Date of Award
Doctor of Philosophy
Patricia A. Thiel
This dissertation describes detailed studies of metal nanoparticles that are encapsulated beneath the surface of graphite. The goal of this research is to explore the possibility of such encapsulation. This is in contrast to graphite intercalation compounds where metal intercalation occurs in the bulk of graphite. The outcome of this research is novel and unanticipated on three fronts: the structure of encapsulated metal, the type of metal that can be encapsulated, and the generality of the encapsulation phenomenon.
The metals studied include elemental transition metals Cu, Fe, Ru, noble metals Ag, Au, Pt, and rare earths Dy, Gd, Yb. The graphite substrate is commercially available highly oriented pyrolytic graphite (HOPG). Via careful exploration and tuning of parameters, we have successfully established a robust synthetic strategy to achieve surface encapsulation. The strategy is effective when two conditions are operative: (i) ion-induced defects must be present on the graphite surface, which is achieved by Ar+ ion bombardment, and (ii) the graphite substrate must be heated to elevated temperature during metal deposition, which is referred to deposition temperature, Tdep.
The encapsulation results in nanostructures composed of crystalline metal nanoparticles that are sandwiched and protected between graphene layers. In order to synthesize and characterize the nanostructures and encapsulated nanoparticles, we utilize ultrahigh vacuum (UHV) techniques including electron beam heating, ion bombardment, physical vapor deposition, scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). Furthermore, we use density functional theory (DFT) to elucidate the formation of encapsulated metal nanoparticles. Notably, the DFT results offer predictive capabilities based on the energetics of a single metal atom.
The nanostructures synthesized are relevant to technological areas such as heat transfer, plasmonics, lithium ion batteries, and magnetism. Moreover, the synthetic strategy and insights from this research may be extended beyond graphite to other layered materials or supported two-dimensional materials.
Lii-Rosales, Ann, "Encapsulation of metal nanoparticles near the graphite surface: From a survey of metals to revealing a general phenomenon" (2019). Graduate Theses and Dissertations. 17241.