Al Films Research Articles

Effect of Al doping on the electrochromic properties of WO3 thin films

Effect of Al doping on the structural, optic, and electrochromic properties of tungsten trioxide (WO3) thin films was investigated through X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, optic transmittance, spectral ellipsometry, cyclic voltammetry and chronoamperometry measurements. Undoped and 0.7–4.3% Al doped WO3 films were grown by radio frequency magnetron sputtering. All of the WO3:Al films investigated grew in amorphous phase. The thicknesses of the films varied between 113 and 124 nm. X-ray photoelectron spectroscopy analysis indicated that tungsten atoms exist as W6+ in both undoped and Al doped WO3 films. The optical transmittance of WO3 films is not affected by the Al doping. Their transparency in the visible range is around 90% while the transmittance in the near infrared region seems to slightly increase (around 5%) with increasing Al doping. The optical band gap energies increase with Al doping concentrations exceeding 1.5%. Variation of the coloration / bleaching times and coloration efficiency of the WO3 films with Al doping was analyzed. The highest optical modulation of 44% was obtained for 1.5% Al doped WO3 film at 630 nm.

Development of a highly sensitive UV sensor using Al, Ga, and In-doped NiO thin films via nebulizer spray pyrolysis method for photodetector applications

Development of a highly sensitive UV sensor using Al, Ga, and In-doped NiO thin films via nebulizer spray pyrolysis method for photodetector applications

Microstructure and Mechanical Properties of AlN/Al Joints Brazing by a Sputtering Al/Cu Bilayer Film Solder.

This paper presents a magnetron sputtering Al/Cu bilayer film solder to realize the brazing of AlN ceramic and Al metal. The effect of different temperatures on the structure and mechanical properties of brazed joints is studied. The results show that the sputtered Al particles have a sputtering wetting effect on AlN ceramic. The contact angle of molten Al on AlN ceramic with Al film deposited at 700 °C is as low as about 30°. While the contact angle of molten Al on AlN ceramic without Al film deposited at 1000 °C is about 89°. There is a large amount of Cu enrichment in brazed joints at 600 °C. The weld structure is a mixture of Al solid solution and AlCu compound. The shear strength of the brazed joint is only 70.6 MPa, and the joint fracture shows a large number of brittle fracture morphologies. With the increase of brazing temperature, the phenomenon of Cu enrichment in the joint gradually weakens, and the weld structure gradually transforms into a solid solution of Cu in Al. The shear strength of the brazed joint continues to increase, and the joint fracture morphology gradually changes from brittle fracture to furrow-like plastic fracture morphology. When the brazing temperature is increased to 660 °C, the distribution of Cu in the joint is evenly dispersed, and the shear strength of the brazed joint reaches the highest value of 107.8 MPa. The joint fracture is completely furrow-like plastic fracture morphological composition.

In Situ Epitaxy of Pure Phase Ultra-Thin InAs-Al Nanowires for Quantum Devices

We demonstrate the in situ growth of ultra-thin InAs nanowires with an epitaxial Al film by molecular-beam epitaxy. Our InAs nanowire diameter (∼30 nm) is much thinner than before (∼100 nm). The ultra-thin InAs nanowires are pure phase crystals for various different growth directions. Transmission electron microscopy confirms an atomically abrupt and uniform interface between the Al shell and the InAs wire. Quantum transport study on these devices resolves a hard induced superconducting gap and 2e-periodic Coulomb blockade at zero magnetic field, a necessary step for future Majorana experiments. By reducing wire diameter, our work presents a promising route for reaching fewer sub-band regime in Majorana nanowire devices.

A highly sensitive PNA-microarray system for miRNA122 recognition.

Surface chemistry is a fundamental aspect of the development of the sensitive biosensor based on microarray technology. Here, an advanced PNA-microarray system for the detection of miRNA, composed by a multilayered Si/Al/Agarose component, is described. A straightforward optical signal enhancement is achieved thanks to a combination of the Al film mirror effect and the positive interference for the emission wavelength of the Cy5 fluorescent label tuned by the agarose film. The PNA-microarray was investigated for the detection of miRNA_122, resulting in a sensitivity of about 1.75μM-1 and Limit of Detection in the range of 0.043nM as a function of the capture probe sequence. The contribution, in terms of H-bonds amounts at 298 and 333 K, of the agarose coating to the dsPNA-RNA interactions was demonstrated by Molecular Dynamic simulations. These results pave the way for advanced sensing strategies suitable for the environmental monitoring and the public safety.

