Graphene Visualizes the Ion Distribution on Air-Cleaved Mica

Abstract

The distribution of potassium (K+) ions on air-cleaved mica is important in many interfacial phenomena such as crystal growth, self-assembly and charge transfer on mica. However, due to experimental limitations to nondestructively probe single ions and ionic domains, their exact lateral organization is yet unknown. We show, by the use of graphene as an ultra-thin protective coating and scanning probe microscopies, that single potassium ions form ordered structures that are covered by an ice layer. The K+ ions prefer to minimize the number of nearest neighbour K+ ions by forming row-like structures as well as small domains. This trend is a result of repulsive ionic forces between adjacent ions, weakened due to screening by the surrounding water molecules. Using high resolution conductive atomic force microscopy maps, the local conductance of the graphene is measured, revealing a direct correlation between the K+ distribution and the structure of the ice layer. Our results shed light on the local distribution of ions on the air-cleaved mica, solving a long-standing enigma. They also provide a detailed understanding of charge transfer from the ionic domains towards graphene.

Charge Induced Dynamics of Water in a Graphene–Mica Slit Pore

“… 7 , 11 , 16 − 18 The film has been shown to consist of two water layers. 19 − 21 A schematic illustration of the sample under ambient conditions is depicted in Figure 1 a. Note that the schematic illustration is not to scale.…”

“…Additional evidence comes from conductive AFM measurements, in which a higher conductivity of the graphene areas with only one water layer was observed. 21 We anticipate that the second layer will exhibit less order. Additionally, due to intermolecular interactions, only a small part of the water molecules will face the mica with the OH bonds.…”

The endothelial glycocalyx anchors von Willebrand factor fibers to the vascular endothelium

“…This imaging technique has been established by material scientists to detect, for example, charge distributions on nonbiological surfaces. 48 Although the physicochemical characterization of biological samples by AFM is less frequently reported, [49][50][51] we selected this method because the direct detection of cell-bound COSs by fluorescence microscopy failed (data not shown). AFM enabled us to measure an increased friction between the scanning probe and the endothelial cell surface after treatment with COSs (Figure 2A lateral deflection image).…”

Time-of-flight secondary ion mass spectrometry analyses of vancomycin

“…We tested this hypothesis by spin-coating aqueous solution of vancomycin on cleaved mica, which is a hydrophilic surface as it is terminated by oxygen groups (and potassium ions). 31 As shown in Fig. 6(d) the vancomycin layer is smooth, with a root mean square roughness of only 0.2 nm.…”

“…The potassium ions are present between the silicate sheets. 31 We noticed that negative ions from the mica substrate, such as SiO 2 À , SiO 3 À , and SiO 3 H À are relatively weak in the negative secondary ion mass spectrum of the vancomycin film [lower panel in Fig. 2(b)].…”