Stephen M. Driver

Proline-Derived Structural Phases on Cu{311}

Structural phases formed by adsorption of l-proline onto a Cu{311} surface in ultra-high vacuum were investigated using reflection–absorption infrared spectroscopy, low-energy electron diffraction and scanning tunnelling microscopy. An ordered structural phase formed by self-assembly of l-prolinate with (2,1;1,2) periodicity, and a transition from pure μ3 bonding to a mixture of μ3 and μ2 bonding with increasing exposure at 300xa0K, were observed. This behaviour has broad parallels with that previously seen with alaninate and glycinate on Cu{311}, but the detailed correlation between structure and bonding, and their evolution during subsequent annealing, are markedly different for prolinate as compared to alaninate and glycinate. At annealing temperatures around 480–490xa0K, a new structural phase with (5,3;4,6) periodicity emerges. We tentatively attribute this to pyrrole-2-carboxylate, formed by dehydrogenation and aromatization of the pyrrolidine ring of prolinate. The observation of equal areas of the two possible mirror domains associated with the two possible adsorbate–substrate bonding enantiomers implies a prochiral intermediate.

Structural phases formed by NO2/CO co-adsorption on Au{111} surfaces

Exposing a Au{111} surface to NO(2) and then to CO at temperatures around 120 K in ultra-high vacuum gives rise to molecular overlayers in which the two species are co-adsorbed, which we have investigated using low-temperature scanning tunnelling microscopy. Under NO(2)-rich conditions, a (√7 × √7)R19.1° phase with 3:1 NO(2):CO stoichiometry forms. Under CO-rich conditions, this phase co-exists with other phases having 2:1 and 1:1 NO(2):CO stoichiometries and different symmetries, and with bare Au surface. Structural models for these phases are discussed. Individual domains of the (√7 × √7)R19.1° phase are chiral, by virtue of the arrangement of their achiral components, an observation that may have more general implications.