Quantitative studies of the structure and chemistry of materials at the nano- and atomic-scale

Bigatti, Marco (2015) Quantitative studies of the structure and chemistry of materials at the nano- and atomic-scale. PhD thesis, University of Glasgow.

Abstract

In this thesis electron microscopy was employed to characterise the nanoscale and atomic scale structure and chemistry of organic and inorganic materials.
In chapter 4, the thin film morphology of the organic blend of [poly(9,9-dioctylfluorene- co-benzothiadiazole)] (commonly referred as F8BT) and poly[9,9-dioctyfluorene-co- N-(4-butylphenyl)-diphenylamine] (abbreviated as TFB) was investigated, mainly by bright field transmission electron microscopy (BF-TEM).
F8BT and TFB are conjugated polymers, which are candidates to replace inorganic semiconductors in many applications because of their simple preparation and processing procedures. The phase separation of the F8BT:TFB blend was investigated at different compositions. Polymer domains were found in the thin film, with sub- micrometer size which varies with concentration. The 1:1 weight ratio sample showed sub-micrometer TFB rich areas in a F8BT matrix, while the 1:4 weight ratio thin film presented F8BT phases, whose areas are mostly below 0.02 μm2, in a TFB layer. Since some electronic applications, especially in optoelectronics, show increased efficiency after addition of quantum dots in the polymer blend, the effect of CdSe quantum dots on the phase separation of the organic blend was investigated together with their effect on the nanoscale morphology. The CdSe quantum dots were found to aggregate in clusters with limited dispersion within the polymer domains, which did not present significantly morphology changes as a consequence of quantum dots (QDs) addition.
The atomic structure and chemistry of the inorganic Ba6−3xNd8+2xTi18O54 microwave ceramic was quantitatively investigated in chapter 4, using high resolution scanning transmission electron microscopy (HR-STEM) and electron energy loss spectroscopy (EELS). These materials are an essential part of telecommunication systems, they can be found in components such as resonators and antennas, on account of their high permittivity, temperature stability and the very low dielectric loss at microwave frequencies. The unit cell was refined with sub-Å precision based on extensive data analysis of HR-STEM images and the unit cell structure showed no significant changes as a consequence of changes in composition or cooling rate after annealing. Ba was found to substitute preferentially to specific Nd atomic columns in the structure, and these trends apply across the whole composition range. These results were confirmed by comparisons with image simulations and provided a starting point for improved refinements of X-ray data.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Electron microscopy, TEM, HAADF, EELS, microwave dielectric, Ba6−3xNd8+2xTi18O54, unit cell, statistical data processing, QD, F8BT, TFB
• Subjects: Q Science > QA Mathematics > QA76 Computer software; Q Science > QC Physics; Q Science > QD Chemistry
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Supervisor's Name: MacLaren, Dr. Ian
• Date of Award: 2015
• Depositing User: Mr Marco Bigatti
• Unique ID: glathesis:2015-6393
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 28 May 2015 09:41
• Last Modified: 04 Jun 2015 15:38
• URI: https://theses.gla.ac.uk/id/eprint/6393