Accession Number : ADA308701

Title :   Epitaxial Interactions Between Molecular Overlayers and Ordered Substrates.

Descriptive Note : Technical rept. 11 May 95-30 Jun 96,

Corporate Author : MINNESOTA UNIV ST PAUL DEPT OF CHEMICAL ENGINEERING AND MATERIALS SCIENCE

Personal Author(s) : Hillier, Andrew C. ; Ward, Michael D.

PDF Url : ADA308701

Report Date : 13 MAY 1996

Pagination or Media Count : 28

Abstract : A framework for evaluating the epitaxy of ordered organic overlayers of generic symmetry on ordered substrates is described that combines a computationally efficient method for explicit determination of the type of epitaxy (i.e., commensurism, coincidence, or incommensurism) and overlayer azimuthal orientation with an analysis of the elastic properties of the overlayer and the overlayer-substrate interface. The azimuthal orientations predicted by this function agree with values predicted by semi-empirical potential energy calculations and observed experimentally for previously reported organic overlayers which are demonstrated here to be coincident, including electrochemically grown overlayers of molecular conductors. Calculations based on this analytical approach are much less computationally intensive than potential energy calculations as the number of computational operations is independent of the overlayer size chosen for analysis. This enables analyses to be performed for the large overlayer basis sets common for molecular overlayers. Furthermore, this facilitates the analysis of coincident overlayers, for which the overlayer size needs to be large enough to establish the phasing relationship between the substrate and large non-primitie overlays supercell so that the global minimum with respect to azimuthal angle can be determined. The computational efficiency of this method also enables convenient examination of numerous possible reconstructed overlayer configurations in which the lattice parameters are bracketed around those of the native overlayer, thereby allowing examination of possible epitaxy-driven overlayer reconstructions. When combined with calculated intralayer and overlayer-substrate elastic constants this method provides a strategy for the design of heteroepitaxial molecular films.

Descriptors :   *EPITAXIAL GROWTH, *MOLECULAR STRUCTURE, *MOLECULE MOLECULE INTERACTIONS, LAYERS, CRYSTAL LATTICES, ELASTIC PROPERTIES, THIN FILMS, ELECTROCHEMISTRY, SUBSTRATES, CRYSTALLIZATION, NUCLEATION, ATOMIC SPECTROSCOPY, ELECTROLYTES, POTENTIAL ENERGY, POLYMORPHISM, ATOMIC STRUCTURE, MOLECULAR ENERGY LEVELS.

Subject Categories : Atomic and Molecular Physics and Spectroscopy

Distribution Statement : APPROVED FOR PUBLIC RELEASE