An electro-mechanical setup for the measurement of AC-forces in a low-temperature tunnelling microscope has been developed, which enables extremely high force resolution. The crosstalk of vibrations onto the tunnelling current is used to measure the deflection of a force-sensing cantilever beam. We demonstrate its capability to measure the noise of the force at a tunnelling contact using polycrystalline Iridium. Depending on temperature, spring constant and current, a resolution in the range of fN/Hz is possible. We observe peak levels of the force-noise at the energy of the expected phonon maximal density of states, which suggests that inelastic transport processes contribute to force fluctuations.
@article{arxiv.1507.00242,
title = {Force-noise spectroscopy by tunnelling current deflection sensing},
author = {Markus Herz and Elke Scheer},
journal= {arXiv preprint arXiv:1507.00242},
year = {2016}
}