plain coating. The micro-hardness values of the composite coating before and after the heat treatment were higher than the plain coating. Also, the Ni-P-MOF coating has a lower wear rate both before and after the heat treatment due to an improvement in its micro-hardness.

Electron energy-loss spectroscopy investigation of multipolar behavior in Al nanostructure as a function of surface coating with PVP and oxidation

The inherent, self-limiting oxidation characteristics of Aluminum (Al) nanospheres and nanocubes of similar dimensions (100 nm edge length) are illustrated utilizing the MATLAB based boundary element method (MNPBEM17) optical and electron energy loss spectroscopy (EELS) simulations. Such model systems conveniently establish not only the distinct dipolar and multi-polar plasmonic resonance behaviors with reference to their respective passivated ligand PVP as well as their self-limiting surface conformal/non-conformal oxide layers, demonstrating the vital fact that Al nanostructures could be a suitable substitution of conventional noble metals, especially for UV-plasmonic applications. In the case of Al nanocubes, both oxidation processes were found to be strongly site-selective (edges, corners and faces), whereas a differential variation is observed in Al nanospheres from the center to the surface, effectively corroborated through the simultaneous correlation of optical spectra with the spatially and energetically resolved EELS maps. Moreover, the robust contribution from dark plasmon resonances was also confirmed in the EELS data along with the induced surface charge distribution calculations, further substantiating their strong dependence on the surrounding dielectric environment concerning their oxide passivation as well. Thus, our present results demonstrate a better understanding of the spatial coherence of the plasmonic behavior with reference to the passivated ligand and (non)-conformal oxidation processes of Al nanostructures, in general, thereby providing a fundamental understanding of the plasmon physics necessary to improve the design and optimization of new nanostructures for nanophotonic, nanoantenna and sensing applications.

Flexible Plasmonics Using Aluminum and Copper Epitaxial Films on Mica.

We demonstrate here the growth of aluminum (Al), copper (Cu), gold (Au), and silver (Ag) epitaxial films on two-dimensional, layered muscovite mica (Mica) substrates via van der Waals (vdW) heteroepitaxy with controllable film thicknesses from a few to hundreds of nanometers. In this approach, the mica thin sheet acts as a flexible and transparent substrate for vdW heteroepitaxy, which allows for large-area formation of atomically smooth, single-crystalline, and ultrathin plasmonic metals without the issue of film dewetting. The high-quality plasmonic metal films grown on mica enable us to design and fabricate well-controlled Al and Cu plasmonic nanostructures with tunable surface plasmon resonances ranging from visible to the near-infrared spectral region. Using these films, two kinds of plasmonic device applications are reported, including (1) plasmonic sensors with high effective index sensitivities based on surface plasmon interferometers fabricated on the Al/Mica film and (2) Cu/Mica nanoslit arrays for plasmonic color filters in the visible and near-infrared regions. Furthermore, we show that the responses of plasmonic nanostructures fabricated on the Mica substrates remain unaltered under large substrate bending conditions. Therefore, the metal-on-mica vdW heteroepitaxy platform is suitable for flexible plasmonics based on their bendable properties.

Towards realistic modeling of plasmonic nanostructures: a comparative study to determine the impact of optical effects on solar cell improvement.

Plasmonic structures may improve cell performance in a variety of ways. More accurate determining of the optical influence, unlike ideal simulations, requires modeling closer to experimental cases. In this modeling and simulation, irregular nanostructures were chosen and divided into three groups and some modes. For each mode, different sizes of nanoparticles were randomly selected, which could result in pre-determined average particle size and standard deviation. By 3D finite-difference time-domain (3D-FDTD), the optical plasmonic properties of that mode in a solar cell structure were investigated when the nanostructure was added to the buffer/active layer of the organic solar cell. The far- and near-field results were used to compare the plasmonic behavior, relying on the material and geometry. By detailed simulations, Al and Ag nanostructure at the interface of the ZnO/active layer can improve organic solar cell performance optically, especially by the near-field effect. Unlike Au and relative Ag, the Al nanostructured sample showed less parasitic absorption loss.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10825-021-01829-x.

Correlating Optical Reflectance with the Topology of Aluminum Nanocluster Layers Growing on Partially Conjugated Diblock Copolymer Templates.

