Visualizing mineral-solution interfaces using 3D atomic force microscopy*

Understanding processes at solid-liquid interfaces is a key challenge for multiple research fields ranging from surface chemistry and catalysis to bio-membranes and living cells. Recent advances in atomic force microscopy–specifically 3D fast force mapping in amplitude modulated mode–have allowed the direct observation of interfacial solution structure with sub-nanometer resolution. We use this capability to probe multiple mineral-solution systems, including layered silicates (phlogopite and muscovite mica) and aluminum (oxy)hydroxides (boehmite and gibbsite) exposed to salt solutions of different pH and ionic strength. Depending on the system, our data show 3-5 structured layers spaced 0.2–0.5 nm apart and extending ~1.5 nm from the surface, with lateral features templated by the underlying crystal lattice. We compare the results to molecular dynamics simulations and discuss the promises and limitations of this exciting technique.