Non-templated selective self-assembly of different molecules on the same surfaces is an effective technique of controlling multiple functionalities on surfaces to develop sensors and devices, as well as catalyst and adhesives. To study the mechanism of non-templated selective self-assembly, two molecules with different sizes and different functional groups, 3,4,9,10-perylene-tetracarboxylicacid-dianhydride (PTCDA) and 2,5-dimethyl-N,N'-dicyanoquinonediimine (DMe-DCNQI), are evaporated on a designed Ag(775) substrate with two facets subsequently. PTCDA self-assembles on {111} flat facet selectively while DMe-DCNQI on stepped {221} facet. Both molecules self-assemble into ordered structures. Flat Ag(111), stepped Ag(221) surfaces and several stepped silver surfaces with different step widths and height are considered using DFT calculations. We found that the morphology of the surfaces, the size of the adsorbate, and the interaction between molecules and surfaces all account for the selective adsorption. If the adsorbate has suitable size with the step width of surfaces, it prefers to stay on stepped surfaces. We also report FePc molecules selectively self-assemble on the face-centered cubic and the hexagonal close-packed regions of Au(111) at submonolayer coverages, indicating that tiny difference of substrate also affects the molecule-substrate interaction, thereby determining the selectivity.
This work is in collabaration with H.J. Gao, W. Ji, Z.H. Cheng (Institute of Physics, Chinese Academy of Sciences, China), C. Seidel, H. Fuchs (Physics Institute, Muenster University, Muenster, Germany), S.J. Pennycook (Condensed Matter Sciences Division, Oak Ridge National Laboratory, USA), L. Tsetseris and S. T. Pantelides (Department of Physics, Vanderbilt University, Nashville, USA).
Reference:
1. S. X. Du et al., Phys. Rev. Lett. 96, 226101 (2006).
2. Z. H. Cheng et al., J. Phys. Chem. C 111, 2656 (2006).
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