Published: August 6th, 2021
Here, we present a protocol for using three-dimensional fast force mapping - an atomic force microscopy technique - for visualizing solution structure at solid-liquid interfaces with the subnanometer resolution by mapping the tip-sample interactions within the interfacial region.
Amongst the challenges for a variety of research fields are the visualization of solid-liquid interfaces and understanding how they are affected by the solution conditions such as ion concentrations, pH, ligands, and trace additives, as well as the underlying crystallography and chemistry. In this context, three-dimensional fast force mapping (3D FFM) has emerged as a promising tool for investigating solution structure at interfaces. This capability is based on atomic force microscopy (AFM) and allows the direct visualization of interfacial regions in three spatial dimensions with sub-nanometer resolution. Here we provide a detailed description of the experimental protocol for acquiring 3D FFM data. The main considerations for optimizing the operating parameters depending on the sample and application are discussed. Moreover, the basic methods for data processing and analysis are discussed, including the transformation of the measured instrument observables into tip-sample force maps that can be linked to the local solution structure. Finally, we shed light on some of the outstanding questions related to 3D FFM data interpretation and how this technique can become a central tool in the repertoire of surface science.
Many interesting phenomena occur within a few nanometers of a solid-liquid interface where classical theories for colloidal interactions break down1. Solvent molecules and ions organize into unexpected patterns2 and diverse processes, such as catalysis3, ion adsorption4,5, electron transfer6,7, bio-molecular assembly8, particle aggregation9, attachment10,11, and assembly
1. Loading and calibrating the AFM tip
Figure 2A presents a schematic of 3D force mapping. Similar to other AFM techniques operating in amplitude modulated mode, an oscillating cantilever is scanned across the surface. In addition to the tip height at each coordinate, instrument observables such as phase shift and amplitude are collected as the tip approaches and retracts from the surface. The result is a 3D dataset of observables-notably the oscillation amplitude, phase shift, and tip deflection-that can be readily converted int.......
Selecting the AFM tip
As with any AFM application, the key characteristics of the probe tip are the resonance frequency, cantilever size, tip radius, tip material, and spring constant. Almost all the 3D FFM literature to date has reported the use of stiff, high-frequency tips. The most common examples are silicon-based tips (e.g., AC55TS, PPP-NCH, Tap300-G, etc.) tips that can be utilized in their higher resonance modes14. Other research groups have opted for USC-F5-k30-10 c.......
We thank Dr. Marta Kocun (Asylum Research), Dr. Takeshi Fukuma (Kanazawa), Dr. Ricardo Garcia (CSIC Madrid), Dr. Angelika Kühnle (Bielefeld), Dr. Ralf Bechstein (Bielefeld), Sebastien Seibert (Bielefeld), and Dr. Hiroshi Onishi (Kobe) for useful discussions.
Development of the 3D FFM experimental protocol was supported as part of IDREAM (Interfacial Dynamics in Radioactive Environments and Materials), an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science (SC), Office of Basic Energy Sciences (BES). Development of the 3D FFM data analysis code was supported by the Laboratory Directed Researc....
|AC55TS AFM tip
|Cypher VRS Atomic Force Microscope
|PPP-NCH AFM tip
|Tap300-G AFM tip
|USC-F5-k30-10 AFM tip
|(Note only one of the AFM tip options is required)
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