Interface kinetics and mechanism of a new organometallic coordination compound: ATMB crystal

Abstract

Fe and its oxides have been made in the fonn of nanocrystalline powders. The chemical as well as the vacuum deposition technologies were used to produce a great variety of microstructure, such as with different grain size, internal strain and inhomogeneity. The whole X -ray diffi·action patterns of these smnples were processed by Rietveld analysis using DBWS-9411 code supplied by Prof. R.A. Yotmg. On the other side, the interfaces of these nanocrystals were simulated by molecular dynamics with several theoretical structural models. After sufficient atomic relaxation the interface structrn·e reached equilibrium. Then the theoretical effect of interfaces on the whole X -ray diffraction pattern can be evaluated in detail. The comparison between the theoretical and experimental diffraction patterns gave a possibility to select the correct structural models as well as the interatomic potentials and related parllil1eters. Using the correct interface structure one can predict a series of physical and mechanical properties of nanocrystals on a much sounder basis as compm·ed to usual methods. This is important especially for those properties which are very difficult to measure experimentally. In this work we present a mathematical model capable of describing in detail the atomic structure of arbitrary grain boundaries (GB) in metals and other materials and constitutes the first step towards a complete crystallographic description of GBs. Due to its evident technological implications, GB have been intensely studied in the past with limited success, due, mostly, to the absence of a complete model accounting for the structure of arbitrary GB. This has hllil1pered the establishment of a correlation between bmmdary structrn·e and properties.Using tools closely related to those used in Quasi crystals, the present model describes in detail the atomic structure of arbitrwy GB, not being restricted to those known as "special" and establishes a link between the fields of quasicrystals and GB, permitting a better understanding of both. The model replaces the notion of "coincidence sites" by "best possible fit" and it is continuous (as the 0-lattice) over all the angular range.Om results show that the value of Sigma alone is not enough to characterize special boundaries. In particular, it has been found that some low Sigma GB in FCC metals have a very poor fit (Sigma 17) while others with higher Sigma are SUiprisingly good (Sigma 41 ), thus explaining previous experimental results indicating that Sigma 41 is a special boundary. TEM and AFM studies have been carried out to demonstrate the influence of growth parllil1eters and substr11te orientation on the structure of SiC films deposited simultanously and alternately from two sources by solid-somce molecular be= epitaxy at low substrate temperatures (750 C-900 C). At 750 C and high growth rates (>2nm/min) polycrystalline columnar films were grown which show a weak orientation relationship to the substrate. While growing the films under conditions for Si stabilization at the surface a...