Simulation of Multicomponent Thin Film Deposition and Growth
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These theoretical shortcomings stem in part from the complexity of thin film deposition processes. I Some of the many possible variables include substrate type, orientation, and defect density, substrate or ambient temperature, deposition technique, source ratios, deposition atmosphere, deposition rate, and post annealing processes. Many of these variables, like temperature and the coefficient of thermal expansion of the substrate, are related in a complex fashion. While the large number of thin film studies are providing insight into the general effects of specific deposition conditions on thin film growth, it is difficult to design an ideal experiment that precisely controls all but one of the many variables to allow investigation of the effect of a particular parameter on film growth. In this, computer simulation can provide the degree of control over "experimental" conditions and the spatial and temporal resolution necessary to complement experimental studies of thin film systems. In what follows, results of a multicomponent Monte Carlo simulation of YBa 2 Cu 30 7 are presented. MODEL AND PREVIOUS FINDINGS 2 The details of the simulation method used in this study have been published elsewhere. In brief, simulation particles representing yttrium and barium perovskite units, and a copperoxygen unit are deposited into a three dimensional cubic lattice with periodic boundary conditions in the x and y directions (in the conventional sense) with the z direction being bounded by the substrate below and a free boundary above. Interactions are a function of particle type and crystallographic direction and act only between nearest neighbors. Three simulation
59 Mat. Res. Soc. Symp. Proc. Vol. 389 01995 Materials Research Society
excitation modes are performed representing deposition, surface diffusion, and bulk annealing. The latter mode acts to attempt a realignment of the deposition particle's "spin" property, a property which specifies the current orientation of its crystal domain. In previous studies, two distinct epitaxial variants were found to occur. These were individually characterized as an 'a' type, with [100] direction oriented perpendicular to the substrate, and a 'c' type, with [001] direction oriented perpendicular to the substrate. Through a systematic variation of deposition rate and substrate temperature during in-situ deposition, it was observed that transitions between these different growth variants occurred. At constant substrate temperature, very low deposition rates produced films with a 'c' type morphology. Higher deposition rates yielded 'a' type morphology. Increasing the deposition rate further leads to defected 'c' type films and then ultimately to nearly amorphous films. A similar behavior was observed as a function of substrate temperature. Low and high substrate temperatures at a constant deposition rate yielded 'c' type films while an intermediate substrate temperatures yielded a 'a' type morphology. A subsequent investigation 3 of the influence of substrate mismatch on film growth sug
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