Automated Cantilever Exchange and Optical Alignment for High-Throughput, Parallel Atomic Force Microscopy

Abstract

The atomic force microscope (AFM) force curve has been widely used for determining the mechanical properties of materials due to its high resolution, whereby very low (piconewton) forces and distances as small as nanometers can be measured. To increase the throughput of AFM in industrial applications, the ability to automatically exchange and align the cantilever in a very short time with sufficient accuracy is required. However, sometimes the resultant force curve obtained from AFM is slightly different from those obtained from a more typical nanoindentation force curve due to the AFM piezo’s hysteresis. Recently a new microcantilever design was introduced to achieve higher-harmonic nonlinear atomic force microscopy (AFM) by utilizing the benefits of intentional nonlinearity in design (Jeong et al., 2016). We investigated the apparent Young’s modulus, Em, of soft materials with the surface tilt angle, as measured by colloidal probe atomic force microscopy (AFM). The AFM measurements of soft polymer hydrogels and natural unfertilized eggs showed a clear universal behavior of Em as a function of the tilt angle, θ, of the sample surface at the local contact area. This microcantilever was designed with an inner Si paddle so that the linearized frequencies of the leading-order bending modes of the base beam and the inner paddle are in 1:3 rational relationships.