Optical and X-ray Spectroscopy of Wide Band Gap Semiconductors and Organic Thin Films

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Student thesis: Doctoral ThesisDoctor of Philosophy

Original languageEnglish
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Award date28 May 2010
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Abstract

This thesis reports upon synchrotron based luminescence studies of wide band gap semi-conductors and organic thin films.
The optical and structural electronic properties of cubic and hexagonal boron nitride have been studied using X-ray Excited Optical Luminescence (XEOL) and Optically Detected X-ray Absorption Spectroscopy (OD-XAS). UV/visible emission was identified in both h-BN and c-BN with additional exciton related deep UV emission for the former. UV excited luminescence measurements were used to determine the band gap energies of h-BN and c-BN, these were found to be 5.96eV ± 0.04eV and 6.36eV ± 0.03eV respectively. Spatially resolved XEOL and OD-XAS was used to investigate c-BN microcrystals revealing lateral differences in luminescence and local structure. Synchrotron/laser pump probe spectroscopy was applied to investigate defect states in h-BN and c-BN. Subsequent correlation to the XEOL emission was made proving these defects states to be responsible for the lowest energy emission bands in both materials.
Angular resolved NEXAFS, photo-luminescence (PL) and OD-XAS was used to characterise spin coated thin organic films of poly(phenylamine). The material was shown to exhibit preferred orientation within the film, but spatially resolved imaging OD-XAS revealed lateral variation in the molecular orientation. Electrospray deposition was developed for the growth of thin organic semiconducting films in ultra high vacuum. PL and OD-XAS studies were carried out on pure and mixed films of tetra sulfonated copper phthalocyanine (tsCuPc) and poly(ethyleneoxide) (PEO). Only the mixed complexes displayed infrared emission resulting from disstacking of the tsCuPc by the PEO within the film.