Direct mapping of the solid–liquid adhesion energy with subnanometre resolution

Abstract

Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Atomic force microscopy's 7 (AFM) ability of visualizing the topography and the property of surfaces and interfaces at a molecular level 8 has enabled a rapid development in the understanding of surface phenomena. Its versatility allows the exploration of hard and soft materials in vacuum 9-12 , in air 13 , but also in complex liquids 14,15 , often allowing imaging at sub-nanometre and sometimes atomic resolution 16 . In dynamic mode 17 (vibrating cantilever), AFM has proven sensitive to the interfacial compliance of viscous liquids and provided quantitative information about the structure of liquid layers between the AFM tip and the solid surface 18 , with, in some cases, atomic resolution 15 . However, specialized instruments were used and the nature of the tip-sample interaction remains an issue of debate. Dynamic AFM has the ability to probe the solid-liquid interface [18][19][20][21] , but an interpretation of experimental results remains difficult 22,23 . Traditionally, interfaces are characterized by an interfacial energy, IE, the sum of the two surface energies in vacuum minus the work of adhesion (W SL ) necessary to separate the surfaces (Dupré Equation 24 ). The latter is de facto the energy spent to restructure the interface due to the atomistic interaction between the two materials (Fig. 1c). In practice at a solid-liquid interface this is the energy that generates density variations and structuring of the liquid close to the interface. Hereafter we will call this layer of liquid which differs from the bulk

In Situ Mapping of the Molecular Arrangement of Amphiphilic Dye Molecules at the TiO2 Surface of Dye-Sensitized Solar Cells

“…In these particular imaging conditions, the energy dissipated by the vibrating AFM tip is not sufficient to fully remove the liquid between the tip and the sample, and the tip mainly probes the properties of the interfacial liquid at the surface of the sample. 12,22,28 The phase contrast is then related to the local 'wetting' properties of 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 6 the sample, i.e. the local solvation free energy 12,22 or, at the macroscopic level, the solid-liquid work of adhesion.…”

“…12,22,28 The phase contrast is then related to the local 'wetting' properties of 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 6 the sample, i.e. the local solvation free energy 12,22 or, at the macroscopic level, the solid-liquid work of adhesion. In practice, imaging over the TiO 2 substrate provides a darker phase contrast than over the Z907 regions, indicating a higher affinity of the solvent for the substrate than for the dye-covered surface (Fig.…”

“…This phase contrast indicates a higher affinity of the solvent for the TiO 2 than for the dye, and could be consistently used throughout this study to identify dye-covered (light) and uncovered (dark) regions. 12,22 At 30 % mass coverage, the dye layer exhibits dark spots in the phase, suggesting that uniform gaps exist between the adsorbed Z907 molecules. These gaps give the apparent sponge-like appearance to the dye layer topography.…”

“…19 Recently developments in the field of AFM have made it possible to achieve sub-nanometer mapping of soft and hard surfaces in solution paving the way for in-situ local observations of a functional DSC's surface. [20][21][22] Here we report in situ molecular-level AFM images of adsorbed dye molecules at mesoporous and flat TiO 2 surfaces in a device-relevant liquid. We used the amphiphilic ruthenium complex Z907 (diphenyl-nonyl diphenyl-carboxyl dithio octaruthenium) dye (insert in Figure 2) due to its wide-spread use in DSCs, its good performance in long-term stability tests, and the fact that it is less prone to aggregation than other dyes.…”

Growth and Dissolution of Calcite in the Presence of Adsorbed Stearic Acid

“…Several studies have examined the interaction of organic molecules with calcite's surface under different circumstances, [29][30][31] but the inherent complexity of the system and the large number of variables able to influence calcite's surface dynamics often result in conflicting findings. 23,32 Here we use high-resolution amplitude-modulation atomic force microscopy (AM-AFM) in liquid 33,34 to follow in real-time and with nanometer precision the evolution of calcite (101 ത 4) coated with stearic acid (SA) and exposed to different saline solutions. Calcite could grow or dissolve, depending on the ionic content of the solution (referred to as 'brines').…”