Aluminum Nanowires Research Articles

Al nanowire-embedded silicon for broadband optical modulation: Forming mechanism and optical performance

In recent decades, silicon has been widely used in light regulation devices, owing to its wideband high refractive index and low dispersion. To meet the increasing demands for various applications, optical modulation techniques appear of great potential to enhance the optical performance of Si-based devices. However, challenges still remain in achieving precise control over the band structure and resonance modes without introducing complex artificial structures. In this study, a composite film composed of silicon embedded with high fraction aluminum nanowires was developed by magnetron sputtering. It was revealed that the formation of aluminum nanowires was attributed to the spontaneous phase separation between silicon and aluminum, which was strongly dependent on the filling fraction and surface diffusion length of the aluminum during the co-sputtering process. The composite microstructure was precisely regulated by manipulating adatom diffusion and reevaporation through ion bombardment, thereby modifying its broadband optical properties. Moreover, exceptional electromagnetic properties were achieved by incorporating aluminum nanowires into silicon, as evidenced by the metallic behaviors in the short-wavelength regime and dielectric properties in the infrared spectrum range.

Phase field simulations of surface- and thermal-induced melting of finite length aluminum nanowires: size effect on the melting temperature

Phase field simulations of surface- and thermal-induced melting of finite length aluminum nanowires: size effect on the melting temperature

Interface catalytic reduction of alumina by nickle for the aluminum nanowire growth: Dynamics observed by in situ TEM

Metal nanowires show promise in a broad range of applications and can be fabricated via a number of methods, such as vapor–liquid–solid process and template-based electrodeposition. However, the synthesis of Al nanowires (NWs) is still challenging from the stable alumina substrate. In this work, the Ni-catalyzed fabrication of Al NWs has been realized using various Al2O3 substrates. The growth dynamics of Al NWs on Ni/Al2O3 was studied using in situ transmission electron microscopy (TEM). The effect of alumina structures, compositions, and growth temperature were investigated. The growth of Al NWs correlates with the Na addition to the alumina support. Since no eutectic mixture of nickel aluminide was formed, a mechanism of Ni-catalyzed reduction of Al2O3 for Al NWs growth has been proposed instead of the vapor–liquid–solid mechanism. The key insights reported here are not restricted to Ni-catalyzed Al NWs growth but can be extended to understanding the dynamic change and catalytic performance of Ni/Al2O3 under working conditions.

Thermo-electro-optical properties of seamless metallic nanowire networks for transparent conductor applications.

Rapid reaction time, high attainable temperatures, minimum operating voltage, excellent optical transmittance, and tunable sheet resistance are all desirable properties of transparent conductors, which are important thin-film components in numerous electronic devices. A seamless nanowire network (NWN) refers to a structure composed of nanowires that lack interwire contact junctions, resulting in a continuous and uninterrupted network arrangement. This seamless nature leads to unique properties, including high conductivity and surface area-to-volume ratios, which make it a promising candidate for a vast application range in nanotechnology. Here, we have conducted an in-depth computational investigation to study the thermo-electro-optical properties of seamless nanowire networks and understand their geometrical features using in-house computational implementations and a coupled electrothermal model built in COMSOL Multiphysics software. Sheet resistance calculations were performed using Ohm's law combined with Kirchhoff circuit laws for a random resistor network and compared with those obtained employing COMSOL. In this work, aluminium, gold, copper, and silver nanowires are the materials of choice for testing the transparent conduction performance of our systems. We have studied a wide range of tuning parameters, including the network area fraction, the width-to-depth aspect ratio, and the length of the nanowire segments. We obtained corresponding figures of merit (optical transmittance versus sheet resistance) and temperature distributions to provide a complete characterization of the performance of real-world transparent conductors idealized with seamless NWNs. Our analysis accounted for the thermo-electro-optical responses of the NWNs and the inspection of various controlling parameters depending on system design considerations to shed light on how the electrical transport, optical qualities, and thermal management of these systems can be optimized.

Plasmonic properties of aluminium nanowires in amorphous silicon

Plasmonic structures can help enhance optical activity in the ultraviolet (UV) region and therefore enhancing photocatalytic reactions and the detection of organic and biological species. Most plasmonic structures are composed of Ag or Au. However, producing structures small enough for optical activity in the UV region has proved difficult. In this study, we demonstrate that aluminium nanowires are an excellent alternative. We investigated the plasmonic properties of the Al nanowires as well as the optoelectronic properties of the surrounding a − Si matrix by combining scanning transmission electron microscopy imaging, electron energy loss spectroscopy and electrodynamic modelling. We have found that the Al nanowires have distinct plasmonic modes in the UV and far UV region, from 0.75 eV to 13 eV. In addition, simulated results found that the size and spacing of the Al nanowires, as well as the embedding material were shown to have a large impact on the type of surface plasmon energies that can be generated in the material. Using electromagnetic modelling, we have identified the modes and illustrated how they could be tuned further.

