Relaxation and Vitrification Processes of Disordered Iron Based Systems

摘要

The influence of processes occurring at various stages of crystallization on morphological features and the electronic structure of the surface of iron-based amorphous metallic alloys (AMA) was investigated with use of scanning tunneling microscopy, atomic resolution, tunneling spectroscopy, XPS and EXAFS spectroscopy methods.The results of morphological changes on surface of iron-based AMA during the structural relaxation under heat treatment of amorphous tapes in the range from 250 to 700 °C are shown. The nonmonotonic dependence of subroughness parameters of AMA surface in the annealing range from room temperature to 700 °C is established. The formation of regular shape nanostructures in the form of rods was observed at annealing temperature about 500 °C.For initial amorphous iron-based samples the presence of significantly oxidized surface layer down to a depth of 150 nm was shown. In the case of alloying of amorphous Fe-B system by metalloid its segregation at the surface is observed. During structural relaxation induced by heat treatment a higher redistribution of boron atoms in comparison with Fe and Si atoms occurs. On the surface of investigated AMA carbon is appeared mainly in the oxidized state while in the bulk it forms compounds with silicon.The low conductivity regions typical for the Fe-Si and Fe-B nanophase formation were detected by tunneling spectroscopy method. The substantial inhomogeneity of electron density of states at the intercluster boundaries is observed indicating on their complex organization. The Fermi level of investigated alloys is situated at local minimum of electron density of states and thus meets the criterion of Nagel-Tauk for amorphous state formation. Under complete crystallization conditions at 700 °C terraced structures were observed which formed a practically smooth planes of size more than 200 nm. According to EXAFS-studies the increase of Co atoms concentration in the AMA Fe-Co-B system leads to reduction of the radiu