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

Published

March 9, 2006

Author(s)

Donna C. Hurley, Malgorzata Kopycinska-Mueller, D Julthongpiput, Michael J. Fasolka

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

Pub Type

Journals

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Keywords

atomic force microscopy (AFM), nanomechanics, self-assembled monolayer(SAM)

Citation

Hurley, D. , Kopycinska-Mueller, M. , Julthongpiput, D. and Fasolka, M. (2006), Influence of surface energy and relative humidity on AFM nanomechanical contact stiffness, Applied Surface Science, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=50243 (Accessed October 13, 2025)