We present the implementation of a three-dimensional mapping routine for probing solid-liquid interfaces using frequency modulation atomic force microscopy. Our implementation enables fast and flexible data acquisition of up to 20 channels simultaneously. The acquired data can be directly synchronized with commercial atomic force microscope controllers, making our routine easily extendable for related techniques that require additional data channels, e.g., Kelvin probe force microscopy. Moreover, the closest approach of the tip to the sample is limited by a user-defined threshold, providing the possibility to prevent potential damage to the tip. The performance of our setup is demonstrated by visualizing the hydration structure above the calcite (10.4) surface in water.

Control of molecular self-assembly at solid− liquid interfaces is challenging due to the complex interplay between molecule−molecule, molecule−surface, molecule− solvent, surface−solvent, and solvent−solvent interactions. Here, we use in-situ dynamic atomic force microscopy to study the self-assembly of Benzopurpurine 4B into oblong islands with a highly ordered inner structure yet incommensurate with the underlying calcite (10.4) surface. Molecular dynamics and free energy calculations provide insights by showing that Benzopurpurine 4B molecules do not anchor to the surface directly but instead assemble on top of the second hydration layer. This seemingly peculiar behavior was then rationalized by considering that hydrophobic molecules placed atop the second water layer cause the least distortion to the existing hydration structure. Further experiments for the adsorption of Benzopurpurine 4B on other minerals indicate that the specific interfacial water structure on calcite is decisive for rationalizing the self-assembly of Benzopurpurine 4B in this system.

In this work, we present the stabilization of polar step edges along the [010] direction of calcite (10.4) by the presence of a water-soluble organic molecule, namely Congo Red. While characteristic etch pits are observed on the surface in the absence of the additive, no etch pits can be found in the presence of the additive. Using atomic force microscopy, we can directly follow the restructuring of the surface. Upon addition of Congo Red, the charge-neutral step edges confining the characteristic etch pits vanish, while polar step edges along the [010] direction appear on the surface, which are entirely decorated by well-ordered molecular islands of the additive. After the restructuring has taken place, the surface exclusively exhibits these polar step edges. Our results give direct evidence of the fact that these polar step edges become thermodynamically favored when Congo Red is present.

We study the influence of Alizarin Red S deprotonation on molecular self-assembly at the solid-liquid interface of the natural cleavage plane of calcite immersed in aqueous solution. To elucidate the adsorption details, we perform pH dependent high-resolution atomic force microscopy measurements.When Alizarin Red S is deposited onto calcite(10.4) in a liquid environment at an acidic pH of 5, weakly bound, ordered islands with a (3 Â 3) superstructure are observed. A sharp structural transition is revealed when increasing the pH above 8. Above this pH, stable needle-like structures oriented along the [01.0] direction form on the surface. Comparing these results with potentiometric titration data allows for unambiguously assigning the two molecular structures to the single and two-fold deprotonated moieties of Alizarin Red S. Our work, thus, illustrates the decisive impact of the protonation state on molecular self-assembly.

This study describes the deposition and recording of surface charges on polyimide with a scanning Kelvin probe microscope. The apparatus used here works with a needle tip whose movements and oscillations are controlled and driven by an electromechanical system. To deposit charges the probe tip touches down to the insulator surface and with an external voltage the contact charging is performed. After the charge deposition the same system works as a vibrating scanning Kelvin probe to measure the charged surface area. This Kelvin probe system has the advantage of a controlled tip oscillation compared to a conventional AFM probe with a free oscillating cantilever. Electrostatic forces cannot stick the tip to the surface. In an additional experiment the charges deposited around an electrode as known from Lichtenberg figures are detected.