Novel scanning probe methods for manipulating and characterising pentacene thin films and crystals
File(s)
Author(s)
Bryan, Emma Grace
Type
Thesis
Abstract
Molecular semiconductors are rapidly emerging as a key enabling technology in fields such as quantum sensing, neuromorphic computing and energy generation. Their flexibility, tunability and low-cost fabrication make them promising materials for the highly-integrated electronic architectures of future technology. This thesis devises strategies to control and optimise the functional properties of molecular thin films and crystals for organic electronic applications.
With charge carrier mobility comparable to amorphous silicon, pentacene is one of the most well-researched molecular semiconductors, both as a model system and for its own technological utility. Like other small-molecule semiconductors, the functional properties of pentacene such are highly orientation-dependent, which currently limits its applications in devices such as photovoltaics. Strongly-interacting substrates can be used to template the molecular orientation of thin films and improve charge transport and light-matter interactions. This thesis identifies poled ferroelectric polymer thin films as effective templating layers for pentacene. Molecular orientation is correlated to optoelectronic properties and a higher out-of-plane mobility is demonstrated for the flat-lying (edge-on) pentacene compared to the upright (end-on) orientation. In the pursuit of high-performance nanoscale devices, the efficacy of oxidation lithography is demonstrated for defining nanoscale conductive channels in pentacene thin films and crystals.
Scanning probe methods based on atomic force microscopy provide the nanoscale imaging capability, sensitivity and versatility to shed light on the properties of these functional materials. This thesis applies advanced modes such as piezoresponse force microscopy, Kelvin probe force microscopy, conductive AFM and local anodic oxidation to investigate both pentacene and the ferroelectric polymer poly(vinylidene fluoride–trifluoroethylene). Developing reliable methods to compare properties on the nanoscale, microscale and macroscale is of paramount importance for the optimisation of organic electronic device materials. A robust multi-modal approach is developed including scanning probe microscopy, spectroscopy and in-situ x-ray scattering to explore orientation, order and performance of molecular semiconductors.
With charge carrier mobility comparable to amorphous silicon, pentacene is one of the most well-researched molecular semiconductors, both as a model system and for its own technological utility. Like other small-molecule semiconductors, the functional properties of pentacene such are highly orientation-dependent, which currently limits its applications in devices such as photovoltaics. Strongly-interacting substrates can be used to template the molecular orientation of thin films and improve charge transport and light-matter interactions. This thesis identifies poled ferroelectric polymer thin films as effective templating layers for pentacene. Molecular orientation is correlated to optoelectronic properties and a higher out-of-plane mobility is demonstrated for the flat-lying (edge-on) pentacene compared to the upright (end-on) orientation. In the pursuit of high-performance nanoscale devices, the efficacy of oxidation lithography is demonstrated for defining nanoscale conductive channels in pentacene thin films and crystals.
Scanning probe methods based on atomic force microscopy provide the nanoscale imaging capability, sensitivity and versatility to shed light on the properties of these functional materials. This thesis applies advanced modes such as piezoresponse force microscopy, Kelvin probe force microscopy, conductive AFM and local anodic oxidation to investigate both pentacene and the ferroelectric polymer poly(vinylidene fluoride–trifluoroethylene). Developing reliable methods to compare properties on the nanoscale, microscale and macroscale is of paramount importance for the optimisation of organic electronic device materials. A robust multi-modal approach is developed including scanning probe microscopy, spectroscopy and in-situ x-ray scattering to explore orientation, order and performance of molecular semiconductors.
Version
Open Access
Date Issued
2025-10-28
Date Awarded
2026-03-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Heutz, Sandrine
Curson, Neil
Sponsor
Engineering and Physical Sciences Research Council
Grant Number
EP/S023259/1
Publisher Department
Department of Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)