Mark Hagmann

In 1986 Gerd Binnig and Heinrich Rohrer at IBM Zurich received the Nobel Prize for Physics for inventing Scanning Tunneling Microscopy (STM) in 1981. A DC voltage between a nanoscale metal tip and a sample causes quantum tunneling. The exponential dependence of this current on the tip-sample distance enables imaging the sample surface with a resolution as fine as 0.1 nm as the tip is scanned over the sample. STM has many scientific and industrial applications including studying the atomic structure of DNA.

When a mode-locked laser is focused on the tunneling junction of an STM microwave harmonics are generated at integer multiples of the laser pulse repetition frequency. For example, the 200^th harmonic at 14.85 GHz with a power of only a few attowatts has a signal-to-noise ratio of 20 dB because each harmonic sets the present state-of-the-art for narrow linewidth at its frequency which reduces the noise.

In Scanning Frequency Comb Microscopy (SFCM) we use the power at the harmonics for feedback control of the tip-sample distance instead of using the tunneling current which is done in STM. No DC bias is used which mitigates the damage that STM causes in the samples. Our simulations suggest that imaging can be much faster with much finer resolution. 

Applications to semiconductor characterization and biomedical imaging will be described. For further information please go to www.newpathresearch.com where you can download free LabVIEW VI’s simulating the full operation of STM or SFCM with documentation. You may also join the “Scanning Frequency Comb Spectroscopy and Microscopy” Group on LinkedIn.