PLASMON-INDUCED TUNNELING CURRENTS: THE INFLUENCE OF TIP MODES

The interaction of propagating surface plasmons (PSP) excited in a silver film with the tunneling junction of a scanning tunneling microscope has been investigated. Under particular conditions we find a strong plasmon-induced current (PIC) superimposed on the tunneling current. The generation of the PIC is in our view due to the rectification of the optical electric field by the nonlinearity of the tunneling junction. To obtain a PIC with detectable magnitude an enhancement of the optical field between tip and sample by several orders of magnitude is required. The observed dependence of the field enhancement (FE) on the tip material and the geometry of the tunneling junction will be discussed in terms of localized surface plasmons.