Cancelling Ambient Noise in Spectroscopic Images on a Scanning Tunneling Microscope

Scanning tunneling microscopy (STM), a technique to measure the electronic structure of condensed matter systems with atomic resolution, requires an extremely stable environment to operate. Modern ultra-quiet STMs typically employ a combination of pneumatic suspensions and massive inertial blocks to reduce ambient vibrations to the sub-nanometer scale. Yet the tip-sample junction still experiences picometer vibrations that limit the signal-to-noise ratio in the tunneling current. Here we demonstrate a measurement scheme and software algorithm that reduces the effects of residual sub-picometer vibrations by order 50% in both topographic and spectroscopic images. We first calibrate a transfer function between a sensitive geophone on the STM head, and the STM tip-sample distance itself. We then use the simultaneously measured geophone output and tunneling current to cancel the effects of vibrations in the STM data in a 300Hz bandwidth.