Radio-frequency scanning tunnelling microscopy
The scanning tunnelling microscope (STM) relies on localized electron tunnelling between a sharp probe tip and a conducting sample to attain atomic-scale spatial resolution. In the 25-year period since its invention, the STM has helped uncover a wealth of phenomena in diverse physical systems -— ranging from semiconductors to superconductors to atomic and molecular nanosystems. A severe limitation in scanning tunnelling microscopy is the low temporal resolution, originating from the diminished high-frequency response of the tunnel current readout circuitry. Here we overcome this limitation by measuring the reflection from a resonant inductor–capacitor circuit in which the tunnel junction is embedded, and demonstrate electronic bandwidths as high as 10 MHz. This ~100-fold bandwidth improvement on the state of the art translates into fast surface topography as well as delicate measurements in mesoscopic electronics and mechanics. Broadband noise measurements across the tunnel junction using this radio-frequency STM have allowed us to perform thermometry at the nanometre scale. Furthermore, we have detected high-frequency mechanical motion with a sensitivity approaching ~15 fm Hz^(-1/2). This sensitivity is on par with the highest available from nanoscale optical and electrical displacement detection techniques, and the radio-frequency STM is expected to be capable of quantum-limited position measurements.
Additional Information© 2007 Nature Publishing Group. Received 19 April; accepted 7 September 2007. We thank D. M. Karabacak for help with optical interferometry and A. Vandelay for discussions. This work was supported by the National Science Foundation through the Division of Materials Research (IMR Programme), the Division of Civil, Mechanical and Manufacturing Innovation (MDSE Programme) and the Cornell Center for Materials Research. Supplementary Information is linked to the online version of the paper at www.nature.com/nature.
Supplemental Material - nature06238-s1.pdf