Aluminum Thin Films Research Articles

Machine learning-based run-to-run control of a spatial thermal atomic layer etching reactor

In response to the next technological revolution, atomic layer processes have emerged to produce high-performing, thin-film semiconductor materials. To overcome the long purging times required for conventional atomic layer processes, spatial atomic layer processes have been recognized for their ability to reduce processing times; however, they lack characterization and control. This research aims to construct two novel run-to-run (R2R) control systems using a machine learning model with an artificial neural network (ANN) and an exponentially weighted moving average (EWMA) method for the spatial thermal atomic layer etching (SALE) of aluminum oxide thin films. The two R2R controllers are used in conjunction with a multiscale computational fluid dynamics model of a SALE process with various disturbances to test their effectiveness. Closed-loop simulation results demonstrate that the ANN-based R2R control system reduces etching per cycle variability, maintains the process output within a small region around the setpoint, and outperforms the traditional EWMA-based R2R control system in efficiency.

Formation of adsorbent thin layer on aluminum sheet by using a silane coupling agent for vapor adsorption refrigeration system

Recently adsorbent coating technique was pointed for the aluminum fin in the ad/desorption chamber of an adsorption heat pump/chiller. This research proposes an aluminum substrate adsorbent coating method including examination of characteristics and adsorption isotherms. An aluminum substrate was dipped into the adsorbent-suspended solution to form a composite adsorbent layer on its surface. The adhesion of the adsorbents onto the aluminum substrate was evaluated by the peeling test. The aluminum oxide film on the aluminum substrate promotes the adhesion between adsorbent and aluminum substrate referring to the residual ratio. The suitable anodization condition of the aluminum oxide film is 150 volts for 2 min yielding the thin aluminum oxide film layer upon the aluminum substrate 67 nm of thickness. The suspended adsorbent solution was prepared at a mass ratio of 3 g-adsorbent g−1-coupling agent that provided the thickest adsorbent-coated layer by dip coating. Zeolite AQSOA-Z01 is a good choice to coat the aluminum substrate because it satisfied the adhesion strength and specific cooling capacity of 239.4 kJ kg−1 in the operating relative pressure range of adsorption heat pumps/chillers.

Chemical Stability of Atomic Layer Deposited (ALD) Alumina Thin Films in Aqueous Solutions

Aluminum oxide (alumina) thin films deposited through atomic layer deposition (ALD) are of great interest in chemical barrier and corrosion protection applications. However, the stability of ALD alumina in aqueous solutions is still not fully understood. Due to its metastable amorphous phase, the hydration and degradation behavior of ALD alumina films behaves differently from its crystalline Al2O3 counterpart. A full understanding of why these films hydrate and/or dissolve requires the exploration of different deposition conditions and ion content in solutions used. This talk will discuss efforts to further elucidate the hydration and dissolution behavior of ALD alumina films. For this study, alumina thin films were ALD deposited onto silicon substrate at 150 °C using trimethylaluminum (TMA) and H2O. These films were then studied in Type 1 DI water, 2M NaCl, .5M NaCl, and .1M NaCl solutions at room temperature. Films were gently dried using a nitrogen gun and thickness was measured using a Cauchy ellipsometry model. After 15 days of immersion in Type 1 DI water, significant thickness growth is observed at twice (27 days) and 2.5 times (33 days) the normalized thickness. Similar hydration is not observed in salt-containing aqueous solutions nor upon exposure to air. We will discuss the possible effects of CO2 dissolution and carbonate formation as well as ionic species on the hydration and dissolution processes of these alumina films. Finally, we will show how a post-ALD plasma treatment to the film’s surface alters the hydration and dissolution behavior, improving stability in several aqueous conditions.

Features of the porous morphology of anodic alumina films at the initial stage of disordered growth

A characteristic feature of disordered porous anodic film growth at the initial stage of aluminum anodizing was revealed by varying the electrolyte type and anodizing voltage. The samples were obtained by the electrochemical oxidation of thin aluminum films (100 nm thick) on SiO2/Si substrates in a 0.3 M oxalic acid at 10–50 V and were studied by SEM. The ImageJ analysis of the images revealed the simultaneous development of two large groups of pores: major pores with a large diameter and minor pores with a smaller diameter. When anodizing in oxalic acid at 10–50 V, it has been shown that the ratio of the diameters of the major and minor pores remains constant and is about 1.17. Using a geometric model, we demonstrated that the centers of the minor pores are located inside the elementary hexagonal cell formed by the centers of the major pores. Moreover, our results are very close to the theoretical value of 2/√3. At the initial stage of disordered pore growth, the development of minor pores rather than major pores is not a random process and is determined by energy-efficient conditions for the development of pores inside the hexagonal cells formed by the major pores. The increase in compressive mechanical stress in the anodic film leads to an interruption in the development of such pores.

