THE PHOTON SCANNING TUNNELING MICROSCOPE

The tunneling of photons from an evanescent wave to a sharpened optical fiber probe tip provides the basis for an analogous instrument to the electron scanning tunneling microscope. The transmission and reflection coefficients for s-polarized photons are exactly the same as those for electrons. Imaging at subwavelength resolution is made possible by the exponential character of the tunneling. We have constructed several photon scanning tunneling microscopes (PSTMs) and successfully imaged the topography of a number of samples placed on microscope slides. Each slide is coupled to a prism with an index matching gel and light is internally reflected within the sample. The reflection is frustrated as tunneling sets in when the probe tip is brought close to the surface. The electronics and software used are similar to those used in our electron STMs. Lateral resolution of lambda /12 has been obtained and high-resolution spectroscopy has also been accomplished simultaneously. Images of several types of samples, including biological samples will be presented.