Method for investigating surfaces at nanometer and picosecond resolution and laser-sampled scanning tunneling microscope for performing said method

摘要

For observing material structures and/or dynamic processes at surfaces, the known scanning tunneling microscope (STM) is combined with a photoexcitation process leading to photon-assisted tunneling. Thereby, the very fine spatial resolution of the STM is combined with the picosecond or even femtosecond time resolution of laser pulses.;The tunnel tip (20) of a scanning tunneling microscope is positioned at tunnel distance with respect to the surface of the sample (27) to be investigated, with an appropriate potential (U_t) applied across the gap between tunnel tip (20) and sample (27). The tunneling current is gated by means of at least one pulsed laser beam (26) directed at the tunneling region and/or at the tunnel tip (20).;In one embodiment, by a first laser beam a bunch of hot-electrons is excited in the sample to an energy just below the material's work function and caused to travel within the sample. A second laser beam at the location of the tunnel tip gates the tunneling current in accordance with the pulse pattern of the lasers.;In another embodiment, the gating action occurs at the tunnel tip (20) where a laser beam (26) is used to change the resistance of a photoconductor layer (23) arranged between the tunnel electrode (22) and the associated electronics (24, 25).