UC Irvine

Nanoparticle (NP) growth mechanisms have received attention due to the many potential applications such as biomedicine, catalysts, fuel cell, and solar cells. Here in this dissertation, I focus on developing a new tool to study the fundamental growth mechanisms of NP growth. This system relies on the use of highly oriented pyrolytic graphite (HOPG) as a substrate for deposition of metal NPs.

HOPG is layers of graphene stacked in a parallel arrangement. It is a useful substrate to study the growth of metal NPs due to its inert nature of surface. This system provides many advantages of fundamental studies of metal NP growth (discussed in chapter 1 introduction) the most critical point, for the purpose of this dissertation, being the separation of NP growth mechanism from substrate effects.

In the subsequent chapters, I focus on three major studies: 1) fabrication of linearly ordered Fe NP growth along the step edges of HOPG to study fundamental mechanisms of seed-mediated growth of pyrite, 2) photocatalytic properties of a bimetallic system composed of photodeposited Pt onto the fabricated Fe NP arrays, and 3) the improvement of the detection limit of this Fe NP system to better theoretical research on NP growth.

The first three chapters focus on the studies of NP growth on HOPG. Chapter 1 shows the successful and selective deposition of linearly ordered Fe NPs on the step edges of HOPG. Using these Fe NP arrays, the study of using different precursors to convert Fe oxide to FeS2 (pyrite) is discussed in chapter 2. Despite the interest in pyrite due to its promising properties for solar cell applications, pyrite devices suffer from low efficiency. This is partly due to a lack of understanding of which parameters are required for preferential growth of a pure pyrite phase. Therefore, using the Fe NP system on HOPG provides a toolkit for studying the fundamental properties of particle growth at very early stages. Seed-mediated growth of pyrite NPs by atmospheric-pressure chemical vapor deposition in the context of different precursors is discussed in chapter 3. The results are promising yet many discussions can be raised as to using my system to improve pure pyrite phase growth in the future.

In chapter 4, I focus on generating a bimetallic system using the Fe NPs on HOPG to study photocatalytic properties. Photodeposition of Pt NPs on Fe oxide NP arrays is demonstrated for the first time. I show that generation of this Pt-Fe oxide bimetallic system actually improves the photocatalytic activity as assessed by methylene blue degradation studies under UV exposure.

Lastly, in chapter 5, an attempt was made to improve the HOPG NP system to improve the surface characterization detection limit. This was done by studying Fe NP growth on oxygen plasma treated modified surfaces of HOPG. The plasma treatment creates more defect sites on the surface of HOPG leading to higher-density deposition of Fe oxide NPs that significantly improves the low detection limit of the original HOPG NP system.