| AVS 58th Annual International Symposium and Exhibition | |
| Surface Science Division | Monday Sessions |
| Session SS2-MoA |
| Session: | Molecular Ordering and Electrochemical Interfaces |
| Presenter: | Ludwig Bartels, University of California, Riverside |
| Authors: | L. Bartels, University of California, Riverside J. Wyrick, University of California, Riverside Z. Cheng, University of California, Riverside D. Sun, University of California, Riverside D. Kim, University of California, Riverside T.L. Einstein, University of Maryland |
| Correspondent: | Click to Email |
Anthraquinone self-assembles on Cu(111) into a giant honeycomb network with exactly three molecules on each side. Here we propose that the exceptional degree of order achieved in this system can be explained as a consequence of the confinement of substrate electrons in the pores, with the pore size tailored so that the confined electrons can adopt a noble-gas-like two-dimensional quasi-atom configuration with two filled shells. Formation of identical pores in a related adsorption system (at different overall periodicity due to the different molecule size) corroborates this concept. A combination of photoemission spectroscopy with density functional theory computations (including van der Waals interactions) of adsorbate-substrate interactions allows quantum mechanical modeling of the spectra of the resultant quasi atoms and their energetics.
The resultant pores have about 4 nm in diameter. In this study we explore how the behavior of adsorbates inside them differs from that on extended terraces. CO molecules and adlayers exhibit properties under such nanoscale confinement that markedly depart from those of extended adlayers: a) the confinement stabilizes dislocation lines (anti-phase domain boundaries) in the adlayer that affect roughly ¼ of the adsorbed molecules; b) confinement prevents the formation of dense islands of adsorbed molecules, depending on coverage either causing dispersion of vacancies in the adlayer or preventing the growth of molecular islands; c) at a coverage of just a few molecules on the facet, we observe that a molecular shell structure is formed, resembling in its underlying mathematics the atomic model. Confined structures are an ideal test bed for measurement of the coverage dependence of molecular diffusion and in this study we find a reduction of the diffusion barrier at a slope of 57%/ML.