Lateral resolution and spectral bandwidth of local dielectric spectroscopy

Local Dielectric Spectroscopy (LDS), based on Atomic Force Microscopy (AFM), is emerging as a unique tool for the investigation of dielectric relaxation dynamics resolved in real space with nanometer scale resolution. While state of the art performance provides a frequency range of about 5 decades and a spatial resolution of 20-30 nm, recent efforts have been devoted in our group to the improvement of both spectral range and spatial resolution of LDS. Wider spectral bandwidth is desirable to follow the dynamics over a broader range of relaxation times and better resolve the shape of the relaxation functions. On the other hand, increasing the resolving power down to a few nanometers would give access to a number of characteristic length scales of physical interest, like for instance the dynamic correlation length in glass-forming systems or the mobility gradient for polymers close to nanointerfaces. In this seminar, the operation principle of Broadband Local Dielectric Spectroscopy (BLDS) is recalled, and some experimental results on polymeric nanocomposites reviewed. Recent results on spatial resolution improvement of local dielectric measurements down to 2-3 nm will be also shown, obtained by exploiting a peculiar operation mode of AFM named constant-excitation frequency-modulation (CE-FM) mode, that facilitates operation in ambient conditions. These results are a promising step towards application to LDS, to achieve the same degree of local resolution also in spectroscopic measurements.