Ultrafast AFM: sub-femtosecond time resolution at the nanometer scale

Advancing the time resolution of AFM has been a primary pursuit of multiple research groups. This would enable the measurment of photocarriers, ion mobility in battery cathodes or molecular motions with nm spatial resolution. As we have recently demonstrated, time resolution in force measurments is not limited by the (slow) mechanical time constants of force transducing cntilevers. It is limited by the smallest measurable energy [Appl. Phys. Lett. 110 (2017) 053111].

We experimentally demonstrated this by achieving picosecond time resolution with nc-AFM and ultrafast laser pulses in low temperature grown GaAs. In this presentation we will discuss our most recent advances, enabling sub-fs time resolution. Specifically, we developed an autocorrelation measurement for ultrashort laser pulses by force detection. A non-linear crystal is used to generate an electric field which follows the intensity of the impinging ultrashort laser pulse; we directly trace the emitted electric field with attosecond temporal, and nanometer spatial, resolution using our nc-AFM setup. As such, we are able to demonstrate that the lower limit of time resolution in AFM is solely given by the minimal time delay achievable by the optical setup and the thermal noise of the nc-AFM.