Hydrodynamics of torsional probes for atomic force microscopy in liquids

Improving the force resolution of atomic force microscopy for soft samples in liquid requires soft cantilevers with reduced hydrodynamic cross section. Single and dual axis torsion levers [Beyder and Sachs, 2006] are an attractive technology. They have reduced area and reduced drift due to the symmetric support [Beyder, 2006] can add a second dimension using two independent axes. Here we investigate the hydrodynamics of these probes using three-dimensional transient fluid-structure interaction models with comparison to the experimental data. The computed Q factors and wet/dry resonance frequencies of different modes compare well with experimental measurements indicating that continuum viscous hydrodynamics can be used effectively to predict probe performance. The modeling further explores cross-axis hydrodynamic coupling and the influence of a nearby sample plane to provide guidance on approach algorithms and the possibilities of parametric detection.