UC Berkeley

Interest in low-dimensional (<= 2-dimensional) semiconducting materials is ever growing as electronic device sizes shrink and new physics continues to emerge at such a microscopic scale. Heterostructures allow for a set of physical building blocks made from low-dimensional materials that can be used to tailor devices to obtain precise and unique electronic interactions and device characteristics. Over time as this field has grown, certain research materials that for a time were overlooked in favor of other materials have come into renewed interest as a result of their unique properties that were previously deemed not as useful or were simply left undetected. One such example of this is the family of thin film transition metal dichalcogenides (TMDs), whose unique monolayer and thin film photoluminescence, band gap transition, and spin-orbit-coupling-induced physics has recently been studied intensely as a result of their unique spintronics and valleytronics applications. Another example is C60 which has an extremely unique low-dimensional buckyball molecular structure. It too can take on a crystalline thin film form to be used in heterostructures and electronic devices, but experimental evidence of long-range electronic order in thin film C60 has been lacking until now.

This dissertation presents angle-resolved photoemission spectroscopy (ARPES) studies of multiple TMD and C60 compounds with supporting theory calculations to investigate the electronic stucture of these materials. Specific attention is given to the effects of spin-orbit coupling and orbital character. The relationship between the electronic properties of bulk and thin film TMDs is elaborated in detail with a focus on the valence band splitting at the K point. The first observation of a dispersive thin film C60 band structure is discussed as well as the unique photoemission traits of the C60 band manifolds. Study of the electronic properties of these low-dimensional TMD and C60 materials provides important considerations for current and future cutting-edge electronic device applications.