Ultrafast spectroscopy with a scanning tunneling microscope

We present a method combining a scanning tunneling microscope and a pulse generator to achieve unprecedented spatiotemporal resolution for spectroscopy at surfaces. Using the so-called pulsed scanning tunneling spectroscopy (P-STS) we identify the stacking schemes at the surface of graphite with a probe time down to 300 ps while conserving atomic resolution. The technique is simple to implement and requires only increasing the signal bandwidth on the bias side of the tunneling junction. We foresee the P-STS as a highly versatile dynamical probe which could be applied to track in time the variation in the sample local density of states induced by any possible excitation. (C) 2011 American Institute of Physics. [doi:10.1063/1.3597351]