Ultrafast scanning probe microscopy

We have measured the response of the tunneling gap of a scanning tunneling microscope to excitation by a subpicosecond electrical pulse. Combining ultrashort laser pulses techniques with scanning tunneling microscopy (STM), we have obtained simultaneous 2‐ps time resolution and 50‐A spatial resolution. This is a 9 orders of magnitude improvement in the time resolution currently attainable with STM. The potential of this powerful technique for studying ultrafast dynamical phenomena on surfaces with atomic resolution and mesoscopic electronic device physics is discussed.