Large-scale fabrication of metal cluster layers for usage in sensor applications and photovoltaics is a huge challenge. Physical vapor deposition offers large-scale fabrication of metal cluster layers on templates and polymer surfaces. In the case of aluminum (Al), only little is known about the formation and interaction of Al clusters during sputter deposition. Complex polymer surface morphologies can tailor the deposited Al cluster layer. Here, a poly(methyl methacrylate)-block-poly(3-hexylthiophen-2,5-diyl) (PMMA-b-P3HT) diblock copolymer template is used to investigate the nanostructure formation of Al cluster layers on the different polymer domains and to compare it with the respective homopolymers PMMA and P3HT. The optical properties relevant for sensor applications are monitored with ultraviolet-visible (UV-vis) measurements during the sputter deposition. The formation of Al clusters is followed in situ with grazing-incidence small-angle X-ray scattering (GISAXS), and the chemical interaction is revealed by X-ray photoelectron spectroscopy (XPS). Furthermore, atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) yield topographical information about selective wetting of Al on the P3HT domains and embedding in the PMMA domains in the early stages, followed by four distinct growth stages describing the Al nanostructure formation.

Fabrication of low cost highly structured silver capped aluminium nanorods as SERS substrate for the detection of biological pathogens

We report the fabrication of low cost highly structured silver (Ag) capped aluminium (Al) nanorods (NRs) as surface enhanced Raman spectroscopy (SERS) substrate utilising the glancing angle deposition technique. The nano-capping of silver onto the Al NRs can concentrate the local electric field within the minimal volume that can serve as hotspots. The average size of the Ag nanocaps was 50 nm. The newly proposed nanoporous Ag capped Al NRs as SERS substrate could detect the Raman signal of rhodamine 6G (R6G) up to 10−15 molar concentration. The significant enhancement in the Raman signal of 107 was achieved for Ag capped Al NRs considering R6G as a probe molecule. Using the developed SERS substrate, we recorded Raman spectra for Escherichia coli bacteria with its concentration varying from 108 colony forming units per ml (CFU ml−1) up to 102 CFU ml−1. All the reported Raman spectra were acquired by a portable handheld Raman spectrometer. Hence, this newly proposed low cost, effective SERS substrate can be used commercially for the onsite detection of clinical pathogens. The 3D finite difference time domain simulation model was performed for Ag capped Al nanostructure to understand the generation of hotspots. The simulated results show excellent agreement with the experimental results. We fabricated uncapped Ag nanorods of similar dimensions and performed the experimental measurements and simulations for comparison. We found a significant enhancement in Ag capped Al NRs compared to the long Ag NRs. The description of the Raman signal enhancement has been elaborated.

Tuning the Localized Surface Plasmon Resonance of Al-Al2O3 Nanosphere Towards NIR Region by Gold Coating

Background: A relatively narrow LSPR peak and a strong interband transition ranging around 800 nm make Al a strongly plasmonic active material. Usually, Al nanoparticles are preferred for UV-plasmonic as the SPR of small size Al nanoparticles is located in the deep UV-UV region of the optical spectrum. This paper focused on tuning the LSPR of Al nanostructure towards the infrared region by coating the Au layer. The proposed structure has Au as the outer layer, which prevents further oxidation of Al nanostructure. Methods: The Finite Difference Time Domain (FDTD) and Plasmon Hybridization Theory has been used to evaluate the LSPR and field enhancement of single and dimer Al-Al2O3-Au MDM nanostructure. Results: It is observed that the resonance mode shows dependence on the thickness of the Al2O3 layer and also on the composition of the nanostructure. The Au layered MDM nanostructure shows two peaks of equal intensities simultaneously in UV and visible region tuned to the NIR region. The extinction spectra and electric field distribution profiles of dimer nanoparticles are compared with the monomer to reveal the extent of coupling. The dimer configuration shows higher field enhancement ~107 at 1049 nm. By optimizing the thickness of the dielectric layer, the MDM nanostructure can be used over the UV-visible-NIR region. Conclusion: The LSPR peak shows dependence on the thickness of the dielectric layer and also on the composition of the nanostructure. It has been observed that optimization of size and thickness of the dielectric layer can provide two peaks of equal intensities in the UV and Visible region, which are advantageous for many applications. The electric field distribution profiles of dimer MDM nanostructure enhanced the field by ~107 in visible and NIR region showing its potential towards SERS substrate. The results of this study will provide valuable information for the optimization of LSPR of Al-Al2O3- Au MDM nanostructure to have high field enhancement.