Oxidized thin aluminum films used as the polarized liquid-liquid interface support for norcocaine detection

In this work, the surface of thin (around 100 nm thick) porous aluminum film was thermally oxidized and used as the electrified liquid-liquid interface support. Constructed platforms provided quasi-sigmoidal voltammetric characteristic for the forward interfacial transport of all studied model ions (quaternary ammonium cations) typical for the microscopic liquid-liquid interfaces supported with pore(s) with a diameter exceeding the support thickness. Thin aluminum films before and after heat treatment were characterized using ion transfer voltammetry, scanning electron microscopy, optical profilometry and contact angle measurements. Finally, the utility of the constructed devices was verified during voltammetric norcocaine sensing in artificial and spiked real urine samples. Norcocaine gave a clear signal recorded within the available potential window and could be detected from the concentration equal to around 10 µM. The parameters such as limit of detection, limit of quantification, detection sensitivity, diffusion coefficient, and water/1,2–dichloroethane partition coefficient are also provided and tabulated.

Spectrophotometric Characterization of Thin Semi-Transparent Aluminum Films Prepared by Electron Beam Evaporation and Magnetron Sputtering

Aluminum thin films with thicknesses between approximately 10 and 60 nm have been deposited by evaporation and sputtering techniques. Layer characterization focused on reflectance, optical constants, and surface quality. Reflectance fits have been performed using a merger of three standard dispersion models, namely the Drude model, the Lorentzian oscillator model, and the beta-distributed oscillator model. A thickness dependence of the optical constants could be established in the investigated thickness range.

Angle and polarization dependent coupling of surface plasmon and gap modes in plasmonic gap metasurfaces

Plasmonic metasurfaces with coupled gap and collective surface plasmon polariton modes are of interest for a variety of optoelectronic devices. The coupling between the gap and plasmon polariton modes leads to tunable extinction spectra that provide flexibility when used in various photonic applications. We demonstrate both experimentally and numerically the polarization and angle dependent tunable optical extinction spectra of a gold nanoparticles monolayer on a glass substrate in close proximity to a thin aluminum film. The monolayer of gold nanoparticles is separated from the aluminum thin film by a dielectric shellac spacer. We observe three angle and polarization dependent peaks in the extinction spectra when the shellac spacer is 10 nm. The three peaks degenerate into one hybrid mode when the spacer thickness is 30 nm. By using a finite-difference-time-domain (FDTD) numerical method, we confirm the position of both the collective surface plasmon and the gap modes. Changing the polarization of the incident light leads to a change of the width and a shift of the wavelength of the peaks.

Photonic-plasmonic hot-electron-based photodetection with diffracted-order-resolved leaky plasmonic mechanisms

Abstract Although hot-carrier-based photodetection using plasmonic effects has been widely investigated, photodetectors of this type with an external quantum efficiency (EQE) > 1 % ${ >}1\%$ and an active area of < 1 ${< }1$ mm2 remain out of reach even in the visible frequencies. In this work, a novel hot-electron-based, non-trench-type photodetector exploiting pure photoexcitation in a thin aluminum (Al) film and leaky plasmonic modes at and between its heterojunctions is proposed, analyzed, and experimentally demonstrated. Combining diffracted-order-resolved analytical analysis and numerical computations unravels the optical absorption mechanism of the innovative design. Leaky surface plasmon resonance (with leakage radiation into the air) produced by a propagating diffracted order and quasibound supermodes (with power leakage via coupled gap plasmon polariton and bound surface plasmon polariton modes) excited by evanescent diffracted orders are shown to significantly contribute to the absorptance in the preferred thin Al film where hot electrons are generated. At 638.9 nm and electric bias −0.9951 V, the measured per-unit-area responsivity, detectivity, and the external quantum efficiency reach 298.1444 μA/mW/mm2, 4.3809 × 109 cm Hz1/2/W, and 2.6878%, respectively, from an active area of 4.6457 × 10−2 mm2. The performance is among the best of those previously reported operating at similar wavelengths and biases. The RC time constant is estimated to be about 1.673 μs from the current-voltage measurements. The physical insight into the innovative, experimentally demonstrated device could lay the groundwork for the practical use of low-voltage, metal-based photodetection.

