Thermodynamic Determination of Bimetallic Particle Geometry: Suitability of Poorly Miscible Alloys for Surface-Enhanced Raman

Abstract

Bimetallic nanoparticles formed of poorly miscible alloys are attractive for applications in surface-enhanced Raman scattering (SERS), as they could allow the detection and study of analytes that do not bind well to typical plasmonic substrates, particularly important biomolecules such as serotonin. Despite their potential importance for SERS applications, the plasmonic and geometric properties of these alloys are not well characterized. Here, we present a method for calculating the thermodynamically minimized geometries of these nanoparticles as a function of their surface, bulk, and metallic phase interface energies. We show how the geometry varies as a function of composition, from core–shell, to Janus, to phase-separated, and discuss the importance of accurately modeling the metallic phase interface region to capture particle geometries. Finally, we use the calculated Janus geometries for the AuNi and AgNi systems to explore the suitability of these particles for use in SERS and identify the ideal compositions to maximize local field enhancement on the Ni-rich phase of the particle using the finite-difference time-domain method.