A high-eigenfrequency differential stiffness probe for high-speed scanning probe microscopy

Abstract

Microcantilever probes used for high-speed scanning probe microscopy are typically required to satisfy two mutually contradicting objectives: high eigenfrequency ( ω n ) and low flexural rigidity ( k b ). The conventional design approach shortens the microcantilever’s length to increase the eigenfrequencies (as ω n ∝ 1 / L 2 ); however, this also increases the probe’s rigidity (as k b ∝ 1 / L 3 ). This paper demonstrates—through experiments and physical modelling—the design of a novel high-eigenfrequency probe by redistributing the microcantilever’s mass along its length. A 100% increase in the probe’s eigenfrequency is achieved with this modified design, even while reducing its stiffness by 50%. Through experiments, this reduced stiffness has been found to enhance the probe’s force sensitivity . Also, the probe’s design facilitates redistributing the fluid pressure between its underside surface and the sample, thereby improving the quality factor by more than 100%. Significant reduction in ‘overshoot’ and ‘parachute’ is observed in contact mode scanning at the video rate. The improvements in the image resolution are proven for a variety of sample surfaces at very high scan rates up to 40 Hz (corresponding to a linear speed of 3.20 mm s − 1 ) upon scanning over an area of 40 × 40 μ m and are successfully demonstrated to map topographies with negligible image artefacts.