Mechanical optimization of an Al-Al2O3 composite nanowire via molecular dynamics simulation and metaheuristic optimization

In the present study, mechanical properties optimization is investigated for an Al-Al2O3 composite nanostructure. The Al-Al2O3 composite nanostructure is considered an Aluminum nanowire reinforced by spherical Al2O3 particles. The structure tensile test is simulated via molecular dynamics simulation using LAMMPS. The mechanical properties of the composite are extracted from the obtained stress-strain curve of the composite. The important mechanical properties include maximum stress and toughness. An optimization process is then applied to maximize the mechanical properties of the composite via metaheuristic optimization algorithms including Genetic Algorithm (GA), Ant Colony (ACO), and Grey Wolf Optimizer (GWO). Since the studied nanostructure is mono crystal, the reinforcing mechanism differs from that of a grained macro material. Therefore, the optimization variables are not confined to size and volume fraction but they also include the location of the particles. The optimization is performed for 0.05 and 0.10 volume fractions and different particle sizes with respect to the location of particles. Applying the optimization process, the mechanical properties of the studied composite nanowire are substantially improved for tensile loading. The results reveal that the placement of the particles has a considerable effect on the improvement of mechanical characteristics. At last, a pattern is presented for the placement of particles to achieve the highest tensile characteristics of Al-Al2O3 composite nanowires.

Thermal Stability of Black Aluminum Films and Growth of Aluminum Nanowires from Mechanical Defects on the Film Surface during Annealing

Thermal Stability of Black Aluminum Films and Growth of Aluminum Nanowires from Mechanical Defects on the Film Surface during Annealing

Optoelectronic Behavior of Free Standing Al Wire Over Monolayer WSe2

In this manuscript, we reported the electronic and optical behavior of free standing Aluminium nanowire mounted on tungsten diselenide (WSe2) sheet. The density functional theory has been used as a toolset for all computational calculations. We mounted the aluminum nanowire over a 2-dimensional sheet of tungsten diselenide and investigated the modulated optoelectronic properties of it. Based on our studies, we majorly found a conductive behavior of the proposed structure along with a strong absorption in visible range. Due to its prominent optical properties, the proposed structure will be very useful in futuristic optoelectronics devices such as photovoltaic, laser, optical sensors.

An Effective Strategy for Template-Free Electrodeposition of Aluminum Nanowires with Highly Controllable Irregular Morphologies.

Aluminum nanowires with irregular morphologies were prepared by template-free electrodeposition from a room-temperature chloroaluminate ionic liquid. The effects of the diffusion condition and deposition potential on the morphologies of Al nanowires were investigated. The decrease of diffusion flux leads to the formation of particular segmented morphologies of Al nanowires. A dynamic equilibrium between the electrochemical reaction and the diffusion of Al2Cl7− results in the current fluctuation and the periodical variation of diameters in the Al nanowires growth period. Al nanowires with several kinds of morphologies can be controllably electrodeposited under a restricted diffusion condition, without using a template. Increasing the overpotential shows the similar influence on the morphology of Al nanowires as the decrease in diffusion flux under the restricted diffusion condition. Most of the segmented Al nanowires have a single crystalline structure and grow in the [100] orientation. This work also provides a new strategy for the fabrication of nanowires with highly controllable irregular morphologies.

Thermal superconducting quantum interference proximity transistor

Superconductors are known to be excellent thermal insulators at low temperature owing to the presence of the energy gap in their density of states (DOS). In this context, the superconducting \textit{proximity effect} allows to tune the local DOS of a metallic wire by controlling the phase bias ($\varphi$) imposed across it. As a result, the wire thermal conductance can be tuned over several orders of magnitude by phase manipulation. Despite strong implications in nanoscale heat management, experimental proofs of phase-driven control of thermal transport in superconducting proximitized nanostructures are still very limited. Here, we report the experimental demonstration of efficient heat current control by phase tuning the superconducting proximity effect. This is achieved by exploiting the magnetic flux-driven manipulation of the DOS of a quasi one-dimensional aluminum nanowire forming a weal-link embedded in a superconducting ring. Our thermal superconducting quantum interference transistor (T-SQUIPT) shows temperature modulations up to $\sim 16$ mK yielding a temperature-to-flux transfer function as large as $\sim 60$ mK/$\Phi_0$. Yet, phase-slip transitions occurring in the nanowire Josephson junction induce a hysteretic dependence of its local DOS on the direction of the applied magnetic field. Thus, we also prove the operation of the T-SQUIPT as a phase-tunable \textit{thermal memory}, where the information is encoded in the temperature of the metallic mesoscopic island. Besides their relevance in quantum physics, our results are pivotal for the design of innovative coherent caloritronics devices such as heat valves and temperature amplifiers suitable for thermal logic architectures.

