Orientational ordering on a corrugated substrate: Novel pinwheel structure for N-2 adsorbed on Cu(110)

The structure and orientational ordering of N-2 molecules adsorbed on the Cu(110) surface is investigated in a combined experimental and theoretical study. Using He atom diffraction we find that monolayer N-2 forms a high-order commensurate phase with an oblique unit cell, Minimum energy calculations based on realistic potentials show that the unit cell contains seven N-2 molecules arranged in a novel type of pinwheel structure unexpected for linear molecules adsorbed on a smooth surface. Molecular dynamics simulations corroborate this structure and its remarkable thermal stability.