Film thickness and architecture effects in biaxially strained polymer supported Al/Mo bilayers

Multilayers on polymer substrates are of interest for several technical applications. However, the true understanding of how one layer affects the other during mechanical loading is still unknown. In order to address this lack of knowledge, single and bilayer thin films of Al (250, 125, and 75 nm) and Mo (50 nm) were sputter deposited onto polyimide (PI, 50 µm) and biaxially strained in-situ with X-ray diffraction. The technique allows for the simultaneous measurement of lattice strains of Al and Mo to correlate the observed mechanical behavior of both materials. Using the evaluated film stress and full width at half maximum evolutions, four domains of mechanical behavior are identified. The presence of the domains in either Al or Mo depends on the thickness of the Al films and, more importantly, the bilayer architecture (Al/Mo/PI vs. Mo/Al/PI). Domain boundaries in Al were found to correspond well with domain boundaries in the Mo, such as necking in Al with fracture in Mo or simultaneous fracture in both materials. The maximum stress achieved in the Mo layers during biaxial straining was also found to highly depend on the architecture and depend less on the Al film thickness. Results will demonstrate that the film architecture (layer order) is more important than the film thickness to enhance fracture resistance.

Ultrafast imaging analysis of femtosecond laser induced periodic nanoripples on Al film

Ultrafast imaging analysis of femtosecond laser induced periodic nanoripples on Al film

Stability of Al and Ag metallic thin film mirrors in a space environment under the implantation of low energy helium ions

The stability of aluminum (Al) and silver (Ag) metallic thin films (MTFs) under helium ion bombardment has been investigated in the laboratory to replicate the effect of alpha particle bombardment on spacecrafts and satellites in a space environment. The implanted helium ions have varying fluence and energies ranging from 0.5 - 3 keV. The helium ion fluence in the present study has been chosen according to 4 and 6 years journey of a solar orbiter. The reflectivity of Al and Ag MTFs is investigated over a wide range of electromagnetic radiation covering ultraviolet to near infrared (200 - 2500 nm), prior and post helium ion implantation. It is observed that the degradation in the reflectivity of the above-mentioned MTFs is reasonably low for helium ion implantation and no significant impact is observed on reflectivity of both (Al and Ag) MTFs in the investigation. This opens a channel of utilization of these MTFs to provide better protection for the optical components used in spacecrafts. Surface characterization such as surface roughness is carried out to investigate the surface morphology of MTFs prior and post implantation using atomic force microscopy (AFM). It is observed that the effect of implantation on surface morphology is in accordance with the experimental results of reflectivity. SRIM/TRIM simulations help to obtain the distribution profile and penetration depth of helium ions inside the Al and Ag MTFs.

First-principles simulation of the electronic stopping power of He ions in Al at finite temperature

The electronic stopping power of low-energy He projectile particles moving through an Al film under channeling and off-channeling trajectories and its temperature dependence are studied by combining the time-dependent density-functional-theory method with molecular dynamics simulations. The results show that the effect of target temperature on target stopping power can be divided into two aspects which are derived from the target electron and target ion. Below 500 K, the effect of the target-electron temperature on target stopping power is almost negligible. The influence of the target-ion temperature on target stopping power can be divided into two aspects which are derived from the displacement and energy dissipation of target ions. The displacement of the target ion can result in two trends that change the target stopping power: (1) The target ion is closer to the center of lattice channel after displacement, which leads to the increase of target stopping power. (2) The target ion is farther away from the center of the lattice channel after displacement, which leads to the decrease in target stopping power. As the temperature increases, the target ions are more likely to appear farther away from the lattice channel than closer to the center of the lattice channel, so the average displacement of the target ions will lead to a decreasing trend of the target stopping power with the increase of temperature. Under the condition of a given ionic density in the target, the energy dissipation capacity of target ions increases with the increase of temperature, resulting in the tendency of the target stopping power to increase with the increase of temperature. Our calculated stopping powers are in good agreement with the experimental data and reproduced the deviation from velocity proportionality found in the experimental results for a ${\mathrm{He}}^{+}$ ion in Al, validating our approach and numerical implementation.

