Femtosecond laser assisted scanning tunneling microscopy

The excitation of the tunneling junction of a scanning tunneling microscope using ultrashort laser pulses combined with detection of a tunneling curre nt component which depends nonlinearly on the laser intensity allows, in pr inciple, to simultaneously obtain ultimate spatial and temporal resolution. To achieve this goal, a laser system that produces ultrashort laser pulses is combined with an ultrahigh vacuum scanning tunneling microscope. The ba sic technical considerations are discussed and it is shown that atomic reso lution can be achieved under pulsed laser excitation of the tunneling junct ion. The pulsed illumination gives rise to several contributions to the mea sured total current. Experimental evidence for signal contributions due to thermal expansion, transient surface potentials and multiphoton photoemissi on are presented. (C) 2000 American Institute of Physics. [S0021-8979(00)02 020-X].