Novel structural design of wearable thermoelectric generator with vertically oriented thermoelements

Energy harvesting technology has become important for wearable electronics, where a continuous power supply is essential. Although a wearable thermoelectric generator (TEG) is a promising option in this context, maintaining a substantial temperature gradient (ΔT) between the hot and cold sides of the TEG and a low thermal contact resistance between the TEG and the human body is challenging due to its structural configuration. Herein, a novel structural solution to these problems has been presented with vertically aligned p-type poly (3,4-ethylene-dioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) thin film and n-type aluminum wire-based thermoelements integrated wearable TEG. The developed wearable TEG with five pairs of thermoelements reported an open-circuit voltage (Voc) of up to 1.46 mV when applied to the wrist. Subsequently, the generator was tested at a higher temperature, and the characterization results revealed that the TEG produced a maximum Voc of 5.15 mV at a ΔT of 80 °C. Inclusively, the TEG provided a maximum output power and an output power density of ∼2.4 nW and 1.5 nWcm−2, respectively, at a ΔT of 80 °C. The proposed TEG design concept demonstrates elevated performance with great flexibility and has the potential to act as a viable alternative for next-generation energy harvesting devices.

Surface processes on thin layers of black aluminum in ultra-high vacuum

Thin films of black aluminum (B–Al) were prepared by pulsed DC magnetron sputtering in a mixture of argon + nitrogen (Ar + N2) gases with concentration of nitrogen 6%. At this concentration the process of anti-reflective surface (UV to near IR diffuse reflectance below 4%) formation is favored. The properties of such layers have been investigated using methods allowing to follow near-surface processes by means of thermally stimulated desorption (TSD) and thermally stimulated exo-electron emission (TSEE) in ultra-high vacuum conditions (p < 2.10−7 Pa). It is shown that at certain temperatures some adsorbed particles are desorbed and at the same time negative charges are emitted. In some cases, the emission sites are common. Comparison of TSEE measurements at three different excitations (α, proton irradiation and UV illumination) was performed. Common measurements together with calculations of the activation energies of desorption as well as electron emission sufficiently describe the centers responsible for these processes. In particular, the atomic oxygen Oat, the AlOH radical and partly the atomic nitrogen Nat together with the AlN radical are shown to play a significant role in this surface process.

Photonic Sintering of Oxide Ceramic Films: Effect of Colored FexOy Nanoparticle Pigments

Alumina and zirconia thin films modified with colored nano-FexOy pigments were sintered by the flash-lamp-annealing method. We selected a nano α-Al2O3 and micron α-Al2O3 bimodal mixture as the base precursor material, and we doped it with 5 vol% of FexOy red/brown/black/yellow pigments. The coatings were deposited from nanoparticle dispersions both on glass and on flexible metal foil. The characteristics of the thin films obtained with the use of various additives were compared, including the surface morphologies, optical properties, crystallinities, and structures. Flash lamp annealing was applied with the maximum total energy density of 130 J/cm2 and an overall annealing time of 7 s. Based on the simulated temperature profiles and electron-microscopy results, a maximum annealing temperature of 1850 °C was reached for the red Al2O3: Fe2O3 ceramic film. The results show that red α-Fe2O3 pigments allow for the achievement of maximum layer absorption, which is effective for flash lamp sintering. It was also possible to use the selected red α-Fe2O3 particles for the flash-lamp-assisted sintering of ZrO2 on a 30 µm-thin flexible stainless-steel substrate.

Spin-Mixing Enhanced Proximity Effect in Aluminum-Based Superconductor-Semiconductor Hybrids.

