  Scanning probe microscopes are notoriously sensitive to many types of
external and internal interference including electrical, mechanical and
acoustic noise. Sometimes noise can even be misinterpreted as real features in
the images. Therefore, quantification of the frequency and magnitude of any
noise is key to discovering the source and eliminating it from the system.
While commercial spectrum analyzers are perfect for this task, they are rather
expensive and not always available. We present a simple, cost effective
solution in the form of an audio output from the instrument coupled to a smart
phone spectrum analyzer application. Specifically, the scanning probe signal,
e.g. the tunneling current of a scanning tunneling microscope is fed to the
spectrum analyzer which Fourier transforms the time domain acoustic signal into
the frequency domain. When the scanning probe is in contact with the sample,
but not scanning, the output is a spectrum containing both the amplitude and
frequency of any periodic noise affecting the microscope itself, enabling
troubleshooting to begin.
