Resonant electromagnetic field cavity between scanning tunneling microscope tips and substrate

Confined electromagnetic fields are created at the surface of various substrates such as indium-tin-oxide (ITO) and gold films. Two scanning tunneling microscope tips (Pt-Ir and W) are used to create a localized perturbation. With ITO as a substrate, an evanescent field is observed without a tip-substrate interaction. Conversely, with a gold film surface formation of "gap modes," the particle-substrate cavity is seen. Gap modes at the interface of a metallic film are involved essentially when the modulation amplitude of the particle is below 100 nm. In the context of apertureless near-field microscopy, this demonstrates the influence of tip-surface coupling in scanning plasmon near-field microscope (SPNM) signals. The strong interaction of the tip with the metal substrate, through its surface plasmon, when combined with SPNM, may result in inaccuracies in the claimed chemical identification or intrinsic optical properties of the particle. (C) 2002 American Institute of Physics.