An Investigation of C60/Semiconductor and C60/Ferromagnetic Interfaces using a Metastable Helium Beam

This thesis describes the further development of an existing facility for performing electron spectroscopy, and its application to the study of organic/semiconductor and organic/oxide interfaces. A monochromated x-ray source has been installed on the system to allow x-ray photoelectron spectroscopy (XPS) to be performed in addition to ultraviolet photoelectron spectroscopy (UPS) and the uncommon technique of metastable de-excitation spectroscopy (MDS). The resulting instrument is the first of its kind in the world, allowing XPS, UPS, and MDS to all be performed on the same surface, revealing detailed and complementary information on the electronic, magnetic, and chemical properties of the sample.
To test the instrument and gain experience in XPS, a detailed study of the carbon chemistry of graphene oxide prepared under different conditions was conducted. Additional experience in the application of spin-polarised MDS, obtained during a three-month visit to the National Institute for Materials Science (NIMS) in Tsukuba, Japan, is described culminating in a study of Fe/Fe3O4 interfaces. It is shown that the two layers in this system are ferromagnetically coupled which leads to potential applications as a synthetic antiferromagnet in a spintronics device. The ability to grow high-quality Fe3O4 thin films on the York system is also demonstrated.
The final chapters of the thesis describe the study of interfaces formed from C60 deposited on a Si(111) substrate and a La0:66Sr0:33MnO3 (LSMO) substrate. The former study was conducted to gain experience in the preparation of organic interfaces but revealed important details on the nature of this technologically-relevant interface. It also demonstrates the power of MDS in revealing intramolecular electronic structure that is not observable using UPS. Similarly, the study of C60/LSMO interfaces is relevant to the development of organic spintronics devices. However, it is shown that C60 adsorbs on LSMO in clusters at low coverage with a flat film only forming at coverages of 25 monolayers and above. These findings will help in the effort to incorporate these materials in future organic devices.