Doctor of Philosophy (PhD)


Electrical and Computer Engineering

Document Type



Two-dimensional material graphene has proven to have remarkable electrical and photonic properties, opening the door to a wide range of uses, including employment in the harsh environs of space. The creation of graphene on various substrate types is known to be possible via a number of approaches, including direct deposition and the substrate transfer process. In this work, we use an argon plasma, methane as a carbon source, and a nanoCVD-8G graphene reactor to deposit monolayer graphene on transition metal substrates while studying the effects of gamma irradiation. Graphene's crystalline structure is investigated utilizing Raman and X-ray Photo Electron Spectroscopy (XPS) techniques before and after the gamma irradiation. Raman spectra and XPS findings on monolayer graphene (MLG) show that point defects predominate following gamma irradiation. To comprehend the relationship between the defected structure and the electronic properties, density functional theory (DFT) simulations are performed.

Two-dimensional transition metal dichalcogenides (2D-TMDs) have been proposed as novel optoelectronic materials for space applications due to their relatively light weight. MoS2 has been shown to have excellent semiconducting and photonic properties. Although the strong interaction of ionizing gamma radiation with bulk materials has been demonstrated, understanding its effect on atomically thin materials has scarcely been investigated. Here, we report the effect of gamma irradiation on the structural and optical properties of a monolayer of MoS2. We perform Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) studies of MoS2, before and after gamma ray irradiation with varying doses and density functional theory (DFT) calculations. The Raman spectra and XPS results demonstrate that point defects dominate after the gamma irradiation of MoS2. DFT calculations elucidate the electronic properties of MoS2 before and after irradiation. Our work makes several contributions to the field of 2D materials research. First, our study of the phonon density of states and the electronic properties of a MoS2 monolayer irradiated by gamma rays sheds light on the properties of a MoS2 monolayer under gamma irradiation. Second, our study confirms that point defects are formed as a result of gamma irradiation. And third, our DFT calculations qualitatively suggest that the conductivity of the MoS2 monolayer may increase after gamma irradiation due to the creation of additional defect states.



Committee Chair

Veronis, Georgios

Available for download on Thursday, October 31, 2030