High-resolution capacitive load-displacement transducer and its application in nanoindentation and adhesion force measurements
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A high-resolution load-displacement transducer is developed based on a capacitive-plate configuration. The transducer applies a force via electrostatic actuation and senses displacement via monitoring the change in capacitance. The external applied load on the transducer is measured as the difference between the electrostatic force and the spring force induced by the displacement. Compared to a conventional design, the present improved transducer offers not only enhanced reliability, but also much less moving mass and better electronic circuitry, thus improved practical load and displacement resolutions. It is found that the present transducer has a rms load resolution of 3 nN when tested in a reduced vibration environment, and 10-20 nN when directly attached on a multimode AFM for performing realistic experiments. Similarly, the displacement resolution of the present transducer is 0.05 and 0.12 nm under reduced vibration and attached on the AFM, respectively. Subsequently, the new transducer is integrated with a multimode AFM to perform in situ nanoindentation and adhesion (pull-off) force measurements to illustrate the improved capability of the transducer. The high resolution of the present transducer enables the observations of clear loading-unloading curves in the sub- 10-nm nanoindentation and "jump-on" phenomena in pull-off force measurements, both of which were previously masked by noise when using a commercially available similar transducer. © 2005 American Institute of Physics.
author list (cited authors)
Yu, N., Bonin, W. A., & Polycarpou, A. A.