Aluminum Thin Films Research Articles

Effect of various additives on aluminum oxide thin films prepared by dip coating, thermal behavior, kinetics and optical properties

Aluminum oxide thin films attract research interest due to their properties. Aluminum acetate was used as an Al source with acetic acid, oxalic acid, and nitric acid as additives. The transmittance and the thickness of the films strongly depend on the additives, with the approximate bandgap energy changing from 5 ev to 5.4 ev. The aluminum oxide film deposited by dip-coating is presented great uniform surface morphology. The knowledge of the degradation kinetics of materials is essential for investigating the thermal stability of compounds. The acetic acid thin film proved to be the most efficient additive by demonstrating interesting optoelectronic properties. The thin films deposited by dip-coating were characterized by using X-ray grazing incidence diffraction, SEM, UV-Visible spectroscopy. Gamma aluminum oxide thin films prepared by acetic acid can be a good candidate for a wide range of optical applications.

Influence of synthesis parameters and thermal annealing on grain size of polycrystalline aluminum thin film

The thin polycrystalline aluminium films were synthesized on monocrystalline silicon substrates by ion-plasma sputtering. The synthesis was carried out at temperatures of 80 and 160°C and deposition rate of 10 and 110 nm/min. As-deposited films were annealed for 15 h at 550°C. The morphology of aluminium films before and after annealing was obtained using SEM images. The surfaces of as-deposited Al thin films, synthesized at high temperature, were uneven, while for low temperature films they were smooth enough with Al hillocks on the top of the film. After thermal annealing, morphology of the films was changed slightly. XRD patterns were obtained to calculate the average Al grain size of as-deposited and annealed films. The XRD analysis showed that an increase in the synthesis temperature leads to an increase in the average grain size from 50 to 84 nm and that increase in the rate of Al film synthesis leads to an increase in the average grain size from 50 to 63 nm. As the result of annealing, the average grain size increased for all samples and the final meaning was from 78 to 140 nm.

Orientation Gradients in Rapidly Solidified Pure Aluminum Thin Films: Comparison of Experiments and Phase-Field Crystal Simulations.

Rapid solidification experiments on thin film aluminum samples reveal the presence of lattice orientation gradients within crystallizing grains. To study this phenomenon, a single-component phase-field crystal (PFC) model that captures the properties of solid, liquid, and vapor phases is proposed to model pure aluminium quantitatively. A coarse-grained amplitude representation of this model is used to simulate solidification in samples approaching micrometer scales. The simulations reproduce the experimentally observed orientation gradients within crystallizing grains when grown at experimentally relevant rapid quenches. We propose a causal connection between defect formation and orientation gradients.

Laser blow-off with photodiode detection system at the helically symmetric experiment

A laser blow-off (LBO) system has been installed in the HSX stellarator to investigate impurity transport. A Nd:YAG laser is used to ablate a target area on a glass slide that has been coated with a thin film of aluminum and rapidly deposits a small, controlled quantity of aluminum atoms into HSX plasma. To study the radial propagation and confinement of the injected aluminum impurities, time-resolved emission measurements are made using a 20 channel AXUV photodiode detection system. The LBO system has achieved its design purpose, most notably the ability to make controlled impurity injection without significant perturbation to the background plasma. A detailed description of the setup as well as initial results of operation are presented.

Predicting Fracture Propensity in Amorphous Alumina from Its Static Structure Using Machine Learning.

Thin films of amorphous alumina (a-Al2O3) have recently been found to deform permanently up to 100% elongation without fracture at room temperature. If the underlying ductile deformation mechanism can be understood at the nanoscale and exploited in bulk samples, it could help to facilitate the design of damage-tolerant glassy materials, the holy grail within glass science. Here, based on atomistic simulations and classification-based machine learning, we reveal that the propensity of a-Al2O3 to exhibit nanoscale ductility is encoded in its static (nonstrained) structure. By considering the fracture response of a series of a-Al2O3 systems quenched under varying pressure, we demonstrate that the degree of nanoductility is correlated with the number of bond switching events, specifically the fraction of 5- and 6-fold coordinated Al atoms, which are able to decrease their coordination numbers under stress. In turn, we find that the tendency for bond switching can be predicted based on a nonintuitive structural descriptor calculated based on the static structure, namely, the recently developed "softness" metric as determined from machine learning. Importantly, the softness metric is here trained from the spontaneous dynamics of the system (i.e., under zero strain) but, interestingly, is able to readily predict the fracture behavior of the glass (i.e., under strain). That is, lower softness facilitates Al bond switching and the local accumulation of high-softness regions leads to rapid crack propagation. These results are helpful for designing glass formulations with improved resistance to fracture.