Quantum interference in asymmetric superconducting nanowire loops

Macroscopic phase coherence in superconductors enables quantum interference and phase manipulation at realistic device length scales. Numerous superconducting electronic devices are based on the modulation of the supercurrent in superconducting loops. While the overall behavior of symmetric superconducting loops has been studied, the effects of asymmetries in such devices remain under-explored and poorly understood. Here we report on an experimental and theoretical study of the flux modulation of the persistent current in a doubly connected asymmetric aluminum nanowire loop. A model considering the length and electronic cross-section asymmetries in the loop provides a quantitative account of the observations. Comparison with experiments give essential parameters such as persistent and critical currents as well as the amount of asymmetry which can provide feedback into the design of superconducting quantum devices.

Effect of low aspect ratio one-dimensional nanoparticles on properties of photocrosslinked alginate nanocomposite hydrogels

One-dimensional nanoparticles such as fibers, wires, represent an exciting type of filler for obtaining nanocomposite hydrogels due to their high aspect ratio. Unlike continuous fibers, in composites with short fibers, stress transfer occurs not only at the cylindrical surface of the fiber but also at the fiber ends. This work aimed to study the influence of the length of low aspect ratio one-dimensional nanoparticles on the rheological, swelling and thermal properties of nanocomposite hydrogels. We synthesized nanocomposite hydrogels via photopolymerization of methacrylated alginate macromonomers and aluminum oxide nanoparticles, nanowires and nanofibers as fillers. The main difference between the nanoparticles lies in their length. Longer nanoparticles (nanofibers) provided a glassier structure and a more significant reinforcement to the hydrogel, for example, at the concentration of 0.5 wt% the complex modulus increased approximately 2-fold and 8-fold for nanowires and nanofibers, respectively. Similarly, the incorporation of nanofibers produced hydrogels with a lower swelling capacity (2.5-fold decrease), which was attributed to a more connected network structure due to the higher aspect ratio of the nanofibers. Finally, both nanoparticle types produced an increase in the activation energy of thermal degradation.

Thermal Stability of Black Aluminum Films and Growth of Aluminum Nanowires from Mechanical Defects on the Film Surface during Annealing

The thermal stability of black aluminum (Black Al) films deposited on unheated fused silica substrates by pulsed DC magnetron sputtering is investigated. The deposited films have porous moth‐eye morphology and a relatively soft surface that can be easily damaged mechanically. Photothermally stimulated exoelectron emission (PTSE) spectra of the films have emission peaks at 180 and 300 °C, which can be associated with processes of aluminum recrystallization occurring at these temperatures. The total emitted charge of PTSE decreases according to a power law with each subsequent heating, indicating that the most pronounced structural changes on the film surface occur during its first annealing. The shape of the mechanically intact pores of the films does not change after heating. However, spiral‐shaped aluminum nanowires grow from scratches and abrasions on the film surface already after heating up to 200 °C due to the stress‐induced migration of aluminum atoms. When scratches are deliberately applied to the surface of an already annealed film, the nanowires do not grow when the film is reheated. The results of this study show that mechanically intact as‐deposited Black Al films are thermally stable up to temperatures of at least 400 °C.

Visualizing the Electron Wind Force in the Elastic Regime.

With continued scaling toward higher component densities, integrated circuits (ICs) contain ever greater lengths of nanowire that are vulnerable to failure via electromigration. Previously, plastic electromigration driven by the "electron wind" has been observed, but not the elastic response to the wind force itself. Here we describe mapping, via electron energy-loss spectroscopy, the density of a lithographically defined aluminum nanowire with sufficient precision to determine both its temperature and its internal pressure. An electrical current density of 108 A/cm2 produces Joule heating, tension upwind, and compression downwind. Surprisingly, the pressure returns to its ambient value well inside the wire, where the current density is still high. This spatial discrepancy points to physics that are not captured by a classical "wind force" model and to new opportunities for optimizing electromigration-resistant IC design.

Probability distribution for heat exchange in plastic deformation.

Fluctuation theorems allow one to obtain equilibrium information from nonequilibrium experiments. The probability distribution function of the relevant magnitude measured along the irreversible nonequilibrium trajectories is an essential ingredient of fluctuation theorems. In small systems, where fluctuations can be larger than average values, probability distribution functions often deviate from being Gaussian, showing long tails, mostly exponential, and usually strongly asymmetric. Recently, the probability distribution function of the van Hove correlation function of the relevant magnitude was calculated, instead of that of the magnitude itself. The resulting probability distribution function is highly symmetric, obscuring the application of fluctuation theorems. Here, the discussion is illustrated with the help of results for the heat exchanged during plastic deformation of aluminum nanowires, obtained from molecular dynamics calculations. We find that the probability distribution function for the heat exchanged is centrally Gaussian, with asymmetric exponential tails further out. By calculating the symmetry function we show that this distribution is consistent with fluctuation theorems relating the differences between two equilibrium states to an infinite number of nonequilibrium paths connecting those two states.

