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University Oral Exam - Fan Yang: The Effect of Pressure on the Properties of Carbon-based Nanomaterials

Date and Time: 
September 22, 2017 -
2:00pm to 3:00pm
Location: 
GESB 365
Contact Email: 
ylopez@stanford.edu
Contact Phone: 
650-723-0848
Event Sponsor: 
Department of Geological Science

The Effect of Pressure on the Properties of Carbon-based Nanomaterials

High pressure, which can dramatically decrease the atomic volume and increase the electronic density of the reactants, could result in novel and special chemical reactivity, kinetics and reaction mechanisms. Thanks to the development of various pressure devices and probing technology, high pressure research has been advancing so rapidly over the past several decades. High pressure studies have greatly enhanced our understanding in a number of scientific fields, such as condensed matter physics, chemistry, material sciences and Earth and planetary sciences. Carbon forms a variety of stable and metastable phases with exceptional physical and chemical properties. Carbon and carbon-based materials have attracted significant interests due to their unique properties and various possible applications. 

Throughout my PhD years, I have worked on the high pressure study of several carbon based nanomaterials. This dissertation talk will focus on how the effect of pressure affects material’s bonding and electronic properties, particularly in a series of carbon based nanomaterials namely diamondoid, its functionalized derivatives and carbon-nanotube. 

Before delving into more specific topics described later, I will begin the talk with explanation of several elementary, but extremely important concepts in high pressure science and also briefly discussing the laboratory devices used to produce pressure, addressing the issue of hydrostaticity and etc. Then I will discuss our discovery of the pure diamondoids under pressure. We found most of them underwent pressure induced phase transition easily and some of the phase transitions are extremely sensitive to the deviatoric stress. We also found that the compressibility of pure diamondoid crystals has a strong correlation with the diamondoid molecular geometry. Our collaborator in the Department of Material Science and Engineering has successfully synthesized a serious of metal organic chalcogenide (MOCs) with different molecular geometries based on the diamondoids and its analogs. They all have core-shell structures with metal chalcogenide in the core and the organic molecules as the shell which form the nanowires structures. I will discuss our observations of steric-controlled pressure driven chemical reactions in these compounds which represent as an example of the rarely reported mechanochemistry process. In the final part, I will discuss our work using pressure and temperature as tuning parameters to derive graphene nanoribbon from carbon-nanotubes which established a new approach in synthesizing graphene nanoribbon.