  We reveal the existence of the surface plasmonic lattice solitons (surface
PLSs) at the boundary of a semi-infinite metallic-dielectric periodic
nano-structure. We find that the truncation of the periodic structure imposes a
threshold power for the existence of surface PLSs, and enhances significantly
the modal localization. The propagation and excitation of surface PLSs as well
as their potential application in the all-optical subwavelength switching are
also demonstrated.