In superconducting quantum circuits, aluminum is one of the most widely used materials. It is currently also the superconductor of choice for the development of topological qubits. However, aluminum-based devices suffer from poor magnetic field compatibility. Herein, this limitation is resolved by showing that adatoms of heavy elements (e.g., platinum) increase the critical field of thin aluminum films by more than a factor of two. Using tunnel junctions, it is shown that the increased field resilience originates from spin-orbit scattering introduced by Pt. This property is exploited in the context of the superconducting proximity effect in semiconductor-superconductor hybrids, where it is shown that InSb nanowires strongly coupled to Al/Pt films can maintain superconductivity up to 7T. The two-electron charging effect is shown to be robust against the presence of heavy adatoms. Additionally, non-local spectroscopy is used in a three-terminal geometry to probe the bulk of hybrid devices, showing that it remains free of sub-gap states. Finally, it is demonstrated that proximitized semiconductor states maintain their ability to Zeeman-split in an applied magnetic field. Combined with the chemical stability and well-known fabrication routes of aluminum, Al/Pt emerges as the natural successor to Al-based systems and is a compelling alternative to other superconductors, whenever high-field resilience is required.

Study of Etch Stop Layer on Characteristics of Amorphous Aluminum Oxide Thin Film

To protect the active layer, which are inter layer dielectrics (ILD) and metal lines, from being damaged by UV laser during the etching process, etch stop layers (ESL) are used in patterning process of the integrated circuits (ICs) fabrication in back end of line (BEOL). The ESL material should have a higher etch selectivity than the active layer. Therefore, it must have a low dielectric constant and high chemical resistance. Aluminum oxide compounds (AlOx, AlOC, AlON, etc.) are highly suitable for use as ESL due to the low dielectric constant between about 4 and 9, high etch selectivity, high density (2.5-3.8 g/cm3) and pattern transfer capability. We focused on lowering the dielectric permittivity and increasing the density by controlling the precursor/reactant pulsed time of atomic layer deposition (ALD).

Analysis of Deterioration Mechanism of Al-Pouch Film Used As Packaging Materials for Lithium Ion Batteries

Generally, lithium ion batteries (LIBs) can be divided into three different types: cylindrical, prismatic, and pouch-type LiBs with regard to the packaging form. Contrary to cylindrical or prismatic type batteries, pouch-type battery uses a pouch as an exterior material to protect inside of the cell from external influences, and have a metal lead-taps to receive and deliver electricity from external source. To safeguard the inside of the lithium ion battery, the pouch must have high resistance to gas and moisture permeability and excellent corrosion resistance to electrolytes.However, Al-pouch can be prone to contamination from electrolyte containing lithium salt during the electrolyte injection process, a key part of their manufacturing process. This electrolyte contamination can be fatal to the long-term reliability or durability of pouch-type LiBs. In this study, we investigate deterioration behavior of aluminium pouch film due to the electrolyte contamination. In order to clarify deterioration mechanism of Al-pouch film, we prepared exposure test of Al-pouch film and dummy cell samples which were stained by electrolyte droplet (LiPF6 in EC:EMC=1:2 (v/v) + 2 % VC). The change of micro-structure of the samples was tracked during 20 weeks by storing them under accelerated test conditions (RH 95 %, 60 ℃). As a result, we find out severe defect of the samples of Al-pouch film by damage to outermost nylon film and aluminium layer, and confirmed the effects on the battery after the defects occurred.To understand such phenomena, the micro-defect of Al-pouch films was observed by characterization techniques (XRD, FT-IR, SEM, EDX). We demonstrate that outermost layer of nylon film is damaged when it reacts with an electrolyte containing LiPF6 salt such as decreasing crystallinity, surface crazing, forming microdefects. The degradation of nylon film leads to severe surface cracking, followed by nylon locally peeling off from the Al-pouch. Peeling of the nylon film causes to expose the underlying thin aluminum film that constitute the middle layer of Al-pouch. Once partially exposed to the atmosphere, severe pitting corrosion of the aluminum film occurs due to atmospheric moisture and acids produced by LiPF6. Finally, a large amount of moisture to easily penetrate pouch-type LiBs through these corroded pits, showing the detrimental effects of electrolyte contamination on pouch-type LiBs’ long-term durability and reliability. Figure 1

Microscopic quantum point contact formation as the electromigration mechanism in granular superconductor nanowires

Granular aluminium is a high kinetic inductance thin film superconductor which, when formed into nanowires can undergo an intrinsic electromigration process. We use a combination of experimental and computational approaches to investigate the role of grain morphology and distribution in granular aluminium thin films, when formed into nanowire constrictions. Treating the granular aluminium film as a network of randomly distributed resistors with parameters motivated by the film microstructure allows us to model the electrical characteristics of the nanowires. This model provides estimates of the dependence of sheet resistance on grain size and distribution, and the resulting device to device variation for superconducting nanowires. By fabricating a series of different length nanowires, we study the electromigration process as a function of applied current, and then compare directly to the results of our computational model. In doing so we show that the electromigration is driven by the formation of quantum point contacts between metallic aluminium grains.

