Three-dimensional atomic force microscopy mapping at the solid-liquid interface with fast and flexible data acquisition

Söngen H, Nalbach M, Adam H, Kühnle A. Three-dimensional atomic force microscopy mapping at the solid-liquid interface with fast and flexible data acquisition. Review of Scientific Instruments. 2016;87(6):63704.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. Published by AIP Publishing

Three-dimensional atomic force microscopy mapping at the solid-liquid interface with fast and flexible data acquisition

Söngen H, Nalbach M, Adam H, Kühnle A. Three-dimensional atomic force microscopy mapping at the solid-liquid interface with fast and flexible data acquisition. Review of Scientific Instruments. 2016;87(6):63704.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. Published by AIP Publishing

Generic nature of long-range repulsion mechanism on a bulk insulator?

Neff JL, Richter A, Söngen H, et al. Generic nature of long-range repulsion mechanism on a bulk insulator? Faraday Discussions. 2017;204:419-428

The weight function for charges-A rigorous theoretical concept for Kelvin probe force microscopy

Söngen H, Rahe P, Neff JL, et al. The weight function for charges-A rigorous theoretical concept for Kelvin probe force microscopy. Journal of Applied Physics. 2016;119(2):25304.A comprehensive discussion of the physical origins of Kelvin probe force microscopy (KPFM) signals for charged systems is given. We extend the existing descriptions by including the openloop operation mode, which is relevant when performing KPFM in electrolyte solutions. We define the contribution of charges to the KPFM signal by a weight function, which depends on the electric potential and on the capacitance of the tip-sample system. We analyze the sign as well as the lateral decay of this weight function for different sample types, namely, conductive samples as well as dielectric samples with permittivities both larger and smaller than the permittivity of the surrounding medium. Depending on the surrounding medium the sign of the weight function can be positive or negative, which can lead to a contrast inversion for single charges. We furthermore demonstrate that the KPFM signal on thick dielectric samples can scale with the sample size-rendering quantitative statements regarding the charge density challenging. Thus, knowledge on the weight function for charges is crucial for qualitative as well as quantitative statements regarding charges beneath the tip. (C) 2016 AIP Publishing LLC

Hydration layers at the graphite-water interface: Attraction or confinement

Söngen H, Morais Jaques Y, Zivanovic L, et al. Hydration layers at the graphite-water interface: Attraction or confinement. Physical Review B. 2019;100(20):205410

Quantitative atomic force microscopy

A variety of atomic force microscopy (AFM) modes is employed in the field of surface science. The most prominent AFM modes include the amplitude modulation (AM) and the frequency modulation (FM) mode. Over the years, different ways for analyzing data acquired with different AFM modes have been developed, where each analysis is usually based on mode-specific assumptions and approximations. Checking the validity of the seemingly different approximations employed in the various analysis methods can be a tedious task. Moreover, a straightforward comparison of data analyzed with different methods can, therefore, be challenging. Here, we combine the existing evaluation methods which have been separately developed for the different AFM modes and present a unifying set of three equations. These three AFM equations allow for a straightforward analysis of AFM data within the harmonic approximationregardless of the AFM mode. The three AFM equations provide the three and only pieces of information about the tip-sample force available within the harmonic approximation. We demonstrate the generality of our approach by quantitatively analyzing three-dimensional AFM data obtained in both the AM and FM mode

Does the Structural Water within Gypsum Remain Crystalline at the Aqueous Interface?

Söngen H, Silvestri A, Roshni T, et al. Does the Structural Water within Gypsum Remain Crystalline at the Aqueous Interface? The Journal of Physical Chemistry C. 2021;125(39):21670-21677

Water structure on gypsum (0-10) - MD simulation and experiment

Söngen H, Silvestri A, Roshni T, et al. Water structure on gypsum (0-10) - MD simulation and experiment. Bielefeld University; 2021.Interactive comparison of the results from force-field molecular dynamics calculations and atomic force microscopy. A web version of the visualization can be found [here](https://pc1.pages.ub.uni-bielefeld.de/pub/2021-Gypsum/gypsum.html)

Three-dimensional solvation structure of ethanol on carbonate minerals

Söngen H, Jaques YM, Spijker P, et al. Three-dimensional solvation structure of ethanol on carbonate minerals. Beilstein Journal of Nanotechnology. 2020;11:891-898.Calcite and magnesite are important mineral constituents of the earth’s crust. In aqueous environments, these carbonates typically expose their most stable cleavage plane, the (10.4) surface. It is known that these surfaces interact with a large variety of organic molecules, which can result in surface restructuring. This process is decisive for the formation of biominerals. With the development of 3D atomic force microscopy (AFM) it is now possible to image solid–liquid interfaces with unprecedented molecular resolution. However, the majority of 3D AFM studies have been focused on the arrangement of water at carbonate surfaces. Here, we present an analysis of the assembly of ethanol – an organic molecule with a single hydroxy group – at the calcite and magnesite (10.4) surfaces by using high-resolution 3D AFM and molecular dynamics (MD) simulations. Within a single AFM data set we are able to resolve both the first laterally ordered solvation layer of ethanol on the calcite surface as well as the following solvation layers that show no lateral order. Our experimental results are in excellent agreement with MD simulations. The qualitative difference in the lateral order can be understood by the differing chemical environment: While the first layer adopts specific binding positions on the ionic carbonate surface, the second layer resides on top of the organic ethyl layer. A comparison of calcite and magnesite reveals a qualitatively similar ethanol arrangement on both carbonates, indicating the general nature of this finding