Two-Photon-Excited Photoinduced Force Microscopy.
basic_science · Level V
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- Record sourced from PubMed, PMID 41420627.
- Also identified by DOI 10.1021/acs.nanolett.5c04444.
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Abstract
Sensing photoexcitation-induced forces via atomic force microscopy (AFM) has attracted much attention as a promising nanoscale molecular imaging modality. However, most such nanospectroscopies suffer from linear background and noise under single-photon excitation, including scattering into a quadrant detector or photothermal response from the cantilever or substrate. Here, we present two-photon-excited photoinduced force microscopy (TP-PiFM) to suppress these unwanted linear effects. A theoretical analysis shows that signal demodulation at ω<sub>tip</sub> ± 2ω<sub>opt</sub> can efficiently isolate the photothermal signal under intensity modulation on the pulse train at ω<sub>opt</sub> and tip driving at ω<sub>tip</sub>. As a proof-of-concept demonstration, we obtained TP-PiFM images of 40 nm gold nanoparticles with a higher resolution than that of AFM topography. Backgrounds in TP-PiFM images were suppressed through the demodulation technique as well as a fitting analysis to extract signals quadratically scaling on the illumination power. These results establish TP-PiFM as a robust, background-free nanoimaging method.