A flexible aluminum thin film electrode with enhanced electrical property and stability via a facial method

A flexible aluminum thin film electrode with enhanced electrical property and stability via a facial method

Atomic layer deposition of alumina onto yolk-shell FeS/MoS2 as universal anodes for Li/Na/K-Ion batteries

Transition metal sulfides are regarded as a category of promising electrodes for alkaline ion batteries because of their high theoretical capacities, fast ionic conductivity and low cost, but they also face many challenges on large volume changes, sluggish kinetics and instability of solid electrolyte interphase (SEI). To tackle these issues, this work designs iron sulfide/molybdenum disulfide (FeS / MoS2) yolk-shell sphere electrodes coated by few-nanometer thick alumina film. Such alumina film is adopted to minimize side reactions, promote the formation of stable SEI, and enhance the mechanical stability of the electrode. Specifically, when used as anode materials at 100 mA g−1 in Li/Na/K-ion batteries, the coated electrode (ALD-40-E) can deliver reversible capacities of 1007, 570 and 367 mAh g−1 after 100 cycles, respectively, which are substantially larger than those of bare FeS / MoS2 electrode (ALD-0-E: 538, 311 and 213 mAh g−1) and FeS / MoS2 with direct alumina coating on powder surface (ALD-40-P: 429, 116 and 86 mAh g−1). Good electrochemical properties are mainly ascribed to the yolk-shell structure, and the alumina thin film on the electrode, which work synergistically to maintain the electrical contact, facilitate the ion/electron diffusion paths, accommodate volume change and preserve structural stability.

Microscopic and data-driven modeling and operation of thermal atomic layer etching of aluminum oxide thin films

With increasing demands for microchips and increasing needs in the nano-scale semiconductor manufacturing industry, atomic layer etching (ALE) has been developing into a critical etching process. Unlike its counterpart in the film deposition domain, atomic layer deposition (ALD), which has been extensively studied, ALE has not been fully studied yet from a modeling and operation point of view. Therefore, this work develops microscopic models to characterize the thermal ALE process of aluminum oxide thin films with two precursors (hydrogen fluoride and trimethylaluminum). First, the reaction mechanisms for the two half-cycles for the thermal ALE process are established. Electronically predicted geometries of the Al2O3 structure with two precursors are optimized. Along with the optimized geometries, possible reaction pathways are proposed and calculated by density functional theory (DFT)-based electronic structure calculations. The proposed reaction paths and their kinetic parameters are used in a kinetic Monte Carlo (kMC) algorithm, which is capable of capturing the features of the thermal ALE of aluminum oxide. The kMC simulation provides an etch time for the given steady-state operating conditions, which are validated via comparison with available experimental results. Finally, data sets collected from the kMC simulation are used to train a feed-forward artificial neural network (FNN) model. The trained FNN model accurately predicts an etch time and dramatically reduces the computation time compared to the kMC simulation, thereby making it possible to carry out real-time, model-based operational parameter calculations. In addition, the trained FNN model can be used to establish a feasible range of operating conditions without demanding experimental work.

Effect of Al doping on morphology and optical properties of spray pyrolized MgO thin films

Thin films of magnesium oxide (MgO) and aluminium (Al) doped MgO were deposited onto glass substrate at 350 °C by spray pyrolysis technique. The microstructure, morphology and optical properties of the MgO films have been investigated and characterized as a function of Al doping concentration (0–2) mol%. X-ray diffraction study confirms the successful fabrication of MgO thin films. The surface morphology of the films reveals that the morphology of the MgO films greatly changes with Al doping concentration. The optical properties like optical transmittance, optical band gap, refractive index, extinction coefficient, real & imaginary part of the dielectric constant, electron energy loss function and optical conductivity have been characterized and discussed. It has been found that the optical properties of MgO films have been changes significantly with Al doping concentration.

