STM Structure Determination of Adenine Bilayers by Moiré Interpretation

Scanning tunnelling microscopy (STM) has been performed in air at room temperature on bilayers of the nucleic acid base adenine, adsorbed to a graphite surface following evaporation of saturated aqueous solutions. Our results indicate that the upper layer of the bilayer structure shows a structural change compared to the layer adsorbed directly to the graphite. The upper layer has a slightly larger unit cell, and is slightly sheared and rotated with respect to the layer directly adsorbed to the substrate. We can interpret these observations in terms of a model of rows of the adsorbate molecules stabilised by intermolecular hydrogen bonds.