Autofluorescence Imaging of Living Yeast Cells with Deep-Ultraviolet Surface Plasmon Resonance

Autofluorescence in living cells on aluminum thin film was excited with deep-ultraviolet surface plasmon resonance (deep-UV SPR). Deep-UV SPR under aqueous medium was excited with Kretschmann configuration by using a sapphire prism. Deep-UV SPR is one of the promising techniques for high-sensitive autofluorescence imaging of living cells without staining. Label-free observation is significant for the structural analysis of living cells. We demonstrated the high-sensitive autofluorescence imaging of living yeast cells with deep-UV SPR. We applied a high refractive index prism, such as sapphire, which is suitable for the observation of specimens in aqueous medium, to excite deep-UV SPR. Although typical autofluorescence from living cells is buried in background noise, deep-UV SPR enhances the autofluorescence signal. The deep-UV SPR excitation of an aluminum thin film through a sapphire prism was investigated theoretically and experimentally. It showed that the fluorescence intensities are increased 2.8-fold. Deep-UV SPR enhanced the autofluorescence of cell structures, and yeast cells were found to be very sensitive. As a result, for water-immersed specimens, the sapphire-prism-based Kretschmann configuration excited SPR in deep-UV. Findings from this study suggest that deep-UV SPR can be considered an effective technique for attaining high-sensitivity observation of biological samples.

New method for the determination of photoabsorption from transmittance measurements in the extreme ultraviolet.

We have developed a new method for the determination of photoabsorption at extreme ultraviolet wavelengths longer than 20 nm, where reliable refractive index values are sparse or non-existent. Our method overcomes the obstacle of multiple reflections that occur inside thin films in this spectral range, which up until now has prevented the accurate determination of photoabsorption from transmittance measurements. We have derived a mathematical expression that is independent of internal reflection amplitudes, while taking advantage of the transmittance oscillations stemming from such reflections. The method is validated on measurements of aluminum thin films. This advance will enable accurate refractive index values for many important materials for optical instrumentation, thus facilitating high-priority research on topics including coherent light sources, planetary and solar physics, and semiconductor manufacturing.

Characterization of Aluminum Oxide Thin Films Formed on Surfaces of FeCo-V Alloys by Annealing under a Low Partial Pressure of Oxygen

Characterization of Aluminum Oxide Thin Films Formed on Surfaces of FeCo-V Alloys by Annealing under a Low Partial Pressure of Oxygen

Improving the Stability of Lithium Aluminum Germanium Phosphate with Lithium Metal by Interface Engineering.

Lithium aluminum germanium phosphate (LAGP) solid electrolyte is receiving increasing attention due to its high ionic conductivity and low air sensitivity. However, the poor interface compatibility between lithium (Li) metal and LAGP remains the main challenge in developing all-solid-state lithium batteries (ASSLB) with a long cycle life. Herein, this work introduces a thin aluminum oxide (Al2O3) film on the surface of the LAGP pellet as a physical barrier to Li/LAGP interface by the atomic layer deposition technique. It is found that this layer induces the formation of stable solid electrolyte interphase, which significantly improves the structural and electrochemical stability of LAGP toward metallic Li. As a result, the optimized symmetrical cell exhibits a long lifetime of 360 h with an areal capacity of 0.2 mAh cm−2 and a current density of 0.2 mA cm−2. This strategy provides new insights into the stabilization of the solid electrolyte/Li interface to boost the development of ASSLB.

Temperature-controlled spatiotemporally modulated phononic crystal for achieving nonreciprocal acoustic wave propagation.

We computationally investigate a method for spatiotemporally modulating a material's elastic properties, leveraging thermal dependence of elastic moduli, with the goal of inducing nonreciprocal propagation of acoustic waves. Acoustic wave propagation in an aluminum thin film subjected to spatiotemporal boundary heating from one side and constant cooling from the other side was simulated via the finite element method. Material property modulation patterns induced by the asymmetric boundary heating are found to be non-homogenous with depth. Despite these inhomogeneities, it will be shown that such thermoelasticity can still be used to achieve nonreciprocal acoustic wave propagation.