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Publication Citation: Influence of surface energy and relative humidity on AFM nanomechanical contact stiffness

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Author(s): Donna C. Hurley; Malgorzata Kopycinska-Mueller; D Julthongpiput; Michael J. Fasolka;
Title: Influence of surface energy and relative humidity on AFM nanomechanical contact stiffness
Published: March 09, 2006
Abstract: The effects of surface functionality and relative humidity (RH) on nanomechanical properties were investigated using atomic force acoustic microscopy (AFAM), a contact scanned probe microscopy (SPM) technique. Self-assembled monolayers (SAMs) with controlled surface energy were studied systematically in a controlled-humidity chamber. AFAM amplitude images of a micropatterned, graded-surface-energy SAM sample revealed that image contrast depended on both ambient humidity and surface energy. Quantitative AFAM point measurements indicated that the contact stiffness remained roughly constant for the hydrophobic SAMbut increased monotonically for the hydrophilic SAM. To correct for this unphysical behavior, a viscoelastic damping term representing capillary forces between the tip and the SAM was added to the data analysis model. The contact stiffness calculated with this revised model remained constant with RH, while the damping term increased strongly with RH for the hydrophilic SAM. The observed behavior is consistent with previous studies of surface energy and RH behavior using AFM pull-off forces. Our results show that surface and environmental conditions can influence accurate measurements of nanomechanical properties with SPM methods such as AFAM.
Citation: Applied Surface Science
Volume: 253
Issue: 3
Pages: pp. 1274 - 1281
Keywords: atomic force microscopy (AFM), nanomechanics, self-assembled monolayer(SAM)
Research Areas: Nanotechnology
PDF version: PDF Document Click here to retrieve PDF version of paper (1MB)