Quantifying the probing depth of mode-synthesizing atomic force microscopy for nanoscale infrared spectroscopy

Advances at the forefront of nanoscale infrared spectroscopy have deepened our fundamental understanding of heterogeneous materials and living systems at the nanoscale. By combining the nanomechanical detection scheme of atomic force microscopy (AFM) and infrared excitation, local properties can be resolved with spatial resolution in the sub-100nm range. However, the complexity of the probing depth contributing to the signal is one of the limitations hampering thr full exploitation of this approach.
By developing model test multi-layered films with top-coats and sub-layers of various thicknesses and various compositions, we will discuss how these parameters impact the probing depth and subsequently the sensitivity and spatial resolution of nanoscale infrared measurements. We will evaluate the ability to distinguish surface from volume contributions using multi-frequency AFM as the new detection scheme of the measurements. We will establish some connections between the underlying parameters involved in spectra and image formation and the resulting spatial resolution and sensitivity. Finally, we will highlight some applications of the instrumental advances to characterize heterogeneous systems of relevance to material and life sciences.