New publication in Applied Physics Letters:
Quantitative mapping of fast voltage pulses in tunnel junctions by plasmonic luminescence
November 14, 2013
Light emission from a tunnel junction can be used to measure voltages at nanosecond speed. This provides a new tool for time-resolved scanning tunneling microscopy: the shape of voltage pulses can be determined non-invasively directly at the point of the experiment.
Measuring the electrostatic potential between tip and sample in a scanning tunneling microscope (STM) is easy as long as the voltage does not change quickly. But measuring a nanosecond-fast voltage transient is hard. Electrical measurement tools such as vector network analyzers require additional high-frequency wires attached to the microscope. By detecting the intensity of plasmon emission from the STM tunnel junction we can obtain direct access to fast voltage profiles
Electrons tunneling between the tip and the sample in an STM can excite a localized plasmon. The decay of such tip-induced plasmons leads to the emission of photons from the tunnel junction. We found that the intensity of this plasmonic light is a quantitative measure for the voltage present in the tunnel junction at the time of the plasmon decay. Time-correlation single photon counting can then be used to acquire a time-resolved profile of the light intensity and hence a time-resolved profile of voltage transients.
This method can be used in conjunction with pulse shaping to correct for pulse distortions directly at the point of the experiment. By this technique we achieved more than tenfold increase in the time resolution of the STM.
This work is a collaboration of the Nanoscale Science Group, Prof. Klaus Kern at the MPI Solid State Research, Stuttgart (http://www.fkf.mpg.de/kern) and the Max Planck Research Group – Dynamics of Nanoelectronic Systems, Dr. Sebastian Loth, Hamburg/Stuttgart.