Nano-viewpoint in Modeling and Investigation of the D/M/D Transparent-Conductive Layer

A transparent-conductive film (TCF) is widely used in various electro-optical devices. The dielectric/metal/dielectric (D/M/D) as one type of TCF has been highly considered due to more advantages, such as the possibility of selecting different materials and engineering other properties. For pre-fabrication design, it is often modeled with a 1D photonic crystal. This model needs to be improved due to the low thickness of the metal layer since a very thin metallic layer leads to a nanostructure instead of a uniform layer. In this study, after proper nanostructure modeling, the 3D-FDTD method was used to simulate different optical properties of the structure. The first aspect of the importance of the nanostructured model is to address the serious plasmonic losses. They are associated with the complicated metallic form in D/M/D that is not considered in conventional modeling. The simulation results showed that for Ag, plasmonic loss peaks demonstrate a wide distribution over the visible spectrum. These peaks show a more significant distribution near the UV–visible border for Al nanostructure. In both, the behavior of optical plasmonic loss tends to redshift compared to their bulk plasmonic peaks. Concerning optical transmission, Al does not offer a notable advantage over Ag. Due to the intense excitation of plasmonic modes when the metal layer has pores, a layer of entirely connected nanoparticles with the least possible thickness can have the desired optical properties. The increased rough surface of the dielectric layer due to the nanostructured metallic layer was also modeled.

Moiré Nanolithography Based on Ultrathin Anodized Aluminium Oxide Membranes

A new nanofabrication method for construction of complex superlattice structure with versatile super-periodicity is developed using the moiré fringe of anodized aluminium oxide (AAO) membranes. Two ultrathin AAO membranes with long-range order holes are stacked to form 2D moiré nanopatterns. Both rotational symmetry and the periodicity of the holes are modified by the relative spatial displacement between the superimposing layers. Using the membranes as metal evaporation masks, a wide assortment of complex Al nanostructures are fabricated by varying the misorientation angle of the two ultrathin AAO membranes. Highly ordered Al nanoparticles with different sizes, shapes, orientations, and arrangements on substrates are achieved, which are expected to give abundant surface plasmon mode.

From Aluminum Foil to Two-Dimensional Nanocrystals Using Ultrasonic Exfoliation

Al nanostructures have unique optical properties such as widely tunable surface plasmon resonances from deep UV to NIR that can be used for label-free fluorescence enhancement and surface-enhanced ...

Nanometer-Thick Al2O3 Layers on Ag–Al Nanostructures as Conductive Electrodes

Silver (Ag) nanostructures are active functional platforms for catalysts, optical sensors, and transparent conductive networks with outstanding performance but present poor stability depending on t...

Improving Aluminum Ultraviolet Plasmonic Activity through a 1 nm ta-C Film.

Aluminum (Al) can actively support plasmonic response in the ultraviolet (UV) range compared to noble metals (e.g., Au, Ag) and thus has broad applications including UV sensing, displays, and photovoltaics. High-quality Al films with no oxidation are essential and critical in these applications. However, Al is very prone to fast oxidation in air, which critically depends on the fabrication process. Here, we report that by leveraging the in situ sputter etching and sputter deposition of a 1 nm tetrahedral amorphous carbon (ta-C) film on the Al nanostructures, Al plasmonic activity can be improved. The prior sputter etching process greatly reduces the oxidized layer of the Al films, and the subsequent sputter deposition of ta-C keeps Al oxidation-free. The ta-C film outperforms the naturally passivated Al2O3 layer on the Al film because the ta-C film has a denser structure, higher permittivity, and better biocompatibility. Therefore, it can effectively improve the plasmonic response of Al and be beneficial to molecule sensing, which is proved in our experiments and is also verified in simulations. Our results can enable the various applications based on plasmon resonance in the UV range.