Deposited Aluminum Films Research Articles

Deposition of Alumina Films on Si (1 0 0) Substrate Using a Low Energy Dense Plasma Focus Device

A 1.5 kJ pulsed low energy Mather type plasma focus (PF) is used to deposit thin films of alumina (α-Al2O3) on Si (1 0 0) substrates. The PF device with its anode made of aluminum was operated with argon-oxygen mixture as the filling gas. The Al2O3 thin film samples were prepared using 10, 20 and 30 successive shots with substrates placed at 60 mm from the top of the anode at approximately zero angular position with respect to the anode axis. The crystallography of the as-deposited and annealed samples was studied by X-ray diffractometry (XRD). Raman Spectroscopy studies verified the formation of α-Al2O3 phase in the annealed films. Scanning electron micrographs (SEM) of the annealed films present many different sized particulates (50–300 nm) distributed upon the film surface. The cross-sectional SEM micrographs show that the thickness of deposited alumina film is linear with a typical rate of 45 nm/shot at focus storage energy of 850 J.

Optical and RF transparent protective alumina thin films

Protective alumina thin films of different thicknesses (35–95 nm) were grown by pulsed RF magnetron sputtering technique at room temperature on germanium (Ge) coated black polyimide or Kapton® substrate which is often employed as sunshield membrane on communications satellite antennas. The thin alumina top layer provides shielding of Ge coating from degradation during storage. The alumina thin film was characterized by X-ray diffraction, field emission scanning electron microscopy and X-ray photoelectron spectroscopy (XPS) techniques to investigate microstructural and electronic characteristics. Thermo-optical properties such as IR emittance, solar absorptance, reflectance and transmittance and electrical property e.g. sheet resistance of the deposited alumina films were measured. The RF losses e.g. insertion loss and return loss were measured in both Ku band (10.5–14.5 GHz) and Ka band (27–40 GHz). Finally, to prove anti-degradation behavior of alumina thin film, water droplet spreading experiments were carried out and evaluated its chemical degradation by XPS.

Powder requirements for aerosol deposition of alumina films

Dry powder aerosol deposition (AD) potentially offers several advantages over conventional ceramic coating processes. AD takes place at room temperature, and a variety of materials can be utilized as the substrate. Deposition occurs at a relatively rapid rate, and the product is a dense, nano-crystalline thick film. One limitation for AD is related to the suitability of powders. In addition to the many other process variables, the success of the deposition depends on the starting powder and its preparation, determined by trial and error. In this work, a broad experimental study about the suitability of 14 alumina powders for AD was carried out on two different substrates, alumina and glass. Three powder properties, particle size, d50, specific surface area, SBET, and compressibility index, CI, were measured and associated with the success of the subsequent deposition. For alumina substrates (high hardness), it was found that a relatively high powder specific surface area (5.5–8 m2/g) correlated with good film deposition and adhesion. For glass substrates, initial deposition was obtained with almost all powders; however, problem with long term stability, apparently related to residual strain, was witnessed using many powders. Hi quality, well-adhered, stable AD films in this case were associated with comparatively lower SBET and a compressibility index within a tight range of about 44–47%.

Corrosion Behaviour of Sputtered Alumina Thin Films

Corrosion studies of sputtered alumina thin films grown on stainless steel (SS) 304 were carried out by linear polarization and electrochemical impedance spectroscopy. Noticeable changes were not observed in morphology and surface roughness of films after carrying out the corrosion test. Corrosion current density (icorr) of alumina coated SS decreased up to 10−10 A cm−2 while icorr value in the range of 10−5–10−6 A cm−2 was observed for bare SS. The direct sputtered film showed superior corrosion resistance behaviour than the reactive sputtered film. This might be attributed to the difference in thickness of the films sputtered by direct and reactive methods. The electronic structure of deposited alumina films was studied both before and after corrosion test by X-ray photoelectron spectroscopy technique which also confirmed no structural changes of alumina film after exposing it to corrosive environment.

Comparative study of porous anodic alumina: effects of aluminium deposition methods

This article reports on the comparative study of the fabrication of porous anodic alumina films by anodisation of the aluminium films on glass substrates which were deposited by direct current sputtering and electron beam evaporation methods. The relationship between surface morphology of the deposited aluminum films and porous anodic alumina films was investigated. A more uniform and ordered porous anodic alumina was obtained by fabricating from electron beam evaporation deposited aluminium film with smaller and compact grains. Two-step anodisation was used to further improve the quality of porous anodic alumina compared to one-step anodisation. The optical transmittance spectra within wavelength of 370–800 nm were obtained and the optical properties were studied.

