Exploring the electronic structure of nanoscale low-dimensional materials through advanced photoelectron spectroscopic techniques
OA Version
Citation
Abstract
Low-dimensional materials exhibit unique properties and behaviors due to their reduced dimensionality, including tunable bandgap, superconductivity, and optical properties, which have gained extensive attention from researchers. However, manipulating the dimensions of low-dimensional materials at the nanoscale to fine-tune their properties remain largely unexplored. Therefore, examining properties at the nanoscale and exploring size-dependent phenomena are of great importance in the field of low-dimensional materials. This dissertation presents a measurement of the electronic structure of quasi one-dimensional blue bronzes and layered two-dimensional metal phosphorus trichalcogenides using photoelectron spectroscopic techniques at the nanoscale. This study first focus on exploring the possibility of synthesizing blue bronzes K0.3MoO3 thin films at the nanoscale via pulsed laser deposition. Different film morphologies of thin film K0.3MoO3 at the nanoscale were achieved by using various substrates with different lattice parameters. The films were characterized by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. Transport properties of the films were measured using four-probe methods and compared to their bulk counterparts. Electronic properties of the core level and valence level of K0.3MoO3 thin films were probed by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy, respectively. Temperature-dependent result suggests that a band gap appears at 34K for thin films K0.3MoO3 at the nanoscale, which has never been observed in bulk samples. For metal phosphorus trichalcogenides, the X-ray absorption spectroscopy for the transition metal L3,2-edge of single crystal NiPS3, MnPS3, MnPSe3, FePS3 and FePSe3 were obtained. The oxidation state and charge-transfer energy of the transition metals were determined with the help of multiplet model calculations by CTM4XAS. Resonant inelastic X-ray scattering spectra of the transition metal L3-edge were obtained for both room temperature (paramagnetic state) and low temperature (antiferromagnetic state) of NiPS3, MnPS3 and FePS3. Then the single crystal NiPS3 was exfoliated into nanoscale thin flakes on doped silicon substrates for angle-resolved photoemission spectroscopy measurements. Room temperature measurements and temperature-dependent measurements were obtained by lab-based and synchrotron-based angle-resolved photoemission spectroscopy, respectively. Photon energy dependent angle-resolved photoemission spectroscopy measurements and dosing measurements were also applied to NiPS3 flakes. This dissertation was the first to obtain the clear band structure and constant energy map of NiPS3. By dosing with potassium, the energy bands of NiPS3 that above the Fermi level can now be observed.
Description
2024
License
Attribution 4.0 International