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The real and imaginary parts of the dielectric function of VO2 thin films, deposited on r-plane sapphire via pulsed laser deposition, are measured by means of visible-infrared ellipsometry for wavelengths ranging from 0.4 to 15 μm and temperatures within its phase transition. For both the insulator-to-metal (heating) and metal-to-insulator (cooling) transitions, it is shown that the two ellipsometric signals exhibit three temperature-driven behaviors, which are well described by appropriate combinations of the Tauc-Lorentz, Gaussian, and Drude oscillator models. By fitting Bruggeman's effective medium model for the dielectric function to the corresponding measured experimental values, using the volumetric fraction of the VO2 metallic domains as a fitting parameter for different temperatures within the VO2 phase transition, we have found that this model is suitable for describing the dielectric function in visible and near-infrared wavelengths (∼0.4 to ∼3.0 μm), but it generally fails for longer infrared ones. Furthermore, the hysteresis loop of the VO2 emissivity averaged over a relevant interval of wavelengths is determined and shown to vary from ∼0.49, in the insulator phase, to ∼0.16, in the metallic one. These values, based on the VO2 dielectric function, are consistent with previous measurements reported in the literature, and therefore, our measured data are expected to be useful for describing the behavior of VO2 films involved in optical and radiative applications. [ABSTRACT FROM AUTHOR]

Abstract: This work studies the ion irradiation-induced phase transformations in thin films of yttrium oxide. The films were deposited using an ion beam sputtering technique that allows the control of the order/disorder of the microstructure. As-deposited (disordered) and annealed (ordered) samples were irradiated by xenon ions at different energies and doses. Two different structural phase transformations were observed: cubic/amorphous-like and cubic/monoclinic. In both cases, it is shown that the pristine structure is of prime importance in the transformation process. The phase transformations are analysed in terms of structural extended defect nucleation originating from the oxygen network behaviour, which leads to polygonisation up to a nanocrystallite-like structure, followed by a phase transformation into a monoclinic structure. [Copyright &y& Elsevier]

Thin films of yttrium oxide, Y2O3, were deposited on Si (1 0 0), MgO and SrTiO3 substrates by ion beam sputtering. The as-deposited samples are under a strong compressive stress whatever the substrates are. Furthermore the in-plane (2 2 2) or (4 0 0) Bragg peaks are shifted and non-symmetric. The high-resolution transmission electron microscopy investigations on the epitaxially grown Y2O3 thin films lead to the conclusion that the ion beam deposition process promotes a strong disorder on the oxygen network. The crystallographic symmetry of the Y2O3 structure which is Th7 becomes a fluorite related symmetry which is Fm3m. Annealing treatments or deposition involving a secondary ion beam assisted deposition process re-orders the Fm3m structure which comes back to the equilibrium Th7 symmetry. [Copyright &y& Elsevier]

Interfacial reactions in thin films of Y2O3 on Si(100) have been studied by means of energy dispersive X-ray analysis and high resolution transmission electron microscopy observations. Thin films of yttrium oxide were deposited at 700 °C by ion beam sputtering and then annealed at 700 and 900 °C under vacuum and in air, respectively. After an annealing treatment of 2 h at 900 °C in air a solid-state amorphization is observed at the interface Y2O3/SiOx. After annealing at 700 °C under vacuum a surprising phenomenon of electron beam irradiation induced epitaxial reconstruction is observed at the Si substrate surface. [Copyright &y& Elsevier]

We report on the elaboration and physical properties of fully epitaxial Fe3O4/Al2O3 bilayers to be included in magnetic tunnel junctions. Uncovered Fe3O4(111) single layers and bilayers were epitaxially grown onto sapphire (0001) substrates. Appropriate growth conditions lead to a stoichiometric Fe3O4 layer both at the Fe3O4/Al2O3 interface and on the whole thickness, as checked by in situ x-ray photoelectron spectroscopy and by the observation of the Verwey transition, respectively. Transmission electron microscopy demonstrates the epitaxial growth of a γ-Al2O3 layer on top of Fe3O4(111), which insulating properties have been monitored by conductive tip atomic force microscopy. [ABSTRACT FROM AUTHOR]

Worm-like buckling structures have been investigated by atomic force microscopy to estimate the relevant parameters for the mechanical stability of Y[SUB2]O[SUB3] thin films deposited by ion beam sputtering technique on GaAs substrates. The internal stresses involving in the observed buckling phenomena have been estimated to be around 8.5 GPa in compression. The critical thicknesses up to which the various damaging mechanisms occur have also been determined. [ABSTRACT FROM AUTHOR]