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D. Haefliger, M. Muhenchinger, G. Schitter, A. Stemmer:
"An integrated piezo-acoustic shear-force distance sensor with nanometer resolution for a micropipette tool";
Sensors and Actuators A: Physical, 103 (2003), 353 - 358.

We present an easy-to-use, piezo-acoustic shear-force detection system for tip-sample distance
control of a micropipette. The setup
provides free workspace around the pipette tip, requires only minor maintenance effort, proves to
be robust and yields high reproducible performance. The micropipette is fixed in an aluminum block
between two piezo-electric elements. One of the piezos excites the pipette at the mechanical
resonance of its tapered tip while the other piezo is used for detection of the vibration. Upon
approach of the pipette towards a sample surface the tip oscillation is damped due to shear-force
interaction. The damping depends on the distance between tip and sample. Control of the tip-sample
separation is accomplished by measuring the amplitude of the attenuated tip oscillation with the
piezo detector. Tracking of a sample surface in closed-loop operation is demonstrated. A
topographical resolution of about 1 nm is achieved with vibration amplitude of less than 40 nm.
This micropipette setup may find application in automated handling of micrometer-sized particles
and mirco-
and nano-structuring of surfaces.

Shear-force distance control; Micropipette; Pick-and-place; Particle handling; Micro-fabrication 1. Introduction Micropipettes offer a versatile tool for the handling of biological cells