What limits time resolution in AFM?

Developing a technique that combines nanometer spatial and sub-femtosecond temporal sensitivity is a crucial step towards exposing the inner mechanisms of chemical reactions, single molecule motion, electron dynamics in solids, and the effects of defects or trap states on electron motion and behavior, amongst many other questions relating to the most fundamental processes in molecular systems.

Our most recent advances in mechanically detecting ultrafast events will be presented. In particular, a non-linear optically induced polarization in a solid will directly lead to a force which can be detected by AFM with its intrinsic nanometer spatial resolution. I will show how one can mechanically measure a change in the sample response as a result of a delay time as short as 25 atto seconds between a pump and probe stimulation pulse on LiNbO3 or monolayers of MoSe2.

The realization of ultrafast AFM opens the door to understanding ultrafast electron dynamics on surfaces. As such, we are able to demonstrate that the lower limit of timing precision in mechanical detection in a pump-probe experiment is determined by the smallest detectable signal, and not, as might be expected, by the mechanical resonance frequency of the oscillator.

Work done in collaboration with Z. Schumacher, R. Rejali, R. Pachlatko, A. Spielhofer, Y. Miyahara, and D. Cooke