A PHYSICAL CONFINEMENT-BASED FORMATION OF SEMICONDUCTOR OXIDE/PLASMONIC NANOPARTICLE HETEROSTRUCTURES

Abstract

In nature, biological organisms have substantial control over processes that lead to the formation of biominerals. For example, magnetotactic bacteria utilize the confined volumes of magnetosomes to crystallize magnetic iron oxide particles that are enclosed in lipid bilayer membranes. The organisms are able to form carefully controlled chains of these particles that they use as a compass to navigate the Earth’s geomagnetic field. By taking inspiration from such naturally occurring processes, we aim to synthesize functional composites under confinement that possess excellent optoelectronic and photocatalytic properties. Semiconductor oxide and plasmonic metal nanoparticle heterostructures are excellent candidates for studying metal-to-semiconductor energy transfer for optoelectronic applications. Entrapment of plasmonic nanoparticles such as gold and silver within semiconducting materials such as copper oxide and zinc oxide, greatly increases their optical absorption and charge transfer. Two typical morphologies of such heterostructures, such as core-shell nanoparticles and preformed semiconductor oxide structures that are decorated with plasmonic nanoparticles, have been well studied, however, these structures both have limitations on the degree of optical enhancement due to the morphology of the structures. In this study, we used a physical confinement-based technique using track-etched polycarbonate membranes to synthesize heterostructures based on a bio-inspired crystal growth approach to incorporate arrays of plasmonic nanoparticles without the use of insulating surface ligands. By carefully controlling the synthesis protocol, we are able to tune the spatial distribution of nanoparticles that are entrapped within the semiconductor matrices which can give rise to diverse splitting and broadening of the plasmon peak in the heterostructures. It is important to expand the viable morphologies of heterostructures used in photovoltaic applications because electronic properties depend on the morphology and nanostructure of the composites. Our results demonstrate the flexibility of the physical confinement-based approach to synthesize crystalline architectures which entrap multiple plasmonic nanoparticles within a semiconducting matrix to access a relatively unexplored morphology that can enable promising optoelectronic properties.