A numerical investigation of the effect of vertex geometry on localized surface plasmon resonance of nanostructures.

Advances in nanofabrication and nano-scale measurement methods now allow for fabrication of highly detailed nanometer-scale topographic features. As geometric features greatly impact the formation of an electromagnetic field in response to incident light, this in turn calls for the study of the effects of new features of nanostructures on their performance in applications such as localized surface plasmon resonance (LSPR) sensing. This paper studies the effects of vertex features of a single nanostructure on its LSPR properties. A general relationship between the LSPR spectra and the vertex features of a nanoparticle is established. The results of electrodynamics calculations show that a delta-star with a relatively small vertex angle exhibits a bigger resonant wavelength than one with a large vertex angle. Moreover, the sensing performance initially increases, and then decreases as angular size of the vertices increases, with a turning point of 30 degrees. It is also shown that for nanostars with different numbers of vertices, the resonant wavelength undergoes a blue shift and the sensing performance grows poorer as the number of vertices increases. A regular vertex angle of 30 degrees displays the greatest figure of merit (FOM) value for LSPR applications, approximately 9.5 RIU(-1).