We demonstrate that quantum scattering of fast atoms and molecules under grazing angles of incidence can be exploited to study the structure of organic molecules on metal surfaces. Making use of keV H and He atoms as well as ${\mathrm{H}}_2$ molecules, the surface structures of the chiral amino acid alanine adsorbed on a Cu(110) surface is studied. We present a detailed investigation on the ($3\times 2$) phase of a monolayer of enantiopure and racemic alanine on Cu(110), revealing the formation of an elongated surface unit cell of $c(n\times 2)$ symmetry with $n=3.16\pm 0.04$ for the sticking out methyl groups of the alanine molecules.

• Received 15 July 2013

DOI:https://doi.org/10.1103/PhysRevLett.111.137601