Optical resonances of hollow nanocubes controlled with sub-particle structural morphologies

The structural details of nanoparticles at the sub-particle level are critical for our understanding of their functionalities and the basic mechanisms involved in their formation. In particular, the geometries of such features determine the particle's overall optical response. Hollow metallic nanoparticles (hollow-MNPs) that have cubic geometries, with varying morphologies on their walls and voids in their body, offer a platform to study the effects of such structural features on the properties of single nanoparticles and their ensemble. Here, we report the control over sub-particle pinholes and voids by modifying the dynamics of the galvanic reaction, and we connect these structures to the optical response of the hollow nanocubes. We observe that symmetry breakage in individual particles, caused by pinholes and voids, has a drastic effect on the plasmon-resonance peak positions in their UV-Vis-NIR spectra. Via electron microscopy imaging, statistical analyses, and electromagnetic simulations, we observe that enlargement in a pinhole's diameter and an increase in their number produce a redshift in the resonance absorption peak of the ensemble. Our results outline nanoparticle design avenues via sub-particle morphologies for several applications, including those operating in the biological window and those carrying chemical payloads in organisms.