Formation mechanism of low-dimensional superstructure of adenine molecules and its control by chemical modification: a low-temperature scanning tunneling microscopy study

The formation mechanism of low-dimensional self-assemblies of adenine, one of the DNA base molecules, on Cu(111) surfaces and its control by chemical modification have been studied using low-temperature (ca. 70 K) scanning tunneling microscopy and molecular orbital calculation. We have elucidated that the most stable hydrogen-bonded dimer plays a very important role as nuclei in the self-assembly formation of the adenine molecule. It was observed that the nuclei hydrogen-bonded dimers diffuse on the substrate, and self-assemble themselves into two different characteristic superstructures, a ‘one-dimensional chain structure’ and a ‘two-dimensional hexagonal structure’, through two distinct kinds of hydrogen bond pattern at low coverage and low deposition rate. It was also found that chemically modified adenine with an alkyl chain, which prevents the formation of the nucleic dimer, forms randomly aggregated small clusters.