Electronic and optical properties of two dimensional Molybdenum Oxide Nanoflakes
Creators: name: Alsaif, Manal M Y A
Publisher: name: RMIT University
Year: 2024

description: In this research, the PhD candidate became involved in the development of gas sensors, plasmonic systems and field effect transistors (FETs) based on a solvent-assisted grinding and sonication liquid-phase exfoliation (LPE) method of two-dimensional (2D) molybdenum oxide nanoflakes. The electronic band structure of this material is highly tunable, making it apposite for a variety of electronic and optical applications. The layered structure α phase of this crystal (α-MoO3) and high surface to volume of 2D α-MoO3 can accommodate a high capacity of intercalated charges and enable adsorption of atoms and molecules at remarkable efficiencies.<br><br>The candidate continued her PhD research by developing conductometric gas sensor films made of 2D MoO3 nanoflakes based on the grinding-assisted LPE technique, and used these sensors for hydrogen (H2) gas detection. The study confirmed that the layered MoO3 nanostructure with high surface-to-volume ratio facilitated the H2 gas interaction and the outcomes were better in comparison to many previous reports for H2 sensing based on other nanostructure morphologies of MoO3.<br><br>In the next stage of this project, the PhD candidate demonstrated the emergence of highly controllable plasmon resonances in 2D molybdenum oxide flakes. The PhD candidate demonstrated that due to the effect of a large depolarization factor in 2D molybdenum oxide, the plasmon resonance peaks could be tuned within the visible range region, which could not be shown for any other 2D materials. Moreover, the biosensing capability of plasmonic 2D molybdenum oxide nanoflakes using bovine serum albumin (BSA) as a model protein was demonstrated.<br><br>In the third stage of this research, in order to show the effect of liquid exfoliation of the 2D flakes and the light illumination parameters, the candidate synthesized 2D molybdenum oxide nanoflakes via the LPE method in five mixtures of water with different solvent types. It was revealed that plasmonic peaks strongly depended on the free electron concentration, and the extinction coefficients of the plasmonic absorption bands of 2D molybdenum oxide nanoflakes in all samples were found to be very high in the order of 109 L.mol-1.cm-1. Moreover, plasmonic biosensing experiments were conducted to reveal the efficient tuning of 2D plasmonic flakes in sensing biological components.<br><br>By using these outcomes drawn from the previous measurements and characterizations, plasmonic 2D flakes were also tested for plasmonic gas sensing. Highly sensitive optical H2 gas sensors based on quasi-metallic Mo4O11 films with plasmonic responses were developed. This study was the first demonstration of using plasmonic properties of 2D materials for gas sensing.<br><br>In the final stage of this PhD project, the candidate fabricated high-performance FETs made from thin film channels, based on the drop-casting of electronic inks. By investigating the performance of these FETs as a function of sub-stoichiometric levels that were obtained under different solar irradiation durations, the candidate found that the electron mobility value for the FET was significantly higher than the mobility of most of the previously reported thin film based transistors made from other 2D materials. In addition, this research revealed that by controlling and manipulating the oxygen deficiencies in 2D flakes, the carrier concentrations, electronic energy band edges, and carrier charge mobilities can be tuned.<br><br>