Photon scanning-tunneling microscopy

Abstract

Photons can be totally internally reflected at the base of a prism just as free electrons in a metal are reflected at the surface barrier. In an electron scanning-tunneling microscope (ESTM), the electrons can be made to tunnel to a metal probe tip placed near the surface. Similarly, if an optical fiber tip is placed near a prism base, photons which would otherwise be totally internally reflected can tunnel to the tip. A target sample placed on the base modulates the transmission coefficient. As the tip is scanned, the tunneling photons are converted to real photons in the fiber, and the flux can be read by a photomultiplier tube. This is the basis for a new instrument developed by the authors, called a photon scanning-tunneling microscope (PSTM). The PSTM resolution is a fraction of the photon wavelength. For visible photons this is not nearly the resolution of the ESTM, but the PSTM can image insulators.