Preliminary demonstration of a persistent Josephson phase-slip memory cell with topological protection

Superconducting computing promises enhanced computational power in both classical and quantum approaches. Yet, scalable and fast superconducting memories are not implemented. Here, we propose a fully superconducting memory cell based on the hysteretic phase-slip transition existing in long aluminum nanowire Josephson junctions. Embraced by a superconducting ring, the memory cell codifies the logic state in the direction of the circulating persistent current, as commonly defined in flux-based superconducting memories. But, unlike the latter, the hysteresis here is a consequence of the phase-slip occurring in the long weak link and associated to the topological transition of its superconducting gap. This disentangles our memory scheme from the large-inductance constraint, thus enabling its miniaturization. Moreover, the strong activation energy for phase-slip nucleation provides a robust topological protection against stochastic phase-slips and magnetic-flux noise. These properties make the Josephson phase-slip memory a promising solution for advanced superconducting classical logic architectures or flux qubits.

Aluminum nanowires and gold nanoparticles – driven stabilization of blue phase liquid crystals

ABSTRACT Blue phases (BPs) in chiral nematic liquid crystals (LC) remained a field of ample research interest due to their exotic optical properties. In the present work, we report the doping effect of dimensionality varying NPs (alumina nanowires [ANWs] and citrate buffer stabilized gold nanoparticles [GNPs]) on the phase transition temperatures and stability of the BP temperature range using polarizing optical microscopy. An increase in the BP thermal stability after the dispersion of NP is observed than an undoped sample. Doping of GNPs and ANWs could expand the BP temperature range of ∼8.0°C and ∼4.5°C respectively at an optimum concentration of dopants. A decrease in BP temperature range is noticed beyond a critical concentration of doped NPs. A platelet type texture, which corresponds to BP-I/BP-II is clearly seen.

Nanopatterned metallic transparent electrodes for the near-infrared spectrum

Near-infrared transparent electrodes constitute an essential component of light-emitting and photovoltaic devices widely employed in short- and long-range communication, light detection and ranging, biodiagnostics, security, virtual and augmented reality, night vision, gas sensing, and solar cells. However, the efficiency of all these devices and related applications suffers from significantly reduced transmittance of the indium tin oxide electrode compared to the visible wavelength range. Here, we explore the potential of randomly and uniformly arranged silver, gold, and aluminum nanopore and nanowire films for the near-infrared optoelectronics. We show that these metallic nanopatterned layers, except for randomly arranged nanoporous configurations, exhibit considerably higher performance than the commonly used indium tin oxide. Furthermore, silver layers possess higher transmittance and lower haze than gold and aluminum ones, while the nanowire configuration overperforms the nanoporous one. The obtained results offer a means for deeper analysis of metallic nanopatterned transparent electrodes for many near-infrared optoelectronic applications.

A novel, structurally coloured coating for aluminium alloys

Current approaches to coat aluminium surfaces that use paints and organic coatings to protect them from corrosion and provide an aesthetic finish, are also energy intensive and involve high emissions of VOCs. The use of these coatings is becoming increasingly restricted by global efforts towards more environmentally sustainable surface finishing technologies. A recent development based on porous anodised aluminium (PAA) and metal nanowire deposits is presented here, which may become a competitive alternative to paint and organic coatings. Anodising and electrodeposition do not emit VOCs and are less energy intensive. By controlling the conditions for anodising and metal electrodeposition, coatings in a wide spectrum of colours can be produced, including greys, black, blues, purples, and greens. Characterisation of the coating morphologies and corresponding colours agrees with simulated results based on the Fresnel equations and Bruggeman Mixed Media Approximations.

Differential electron yield imaging with STXM

Total electron yield (TEY) imaging is an established scanning transmission X-ray microscopy (STXM) technique that gives varying contrast based on a sample’s geometry, elemental composition, and electrical conductivity. However, the TEY-STXM signal is determined solely by the electrons that the beam ejects from the sample. A related technique, X-ray beam-induced current (XBIC) imaging, is sensitive to electrons and holes independently, but requires electric fields in the sample. Here we report that multi-electrode devices can be wired to produce differential electron yield (DEY) contrast, which is also independently sensitive to electrons and holes, but does not require an electric field. Depending on whether the region illuminated by the focused STXM beam is better connected to one electrode or another, the DEY-STXM contrast changes sign. DEY-STXM images thus provide a vivid map of a device’s connectivity landscape, which can be key to understanding device function and failure. To demonstrate an application in the area of failure analysis, we image a 100 nm, lithographically-defined aluminum nanowire that has failed after being stressed with a large current density.