EX SITU STUDY OF THE EPITAXIAL GROWTH OF N-ALKANE THIN FILMS

Abstract

A thorough understanding of the growth mechanism in organic thin film growth is necessary to be able to develop devices based on these materials. In particular, there are open questions about the growth mechanism of multilayered structures beyond the first monolayer. Of particular interest to this work is developing an understanding of the early and intermediate steps of n-alkane film epitaxial growth on highly ordered surfaces. In order to address this question, a technique needs to be used that allows observation of films at intervals during growth, while providing elemental sensitivity, spatial resolution, and orientation information. Photoemission electron microscopy (PEEM) is an electron microscopy technique with high spatial resolution suited to studying thin films in situ. When combined with tunable polarized X-rays from a synchrotron source, PEEM provides a powerful method to study the orientation of molecular films. However, alkane films are sensitive to radiation damage from UV and X-ray light. In addition, an in situ deposition study of n-alkanes cannot be performed without contamination of the vacuum environment. Deposition in PEEM will lead to contamination of other samples when the microscope is subsequently used. Therefore, an ex situ approach is used, where films are grown in high vacuum conditions in an adjacent chamber and analyzed with PEEM immediately after preparation. This method will be used to study the intermediate stages of n-alkane thin film growth. Previous research using linear polarized near edge X-ray absorption spectroscopy (NEXAFS) has proven useful in the study of the various oriented morphologies of n-alkanes grown by physical vapour deposition. Early to mid-stage growth has not been studied in depth however, and there may be a shift in growth modes as the epitaxial interaction with the graphite substrate is reduced as more layers are deposited. The ex situ evaporator has been designed, manufactured, and is operating according to expectations. Experiments have been performed to address the compatibility of these alkanes in the PEEM with x-ray illumination, including normalization techniques and radiation damage assessment.