Kei Kobayashi1
Kyoto University1
We recently developed (classical) scanning thermal noise microscopy (STNM), where the thermal noise spectra of the cantilever were measured at every pixels during the raster scan, from which the resonance frequency (<i>f</i><sub>c</sub>) and <i>Q</i> images are reconstructed by the off-line analysis [1]. We demonstrated visualization of buried Au nanoparticles in a polymer matrix, since the surface viscoelastic property was modulated by the buried Au nanoparticles. STNM is a viscoelastic measurement technique based on the contact-mode AFM but without excitation of the sample stage or the cantilever unlike the conventional viscoelastic measurement techniques. However, collection of the thermal noise spectra typically requires more than 1 h, which has not been practical for wide applications.<br/>In this presentation, we demonstrate the local viscoelastic property measurements of polymeric samples by peak-tracking (PT) STNM, which utilizes two lock-in amplifiers and a feedback loop to enable tracking of the resonance frequency peak in a real-time manner as well as frequency-modulation AFM, but based on the detection of the thermal noise of the cantilever. It allows us to simultaneously measure <i>f</i><sub>c</sub> and <i>Q</i>, which correspond to elasticity and viscosity in the frequency range of typically 100 kHz. The technique is compatible with force curve measurement, which is a low-frequency viscoelastic measurement technique. Therefore, we can obtain quantitative viscoelastic properties in different frequency ranges at the same time, which is useful to study viscoelastic properties of polymeric samples and their composites that are often frequency dependent.<br/> <br/> [1] A. Yao et al. Sci. Rep. <b>7</b>, 42718 (2017).