Intermodulation spectroscopy as an alternative to pump-probe for the measurement of fast dynamics at the nanometer scale

TL;DR

This paper introduces a novel intermodulation spectroscopy technique using AFM to measure fast charge dynamics at the nanosecond scale, offering an alternative to traditional pump-probe methods.

Contribution

It develops a coherent multifrequency lock-in measurement approach to reconstruct charge dynamics from frequency spectra, enhancing temporal resolution in nanoscale measurements.

Findings

Achieved 20 ns time resolution in ambient conditions.

Validated the method with simulations and a control experiment.

Theoretically limited to about 1 ns resolution by measurement time.

Abstract

We present an alternative approach to pump-probe spectroscopy for measuring fast charge dynamics with an atomic force microscope (AFM). Our approach is based on coherent multifrequency lock-in measurement of the intermodulation between a mechanical drive and an optical or electrical excitation. In response to the excitation, the charge dynamics of the sample is reconstructed by fitting a theoretical model to the measured frequency spectrum of the electrostatic force near resonance of the AFM cantilever. We discuss the time resolution, which in theory is limited only by the measurement time, but in practice is of order one nanosecond for standard cantilevers and imaging speeds. We verify the method with simulations and demonstrate it with a control experiment, achieving a time resolution of $20~\mathrm{ns}$ in ambient conditions, limited by thermal noise.