Subnanometer Interfacial Forces in Three-Dimensional Atomic Force Microscopy: Water and Octane near a Mica Surface

Abstract

Three-dimensional force microscopy generates atomically resolved 3D images of solid–liquid interfaces. Here, we investigated the components of the interfacial force exerted by a tip on a mica–liquid interface by comparing density functional theory and experiments. The study involved two liquids: an aqueous solution of KCl (polar) and n-octane as a nonpolar solvent. The comparison between theory and experiments shows the presence of oscillatory and monotonically decaying terms. The periodicity of the oscillation arises from entropic effects associated with the molecular packing of the liquid, while its amplitude carries information on the solid surface (substrate and tip)–liquid interactions. The exponent of the monotonic term comes from cohesive interactions between the liquid molecules, while its amplitude reflects the interactions with the solid surfaces.

In Situ Atomic-Scale Imaging of Interfacial Water under 3D Nanoscale Confinement

“…We have recently published a contribution describing the origins of the oscillatory and monotonically decaying terms. 21 …”

“…The monotonic term comes from cohesive interactions between the liquid molecules and the interactions of the liquid with the solid surfaces. 17,21 This phenomenon happens very close to the solid surface (e.g., within 1 nm from the surface). On the other hand, the formation of a nanoscale water bridge between the tip and the surface modifies the force−distance profile 22 and increases the adhesion force.…”

“…We have recently published a contribution describing the origins of the oscillatory and monotonically decaying terms. 21 The cantilevers (Nanoworld PPP-NCHAuD and Mikro-Masch 160AC-NG) were calibrated by using a contactless method included in the software of the Cypher VRS. The obtained values are summarized in the figure captions.…”

“…The periodicity of the oscillation arises from entropic effects associated with the molecular packing of the liquid which implies local changes in the density of the liquid near the solid surface. The monotonic term comes from cohesive interactions between the liquid molecules and the interactions of the liquid with the solid surfaces. , This phenomenon happens very close to the solid surface (e.g., within 1 nm from the surface). On the other hand, the formation of a nanoscale water bridge between the tip and the surface modifies the force–distance profile and increases the adhesion force .…”

Hydration Dynamics and the Future of Small-Amplitude AFM Imaging in Air

“…Moreover, the user must cope with and understand the character of some dynamic variables, such as the sharpness of the tip [ 9 , 10 ], otherwise referred to as the tip radius, R, in high-resolution imaging applications. Perhaps counter-intuitively to the newcomer, the field has rapidly advanced in two extremes—in liquid [ 11 , 12 , 13 , 14 ] and UHV environments [ 15 ]—while several complex phenomena have hindered the imaging and quantification of phenomena in air [ 16 ] with similar resolutions, controls, or throughputs [ 3 ]. There has been research in air in terms of capillary interactions [ 17 ], spontaneous capillary condensation [ 16 ], and the way the air environment affects surfaces [ 18 ], molecules on it, and modes of imaging [ 3 , 19 , 20 , 21 ].…”