Bulklike monolayer and bilayer picene on Si(111)-(23× 23)-Sn

A bimodal growth of bulklike monolayer and bilayer picene grown on Si(111)-(23× 23)R30°-Sn was reported in combination of low-temperature scanning tunneling microscopy with first principles density functional theory calculations. At low coverage, individual molecules are mobile and selectively adsorbed at H3 sites with an edge-on configuration. At higher coverages, T4 sites are also occupied to form bulklike monolayer and bilayer picene, with adsorption configurations closely resembling the (110) and (111) planes, respectively. STS measurements demonstrate that the HOMO-LUMO gaps are 5.0 and 3.2 eV for the commensurate monolayer and incommensurate bilayer. This strategy to fabricate epitaxial commensurate monolayer and decoupled incommensurate bilayer on semiconductor surfaces may have potential applications in fabricating high-quality organic electronic devices.