摘要： Plasmonic crystals are well known to have band structure including a band gap, enabling the control of surface plasmon propagation and con?nement. The band dispersion relation of bulk crystals has been generally measured by momentum-resolved spectroscopy using far ?eld optical techniques while the defects introduced in the crystals have separately been investigated by near ?eld imaging techniques so far. Particularly, defect related energy levels introduced in the plasmonic band gap have not been observed experimentally. In order to investigate such a localized mode, we performed electron energy-loss spectroscopy (EELS) on a point defect introduced in a plasmonic crystal made up of ?at cylinders protruding out of a metal ?lm and arranged on a triangular lattice. The energy level of the defect mode was observed to lie within the full band-gap energy range. This was con?rmed by a momentum-resolved EELS measurement of the band gap performed on the same plasmonic crystal. Furthermore, we experimentally and theoretically investigated the emergence of the defect states by starting with a corral of ?at cylinders protrusions and adding sequentially additional shells of those in order to eventually form a plasmonic band-gap crystal encompassing a single point defect. It is demonstrated that a defectlike state already forms with a crystal made up of only two shells.