Characterization of conducting polymer films grown via surface polymerization by ion-assisted deposition

Optimization of photonic and electronic devices based on conductive polymers, such as polythiophene and polyphenyl, requires the development of processing methods that can control both film chemistry and morphology on the nanoscale. One such method is explored in this thesis: surface polymerization by ion-assisted deposition (SPIAD).; Polythiophene and polyphenyl thin films are grown on a silicon surface by SPIAD which uses hyperthermal, mass-selected thiophene cations coincident with alpha-thermal beam of aterthiophene (3T) or p-terphenyl (3P) neutrals. Mass spectrometry and x-ray photoelectron spectroscopy are used to verify polymerization of both 3T and 3P. The optimal conditions for the most efficient polymerization reaction and film growth are found by varying ion/neutral ratio and ion energy. The electronic structures of these films are probed by ultraviolet photoelectron spectroscopy (UPS) and polarized near-edge x-ray absorption fine structure spectroscopy (NEXAFS). The conducting polymer films formed by SPIAD display new valence band features resulting from a reduction in both their band gap and barrier to hole injection. These changes in film electronic structure result from an increase in the electron conjugation length and other changes in film structure induced by SPIAD. Scanning electron microscopy and x-ray diffraction are used to demonstrate that SPIAD can control the overall polythiophene and polyphenyl film morphology through the mediation of adsorption, diffusion, sublimation (desorption), and other thermal film growth events by ion-induced processes including polymerization, sputtering, bond breakage, and energetic mixing.; Predicting the electronic properties, growth mechanism and morphology of the SPIAD films should be possible through computer simulations of the controlling phenomenon. Study with first principles density functional theory-molecular dynamics (DFT-MD) simulations indicates that polymerization and fragmentation of ions and/or neutral species are critical steps in the SPIAD process. In addition, the simulations predict that free protons and other radicals are formed during SPIAD that apparently contribute to the properties of the conducting polymer.