Full Field Displacement Measurements of AFM Cantilevers During Loading

Abstract

Research collaboration between the University of Florida and National Institute of Standards and Technology is focused on the development of a reference standard for atomic force microscope (AFM) cantilever stiffness calibration. The end goal is production of flexure-based artifacts that exhibit low fabrication expense, stiffness adjustability by design, insensitivity to load application point, mechanical robustness, and good reproducibility. Experimental determination of AFM cantilever spring constants is important because the measured forces are inferred from the cantilever displacement and a linear relationship between force and displacement. As a first step in this study, we have constructed a test setup that enables us to: 1) monitor AFM cantilever behavior during loading; and 2) record the shape of the cantilever under test during contact to better understand boundary conditions. The fundamental metrology tool employed by the test setup is a three-dimensional optical profiler, or scanning white light interferometer. By locating the cantilever (and test surface) within the measurement area of the profiler, we are able to record “snapshots” of the cantilever shape under various loading conditions. Given the deflected shape, we can make comparisons between the actual shape and the profile that would be obtained by ideal (fixed-free) boundary conditions. Results for cantilevers with various stiffness values (spanning four orders of magnitude) are presented and comparisons with ideal deflected shapes are provided.