Deposition of Alumina Films on Interdigital Transducer/ZnO/Glass Substrates by Electron Beam Evaporation to Improve the Characteristics of Surface Acoustic Wave Devices

ZnO films with c-axis (0002) orientation have been successfully grown by radio frequency magnetron sputtering on glass substrates. The alumina films were deposited on interdigital transducers/ZnO/glass substrates by electron beam evaporation to enhance the performance of the ZnO thin film surface acoustic wave (SAW) devices. The crystalline structure and surface roughness of the films were investigated by X-ray diffraction and atomic force microscopy, respectively. The phase velocity and coupling coefficient of SAW device were apparently increased when we increased the thickness of alumina film. The experimental result is beneficial to improve the characteristics of the ZnO thin film SAW devices on cheap glass substrates.

Changes in the Spectral Characteristics of Aluminum Films Deposited under Assisting Argon Ion Beam

High-reflectance aluminum films are widely used in applied optics. As part of this work, we deposited aluminum films on glass substrates by magnetron sputtering using argon ion beam assistance. The reflectivity of the films obtained was measured on the SF-256 spectrophotometer. The microstructure and topology of the films were examined with a transmission electron microscope (TEM), X-ray diffraction (XRD) and atomic force microscope (AFM). The studies have shown that the aluminum films deposited with ion assistance have higher reflectance in the UV range than the films formed by magnetron sputtering alone. The results of TEM and AFM measurements show that the geometric factor (crystallite size, surface roughness) is not the reason for the increase of reflectivity. X-ray diffraction analyses have shown a significant increase in microstress in the aluminum films deposited with ion assistance, which is caused by an increase in the defect density of the vacancy-type crystal structure. The results have shown that the increase in the density of crystal defects leads to an increase in reflectance in the UV range.

Innovative low temperature plasma approach for deposition of alumina films

Alumina films were deposited from a new plasma method using aluminum acetylacetonate (AAA) powder as precursor. The AAA was sputtered in argon and oxygen plasma mixtures. It was investigated the effect of the oxygen proportion (O2%) on the properties of the coatings. Deposition rate was derived from the layer height measured by profilometry. The elemental composition and molecular structure of the films were determined by Rutherford backscattering and infrared spectroscopies, respectively. Grazing incidence X-ray diffraction was used to investigate the microstructure of the films while hardness was determined by nanoindentation technique. Inspections on the surface morphology and on the film composition were conducted associating scanning electron microscopy and energy dispersive spectroscopy. Incorporation of oxygen affects the plasma kinetics and consequently the properties of the coatings. As moderated concentrations of oxygen (< 25%) are added, the structure is predominantly organic containing stoichiometric amorphous alumina. On the other hand, as high O2% (> 25%) are incorporated, the structure become rich in metallic aluminum with carbon rising at low proportions. The deposited layer is not homogeneous in thickness once the chemical composition of the precursor is changed by the action of the reactive oxygen plasma. Oxygen ablation on the film surface also contributes to the lack of homogeneity of the structure, especially as high oxygen proportions are imposed. Hardness data (0.5-2.0 GPa) corroborated the idea of an amorphous structure. Based on the results presented here it was possible to identify the oxygen concentration in the plasma atmosphere which mostly removed organics while preserving the stoichiometric alumina precipitation, subject of great relevance as one considers the reduction in the energy necessary for the creation of fully oxide coatings.

Optical Properties of Variable-Composition Aluminum/Alumina Thin Films, Part 1

Optical properties of alumina/aluminum thin films with varying compositions deposited by reactive sputtering have been studied. For measurements, ellipsometry has primarily been used, with additional measurements to provide more information. For modeling, the effective medium approximation has been used. This paper presents the ellipsometry and effective medium approximation approaches used. Results are presented for bare glass used as a substrate and for alumina films that are nearly stoichiometric. The microscope glass substrate was found to have much higher levels of absorption than quartz glass (), for which the optical constants are commonly adopted for modeling. If this enhanced absorption had not been identified and quantified, it would have been inaccurately attributed to the deposited alumina films. Alumina films deposited at 5 to 9% oxygen flow ratios were also measured and modeled. Dispersion models (Sellmeier and Lorentz models) showed that, as the oxygen flow ratio decreased, the resonance energy also decreased. This suggests that a decreased oxygen flow ratio induces more defects, which situate themselves below the bandgap and eventually lower the bandgap. For these oxide films, a homogeneous composition assumption seemed satisfactory to describe the variety of optical measurements.

Low surface recombination velocity in n-Si passivated by catalytic-chemical vapor deposited alumina films

The surface recombination velocity (S0) in n-type Si (n-Si) wafers has been reduced below 0.1cm/s by dint of positive fixed charges created by alumina (AlOx) films deposited at a film-temperature of 230°C by catalytic chemical vapor deposition (Cat-CVD) using trimethyl aluminum (TMA) and O2. Positive fixed charges of the order of 1012charges/cm2 can be created in AlOx films deposited under O2/TMA flow-rate ratios in the range of 3.5–6.5. The extremely small S0 has been confirmed to be obtainable mainly due to a band bending effect brought about by the positive charges. The polarity and amount of the fixed charges can be determined by the flow-rate ratio of O2/TMA.

