Stanford Mechanics and Computation

Encased cantilevers and alternative scan algorithms for ultra-gentle high-speed Atomic Force Microscopy

Live cells and many biological samples readily deform under the minimum force required to perform an atomic force microscopy measurement precluding imaging at high temporal and spatial resolution. Encased cantilevers are a new way to overcome the limits of liquid AFM. By fabricating a hydrophobic encasement around the cantilever we keep the cantilever dry, reduce the fluid viscosity but still allow the tip to probe the sample in solution. This results in exceptionally high resonance frequency, Q factor, detection sensitivity, and low force noise enabling gentle high-speed imaging. The encasement not only provides lower damping in liquids by trapping an air bubble, but it can as well serve as a position reference. The gap between encasement and cantilever is used as a Fabry-PĂ©rot optical cavity resonator and enables low-noise interferometric deflection detection. In a second part I will introduce our latest instrumental developments for high-speed scanning. We use alternative scans patterns better suited to drive piezo-based scanners than conventional raster scans. Spiral scanning for instance improve temporal resolution by allowing higher tip velocities without distortion. Image processing to recover high-resolution images from sparse quickly collected non-gridded datasets allows further stretching of the speed limits without applying more force or increasing bandwidth.

Biosketch: Dominik Ziegler studied at EPFL Switzerland, later as visiting researcher at the University of Tokyo he developed BioMEMS for in vivo neural recording. He received his doctorate from ETH Zurich, Switzerland working on the development of new Kelvin Probe force microscopy techniques. Currently as a PostDoc at the Lawrence Berkeley National Laboratory his knowledge in MEMS and scanning probes led to the innovation of encased ultra-low noise force sensors for operation in liquid.