Surface Science and Optical Spectroscopy Studies of Oligothiophene Adsorption on Clean and Oxygen-Dosed Aluminum Surfaces

University Of Massachusetts Lowell Research Foundation, Lowell MA

Investigators

Abstract

The aim of this project is to investigate the adsorption of thiophene oligomers on well-characterized aluminum surfaces are proposed. X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) studies at a variety of temperatures will be performed to examine the organic layer/aluminum interface formed by exposing clean, single crystal and polycrystalline aluminum surfaces to gas phase, vacuum-sublimed, or x-ray-formed oligothiophenes. XPS will provide information regarding chemistry that is occurring at the interface, and UPS will be used to determine the electronic valence structure of the metal and how it changes upon oligothiophene adsorption. These results will be correlated with work function and optical spectroscopy measurements. Adsorption of a variety of substituted thiophene oligomers will also be studied at different temperatures on single crystals of aluminum, and low energy electron diffraction (LEED) and photoluminescence will be performed to search for evidence of oligomer ordering. Surface photovoltaic spectroscopy measurements will also be carried out to investigate changes in the position of the Fermi level that occur upon absorption of light. Oligothiophene coadsorption on oxygen-dosed aluminum surfaces and on aluminum oxide will also be investigated to determine how adsorption on these surfaces differs from on clan aluminum. Weaker chemical interaction is expected on the oxygen-expose surfaces, and possibilities should exist for oligothiophene alignment. Thermal desorption spectroscopy and LEED will be used to assess adsorption/desorption behavior and ordering of the adsorbed oligomers. %%% Aluminum is commonly used as an electrode material for polymeric light-emitting diodes (LEDs), field-effect transistors and photovoltaics, and substituted thiophenes are an important class of polymers for these types of devices. Device materials are of significant importance to industry, and students trained in these areas compete well in the job market. This project is being jointly supported by The Solid-State Chemistry Program in The Division of Materials Research and The Advance Materials and Processing Program in the Chemistry Division.