Influence of Plasma Surface Treatment of Polyimide on the Microstructure of Aluminum Thin Films

The effects of plasma treatment of polyimide substrates on the texture and grain size distribution of aluminum thin films were studied. Oxygen-argon plasma treatment increased the average grain size and enhanced the (111) film texture. For short oxygen-argon plasma treatment times, the deposited Al films showed a (111) texture with a bimodal grain structure and even a {111}<112¯> type in-plane texture. The preferential nucleation and grain growth of (111) grains are discussed in terms of the interface energy anisotropy.

Signatures of superconducting triplet pairing in Ni–Ga-bilayer junctions

Ni–Ga bilayers are a versatile platform for exploring the competition between strongly antagonistic ferromagnetic and superconducting phases. We characterize the impact of this competition on the transport properties of highly-ballistic Al/Al2O3(/EuS)/Ni–Ga tunnel junctions from both experimental and theoretical points of view. While the conductance spectra of junctions comprising Ni (3 nm)–Ga (60 nm) bilayers can be well understood within the framework of earlier results, which associate the emerging main conductance maxima with the junction films’ superconducting gaps, thinner Ni (1.6 nm)–Ga (30 nm) bilayers entail completely different physics, and give rise to novel large-bias (when compared to the superconducting gap of the thin Al film as a reference) conductance-peak subseries that we term conductance shoulders. These conductance shoulders might attract considerable attention also in similar magnetic superconducting bilayer junctions, as we predict them to offer an experimentally well-accessible transport signature of superconducting triplet pairings that are induced around the interface of the Ni–Ga bilayer. We further substantiate this claim performing complementary polarized neutron reflectometry measurements on the bilayers, from which we deduce (1) a nonuniform magnetization structure in Ga in a several nanometer-thick area around the Ni–Ga boundary and can simultaneously (2) satisfactorily fit the obtained data only considering the paramagnetic Meissner response scenario. While the latter provides independent experimental evidence of induced triplet superconductivity inside the Ni–Ga bilayer, the former might serve as the first experimental hint of its potential microscopic physical origin. Finally, we introduce a simple phenomenological toy model to confirm also from the theoretical standpoint that superconducting triplet pairings around the Ni–Ga interface can indeed lead to the experimentally observed conductance shoulders, which convinces that our claims are robust and physically justified. Arranging our work in a broader context, we expect that Ni–Ga-bilayer junctions could have a strong potential for future superconducting-spintronics applications whenever an efficient engineering of triplet-pairing superconductivity is required.

3D Hypersound Microscopy of van der Waals Heterostructures.

The mechanical properties of the layered crystals in the few layer limit are largely unexplored. We employ a picosecond ultrasonic technique to access the corresponding mechanical parameters. Temporal variation of the reflection coefficient of the Al film that covers hBN/WSe2/hBN (where hBN is hexagonal boron nitride) heterostructures on a sapphire substrate after the femtosecond laser pulse excitation is carefully measured using an interferometric technique with spatial resolution. The laser pulse generates a broadband sound wave packet propagating perpendicularly to the Al plane and partially reflecting from the heterostructural interfaces. The demonstrated technique allows one to resolve a WSe2 monolayer embedded in hBN. We apply a multilayered model of the optoacoustical response to evaluate the mechanical parameters, in particular, the rigidity of the interfaces. Mapping of the Fourier spectra of the response visualizes different composition regions and may serve as an acoustic tomography tool. Almost zero phonon dissipation below 150 GHz demonstrates the van der Waals heterostructures' potential for nanoacoustical applications.

A Novel Synthesis of ZnO Nanoflower Arrays Using a Lift-Off Technique with Different Thicknesses of Al Sacrificial Layers on a Patterned Sapphire Substrate.

A novel method to synthesize large-scale ZnO nanoflower arrays using a protrusion patterned ZnO seed layer was investigated. Different thicknesses of aluminum (Al) film were deposited on the concave patterned sapphire substrate as a sacrificial layer. ZnO gel was layered onto the Al film as a seed layer and OE-6370HF AB optical glue was used as the adhesive material. A lift-off technique was used to transfer the protrusion patterned ZnO/AB glue seed layer to a P-type Si <100> wafer. The hydrothermal method using Zn(CH3COO)2 and C6H12N4 solutions as liquid precursors was used to synthesize ZnO nanoflower arrays on the patterned seed layer. X-ray diffraction spectra, field-effect scanning electron microscopy, focused ion beam milling (for obtaining cross-sectional views), and photoluminescence (PL) spectrometry were used to analyze the effects that different synthesis times and different thicknesses of Al sacrificial layer had on the properties of ZnO nanoflower arrays. These effects included an increased diameter, and a decreased height, density (i.e., number of nanorods in μm−2), total surface area, total volume, and maximum emission intensity of PL spectrum. We showed that when the synthesis time and the thickness of the Al sacrificial layer were increased, the emission intensities of the ultraviolet light and visible light had different variations.

