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Thin films of Al₂O₃ were prepared by the sol–gel process. Dip-coating technique was used for deposition of the Al₂O₃ thin films onto glass substrates. Optical and structural properties of the films were investigated with respect to the annealing temperature (100–500°C). The structure of these films was determined by X-ray diffraction (XRD). Scanning electron microscopy (SEM) was performed for the analysis of surface morphology. For determination of the optical constants of Al₂O₃ thin films, UV-Visible spectrophotometry measurements were carried out. Annealing temperature affects the structural and optical properties of the Al₂O₃ thin films. The refractive index and extinction coefficient of the films at 550 nm wavelength increase from 1.56 to 1.66, and from 3.41 × 10^-5 to 5.54 × 10^-5, respectively while optical band gap and thickness of the films decrease from 4.15 eV to 4.11 eV, and 360 nm to 260 nm, respectively, by increasing annealing temperature from 100°C to 500°C.

The powerful RHEED technique has been demonstrated for the structural determination of the nano-crystals grown on metal and oxide substrate surfaces. Pt was electrochemically deposited onto a electrode, while Pb and cobalt were vapor deposited onto Ag(111) and oxide film/NiAl(100), respectively under UHV conditions. At any Pt coverage, 3D-clusters develop for which the Pt clusters grow in (311) orientation on the substrate surface, where the atomic rows of the (311) facet are parallel to the atomic rows of the surface. Due to the strong bonding at Pb/Ag(111) interface, the Pb deposit grows in 2D-islands with a phase (Θ < 1 ML). On the other hand, the β-crystallites of ≈ 1 nm in diameter with inclusion of smaller-sized particles (D < 1 nm) are observed on Θ-Al₂O₃ after Co deposition at room temperature. Annealing at 900 K Co clusters (≈ 3 nm) grow larger at expense of small particles on thin oxide film on NiAl(100) and become better ordered, where the [110] axis of the Co(001) facet is parallel to the [100] direction of the (001)-oxide surface. The in-plane lattice constant of Co clusters is ca. 4 larger than that of bulk Co, yielding less strain at the (001)-oxide surface. These results demonstrate that both orientation and phase of metal nano-clusters are governed by surface structure of the substrate.

Aluminum oxide (Al₂O₃) thin films with Al₂O₃ buffer layer were deposited on Si (100) and Si (111) substrates using RF magnetron sputtering of Al₂O₃ target in Ar atmosphere. The synthesized films were then annealed at the temperature of 400${}^{\circ }$C, 600${}^{\circ }$C and 800${}^{\circ }$C in nitrogen (N₂) environment for 6h. Structural properties and surface morphology are examined by using X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM) and Atomic Force Microscope (AFM). XRD analysis indicated that different orientation of Al₂O₃ were formed with different intensities due to increase in the annealing temperature. From FESEM cross-section analysis results, it is observed that the thickness of films were increased as the annealing temperature increased. EDX analysis shows that the concentration of aluminum and oxygen on both the Si substrates increased with the increase in annealing temperature. The surface roughness of the films were found to be decreased first when the annealing temperature is increased to 400${}^{\circ }$C, yet the roughness increased when the annealing temperature is further increased to 800${}^{\circ }$C.

Surface degradation (oxidation/corrosion/erosion) at elevated temperature is encountered commonly in engineering industries like gas turbines and thermal power plants. MCrAlX coatings which came into the picture in 1960s were used widely for surface protection in the elevated-temperature section of the gas turbine engines and in boilers to combat oxidation/corrosion/erosion. Among them, MCrAlY ($M=\mathrm{\text{Ni}}$, Co or $\mathrm{\text{Co}}+\mathrm{\text{Ni}}$) were developed to be used as the overlay coatings and bond coat (BC), which offer a combination of multiple features such as oxidation, corrosion and ductility. MCrAlY coatings form a second layer of aluminum oxide beneath the chromium oxide layer at elevated temperatures which minimizes the oxidation/corrosion/erosive wear rates. But the desire to increase combustion efficiencies of power plants and gas turbine engines along with lower CO₂ emissions poses a significant challenge for coating design. As the temperature surpasses 900^∘C, NiCrAlY coating degrades quickly due to nonregeneration of chromia or alumina. The research and development (R&D) efforts are focusing continuously on improving the existing MCrAlX coatings or developing new sustainable MCrAlX coatings with improved oxidation performance. In this review, the roles of the alloying elements, microstructures, post-deposition treatment techniques and different deposition processes in the elevated-temperature oxidation/corrosion performance of MCrAlX-based alloys have been explored in detail.

