Abstract

We present an Ultrafast Scanning Tunneling Microscope (USTM) [1,2] with a fiber coupled tip (Fig. 1) The USTM is based on the design in Ref. ¹. The tunneling current is gated with a photoconductive switch in the tunneling current loop. We use low temperature grown GaAs (LT GaAs) as the photoconductive switch subtstrate. The growth and annealing procedure is optimized for a last response and electro-optic sampling measurements have shown a FWHM pulse width of 800fs. The photoconductive switch is integrated into a coplanar transmission line with a 10 µm width and spacing. Five or 10 µm Pt- or Pt/lr wires are attached directly to the transmission line. The small dimensions enable the transmission of frequencies up to the THz regime. The use of LT GaAs instead of ion irradiated SOS results in an increased sensitivity. Moreover, we use an optical fiber attached directly to the photoconductive switch lor gating the tunneling current. By these means, we achieve an increased scanning range and an excellent reproducibility of the lip behavior.

© 1996 IEEE