Wireless Humidity Sensor for Smart Packaging via One‐step Laser‐Induced Patterning and Nanoparticle Formation on Metallized Paper

AbstractIn this work, a scalable and rapid process is developed for creating a low‐cost humidity sensor for wireless monitoring of moisture levels within packaged goods. The sensor comprises a moisture‐sensitive interdigitated capacitor connected to a planar spiral coil, forming an LC circuit whose resonant frequency is a function of environmental humidity. The sensor is fabricated on a commercially available metallized parchment paper through selective laser ablation of the laminated aluminum (Al) film on the parchment paper substrate. The laser ablation process provides a unique one‐step patterning of the conductive Al layer on the paper while simultaneously creating high surface area Al2O3nanoparticles within the laser‐ablated regions. The intrinsic humidity‐responsive characteristics of the laser‐induced Al2O3nanostructures provide the wireless sensor with a tenfold higher sensitivity to humidity than a similar LC resonant sensor prepared by conventional photolithography‐based processes on FR‐4 substrates. The frequency change of the sensor is observed to be a linear function within the range of 0−85% RH, providing an average sensitivity of −87 kHz RH−1with good repeatability and stable performance. Furthermore, the employment of scalable laser fabrication processes using commercially available inexpensive materials renders these technologies viable for roll‐to‐roll manufacturing of low‐cost wireless sensors for smart packaging applications.

Tailoring of embedded dielectric alumina film in AlGaAs epilayer by selective thermal oxidation

Vertical optical confinement is a critical requirement for a wide range of III-V photonic devices where Al2O3 material is the typical oxide used due to its low refractive index. This oxide layer can be formed from the oxidation of AlAs in an epitaxial GaAs/AlAs/GaAs or AlGaAs/AlAs/GaAs stack, with the advantage that the top layer remains single-crystalline. The thick film oxidation of AlAs is required for photonic applications. In this article, we report the oxidation processes developed to fully convert AlAs to AlOx films by analyzing both thin (100 nm) and thick (500 nm) AlAs films on GaAs (001) and 2° miscut GaAs (111)A substrate. Systematic microscopic characterization is performed to demonstrate the absence of any delamination at the oxide interfaces and the evolution of the diffusive oxidation process microscopically characterized is compared with an optical (µ-Raman) characterization. We demonstrate the selectivity of the AlAs oxidation process with respect to the active Al0.18Ga0.82As layer and the GaAs substrate. Finally, the proposed method is adopted to create a high refractive index contrast between the active optical material and the environment in the specific case of a III-V photonic crystal device, highlighting the potential of this approach for non-linear photonic applications.

Influence of growth temperature on light trapping properties of ZnO:Al nanorods grown on seed layers with crater-like structures

We report the growth and characterization of textured ZnO:Al (AZO) films with excellent optoelectronic properties. The surface morphology depended strongly on growth temperature; in particular, the effect of hydrothermal growth temperature on the optoelectronic properties and light trapping abilities of AZO nanorods grown on the crater-like AZO seed layers was investigated systematically. The AZO nanorods grown at 110°C were relatively dense, indicating that hydrothermal growth temperature can promote the growth of AZO nanorods along the direction perpendicular to the substrates. The difference in the height and orientation of AZO nanorods prepared at 100°C resulted in significant enhancement of light trapping abilities. In addition, the textured AZO films maintained low sheet resistance and high total transmittance.

Electron glass signatures up to room temperature in disordered insulators

This paper describes the observation of non-equilibrium field effects at room temperature in four disordered insulating systems: granular Al, discontinuous Au, amorphous NbSi and amorphous indium oxide thin films. The use of wide enough gate voltage ranges and a cautious analysis of the data allow us to uncover memory dips (MDs), the advocated hallmark of the electron glass, in the four systems. These MDs are found to relax slowly over days of measurements under gate voltage changes, reflecting the impossibility for the systems to reach an equilibrium state within experimentally accessible times. Our findings demonstrate that these electrical glassy effects, so far essentially reported at cryogenic temperatures, actually extend up to room temperature.

