Date of Award
Doctor of Philosophy (PhD)
Physics & Astronomy
Alan T. Johnson
Following the isolation of graphene in 2004, scientists quickly showed that it possesses remarkable properties. However, as the scientific understanding of graphene matured, it became clear that it also has limitations: for example, graphene does not have a bandgap, making it poorly suited for use in digital logic. This motivated explorations of monolayer materials “beyond graphene”, which could embody functionalities that graphene lacks. Transition metal dichalcogenides (TMDs) are leading candidates in this field. TMDs possess a wide variety of properties accessible through the choice of chalcogen atom, metal atom and atomic configuration (1H, 1T, and 1T’). Similar to graphene, monolayer TMDs may be produced on a small scale through mechanical exfoliation, but useful applications will require development of reliable methods for monolayer growth over large areas. In this thesis, I report our group’s recent progress in the chemical vapor deposition (CVD) of high quality, large area, monolayer TMDs under a 1H atomic configuration, which were integrated into high-quality biosensor arrays. These devices were incorporated in a flexible platform and were used for electronic read out of binding events of molecular targets in both vapor and liquid phases. I also report our findings on the CVD growth of monolayer TMDs in the 1T’ atomic configuration and measurements of their physical properties. 1T’ TMDs have been labeled the holy grail of materials due to theoretical predictions that they are 2D topological insulators; however they remain relatively unexplored due to the difficulty of monolayer growth and their lack of stability in air. Through careful passivation techniques, we were able to stabilize the as-grown monolayer 1T’ TMD flakes and perform the first characterizations on the structure. Lastly, in-plane 2D TMD heterostructures are promising material systems that combine the unique properties of each TMD. I discuss our results on the synthesis and study of 1H TMD heterostructures and unique 1H/1T’ TMD heterostructures. TMDs, with its many different accessible physical properties, coupled with the large variety of applications, have been classified as the leading nanomaterials in the realm “beyond graphene”.
Naylor, Carl Hugo, "Beyond Graphene: Monolayer Transition Metal Dichalcogenides, A New Platform For Science" (2017). Publicly Accessible Penn Dissertations. 2499.