Resolving structure-function relations in advanced materials by scanning probe and electron microscopies

Naden, Aaron B. (2015) Resolving structure-function relations in advanced materials by scanning probe and electron microscopies. PhD thesis, University of Glasgow.

Abstract

Understanding the links between structural and functional properties is at the heart of materials science and underpins the development of technologically relevant materials. The work presented in this thesis is primarily concerned with development of these links in two distinct material classes by scanning probe and electron microscopies.

After a brief overview of the background and instrumentation (Chapters 1 and 2), Chapter 3 concerns the development of structure-function relations in bottom gate, bottom contact organic transistors employing an active layer comprising a blend of diF-TES-ADT and a polystyrene-like binder. These devices are shown to exhibit electrical performances that are competitive with equivalent amorphous Si (a-Si) devices. The nucleation and growth processes of the semiconductor film, leading to the formation of four structurally distinct crystalline diF-TES-ADT regimes, are described, including evidence of layer-by-layer growth when solution processed. These crystalline regimes – or regions of growth – are linked to electrical characteristics by study of a variety of different device components. One of these regions of growth – region D, the 3D crystals – does not appear to have been previously reported for diF-TES-ADT. The structure-function links are enhanced by direct visualisation of the potential drop across the channel of devices using scanning Kelvin probe force microscopy. The different crystalline regimes are rationalised in the context of a first kinetic description of the film formation process, which can be used to make predictions with regards to device optimisation for more commercially viable, shorter channel length devices.

In Chapter 4, advanced specimen preparation protocols by means of a focused ion beam instrument are addressed; followed by the applicability, advantages and limitations of electron microscopy for the study of organic transistors, employing electron energy loss spectroscopy. Issues of phase segregation and intermixing are addressed in this context, with a combination of atomic force and electron microscopies proving to be particularly successful. The possibility of identifying different organic materials in the absence of unique elements is explored by investigation of spectroscopic fine structure and plasmon energy analysis using electron energy loss spectroscopy. The ability to assess such issues with nanometre resolution is pivotal to developing a thorough and detailed understanding of this class of device.

Chapter 5 considers an entirely separate class of materials, functional metal oxides. An analysis protocol is developed for the quantified assessment of moire fringes arising in scanning transmission electron microscopy. Here, a rigorous and robust mathematical description of the technique is developed and a method for accurate quantification of data is demonstrated. The assessment of strain over large fields of view is investigated and the ability to identify dislocations within crystalline specimens by STEM moire is shown for the first time. Assessment of crystallographic strain over large fields of view with high precision is important for developing structure-function relations of functional oxides since their properties can be carefully controlled by strain engineering. The studies presented here represent an important step forward in understanding this attractive approach.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: atomic force microscopy, transmission electron microscopy, electron energy loss spectroscopy, functional materials, structure-function relations; organic semiconductors; oxide; moire; organic transistors
• Subjects: 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. Donald
• Date of Award: 2015
• Embargo Date: 6 February 2019
• Depositing User: Aaron Benjamin/A.B. Naden
• Unique ID: glathesis:2015-6857
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 12 Nov 2015 11:48
• Last Modified: 19 Dec 2018 16:30
• URI: https://theses.gla.ac.uk/id/eprint/6857