Simulation of thin film deposition, microstructure evolution, and properties in complex oxide systems

Monte Carlo simulation employing three excitation modes to model deposition (sorption processes), surface diffusion, and bulk regrowth is used to study epitaxial growth in the Y-Ba-Cu-O superconducting system. The system is modeled as a ternary system of yttrium, barium, and copper oxides. Interactions between simulation particles are a function of both particle type and misorientation providing for the growth of different crystallographic variants. For the indicated choice of parameters typical morphologies and defect structures are obtained that are remarkably similar to those fabricated experimentally. Only canonical interaction parameters are used in the simulation, illustrating that these features are very robust and do not depend on details of the model. The use of simple, nearest-neighbor pair potentials in the simulation is rationalized by appeal to the "sudden" approximation to Schrodinger's equation. Both in-situ and ex-situ modes of growth are examined and many defects characteristic of this system, such as antiphase boundaries and layer defects, are seen to arise. A careful study of the effect of deposition rate on the morphology of in-situ grown films reveals transitions from the (001) or c type epitaxy at low rates to the (100) or a type epitaxy at higher rates and then back to c type growth at still higher deposition rates. Further analysis demonstrates that these transitions arise due to kinetic effects associated with the strong growth rate anisotropy in this system. An analogous morphological dependence is observed for substrate temperature. The growth rate anisotropy between these a and c variants is understood via a consideration of the need for proper chemical coordination during adsorption. Also investigated are the effects of substrate mismatch in an approximate manner by introducing cation-substrate interactions. It is observed that increasing the substrate interaction with the growing film has the effect of widening the stability regime of the a type film morphology with respect to deposition rate. A study of growth mechanisms in the various morphological regimes indicates that the high deposition rate a and c variants grow via an island or a Volmer-Weber mode while the very low deposition rate c type variant grows via a novel multi-stage cyclic growth mode with both island and layer characteristics. The cyclic growth of unit cell thick layers gives rise to the RHEED oscillations observed experimentally and simulated via roughness measurement in the simulation.; The kinetic behavior in this system is interpreted within a Time-Temperature-Transformation framework modified to adapt deposition rate to time. This yields three curves, one each for the Volmer-Weber growth mode a and c morphological variants, and one for amorphous films against a background of multi-stage cyclic growth c type variant for long times (low deposition rates) and high and low temperatures. This framework neatly encapsulates the morphological behavior observed at constant deposition rate and at constant substrate temperature.; Finally, the means by which the formalism for simulating the deposition and growth of {dollar}rm YBasb2Cusb3Osb7{dollar} thin films to other complex, multicomponent thin films is outlined.