Amino acid and peptides on Cu(1 1 0) surfaces: Chemical and structural analyses of l-lysine

Adsorption of l-lysine on a Cu(1 1 0) surface has been carried out under UHV condition from sublimation of a crystalline phase. The adsorption was characterised by FT-RAIRS, LEED and STM. At room temperature, the adsorption geometry of the lysine molecules varies as a function of the exposure. The low coverage phase sees the molecules adsorbed via the oxygen atoms of the deprotonated carboxylate group and the nitrogen atom of the amino group. Close to saturation monolayer regime, the molecules reorient to be anchored to the surface via one oxygen of a side way tilted carboxylate moiety and the interaction of the N atom of the amino group. When this high coverage phase is annealed up to 425 K, the chemical nature and the adsorption geometry stay similar. However, the study of each of these phases by LEED and STM has shown three different two-dimensional adlayers. At room temperature, the low coverage phase exhibits paired chains of molecules growing symmetrically at ±19° of the [0 0 1] direction, while the high coverage phase presents a chiral (−2, −2; 5, −1) chiral phase with an overall growth direction parallel to the [−1 1 2] direction. Finally, the high coverage phase warmed up to 425 K leads to a (3 × n) structure, which seems to be a stable intermediate overlayer at this temperature, that gives rise to a (3 × 2) structure when annealed to 450 K. A number of schematic adsorption geometry models are proposed for each phase.