Influence of helium incorporation on growth process and properties of aluminum thin films deposited by DC magnetron sputtering

The effect of helium content on the morphology, crystallinity, and composition of aluminum films was investigated by depositing He-loaded Al films onto Si substrates via direct current (DC) magnetron sputtering in different Ar/He plasma mixtures. Three different plasma regimes were identified depending on the percentage of He in the gas phase. For a low He to total gas ratio (ΓHe ≤ 70%), the plasma is dominated by argon, where Ar+ ions contribute to sputter out the target atoms. The films deposited in this regime exhibited the classical dense columnar structure and contain very low amount of He (below 2%). Then, as ΓHe increases, helium ions begin to be formed and more fast He neutrals reach the substrate, affecting the film growth. As He amount increased in the gas phase up to 95%, the proportion of He inserted in the films rised up to ⁓15 at. %. Moreover, bubbles/porosity were formed inside the films; those obtained in pure He plasma presented a highly porous fiberform nanostructure. All results confirmed that the modification of the film characteristics was related to the change of the deposition conditions when Ar was replaced by He and to the insertion/release mechanisms of He during the growth.

Modification of Steel Surfaces with Nanometer Films of Al2O3 and TiO2 Decreases Interfacial Adhesion to Polymers: Implications for Demolding Shape-Engineered Polymer Products

Alumina (Al2O3) and titanium dioxide (TiO2) thin films were deposited by the atomic layer deposition technique on steel substrates used in the polymer injection molding industry. The modified steel surfaces were systematically characterized by SEM, EDS, AFM, XPS, and OCA. Surface energy values were obtained to predict the demolding behavior of modified steel surfaces when in contact with different polymers. The lowest surface energy was obtained using Al2O3 and H2O as an oxygen source on 1.2311 steel (1.2311-Al-H), representing a 30% decrease when compared to 1.2311 bare ground steel. Results were confirmed by the simulation of polymer–mold interaction. The produced polycarbonate surface presents defects with an average diameter of 0.5 μm that result from mimicking of the Al2O3 textured surface (contrasting with the defects with a diameter of 1.85 μm using bare 1.2311 steel). The best compromise between surface energy and roughness was obtained using the TiO2-H2O film (1.2311-Ti-H). The modified steel with TiO2 ALD coating produced the smoothest polymeric surface. The modification of steel surfaces with nanometer films of Al2O3 and TiO2 decreased the interfacial adhesion to polymers, which had implications for demolding shape-engineered polymers, a requirement for high-aspect-ratio parts.

Single germanene phase formed by segregation through Al(111) thin films on Ge(111)

We have obtained single phase monolayer germanene on aluminum (111) thin films grown on a germanium (111) template by atomic segregation epitaxy, a preparation method differing from molecular beam epitaxy used in previous works. This 2 × 2 reconstructed germanene phase matching an Al(111)3 × 3 supercell has been prepared in large areas upon annealing at 430 °C. Detailed studies have been carried out using scanning tunneling microscopy (STM), low-energy electron diffraction, Auger electron spectroscopy, and synchrotron radiation photoemission spectroscopy. First-principles calculations based on the density function theory along with atomic-scale STM images reveal the atomic structure with one protruding Ge atom per 2 × 2 germanene supercell and a characteristic dispersing band originating from the germanene sheet slightly coupled to the first layer Al atoms underneath. Instead, upon annealing at lower temperatures, multi-phase regions comprise twisted germanene domains in correspondence with an Al(111)√7×√7 R ± 19.1° superstructure as obtained in previous studies.

