PSTM: Photon Scanning Tunneling Microscope

Overview:

A Photon Scanning Tunneling Microscope (PSTM) is a device where the object is illuminated by an evanescent wave generated at the face of a prism or slide and the field is detected via a fiber probe in the near-zone of the sample (as in NSOM). PSTM measurements are inherently holographic since the sample is illuminated by an evanescent field and that same field serves as reference. The measurements are thus the near-field equivalent of a Gabor hologram. This hologram may be measured a large fraction of a wavelength from the sample, where the near-field is normally out of focus, as may be seen in reference. It is demonstrated here that the data thus obtained, though not amenable to direct interpretation, provide enough information to determine quantitatively the two-dimensional structure of a thin sample, thus achieving a computational lens for the near-field.

FIG. 1. The PSTM instrument. A HeNe laser (L) emits a collimated beam that is divided at the beam splitter (BS) and propagated on one of two possible paths, (A) or (B), the other path being blocked. The beam is routed by mirrors (M) to the prism at an angle such that the beam in the prism (P) is totally internally reflected. The evanescent field outside the prism interacts with the sample (S) and the total field is detected by the tapered fiber probe (F) which is scanned in a plane at fixed height.

FIG. 2. The data are displayed in panels (a) and (b). The colorbar indicates normalized photocount with the constant background subtracted. The result of the reconstruction algorithm is displayed in panel (c). An AFM image is displayed in panel (d) for comparison. The field of view in each image is 3.4um X 5um.

References:

• P S Carney, R A Frazin, S I Bozhevolnyi, V S Volkov, A Boltasseva, and J C Schotland, "A computational lens for the near-field,"Phys. Rev. Lett.92 163903 (2004). PDF