Organic semiconductors, diamond and fingerprint recovery : measuring the energy levels of materials

Abstract

Optimisation of the energy levels of materials is crucial for the creation of efficient multi-layer electronic devices. This thesis describes measurements of the energy levels of a variety of different types of materials: from cheap, solution processable, organic semiconductors with potential applications from solar cells to OLED displays, to diamond which is expensive but has excellent thermal properties that could make it ideal for high power RF applications. Additionally, common metal surfaces such as brass and iron are studied for small changes in their energy levels at microscopic scales to reveal invisible fingerprints in an energy level map with potential uses within forensic science and policing. These measurements are performed using Kelvin probe and ambient pressure photoemission spectroscopy non-destructive analysis tools.

A simple ambient pressure photoemission technique is used to study the ionisation energy of different conjugated polymers. These results were in good agreement with literature results and DFT calculations showing that this method offers a useful alternative to vacuum photoemission analysis or cyclic voltammetry.

For the first time, a variety of diamond samples were analysed using combined Kelvin probe and photoemission techniques under ambient conditions. Additionally, hydrogen terminated diamond was investigated under different pressures to study the effect of the presence of a surface water layer on the electron energy level behaviour.

A detailed study of fingerprint recovery using the scanning Kelvin probe (SKP) technique across a variety of metal surfaces and donors was conducted. The longevity of the signal was studied with clear identifiable fingermarks revealed from SKP scans after more than three years ageing. As a non-destructive method, SKP analysis of metal surfaces could provide an important first-stage analysis tool for fingerprint recovery or identification of possible touch DNA areas during the investigation of serious and major crime.