This project was motivated by an in situ heating experiment in the transmission electron

microscope (TEM) in which gold (Au) nanoparticles were observed to dissolve tin dioxide (SnO2)

nanowires (NWs) under vacuum. The explanation for this observation was that the hightemperature

and low-pressure environment of the TEM caused the reverse reaction of the wellknown

vapor-liquid-solid (VLS) method commonly used to grow NWs. In the VLS process, a

metal catalyst absorbs reactant vapor until it becomes supersaturated. The precipitation of the NW

occurs at the liquid-solid interface, which ceases when there is no longer reactant vapor, and the

diameter of the NW is determined by the diameter of the original catalyst. The reverse process, the

solid-liquid-vapor (SLV) method occurs when atoms in a solid NW diffuse into the metal catalyst.

Eventually, the metal catalyst becomes supersaturated and the vapor escapes at the liquid-vapor

interface. In this dissertation we demonstrate the combination of the SLV and the VLS mechanisms

to create embedded heterogeneous interfaces in a variety of metal oxides. Metal catalysts are first

used to etch metal oxide surfaces producing hollow channels that we term “negative nanowires”,

and after etching the metal catalyst is reused to grow a NW of a different material from within the

channel to form a crystalline interface. Understanding the chemical structure at these interfaces is

both crucial and fascinating because diverse materials may interact in a variety of ways, including

atomic mixing of the two structures and/or the formation of an abrupt crystalline interface or gap.

We present our approach, therefore, towards gaining a comprehensive understanding of the

structure-function relationship of these materials, focusing on particular on the interfacial region,

to allow the design of new nanomaterials with tailored functionality.