Magnetron sputtering technique for analyzing the influence of RF sputtering power on microstructural surface morphology of aluminum thin films deposited on SiO2/Si substrates

In this research, aluminum (Al) thin films were deposited on SiO2/Si substrates using RF magnetron sputtering technique for analyzing the influence of RF sputtering power on microstructural surface morphologies. Different sputtering RF powers (100–400 W) were employed to form Al thin films. The characteristics of deposited Al thin films are investigated using X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and Fourier-transforms infrared (FTIR) spectroscopy. The X-ray diffraction (XRD) results demonstrate that the deposited films in low sputtering power have amorphous nature. By increasing the sputtering power, crystallization is observed. AFM analysis results show that the RF power of 300 W is the optimum sputtering power to grow the smoothest Al thin films. FTIR results show that the varying RF power affect the chemical structure of the deposited films. The SEM results show that by increasing the sputtering power leads to the formation of isolated texture on the surface of substrate. In conclusion, RF power has a significant impact on the properties of deposited films, particularly crystallization and shape.

Enhancement of the anticoagulant capacity of polyvinyl chloride tubing for cardiopulmonary bypass circuit using aluminum oxide nanoscale coating applied through atomic layer deposition.

For cardiopulmonary bypass, the polyvinyl chloride (PVC) circuit which can initiate the activation of platelets and the coagulation cascade after blood cell contacting is the possible detrimental effect. Surface coating of the PVC tubing system can be an effective approach to enhance circuit's hemocompatibility. In this study, aluminum oxide (Al2 O3 ) thin films were deposited through thermal atomic layer deposition (T-ALD) or plasma-enhanced ALD (PE-ALD) on PVC samples, and the anticoagulation of the Al2 O3 -coated PVC samples was demonstrated. The results revealed that Al2 O3 deposition through ALD increased surface roughness, whereas T-ALD had a relative hydrophilicity compared with blank PVC and PE-ALD. Whole blood immersion tests showed that blood clots formed on blank PVC and that a large amount of red blood cells was found on PE-ALD substrates, whereas less blood cells were noted in T-ALD samples. Both T-ALD and PE-ALD Al2 O3 films did not cause activation of blood cells, as evidenced in CD3+ /CD4+ /CD8+ , CD61+ /CD62P+ , and CD45+ /CD42b+ populations. Analysis of serum coagulation factors showed that a lower amount of prothrombin was absorbed on T-ALD Al2 O3 samples than that on blank PVC. For albumin and fibrinogen immersion tests, immunostaining and scanning electron microscopy further revealed that a thin albumin layer was absorbed on T-ALD Al2 O3 substrates but not on PVC samples. This study revealed that deposition of Al2 O3 films by T-ALD can improve anticoagulation of the PVC tubing system.

Selective laser ablation of molybdenum from aluminium in a multi-layered thin film system

It is challenging to selectively remove a thin film with a high melting temperature from an underlying one with a low melting temperature where precise stops at layer interfaces are required. In this study, an ultrashort laser pulse is used to cleanly ablate a 40 nm thin molybdenum layer from an aluminium thin film in a commercially relevant heterostructure. We observe clean delamination of molybdenum from aluminium. We observe that columnar nanostructures in Mo are generated well below the damage threshold fluence. Both delamination and nanostructure formation are considered in terms of electromechanical forces. At low fluence, only selective removal of the very near surface of the Mo thin film was observed. At higher fluences, ablation of the Mo film occurred without melting of the underlying Al layer. Our computational results confirm the important role of thermionic electron emission and near surface electron-phonon coupling in nanostructure generation. We introduce a thermal boundary resistance effect in the heat diffusion by electrons to more accurately describe the release of the Mo from the Al layer. The comparison of experimental and simulation results confirms that electromechanical stresses can be an important mechanism in selective thin film ablation.

PDMS-ZnO Piezoelectric Nanocomposites for Pressure Sensors.

The addition of piezoelectric zinc oxide (ZnO) fillers into a flexible polymer matrix has emerged as potential piezocomposite materials that can be used for applications such as energy harvesters and pressure sensors. A simple approach for the fabrication of PDMS-ZnO piezoelectric nanocomposites based on two ZnO fillers: nanoparticles (NP) and nanoflowers (NF) is presented in this paper. The effect of the ZnO fillers’ geometry and size on the thermal, mechanical and piezoelectric properties is discussed. The sensors were fabricated in a sandwich-like structure using aluminium (Al) thin films as top and bottom electrodes. Piezocomposites at a concentration of 10% w/w showed good flexibility, generating a piezoelectric response under compression force. The NF piezocomposites showed the highest piezoelectric response compared to the NP piezocomposites due to their geometric connectivity. The piezoelectric compound NF generated 4.2 V while the NP generated 1.86 V under around 36 kPa pressure. The data also show that the generated voltage increases with increasing applied force regardless of the type of filler.

