Progress in Photon Scanning-Tunneling Microscopy (PSTM)

Tunneling of either electrons or photons from a sample to a probe tip yields an exponential signal that permits subwavelength tangential resolution and even better resolution of the tip-to-sample distance. Photon Scanning Tunneling Microscopy (PSTM) provides images of both insulators and conductors that are either thin or not too strongly absorbing at the wavelength used. Scanning Tunneling Microscopy (STM) provides better spatial resolution but poorer spectroscopic resolution, so there are complementary aspects for the two instruments. Our recent progress with the PSTM includes adding a zoom capability, detection of surface-enhanced Raman signals, imaging of photolithographically prepared arrays of isolated silver particles, and studies of tunneling effects on films of photoresist.