LSPR Imaging of Silver Triangular Nanoprisms: Correlating Scattering with Structure Using Electrodynamics for Plasmon Lifetime Analysis

Here, an investigation into the optical response of truncated and nontruncated Ag triangular nanoprisms is presented. Single particle darkfield microspectroscopy and transmission electron microscopy (TEM) are performed to obtain an overview of the relationship between plasmonic properties and nanoparticle structure. A general framework is built to describe the optical response (resonant wavelength lambda(max) and full width at half maximum (fwhm)) of triangle nanoprisms in a size regime (60-140 nm edge length) that has not been investigated previously at this level of detail. The discrete dipole approximation is used to infer the thickness of individual nanoprisms from lambda(max) measurements, thereby determining three-dimensional structures derived from two-dimensional TEM images. This additional structural information allowed the various contributions to the fwhm to be deconvoluted and analyzed. It is shown that electron-interface scattering radiative damping and bulk damping each make similar contributions to the plasmon width of the triangular prisms for the sizes considered in this work. Surface scattering is found to be seriously overestimated if it is assumed that electron collisions with all prism surfaces lead to dephasing. Reasonable comparisons between theory and experiment are found if it is assumed that only electron collisions involving motions parallel to the plane of the prism lead to dephasing. Substrate effects make a comparatively small contribution to the fwhm. Additionally, it is shown that the optical constants of Johnson and Christy [Phys. Rev. B 1972, 6, 4370] provide the best match to the experimental data. We conclude by presenting the design rules for producing Ag triangular nanoparticles with narrow plasmon resonances.