Synthesis and fundamental property studies of energy material under high pressure.

phosphorene;graphene;CVD;characterization;semiconductors;renewable energy

Meysam Akhtar

University:University of Louisville

Department:Physics and Astronomy

关键词: phosphorene;    graphene;    CVD;    characterization;    semiconductors;    renewable energy;   

Others  :  https://ir.library.louisville.edu/cgi/viewcontent.cgi?article=3850&context=etd

美国|英语

来源: The Universite of Louisville's Institutional Repository

【 摘 要 】

Recently, high-pressure science and technology has flourished and rapidly advanced to impact a wide domain of materials and physical sciences. One of the most substantial technological developments is the integration of samples at ultrahigh pressure with a wide range of in-situ probing techniques. Applications of extreme pressure have significantly enriched our understanding of the electronic, phonon, and doping effects on the newly emerged two-dimensional (2D) materials. Under high pressure, materials’ atomic volume radically decreases, and electronic density rises, which will lead to extraordinary chemical reaction kinetic and mechanisms. The promising capability of high pressure combine with the significance of novel emerging 2D materials in energy-related research was the main motivation of this dissertation. Firstly, the application of high pressure to enable the direct synthesis of α-AgGaO2 through a reaction of Ag2O and Ga2O3 is demonstrated. The synthesized samples were extensively characterized, and their crystal phase and chemical composition were confirmed. Especially, the rhombohedral delafossite crystal phase of the prepared sample was verified by electron diffraction. The vibrational phonon modes were investigated using a combination of ab initio density functional theory (DFT) and experimental Raman measurement. In addition, using a modified DFT to calculate the electronic band structure of α-AgGaO2 reported a more accurate valu of theoretical[1] band gap than those have been reported previously. Two-dimensional (2D) materials with efficient ion transport between the layers and the large surface areas have demonstrated promise for various energy-related applications. Few-layer black phosphorus (phosphorene), as a novel two-dimensional (2D) material, is gaining researchers’ attention due to the exceptional properties, including puckered layer structure, widely tunable band gap, strong in-plane anisotropy, and high carrier mobility. Phosphorene application expanded from energy storage and conversion devices to thermoelectrics, optoelectronic and spintronic to sensors and actuators. Several recent theoretical studies have indicated that strain engineering can be a viable strategy to tune the electronic structure of phosphorene. Although several theoretical studies have predicted an electronic phase transition such as direct-indirect bandgap and semiconductor-metal transitions, there is not experimental study to indicate the transition. Next, in this dissertation, a systematic experimental study of in situ high-pressure Raman and PL spectroscopy of phosphorene was reported. Furthermore, short transport growth of bulk black phosphorus and also, liquid-phase exfoliation technique to preparing few-layer black phosphorus was described. The study motivated by a better understanding of high-pressure effects on optical properties and band structure of this material system. This study help to verify