New luminescence scanning tunneling microscope with high detection efficiency

Scanning Tunneling Microscopy (STM)-induced luminescence is a powerful, advanced experimental method to study electroluminescence on the atomic scale. However, obtaining high and reliable count rates has proven to be difficult in the past. Here, we present a self-built STM operating under ultrahigh vacuum and at temperatures below 10 K to address this issue. The setup achieves an outstanding detection efficiency, which is about an order of magnitude higher compared to similar instruments, and count rates of up to 6 × 106 cps at 1 nA from Ag/Ag(111) surface plasmon polariton decay have been observed. This experimentally obtained value translates to a conversion factor in the order of 10-3 photons per tunneling electron. The increased count rate results from the use of a large parabolic mirror, which collects about 65% of the emitted light, together with a robust focusing procedure and the implementation of free-beam optics. Furthermore, the STM is equipped with high frequency compatible cabling with a verified bandwidth of at least 16 GHz for the entire setup, which enables rise times well below the nanosecond range for electrical signals directly in the tunneling junction. The combination of high luminescence detection efficiency and high time resolution allows us to electrically drive individual molecules and study their excitonic behavior in the picosecond range. In addition, the high efficiency simplifies time-consuming experiments, such as spectrally resolved 3D photon maps, and offers the opportunity to study very sensitive emitters that have not been accessible so far.