Surface morphology and IR optical properties modification of Co-based amorphous metallic alloys during initial stages of crystallization
|Kateryna L. Vinnichenko 1, Mykola V. Vinnichenko 1,2, Leonid V. Poperenko 1|
1. National Kyiv Taras Shevchenko University (NKTSU), Volodymyrska 64, Kyiv 01033, Ukraine
The ribbons of Co59Fe5Ni10Si11B15 (at.%) AMA, prepared by a rapid quenching using a melt spinning technique, were annealed in vacuum for 10 min at Ta=350, 400, 425, 450 and 475 С. The crystallization temperature is known from the literature to be around 490 C. The modification of a surface morphology of the AMA due to the treatment is investigated by atomic force microscopy (AFM). The AFM data were contrasted with a plan-view transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopic ellipsometry (FTIR-SE) results. In the as-prepared state the ribbons have smooth surface with a root-mean square (RMS) roughness around 1 nm at the area of 10 μ m x 10 μ m. TEM shows the homogeneous amorphous microstructure and amorphous halo in electron diffraction. Annealing at 350 C leads to a formation of 5-13 nm high and 100-1000 nm wide isolated features at the ribbon surface. In the subsurface layer of the annealed ribbon TEM shows ellipsoidal nanocrystalline inclusions with a characteristic size within the ~15-80 nm range in the field of vision. Using the TEM data, the observed AFM surface features are interpreted as the crystalline nuclei which grow with annealing temperature. Because the features are larger at the ribbon surface than in the subsurface area, it evidences that the crystallization starts from the surface. The RMS values strongly increase at Ta=475 C and its dependence on the Ta can not be described by exponential laws. It points that classical nucleation and growth theory fails and the AMA crystallization can be described using only concomitant theory accounting for a system disorder . The optical conductivity spectral behavior changes from non-Drude-like to Drude-like at Ta=475 C where the ribbon seems to have the highest content of crystallites. It points to the conduction mechanism change due to a film morphology modification.
 A.B. Pevtsov, et al, Phys Rev. B. 52 (1995) 955.
Presentation: poster at E-MRS Fall Meeting 2005, Symposium F, by Kateryna L. Vinnichenko
See On-line Journal of E-MRS Fall Meeting 2005
Submitted: 2005-05-20 16:23 Revised: 2009-06-07 00:44