Self-assembly of Adenine on Cu(110) Surfaces

The adsorption of the nucleic acid base, adenine, on Cu(110) surface has been studied with low-energy electron diffraction, scanning tunneling microscopy (STM), electron energy loss spectroscopy (EELS), and ab initio calculations. STM shows at low coverage an ordered one-dimensional molecular chain growing along (+/-1, 2) directions. At higher coverages, on annealing to 430 K, the chains order into chiral domains of ((1)(2)(6)(0)) periodicity. High-resolution STM images reveal the details of molecular structure within the unit cell. EELS shows that the molecular plane is parallel to the substrate with a tilted C-NH2 bond. Ab initio calculations confirm the molecular orientation and show an sp(3) hybridization on the N (amino) atom, which is directly bonded to the substrate, The origin of the chains lies in the formation of homochiral rows of molecules, linked by two types of H-bonding interactions, commensurate with the substrate.