Kinetics and Thermodynamics of n-Alkane Thin Film Epitaxial Growth

Abstract

Controlling molecular orientation is of great importance in organic thin films due to the fact that the fundamental properties of functional nanomaterials depend on molecular orientation at the nanoscale. However, controlling molecular orientation cannot be achieved without having an extensive understanding about the controlling factors in the organic film growth processes. Most previous studies have been devoted to monolayer structures. The structure of multilayer films has not been well investigated. This study was performed using a phenomenological approach, in which the morphology and orientation of n-alkane thin films were studied as a function of substrate identity, interface treatment, substrate temperature and deposition rate. The experimental techniques that were used include IR-spectroscopy, polarized optical microscopy, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray microscopy. The kinetic and thermodynamic factors that govern the orientation of organic thin films were extracted from the experimental results, and generalized to make a framework by which the morphology and orientation of organic films can be predicted. Epitaxial growth was specifically considered as a method to pattern organic thin films. In epitaxial growth, the oriented crystals of an organic film grow on a crystalline substrate such that the structure of the substrate is copied by the deposit crystals. For epitaxy it is required that the lattice planes of two crystals are parallel and similar in the lattice points spacing. A minor part of this dissertation is devoted to epitaxy in an inorganic system. One of the favorable consequences of epitaxial growth in inorganic systems is lattice strain that alters the electronic properties of semiconductor devices. A synchrotron based experimental method has been developed to quantitatively measure the degree of strain in Si1-xGex alloy films grown epitaxially on the Si(100) substrate.