Localized overheating on aluminum metafilms mediated by surface plasmons

We studied the increase in temperature of systems formed by thin aluminum films deposited on texturized substrates which we denominated aluminum metafilms. By varying the geometric parameters of the metafilms, surface plasmons in the wavelength range of ~420-770 nm were excited. Temperature measurements as a function of the intensity of incident radiation in the interval from 0-to 4X10^18 (photons/s cm^2) using wavelengths of 445, 532 and 650 nm, showed temperature increases up to ~200 K, these attributed to metafilm morphology and hot electrons result of the non-radiative decay of the surface plasmons. Also increases up to 2.3X10^(-4) Ohm cm in electrical resistivity were recorded when the metafilms were radiated for times of ~1 s; when the exposure times were greater than ~4 s, irreversibly changes in the morphology of the samples were observed.

Features of Melt Droplet Formation during Electrical Destruction Aluminum Films on the Semiconductor Surface

The work is devoted to processes during melting of thin aluminium film on silicon surface in pulse current mode. An experiment was conducted to study the dynamics during the onset of the liquid phase on a metal film. Besides, the process of formation droplet localization zones is considered. The experimental part revealed critical current values ​ during an electrical explosion of thin metal films near the thermal shock source. Using the oscillographic method, the temperature profile of the metallization track is calculated.

Determination of the relative humidity at the parts-per-million (ppm) level in gases by a nanoporous alumina thin-film on a surface acoustic wave (SAW) resonator

Moisture measurement in parts per million (ppm) in electronic gases and in liquids for different industrial applications is challenging and a costly affair. There are numerous critical applications of ppm moisture measurement systems such as transformer oil, sulfur hexafluoride gas (SF6) in switchgear and protection, and the electronic industry for integrated circuit (IC) fabrication. Conventionally chilled mirror hygrometer and laser spectroscopy are used but some low-cost solutions using the thin-film capacitive sensors are also available in the market. This paper presents the fabrication of an inexpensive miniature moisture sensor using a commercial low-cost surface acoustic wave (SAW) resonator of 433.92 MHz frequency. To detect moisture, a hydrophilic metal oxide film is deposited on the interdigital electrodes (IDTs) of the SAW device. The film thickness is optimized to provide a sharp resonating peak under dry humidity conditions. Experiments were conducted to determine the frequency shift in the peak with the variation of moisture in nitrogen gas from 6 to 460 ppm using a vector network analyzer. The maximum sensitivity was 24 Hz/ppm with correlation coefficient of linearity equal to 0.99. An effort was also made to develop a prototype meter to measure moisture in ppm. Important features of the sensor are linear response, inexpensive fabrication, and appreciable sensitivity in the ppm range.

Influence of the aluminium doping on the physical and gas sensing properties of SnO2 for H2 gas detection

Tin Oxide (SnO2) thin films were doped with Aluminium (Al) thin films with four different concentrations 0,1,3 and 5 % were deposited using the RF Plasma sputtering method. The objective of this study was to investigate the effect of different concentrations of Al doping on the structural, optical and gas sensing properties of SnO2 thin films. The results of this study showed that the X-ray diffraction (XRD) analyses of the films were polycrystalline nature and tetragonal structure. An increase in the Al doping levels decreased the height of the diffraction peaks and increased their width since the Al ions entered the lattice as substitutions. Analysis of atomic force microscope (AFM) images showed that the average grain size decreased with an increase in the doping concentration. Furthermore, analyzing the optical properties showed that the optical band gap of the films increased with an increase in the doping concentration. SnO2:Al thin films gas sensors were tested using H2 gas, it was seen that the response of these films increased with increased doping levels up to 3 %, but decreased when the doping concentration was 5 %. Excellent hydrogen sensing properties such as high response, fast response time, short recovery time, and good selectivity were obtained. These results prove that the gas sensor performance was enhanced by the additive.