Improved temporal resolution in junction-mixing ultrafast scanning tunneling microscopy

We demonstrate ultrafast dynamical imaging of surfaces using a junction-mixing scanning tunneling microscope. We detect picosecond transient voltage pulses on a microstrip transmission line and demonstrate a temporal resolution (full width at half maximum) of 8 ps. We show that the time resolution achieved in these experiments is limited mostly by the microstrip geometry and can be significantly improved by reducing the value of the transmission line impedance. By dynamically imaging the microstrip line and detecting picosecond voltage pulses propagating on a patterned metal-on-metal (Ti/Pt) structure, we demonstrate that 1 nm spatial resolution is achievable for a 13 ps (full width at half maximum) transient correlated signal.