In the immediate vicinity of a solid surface immersed in liquid, continuum models break down and the liquid will often form a discrete layered structure depending on the shape of the liquid molecules and on the nature of the liquid-solid interaction. Whilst this structure almost certainly plays a role during atomic force microscopy (AFM) imaging in a liquid it is very rarely observed due to the instrument sensitivity which would be required. However, there is substantial motivation for attempting to measure such structure directly as a function of the local surface properties and environment, particularly in aqueous systems. This interest is due to the omnipresence of water, the structure of which is thought to have an impact in areas as diverse as tribology, earth sciences and biological function.

Using an AFM probe tip, of lateral dimensions comparable to that of a single molecule, we have directly measured localized structuring in aqueous environments at small tip-sample separations and have combined this with nanometer resolution images. By diversifying beyond the simple surfaces of graphite and mica, to self-assembled monolayers with varying end groups, we have been able to investigate the role of local surface chemistry and morphology on the measured water structure.

Chemistry: Scratching the surface