We examine the mechanical eigenmodes of a quartz tuning fork (QTF) for the purpose of facilitating its use as a probe for multi-frequency atomic force microscopy (AFM). We perform simulations based on the three-dimensional finite element method (FEM) and compare the observed motions of the beams with experimentally measured resonance frequencies of two QTF systems. The comparison enabled us to assign the first seven asymmetric eigenmodes of the QTF. We also find that a modified version of single beam theory can be used to guide the assignment of mechanical eigenmodes of QTFs. The usefulness of the QTF for multi-frequency AFM measurements is demonstrated through photo-induced force microscopy (PiFM) measurements. By using the QTF in different configurations, we show that the vectorial components of the photo-induced force can be independently assessed, and that lateral forces can be probed in true non-contact mode.

A new method is presented for visualizing the electric field distributions associated with propagating surface-plasmon-polariton (SPP) modes directly in the near-field. The method is based on detecting the photo-induced gradient force exerted by the evanescent field onto a sharp and polarizable tip. Using a photo-induced force microscope (PiFM), images of propagating SPPs are obtained on flat gold surfaces.

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We perform time-resolved pump−probe measurements on heterogeneous samples of (6,5) enriched single-walled carbon nanotubes (SWCNTs), both at the ensemble level using transient absorption measurements and at the nanoscale using timeresolved photoinduced force microscopy (PiFM) measurements. We find that the transient absorption dynamics near the E 22 transition after excitation at 1.55 eV are heterogeneous at the nanoscale, represented by four distinct categories of the temporal response. We find evidence that deviating dynamics are prominent in clustered SWCNTs, suggesting that interactions between nanotubes play an important role in altering the temporal response. At the same time, the main component retrieved from the mixture correlates well with the ensemble-based results. We conclude that ensemble level measurements under the current excitation conditions represent a faithful account of excitation dynamics that appear to be governed predominantly by (6,5) SWCNTs in the heterogeneous mixture.

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