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Calibration of AFM cantilever stiffness: A microfabricated array of reflective springs

Lookup NU author(s): Professor Peter Cumpson, Dr John Hedley

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Abstract

Calibration of the spring constant of atomic force microscope (AFM) cantilevers is necessary for the measurement of nanonewton and piconewton forces, which are critical to analytical applications of AFM in the analysis of polymer surfaces, biological structures and organic molecules. We have developed a compact and easy-to-use reference standard for this calibration. The new artifact consists of an array of 12 dual spiral-cantilever springs, each supporting a mirrored polycrystalline silicon disc of 160μm in diameter. These devices were fabricated by a three-layer polysilicon surface micromachining method, including a reflective layer of gold on chromium. We call such an array a Microfabricated Array of Reference Springs (MARS). These devices have a number of advantages. Cantilever calibration using this device is straightforward and rapid. The devices have very small inertia, and are therefore resistant to shock and vibration. This means they need no careful treatment except reasonably clean laboratory conditions. The array spans the range of spring constant from around 0.16 to 11N/m important in AFM, allowing almost all contact-mode AFM cantilevers to be calibrated easily and rapidly. Each device incorporates its own discrete gold mirror to improve reflectivity. The incorporation of a gold mirror both simplifies calibration of the devices themselves (via Doppler velocimetry) and allows interferometric calibration of the AFM z-axis using the apparent periodicity in the force-distance curve before contact. Therefore, from a single force-distance curve, taking about one second to acquire, one can calibrate the cantilever spring constant and, optionally, the z-axis scale. These are all the data one needs to make accurate and reliable force measurements. Crown Copyright © 2004 Published by Elsevier B.V. All rights reserved.


Publication metadata

Author(s): Cumpson PJ, Zhdan P, Hedley J

Publication type: Article

Publication status: Published

Journal: Ultramicroscopy

Year: 2004

Volume: 100

Issue: 3-4

Pages: 241-251

ISSN (print): 0304-3991

ISSN (electronic): 1879-2723

Publisher: Elsevier BV

URL: http://dx.doi.org/10.1016/j.ultramic.2003.10.005

DOI: 10.1016/j.ultramic.2003.10.005

Notes: Paper originally presented at the 5th International Conference on Scanning Probe Micrscopy, Sensors and Nanostructures, Heythrop Park, Oxfordshire, UK, 23-26 May 2003


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