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Alumina thin coatings were grown on Germanium (Ge) coated black polyimide (GBP) or Kapton which has been used as a sunshield membrane on communication satellite antennas to protect it from environmental degradation during ground storage and implementation. The deposited nanoalumina coatings were found to be optically transparent in solar regime in spectral window while RF characteristic revealed negligible losses. Space worthiness of the coating was examined by simulated environments, e.g. humidity, thermal cycling and thermovacuum tests. No degradation was observed in its microstructural, thermo-optical, electrical, chemical state and RF characteristic in particular Ku and Ka bands. The aforesaid study indicates that the alumina thin coating is able to prevent surface degradation of GBP retaining the thermo-optical properties of the Ge coated Kapton and RF transparency which are functional requirements for communication antenna. The thickness of the optimized alumina coating was ~60 nm. [ABSTRACT FROM AUTHOR]

The E-beam evaporation technique is utilised at room temperature to deposit 90, 120 and 150 nm thin alumina films on 75 μm thin titanium foils. As-grown films are annealed at 500, 700 and 800 °C in air. The phase analysis, morphology and electronic structure of the as-grown and annealed thin films are respectively investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS) techniques. The XRD results show that the as-grown thin films are amorphous. The annealed thin films show crystalline peaks corresponding to a mixture of different phases of alumina. The FESEM studies reveal tripod-like nanostructure and dense nanorods in the alumina thin films annealed at 700 and 800 °C, respectively. These results are explained on the basis of experimental evidences provided by the corresponding XPS studies. [ABSTRACT FROM AUTHOR]

Abstract: Alumina thin films were deposited on titanium (Ti) and fused quartz by both direct and reactive pulsed rf magnetron sputtering techniques. X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy were utilized to study the phases and surface morphology of the films. The as-deposited alumina thin films were amorphous. However, after annealing at 500°C in vacuum, the crystalline peaks corresponding to the Theta (θ), Delta (δ) and Chi (χ) alumina phases were obtained. The optical transmittance and reflectance as well as IR emittance data were also evaluated for the thin films. The transmittance, e.g., (~90%) of the bare quartz substrate was not changed even when the alumina thin films were deposited for an hour. However, further increase in deposition time (e.g., 7h) of the alumina thin films showed only a marginal decrease (e.g., ~5%) in average transmittance of the bare quartz substrate. The direct and indirect optical band gaps and extinction coefficient of the alumina films were estimated from the transmittance spectra. The IR emittance of the Ti substrate (e.g., ~16%) was almost constant after depositing alumina thin films for an hour. Further increase in deposition time showed only a marginal increase (e.g., ~9%) in IR emittance value. Therefore, it is proposed that the alumina films developed in the present work can act as a protective cover for the Ti substrate while retaining the thermo-optical properties of the same. The nanohardness and Young׳s modulus of the alumina thin films were evaluated by the novel nanoindentation technique. The nanohardness was measured as ~6GPa. Further, Young׳s modulus was evaluated as ~116GPa. The magnitudes of the nanomechanical properties of the thin films were a little smaller than those reported in the literature. This was linked to the lack of crystalline phases in the as-deposited alumina thin films. [Copyright &y& Elsevier]

Abstract: Alumina thin films were deposited on SS304 and Ti metal substrates using a pulsed rf magnetron sputtering technique at different radio frequency (rf) powers corresponding to input powers of 300, 500 and 700W. Both direct and reactive sputtering methods were employed to deposit the alumina films. The deposited films were thoroughly characterized by X-ray photoelectron spectroscopy (XPS) to investigate electronic structure and stoichiometry. Further, the effect of different rf powers, role of substrates and effect of deposition methods e.g. direct and reactive sputtering on binding energy, atomic concentration ratio (e.g., oxygen to aluminium ratio, O/Al) and related properties have been studied extensively by XPS. The results suggested that the reactive sputtering method could provide alumina thin films with the chemical composition that matches with the stoichiometric one. Further, the film deposition process by reactive sputtering was not a sensitive function of the variations in the input power. [Copyright &y& Elsevier]