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 the oretical study. Using He atom diffraction we find that monolayer N-2 f orms a high-order commensurate phase with an oblique unit cell, Minimu m energy calculations based on realistic potentials show that the unit cell contains seven N-2 molecules arranged in a novel type of pinwhee l structure unexpected for linear molecules adsorbed on a smooth surfa ce. Molecular dynamics simulations corroborate this structure and its remarkable thermal stability.