Surface plasmon polariton modes in a single-crystal Au nanoresonator   fabricated using focused-ion-beam milling
  We use focused-ion-beam milling of a single-crystal Au surface to fabricate a 590-nm-long linear ridge that acts as a surface plasmon nanoresonator. Cathodoluminescence imaging spectroscopy is then used to excite and image surface plasmons on the ridge. Principal component analysis reveals distinct plasmonic modes, which proves confinement of surface-plasmon oscillations to the ridge. Boundary-element-method calculations confirm that a linear ridge is able to support highly-localized surface-plasmon modes (mode diameter < 100 nm). The results demonstrate that focused-ion-beam milling can be used in rapid prototyping of nanoscale single-crystal plasmonic components. 
E. J. R. Vesseur, R. de Waele, A. Polman, H. J. Lezec, H. A. Atwater   and F. J. Garc\'ia de Abajo