Tuesday  |  Heritage E  |  10:00 AM–10:20 AM

#17965, Effects of Evolving Tip Geometry on Young’s Modulus Maps in Atomic Force Microscopy

Atomic Force Microscopy (AFM) is commonly used to assess elastic properties at the nanoscale, but accurately calculating quantitative values for Young’s modulus from load-displacement data remains a significant challenge. Factors such as sample roughness, depth-dependence, viscoelasticity, adhesion, and the inherent assumptions in calculations all contribute to overall error. Researchers are therefore currently limited to making qualitative comparisons between regions in individual Young’s modulus maps.

One major source of error for these calculations lies in assuming a constant spherical or conical geometry, which often fails to accurately capture AFM tip geometry. Specifically, this assumption fails to account for the drastic geometry changes that can occur during the tens of thousands of indentations required for a typical AFM Young’s modulus map. While some work has been done to model tip wear during mapping (Gotsmann & Lantz, 2008; Liu et al., 2010; Vahdat et al., 2014), these models struggle to accurately identify the current geometry at any specific instance in time.

In this work, we aim to calculate Young’s modulus without fully assuming the instantaneous tip geometry, allowing it to evolve throughout the mapping process. While calculations are typically made using a pair of load and displacement points, our approach developed herein also utilizes the local slope of the force-displacement curve, enabling the quantification of Young’s modulus and a geometric parameter describing the shape of the indenter tip simultaneously. We use this methodology to develop analytical procedures for various initial tip geometries.

These procedures are validated by applying them to experimental load-displacement data from samples with well characterized elastic properties over the lifetime of an indenter tip. Our findings do not only provide insights into the effects of tip geometry on nanoscale Young’s modulus maps computed from AFM data, but also provide guidelines to account for them.

Logan Kirsch   University of Texas at Austin
Gregory Rodin   University of Texas at Austin
Filippo Mangolini   University of Texas at Austin