Atomic Force Microscope Vertical Feedback Control Strategy for Semi-Automated Long-Range Probe Landing.

Traditional Atomic Force Microscopes (AFM) allow a short range displacement of the AFM probe, on the order of several tens of micrometers. When used inside an Electron Microscope (EM), the probe must be able to move on a millimeter scale with nanometer resolution. This is essential for the probe to reach any region of interest on a sample observed by an EM. In this paper, we address a challenging issue related to semi-automated long-range landing of an AFM probe on a sample. The probe is mounted on a piezoelectric inertial actuator. It is initially several millimeters away from the sample and must be safely landed to a distance on the order of hundred of nanometers (intermittent contact region). The control strategy is divided into three steps: (i) long-range velocity control using a stepping control, (ii) short and fine position control using a mixed stepping/scanning control, and (iii) position/force control using a scanning control. While traditional manual landing methods take a tremendous amount of time to complete the procedure, the proposed semi-automated method enables a safe long-range landing in less than 3 minutes. More generally, this is the first experimental demonstration in the literature of such a capability in AFM.