Redshift of surface plasmon modes of small gold rods due to their atomic roughness and end-cap geometry

We use the surface integral technique for calculation of the extinction spectra of small metal particles of different shapes. We consider in detail different nonellipsoidal geometries in the electrostatic limit, including cylinders and a variety of capped cylinders. It is shown that different capping geometries have pronounced effects on the energy and intensity of the longitudinal surface plasmon mode. In addition, we propose that atomic scale surface roughness may also be an important determinant of the surface plasmon peak energy. A surface roughness of 0.10, equivalent to around two atomic layers, can generate redshifts in surface plasmon modes similar in magnitude to the redshifts induced by changes in the end-cap geometry.