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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]

This work is focused on the transformation of the disordered fluorite cubic-F phase to the ordered cubic-C bixbyite phase, induced by isothermal annealing as a function of the residual stresses resulting from different concentrations of microstructural defects in the yttrium oxide, Y 2 O 3 . This transformation was studied using in-situ X-ray diffraction and was modelled using Kolmogorov–Johnson–Mehl–Avrami (KJMA) analysis. The degree of the disorder of the oxygen network was associated with the residual stress, which was a key parameter for the stability and the kinetics of the transition of the different phases that were present in the thin oxide film. When the degree of disorder/residual stress level is high, this transition, which occurs at a rather low temperature (300 °C), is interpreted as a transformation of phases that occurs by a complete recrystallization via the nucleation and growth of a new cubic-C structure. Using the KJMA model, we determined the activation energy of the transformation process, which indicates that this transition occurs via a one-dimensional diffusion process. Thus, we present the analysis and modelling of the stress state. When the disorder/residual stress level was low, a transition to the quasi-perfect ordered cubic-C structure of the yttrium oxide appeared at a rather high temperature (800 °C), which is interpreted as a classic recovery mechanism of the cubic-C structure. [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]

Abstract: In this study temperature dependent Hall effect measurements combined with Fourier Transformed Infra-Red (FTIR) spectroscopy measurements is used to determine the evolution of the scattering mechanisms ascribable to in-grain and grain boundaries on Boron doped ZnO thin films deposited by Low Pressure Chemical Vapour Deposition (LPCVD). Through Hall effect measurements during in situ isothermal annealing, changes in electrical characteristics of zinc oxide could be followed in real time. Whereas only degradation is observed in air, an improvement of layer conductivity could be achieved at low temperatures by annealing under argon atmosphere. A study of the conductivity during isothermal annealing offers the possibility to extract activation energies, which have been compared to migration energies of the different intrinsic defects in ZnO. [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]

According to Cr content, ternary Al1-xCrxNy films structure evolves from hexagonal to cubic phase. Despite numerous studies on their mechanical properties in relation with the deposition process, the relationship between this phase transition and elastic properties has never been deeply studied. In this paper, the transition has been evidenced by picoseconds ultrasonic and Brillouin light scattering at a chromium concentration of 40 at. % and is characterized by a strong increase of C33 and C44 effective elastic constants (respectively, +83% and +70%). [ABSTRACT FROM AUTHOR]

Abstract: Yttrium oxide (Y2O3) thin films deposited on silicon (Si) by an ion beam sputtering technique have been irradiated by 92MeV xenon ions at room temperature. The microstructure of the irradiated thin film has been studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). A complete structural conversion from the cubic C-type to a monoclinic B-type phase is obtained. These results were compared with the phase transformation obtained in Y2O3 thin films by medium energy Xe ion irradiation. In both cases the oxygen network behaviour under irradiation is the key parameter of the phase transformation. [Copyright &y& Elsevier]

Yttrium oxide, Y2O3, thin films are deposited in situ at 700 °C by laser ablation on MgO substrate. Orientation relationships are studied by means of asymmetric X-ray diffraction and HRTEM investigations. A particular attention is paid to the growth of the (1 0 0) orientation of the oxide which seems to be strongly related to the oxygen partial pressure in the deposition chamber. An explanation in terms of a particular dislocation configuration is proposed. This configuration is linked to the oxygen partial pressure through the atom mobility in the thin oxide film. [Copyright &y& Elsevier]

Abstract: Thin films of AlO x N y were deposited by magnetron sputtering in a wide composition range. Different structures and morphologies were observed, depending on the composition and bonding states, which opened the possibility to tailor the properties of this oxynitride system between those of pure Al and those of nitride and oxide films. In a wide range of stoichiometries, one can report the formation of nanocomposite porous films, where Al nanoparticles are dispersed in an amorphous matrix of AlO x N y . The electrochemical behaviour of the films was studied in isotonic NaCl solution. It was observed that the pitting potential characteristic of aluminium disappears with the incorporation of oxygen and nitrogen in the films, being replaced by a smooth current increase. Electrochemical impedance spectroscopy performed during 35 days showed that the corrosion resistance of the films steadily increases. The unusual optical reflectance profile of some films is maintained after immersion for several months. [Copyright &y& Elsevier]

Abstract: Y2O3 thin films deposited on (001)-MgO substrate have been investigated by high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy. Digital processing of the HRTEM images reveals the presence of grains with a crystallographic structure different from that of the rest of the film (Ia3). The spectrum imaging technique has been applied in vicinity of the Y2O3/MgO interface to get a better knowledge of the phases nucleated on the substrate surface. Fine structures of the O K-edge have been studied in detail; actually two kinds of spectra have been detected in the yttrium oxide thin film. These spectra have been compared to self-consistent full multiple scattering calculations (SC-FMS). One family of spectra has then been associated to the well-known Ia3 structure. The other family of spectra has been compared to calculations performed for the other known structures (such as hexagonal or monoclinic) of Y2O3 with a little success. We have finally compared these spectra to calculations performed with a particular atomic arrangement (octahedral) of Y and O atoms, which leads to a good match between experimental and calculated spectra. Our results emphasize the benefit of coupling several techniques such as HRTEM, EELS and SC-FMS for the determination of structures at the nanometric scale. [Copyright &y& Elsevier]