3D Nanoscale Electromechanical Imaging with Interferometric Atomic Force Microscopy (2410.03340v2)

Abstract: Forces acting between an Atomic Force Microscope (AFM) tip and sample are three dimensional. Despite this, most AFM force measurements are confined to one or two dimensions. Extending AFM force measurements into three dimensions has previously required complex, difficult and time-consuming workflows. Here, we demonstrate an accurate, interferometric method for quantifying the full, three-dimensional response of an AFM tip to localized forces. We demonstrate this approach on a series of piezoelectric materials and show that this approach yields quantitative 3D measurement independent of the sample orientation beneath the tip. This approach simplifies existing, angle-resolved piezoresponse force microscopy (PFM) techniques. Our measurements benefit from the greatly reduced noise floor (5 fm per root Hz) and intrinsic accuracy of our interferometric measurements. One important result is that the vertical piezo sensitivity was systematically 2 to 3 times larger than the in-plane piezo sensitivities. A simple analysis of vertical and lateral contact stiffnesses, due to the difference in the Young (vertical) and Shear (lateral) sample yields a factor of 2.5, in good agreement with the measurements. While this work was confined to ferroelectric materials, it provides a general workflow and framework for other AFM based mechanical measurements.