Reduction of surface recombination velocity by rapid thermal annealing of p-Si passivated by catalytic-chemical vapor deposited alumina films

Excellent electrical-passivation of p-type Si (p-Si) in Si solar cells has been achieved by post-deposition rapid annealing of aluminum oxide (AlOx) films prepared by catalytic chemical vapor deposition (Cat-CVD) using trimethyl aluminum (TMA) and O2. Extremely small surface recombination velocity of below 0.1cm/s has been obtained at post-deposition annealing temperatures in the range of 350–400°C for an annealing time of 2min. The reduction of surface recombination velocity has been attributed to band bending induced by a fixed negative charge density of 5×1011charges/cm2 and an additional small interface trapping density of around 1010cm−2eV−1.

Microstructural studies of e-beam evaporated alumina thin films

Alumina thin films of different thicknesses, e.g. 90, 120 and 150 nm, were grown on SS304 thin foil by electron beam evaporation technique. The films were post-heat treated at 500, 700 and 800°C in air and subsequently characterised by X-ray diffraction, atomic force microscopy, field emission scanning electron microscopy and X-ray photoelectron spectroscopy. The effects of thicknesses and post-heat treatment on microstructure have been studied. The deposited alumina film was almost stoichiometric. The alumina film of the lowest thickness, i.e. 90 nm post-heat treated at 700°C, showed preferential growth of nanorods and irregular polygonal nanostructures with random orientation.

Influence of metal electrode stoichiometry on the electron barrier height at CuxTe1−x/Al2O3 interfaces for CBRAM applications

Spectroscopy of Internal photoemission of electrons was applied to reveal the impact of the stoichiometry of CuxTe1−x (0⩽x⩽1) electrodes on the barrier height between the electrode Fermi level and the bottom of the Al2O3 conduction band. The barriers observed in the structures with atomic layer deposited alumina films (20 or 10nm) on (100) Si substrates are compared to the metal/SiO2 barriers in capacitors with thermally grown Si oxide. We found that the CuxTe1−x stoichiometry has a marginal impact on the barrier height, yielding the same value for the Cu metal electrode even for high Te concentration (80%). In the case of pure Te electrode the photoemission spectral threshold is found to be shifted towards higher photon energy by 0.5eV.

Broadband antireflective silicon carbide surface produced by cost-effective method

A cost-effective method for fabricating antireflective subwavelength structures on silicon carbide is demonstrated. The nanopatterning is performed in a 2-step process: aluminum deposition and reactive ion etching. The effect, of the deposited aluminum film thickness and the reactive ion etching conditions, on the average surface reflectance and nanostructure landscape have been investigated systematically. The average reflectance of silicon carbide surface is significantly suppressed from 25.4% to 0.05%, under the optimal experimental conditions, in the wavelength range of 390-784 nm. The presence of stochastic nanostructures also changes the wetting properties of silicon carbide surface from hydrophilic (47°) to hydrophobic (108°).

Preparation of films from aluminum acetylacetonate by plasma sputtering

Aluminum acetylacetonate has been reported as a precursor for the deposition of alumina films using different approaches. In this work, alumina-containing films were prepared by plasma sputtering this compound, spread directly on the powered lowermost electrode of a reactor, while grounding the substrates mounted on the topmost electrode. Radiofrequency power (13.56 MHz) was used to excite the plasma from argon atmosphere at a working pressure of 11 Pa. The effect of the plasma excitation power on the properties of the resulting films was studied. Film thickness and hardness were measured by profilometry and nanoindentation, respectively. The molecular structure and chemical composition of the layers were analyzed by Fourier transform infrared spectroscopy and energy dispersive spectroscopy. Surface micrographs, obtained by scanning electron microscopy, allowed the determination of the sample morphology. Grazing incidence X-ray diffraction was employed to determine the structure of the films. Amorphous organic layers were deposited with thicknesses of up to 7 µm and hardness of around 1.0 GPa. The films were composed by aluminum, carbon, oxygen and hydrogen, their proportions being strongly dependent on the power used to excite the plasma. A uniform surface was obtained for low-power depositions, but particulates and cracks appeared in the high-power prepared materials. The presence of different proportions of aluminum oxide in the coatings is ascribed to the different activations promoted in the metalorganic molecule once in the plasma phase. Copyright © 2013 John Wiley & Sons, Ltd.

