Submolecular-resolution imaging of water clusters on the Cu(110) surface by atomic force microscopy

Abstract

<p indent="0mm">Water/solid interfaces are important to a wide range of scientific and technological processes such as ice nucleation and growth, corrosion, lubrication, heterogeneous catalysis and electrochemistry. It is a key issue to understand the structure and dynamics of water on solid surfaces. However, the atomic-scale characterization of the weakly bonded water clusters on metal surfaces remains challenging. Here, we report submolecular-resolution imaging of the water clusters on the Cu(110) surface using a qPlus-based noncontact atomic force microscope with a CO tip. The configurations of water clusters, including the detailed OH directionalities, could be identified unambiguously by probing the weak high-order electrostatic force between the CO-tip and polar water molecules, which is further confirmed by theoretical simulations. Water clusters composed of 4, 5, and 6 water molecules are observed on the Cu(110) surface, which are mainly built from cyclic tetramers and pentamers. We notice that water hexamers contain three different types of H-bonding configurations, one cyclic tetramer with two additional water molecules adsorbed at <italic>ortho</italic>- or <italic>para</italic>-sites of the tetramer and one pentagonal ring with one additional water molecule. More interestingly, these structures could be interconverted by the tip manipulation, because of the similar adsorption energies. The isolated pentamer would act as a nucleation core for the growth of 1D pentagonal chains on the Cu(110) surface.