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Sensors 2017, 17(10), 2182; https://doi.org/10.3390/s17102182

Tip Pressure on Semicircular Specimens in Tapping Mode Atomic Force Microscopy in Viscous Fluid Environments

1
Institute of Applied Mechanics, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan
2
Department of Mechanical Engineering, National Chung Hsing University, No. 145, Xingda Rd. South Dist., Taichung 40227, Taiwan
3
Department of Civil and Environmental Engineering, National University of Kaohsiung, No. 700, Kaohsiung University Rd., Nanzih District, Kaohsiung 81148, Taiwan
*
Author to whom correspondence should be addressed.
Received: 29 August 2017 / Revised: 21 September 2017 / Accepted: 21 September 2017 / Published: 22 September 2017
(This article belongs to the Section Physical Sensors)
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Abstract

Tapping mode (TM) atomic force microscopy (AFM) in a liquid environment is widely used to measure the contours of biological specimens. The TM triggers the AFM probe approximately at the resonant frequencies and controls the tip such that it periodically touches the specimen along the scanning path. The AFM probe and its tip produce a hydrodynamic pressure on the probe itself and press the specimen. The tip to specimen size ratio is known to affect the measurement accuracy of AFM, however, few studies have focused on the hydrodynamic pressure caused by the effects of specimen size. Such pressure affects the contour distortion of the biological specimen. In this study, a semi-analytical method is employed for a semicircular specimen to analyze the vorticity and pressure distributions for specimens of various sizes and at various tip locations. Changes in pressure distribution, fluid spin motion, and specimen deformation are identified as the tip approaches the specimen. The results indicate the following: the specimen surface experiences the highest pressure when the specimen diameter equals the tip width; the vorticity between tip and specimen is complex when the tip is close to the specimen center line; and the specimen inflates when the tip is aligned with the specimen center line. View Full-Text
Keywords: tapping mode; atomic force microscopy; pressure; vorticity; semi-analytical method tapping mode; atomic force microscopy; pressure; vorticity; semi-analytical method
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Shih, H.-J.; Dai, C.-L.; Shih, P.-J. Tip Pressure on Semicircular Specimens in Tapping Mode Atomic Force Microscopy in Viscous Fluid Environments. Sensors 2017, 17, 2182.

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