Improving the stability of atomic layer deposited alumina films in aqueous environments with metal oxide capping layers

Alumina (Al2O3) films deposited through atomic layer deposition (ALD) are known to be effective permeation barriers due to their uniformity and pinhole-free morphology. However, they suffer from process-induced defects that inhibit their stability in aqueous and hygroscopic environments. We explore the water stability of ALD deposited alumina barrier films capped with nickel oxide (NiOx) and titanium oxide (TiOx) thin films deposited through e-beam or ALD deposition. The performance of the barriers was evaluated by measuring their ability to protect zinc oxide (ZnO) thin film sensors immersed in deionized (DI) water. X-ray photoelectron spectroscopy (XPS) was used to determine the composition of the barrier films with the various capping layers. The characteristic photoluminescence (PL) peak for the ZnO sensor was used as a marker to study changes in peak intensity due to degradation of the barrier films as a function of water immersion time. The TiOx capped films showed remarkable stability when immersed in DI water for 10 days. These results show that TiOx capping layers can offer superior protection to mitigate the water degradation of ALD alumina barrier films. Such composite laminates will enable a wider range of applications for ALD deposited alumina barrier films including aqueous environments.

S114014 エアロゾルデポジション法により成膜した薄膜の強度([S114-01]トライボロジーの基礎と応用(1))

Recent advances in smart surface engineering, coating technologies and cold spray technologies offer unique possibilities for better controlling friction and wear under lubricated rolling, sliding or rotating contact conditions. Smart surface technologies such as laser texturing and/or dimpling, laser glazing, reactive ion etching and shot-peening have also become very popular. Recently, a novel method for depositing ceramic thick films by aerosol deposition (AD) has been developed. Submicron ceramics powders are accelerated by fast gas flow and then impacted on a substrate, to form a dense, uniform and hard ceramic layer at room temperature. In this study, in order to create the textured surface without the thermal effect, AD method was employed. The conditions to deposit alumina films and the adhesive strength of the films were investigated. The thickness of deposited alumina film increased exponentially, as the reciprocating cycles increased in numbers. The deposited films were scratched using a diamond indenter. The reciprocating cycles in depositing exceed 20, the adhesive strength of the films increased from 75N to 90N.

3Pb3-2 Deposition of alumina film on ZnO/Glass substrates by electron beam evaporation to imrove the characteristics of surface acoustic wave devices(Poster Session)

3Pb3-2 Deposition of alumina film on ZnO/Glass substrates by electron beam evaporation to imrove the characteristics of surface acoustic wave devices(Poster Session)

Size Effects in the Electrochemical Alloying and Cycling of Electrodeposited Aluminum with Lithium

The electrochemical alloying and cycling of electrodeposited aluminum films, electron-beam deposited aluminum films, and template-synthesized aluminum nanorods with lithium is presented here. Electrodeposition of aluminum is performed at room temperature using ionic liquid solutions and is shown to exhibit high faradaic efficiency. To study the dependence of lithium-aluminum cycling on size, the thickness of these films is varied between 0.25 μm and 6.2 μm by varying the electrodeposition time. Electrochemical alloying and de-alloying of these films with lithium is observed in lithium half-cells at room temperature. The films reach theoretical capacity for the formation of LiAl (1 Ah g−1). The performance of electrodeposited aluminum films is dependent on film thickness, and the thinnest films exhibit the worst cycling behavior. Cycling of aluminum films formed by electron-beam deposition is in quantitative agreement with that of films formed by electrodeposition, and the two types of films have a similar appearance in SEM images taken after cycling. Synthesis of aluminum nanorod arrays on stainless steel substrates is also demonstrated using electrodeposition into anodic aluminum oxide templates followed by template dissolution. Unlike nanostructures of other lithium-alloying materials, the electrochemical performance of these aluminum nanorod arrays is worse than that of bulk aluminum.

Nanostructured Lithium-Aluminum Alloy Electrodes for Lithium-Ion Batteries

Electrodeposited aluminum films and template-synthesized aluminum nanorods are examined as negative electrodes for lithium-ion batteries. The lithium-aluminum alloying reaction is observed electrochemically with cyclic voltammetry and galvanostatic cycling in lithium half-cells. The electrodeposition reaction is shown to have high faradaic efficiency, and electrodeposited aluminum films reach theoretical capacity for the formation of LiAl (1 Ah/g). The performance of electrodeposited aluminum films is dependent on film thickness, with thicker films exhibiting better cycling behavior. The same trend is shown for electron-beam deposited aluminum films, suggesting that aluminum film thickness is the major determinant in electrochemical performance regardless of deposition technique. Synthesis of aluminum nanorod arrays on stainless steel substrates is demonstrated using electrodeposition into anodic aluminum oxide templates followed by template dissolution. Unlike nanostructures of other lithium-alloying materials, the electrochemical performance of these aluminum nanorod arrays is worse than that of bulk aluminum.