SPECTRAL MODEL OF RESONANT SOFT X-RAY SCATTERING TO RESOLVE MOLECULE SPECIFIC ORGANIZATION IN 3D ORGANIC NANOSTRUCTURES

Thomas  John Ferron

Interest in developing carbon-based materials has increased in recent years due to their advantageous structure and properties. One common challenge in all potential applications is understanding how morphology, in addition to molecular structure, governs the properties and performance. Advances with resonant soft X-ray scattering (RSOXS) have begun to surpass limitations of traditional nanostructure probes that are reliant on electron density contrast alone. RSOXS exhibits enhanced sensitivity to chemical structure through core-shell interactions but, to date, have only provided qualitative descriptions of nanostructures. This dissertation details the development of quantitative spectral modeling of RSOXS to resolve chemical specific organization in organic thin films. Multiphase scattering theory is combined with continuous contrast tuning at the carbon absorption edge to identify origins of scattering and highlight signal from material domains. Additionally, a novel secondary calibration of absolute scattering is developed utilizing X-ray fluorescence of a carbon standard film that allows for a quantitative measurement of RSOXS intensity. Optical models are first demonstrated with a measurement of the scattering invariant on block copolymer assemblies of poly(styrene-block-methyl methacrylate). By isolating scattering from molecular domains, the width of the mixed interfacial region is determined in a series of assembled 3D nanostructures and is found to agree with Flory-Huggins theory. Developed optical models are then combined with X-ray diffraction to quantify the nano-mesoscale morphology of poly(3-hexylthiophene):Phenyl-C61-Butyric acid methyl ester organic photovoltaics. In this follow-up study, a suit of opto-electronic measurements is conducted to rigorously explore a step-by-step characterization of the fundamental charge generation process that occurs within these devices. When paired with the previously developed morphological analysis a direct correlation between nanostructure and electronic properties is established. It was found that the efficiency of charge transfer state separation, as measured on real devices with time-delayed collection field, anti-correlates with the volume of the interfacial mixed phase. These results provide experimental evidence toward an ideal morphology that contains a limited interfacial mixed domain with the necessary energetic landscape for charge generation. The quantitative spectral analysis developed in this work enables RSOXS to identify and characterize a potentially limitless number of unique molecular species in complex organic nanostructures.

SPECTRAL MODEL OF RESONANT SOFT X-RAY SCATTERING TO RESOLVE MOLECULE SPECIFIC ORGANIZATION IN 3D ORGANIC NANOSTRUCTURES

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