Ex) Article Title, Author, Keywords
New Phys.: Sae Mulli 2021; 71: 439-445
Published online May 31, 2021 https://doi.org/10.3938/NPSM.71.439
Copyright © New Physics: Sae Mulli.
Hyoju CHOE1, Dongwon KIM1, Manhee LEE1*, Myungchul CHOI2
1Department of Physics, Chungbuk National University, Seowon-Gu, Cheongju 28644, Korea
We investigate the tip-substrate interaction in shear-mode, quartz-tuning, fork-based atomic force microscopy in air. While the tip-substrate normal interaction in vacuum is usually characterized as a long-range attractive force and a short-range repulsive force, here, in shear-mode atomic force microscopy in air, we observe a negligible shear interaction until the tip abruptly experiences a viscoelastic force at a few nanometers above the sample’s surface. We show that the viscoelastic shear interaction is the result of a capillary-condensed water bridge formed in the nanosized gap between the tip and the substrate and that the shear interaction increases with decreasing tip-substrate separation until hard mechanical contact is made between the tip and the substrate. This shear interaction mediated by the capillary liquid bridge dominates over other interactions; thus, the shear force must be considered when performing shear-mode atomic force microscopy and spectroscopy and manipulation of nano-objects in air.
Keywords: Atomic force microscopy, Shear interaction, Capillary condensation, Viscoelasticity