Optimization of the composition of Al-Mg alloy films for laser-driven flyer

Laser-driven flyer technology attracts tremendous interests owing to the advantage of generating high pressure shocks at a relative simple and low-cost way. However, low energy conversion efficiency between flyer and laser restricts the further application of this technology. To improve the energy conversion efficiency in a laser-driven flyer assembly, Al-Mg alloy films with three varied compositions were fabricated via magnetron sputtering. The composition, surface morphology, light absorption and thermal properties of the films were investigated using energy dispersive spectrometer, atomic force microscopy, ultraviolet–visible spectrophotometer and laser flash method. The reflectivity of the Al-Mg alloy film at 1064-nm wavelength decreases from 87.2% to 69.3% in comparison with Al film. Moreover, the thermal diffusivity of all the Al-Mg alloy films is lower than that of Al film and varies with the composition. The behavior of the plasma induced shock wave evolution was investigated by shadowgraph imaging technique, indicating that the spatial and temporal evolution of the shock wave agrees well with the form of a Taylor-Sedov spherical shock and the calculated shock wave energy of the Al-Mg alloy films can reach up to 1.19 times that of Al film. Furthermore, the ability to launch a 17-μm-thick Al flyer was characterized by a Photonic Doppler Velocimetry, and there is a 20.9% and 46.12% increase in the terminal velocity and energy conversion efficiency of the Al flyers for Al-Mg alloy films compared with Al film, respectively. Therefore, the performance of laser-driven flyer can be significantly improved by adjusting the composition of Al-Mg alloy films.

Effect of Al-Doped on the Electrical Properties of Nb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt; Film Prepared by DC. Plasma Sputtering Technique

Thin films of Niobium oxide (Nb2O5) co-doped with (0.5, 1, and 1.5) %wt. percentages of Aluminum (Al) were prepared on glass substrates by DC. Sputtering plasma technique. The effects of Al concentration on structural, surface morphology, optical and electrical properties of transparent were investigated. Polycrystalline structures without any second phases were observed with preferential orientations along the (001), (100), (101), (002), and (111) planes. The crystalline size as determined from the (001) peaks lay in the range (20-50) two theta and all films of Nb2O5: Al films have pseudohexagonal phase. It was observed that Al doping reduced the crystal size but at the samples 0.5%Al the crystalline size increased slightly. Also, it's observing from SEM images an increase in particle size after Al-doped. The minimum resistivity was found to be 4.79 x104 (Ω.cm) for the Nb2O5 doped with 1.5%Al concentration and maximum resistivity was found to be (4.86 x104 (Ω.cm) for the pure Nb2O5. The doping to the optimum level of 1.5% Al concentration increases the electrical conductivity of Nb2O5. The mobility decreased but the sample 1.5%Al concentration increases and the carrier concentration increased with increasing the doping with Al but the sample 1.5%Al concentration decreases. The analysis of Hall coefficient showed the Nb2O5: Al films were n-type.

Structural and photodetector characteristics of Zn and Al incorporated ZnGa2O4 films via co-sputtering

Zn and Al-incorporated ZnGa2O4 films (ZGO:Zn and ZGO:Al) were deposited on sapphire substrates using radio-frequency magnetron sputtering in this work. The effects of Zn and Al incorporation on the microstructural and optoelectronic properties of ZGO films were systematically investigated and compared with each other. This investigation revealed that incorporation of Al enhanced the characteristics of the ZGO film, whereas incorporation of Zn affected the characteristics of the ZGO film. The annealed ZGO:Al film revealed high crystallinity, average transmittance of >82%, and wide-bandgap of 5.18 eV. First principles calculations were performed to investigate the defects associated with the ZGO:Al structure. The Al incorporated ZGO PD exhibited an optimum metal–semiconductor–metal photodetector achievement with a photo/dark current ratio of ∼104 order and responsivity of 3.01 A/W (at 3 V and 220 nm), demonstrating the responsivity of ZGO PD (0.25 A/W) can be increased up to 12 times by incorporating Al in ZGO films. This enhancement in the characteristics of the ZGO:Al film can be ascribed to the high crystalline nature and the formation of significant amount of oxygen vacancies in this film. These results demonstrate the potential of Al incorporated ZGO films in wide-bandgap devices and deep-ultraviolet applications.