Electrochemical Discharge Machining (ECDM) has combined characteristics of ECM and EDM which is effectively been used for machining electrically nonconductive, hard, and brittle materials like glass, quartz, and ceramics. However, the industrial application of this process is limited due to difficulty in machining micro holes with higher machined depth. To improve the machining performance of the ECDM process, loose abrasive particles have been mixed in an electrolyte while machining blind holes on soda–lime glass. This study is mainly focused on investigating the effect of process parameters (voltage and electrolyte concentration) on the responses (volume of material removed, machined depth and overcut) using CCRD. The significance of process parameters on the responses has been evaluated using ANOVA. A second-order regression equation has been developed for predicting the relation between input process parameters and quality characteristics (i.e. volume of material removed, diameter overcut, and machined depth). It is observed that the addition of Al₂O₃ abrasives has improved the volume of material removed and machined depth. On the other hand, the addition of SiC abrasives into the electrolyte has reduced the diametric overcut due to their specific characteristic.

We report a multilayer moisture barrier structure comprised of alternating inorganic aluminum oxide and plasma-polymerized organic layers. The inorganic and organic layers were grown by atomic layer deposition (ALD) and plasma polymerization in vacuum, respectively. The inclusion of plasma-polymerized layers in the multilayer barrier structure enhanced the moisture barrier performance by around 15% for as-deposited samples. After being subjected to 10 000 bending cycles with a bending radius of 2 cm, however, the moisture barrier performance of the multilayer structure was improved by 50% from that of pure inorganic counterpart.

Dielectric behavior of aluminum oxide (Al₂O₃) thin film under high DC electric field is presented and discussed. Aluminum oxide thin films were prepared starting from aluminum isopropoxide as a precursor via a wet chemistry route. Silicon substrates and silica glass substrates were used to deposit the films via spin-coating technique. The deposited films were then annealed under 450°C–700°C for 2–3 h. Dense, crack-free and uniform films were obtained. The thickness of the films is in the range of 200–800 nm. The films obtained are in amorphous state as revealed by the X-ray diffraction patterns. Voltage–Current (V–I) characteristics of the films were used to study the dielectric behavior of the films. Very low leakage current density J under high DC electric field E can be obtained. The breakdown electric field of the films is around 1.2 MV/cm. The V–I characteristics of the films are slightly nonlinear. With platinum as bottom electrode and gold as top electrode, successive breakdown phenomena of the films under high DC electric field were observed. Each breakdown event of the film corresponds to a sharp spike at the V–I plot of the sample. The shape of the breakdown spots of the films are in crater-like with a breakdown channel of diameter around a few micrometers as revealed by SEM images. The top gold electrode at the breakdown spots either splashed out or ripped off from the breakdown spots, which isolated the breakdown spots from rest of the electrode, and made the successive breakdown of the sample possible. The breakdown spots of the sample are concentrated at the edge of the electrode with proportional spacing, which can be easily understood as the edge effect of the parallel capacitor configuration, while the uniform distribution of the breakdown spots signifies that the uniformity of the films thus prepared are satisfied. Breakdown spots apart from the electrode edge can also be observed. Most of such spots associated with ripped-off gold film electrode in large area. We suppose such breakdown took place at higher electric field after the successive breakdown at the electrode edge and the isolation of the edge part from rest of the sample. Higher energy is needed to tear off larger section of the electrode. The breakdown characteristics of the films reported in this work are useful for the further study to enhance the breakdown strength of the film.

Dielectric capacitors are receiving increasing attention due to the high-power density and fast charge–discharge speed. However, defects are inevitably induced during the preparation process and then weaken the breakdown strength, thereby limiting their energy density. The phenomenon gives rise to self-healing technology. The discovery of sol–gel-derived aluminum oxide with electrolysis and dielectric dual-characteristic provides a novel, simple and cost-effective self-healing method to heal defects and enhance energy density. In this paper, we systematically reviewed the current self-healing technologies and the important progress of electrolysis and dielectric co-existence dielectrics. Finally, we outlook the electrolysis and dielectric co-existence dielectrics and potential challenge.