Title:
Seed-Mediate Synthesis of Gold Nanocrystals: The Effects of Lattice Mismatch on Growth Patterns
Seed-Mediate Synthesis of Gold Nanocrystals: The Effects of Lattice Mismatch on Growth Patterns
Author(s)
Pawlik, Veronica Dana
Advisor(s)
Xia, Younan
Editor(s)
Collections
Supplementary to
Permanent Link
Abstract
Nanomaterials have long fascinated both the casual observer and scientific mind alike. The utility of Au nanocrystals in particular has inspired applications ranging from plasmonics to catalysis. Over time, the ability to finely tune both shape and size has greatly improved their merits for these applications. To further expand and enhance the properties of Au nanocrystals, bimetallic compositions were introduced. Of the various atomic arrangements possible for bimetallic nanocrystals, the core-shell structure is most commonly utilized. This morphology is typically synthesized through a seed-mediated process. Growing one metal on another can introduce challenges. In this dissertation, I explore the effects that increasing lattice mismatch has on the seed-mediated growth of noble-metal nanocrystals.
First, the case of no lattice mismatch was investigated during the growth of Au on Au spherical seeds to generate AuRD fully enclosed by {110} facets. The lack of lattice mismatch led to layer-by-layer growth. The kinetics of the synthesis could easily be tuned to favor either deposition or diffusion to achieve concave RD, trisoctahedra, or octahedra. These AuRD were then utilized in another seed-mediated growth to improve the thermal stability of the AuRD. Specifically, 1 ML of Pt was added and this ultrathin layer of Pt was able to improve the thermal stability of the high energy {110} facets from degrading at 100 °C to persisting at 450 °C. Computational studies revealed that the thermal stability of the Au-supported Pt skin was even greater than that expected for pure Pt. This effect was attributed to the strain induced by the formation of a 3.8% lattice-mismatched Pt overlayer on Au. Finally, single-crystal Rh@Au truncated octahedra were synthesized at a lattice mismatch of 7.2%. The large mismatch led to an island growth mode, which, could be tuned through the use of gentle kinetic knobs. The addition of NaOH indirectly increased the reduction rate to help modulate the number of Au islands formed on the Rh seeds. Conversely, the addition of KBr slowed down the reduction, allowing the Au adatoms to diffuse across the Rh seed. This work provides insight into the effects of lattice mismatch on the growth mode of nanocrystals, moving one step closer to the rational synthesis of novel nanomaterials with desired characteristics.
Sponsor
Date Issued
2023-12-08
Extent
Resource Type
Text
Resource Subtype
Dissertation