Abstract: Over the years, nanomaterials research has advanced towards discovering versatile and readily accessible materials tailored for a diverse range of applications. A comprehensive understanding of materials’ phases and their transformations are integral to this effect to enable better synthetic control as well as the functionalization of nanomaterial properties. Among advanced characterization techniques, the transmission electron microscope (TEM) is a powerful tool that provides direct access to the nanoscale and, therefore, an indispensable tool in studying fundamental materials problems. This dissertation discusses several nanomaterial systems where TEM tools and techniques are utilized to gain a deep understanding of their chemistry. 

This dissertation focuses on structural and phase transformations of nanomaterials using in situ heating in the TEM, which allows direct observation of these dynamic processes. Reported here are studies of the phase transformation and stabilization of the mackinawite phase of iron(II) sulfide nanoplatelets, the structural transformation of gold-catalyzed tin(IV) oxide nanowires into gold core/tin(IV) oxide shell nanowire heterostructures, and finally the interaction between aluminum oxide and lead (at. 17%) lithium alloy proposed for use as a coolant in nuclear fusion reactors. These studies showcase the significance of knowledge of the mechanistic details of phase transformations, with the eventual goal of being able to determine and control structure-property relationships. 

KEYWORDS: phase transformations, nanomaterials, transmission electron microscopy (TEM), in situ TEM