The lower limit for time resolution in frequency modulation atomic force microscopy

TL;DR

This paper analyzes the fundamental limits of time resolution in atomic force microscopy, revealing it is constrained by thermal noise rather than mechanical response, and demonstrates a pump-probe method achieving ~1 ps resolution.

Contribution

It introduces a general analysis showing thermal limits constrain AFM time resolution and presents a pump-probe technique applicable to various excitations, achieving picosecond resolution.

Findings

Time resolution limited by thermal noise, not cantilever response

Pump-probe method applicable to electrical, thermal, magnetic, optical signals

Measured photocarrier decay time of ~1 ps in GaAs

Abstract

Atomic force microscopy (AFM) routinely achieves structural information in the sub-nm length scale. Measuring time resolved properties on this length scale to understand kinetics at the nm scale remains an elusive goal. We present a general analysis of the lower limit for time resolution in AFM. Our finding suggests the time resolution in AFM is ultimately limited by the well-known thermal limit of AFM and not as often proposed by the mechanical response time of the force sensing cantilever. We demonstrate a general pump-probe approach using the cantilever as a detector responding to the averaged signal. This method can be applied to any excitation signal such as electrical, thermal, magnetic or optical. Experimental implementation of this method allows us to measure a photocarrier decay time of ~1 ps in low temperature grown GaAs using a cantilever with a resonance frequency of 280 kHz.