Design of an Inertially Counterbalanced $Z$ -Nanopositioner for High-Speed Atomic Force Microscopy

摘要

In many conventional atomic force microscopes (AFMs), one of the key hurdles to high-speed scanning in constant-force contact mode is the low-feedback control bandwidth of the $Z$ -axis loop. This paper presents the design of a fast $Z$ -nanoposi-tioner to overcome this limitation. The $Z$-nanopositioner has its first resonant mode at 60?kHz and a travel range of 5 $mu$ m. It consists of a piezoelectric stack actuator and a diaphragm flexure. The flexure serves as a linear spring to preload the actuator and to prevent it from getting damaged during high-speed operations. The $Z$-nanopositioner is mounted to an XY-nanopositioner. To avoid exciting the resonance of the XY -nanopositioner, an inertial counterbalance configuration was incorporated in the design of the $Z$-nanopositioner. With this configuration, the resonances of the XY-nanopositioner were not triggered. A closed-loop vertical control bandwidth of 6.5?kHz is achieved. High-speed constant-force contact-mode images were recorded at a resolution of 200?$times$ 200 pixels at 10, 100, and 200?Hz line rates without noticeable image artifacts due to insufficient control bandwidth and vibrations. Images were also recorded at 312- and 400-Hz line rates. These images do not show significant artifacts. These line rates are much higher than the closed-loop bandwidth of a conventional AFM in which this nanopositioner was tested.