ICMCTF2010 Session F1-2: Advances in Characterization of Coatings and Thin Films

The initial, sub-picosecond demagnetization is established at the electronic level through electron-magnon excitations. The subsequent dynamics is characterized by a precessional motion on the 100 picosecond time-scale, around an effective, time-dependent field. Following the full dynamics of M, we have been able to unambiguously determine the temporal evolution of the magneto-crystalline anisotropy, providing the experimental evidence that the precession is triggered by the rapid, optically-induced misalignment between the magnetization vector and the effective field.

The observation of rapid reactions in magnetron sputtered nanoscale multilayers present challenges that require sophisticated analysis methods. Recent advances in fast x-ray diffraction (XRD) detector technology in synchrotron light sources allows direct observation of rapid reactions that occur within milliseconds. We present high-resolution in-situ XRD analysis of rapid reactions in nanoscale foils of Ni_0.9V_0.1-Al using the Mythen II solid-state microstrip detector system at the Material Science beamline of the Swiss Light Source Synchrotron at Paul Scherrer Institut in Villigen, Switzerland along with high speed optical imaging at 40000 fps.

The results reveal a two-step temperature evolution corresponding to the rapid sequential formation of intermetallic phases Ni₂Al₃ and NiAl, vanadium segregation during cooling and formation of internal stresses, determined with high temporal (0.125 ms) and angular (0.004⁰) resolution over a full angular range of 120⁰.

It is known that photocatalytic activity and hydrophilicity of titanium dioxide depends also on phase composition, microstructure and crystallinity. Time and thickness dependences of crystallization of amorphous magnetron-sputtered thin films (of thickness 50−2000 nm) were studied by XRD on post-annealed samples and by in-situ measurement in high-temperature chamber. At room temperature, the films were measured in parallel beam geometry with low angles of incidence and/or exit and by XRD total pattern fitting with our own software the phase composition, lattice parameters, crystallite size and microstrain were obtained. The density, thickness and roughness of the film were estimated from X-ray reflectivity. The roughness increased with the film thickness. Detailed stress/texture analysis revealed the presence of tensile stresses after crystallization. They increased rapidly with the decreasing film thickness. Temperatures of "fast" crystallization (15 min annealing) were found and later refined by in-situ XRD measurements to 220°C for thicker films and 280°C (below 100 nm). For time investigations, lower temperatures (180°C) were selected in order to slow down the process and perform detailed studies in laboratory. Strong dependence of crystallization on the film thickness was confirmed, in particular below about 300 nm. The crystallization was characterized by integrated intensities I_hkl of a few diffraction peaks of anatase. Their evolution could be described by the modified Avrami equation, I = 1-exp[-b(t–t₀)ⁿ)], where the onset of crystallization t₀ is related to the first appearance of diffracted intensity above the background level. It increases abruptly with decreasing thickness while the rate of crystallization b decreases. Low values of n (~ 2) indicate two- dimensional character of the crystallite growth. Profile widths were relatively small from the very beginning of crystallization and did not change with time. This was due to the rapid growth of a few crystallites and it means that it is impossible to prepare nanocrystalline TiO₂ films by annealing of amorphous ones unlike the powders for which this is a technique of preparation of nanocrystals of predefined mean crystallite size. Evolution of preferred orientation and stress generation during the crystallization were observed. Initial (00l) preferred orientation was smoothed out with the time for thicker films (above 100 nm). It was also confirmed from the shifts of diffraction peaks with the time that tensile residual stresses are formed during the crystallization. They were studied in detail at room temperature by direct stress measurement and by total pattern fitting.