A Multi-mode Transverse Dynamic Force Microscope - Design, Identification and Control

The transverse dynamic force microscope (TDFM) and its shear force sensing principle permit true non-contact force detection in contrast to typical atomic force microscopes. The two TDFM measurement signals for the cantilever allow, in principle, two different scanning modes of which, in particular, the second presented here permits a full-scale non-contact scan. Previous research mainly focused on developing the sensing mechanism, whereas this work investigates the vertical axis dynamics for advanced robust closed-loop control. This paper presents a new TDFM digital control solution, built on field-programmable gate array (FPGA) equipment running at high implementation frequencies. The integrated control system allows the implementation of online customizable controllers, and raster-scans in two modes at very high detection bandwidth and nano-precision. Robust control algorithms are designed, implemented, and practically assessed. The two realized scanning modes are experimentally evaluated by imaging nano-spheres with known dimensions in wet conditions.