Polymerization-induced epitaxy: scanning tunneling microscopy of a hydrogen-bonded sheet of polyamide on graphite

A molecularly thin film of a two-dimensional polymer network formed by hydrogen bonding was synthesized and investigated with scanning tunneling microscopy. Poly(in-caprolactam) (nylon 6) was epitaxially grown on the basal plane of graphite and an ultrathin film of the polymer was obtained after the bulk materials had been washed away with solvents. The polymer chain has a planar, all-trans conformation and adjacent chains run in the antiparallel direction. This produces complete pairing of hydrogen bonding groups, with each amide group lying on a straight line perpendicular to the polymer backbone. This hydrogen-bonded sheet is oriented so that each polymer backbone lies in the (1010) direction on the graphite hexagonal lattice, as opposed to the (1120) direction taken by other paraffinic molecules studied so far. This experiment shows that hydrogen bonding can be used to control the orientation of macromolecules in two dimensions.