Adsorption and two-dimensional phases of a large polar molcculc: Sub-phthalocyaninc on Ag(111) S. Berner 1.* M. de Wild,1 L. Ramoino,1 S. Ivan,2 A. Baratoff,1 H.-J. Guntherodt, 1 H. Suzuki,3 D. schlettwein,4 and T. A. Jung5 1National Center of Competence in Research on Nanoscale Science, Department of Physics and Astronomy, University of Bagel,Klingelbergstrasse 82, CH-4056 Basel, Switzerland 2Institute of Organic Chemistry, University of Basel, St. Johanns-Ring 19. CH4056 Basel, Switzerland 3Kansai Advanced Research Center C.R.L. 588-2 Iwaoka, Nishi-ku, Kobe 651-2401, Japan 4Fachbereick Chemie, University of Oldenburg, 26129 Oldenburg, Germany 5Laboratory for Mitno- and Nanostructures, Paul Scherrer lnstitute. CH-5232 villigen, Swizerland (Received 12 March 2003; revised manuscript received 4 June 2003; published 11 September 2003) Abstract The adsorption and the two-dimensional (2D) ordering of chloro[subphthalocyaninato}boron(III) (SubPc) on Ag(111) has been studied in detail by combined scanning tunneling microscopy and photoelectron spcctros- copy at room temperature. SubPc is a Polar, highly symmetric molecule, consisting of an extended aromatic system and a central B-CI bond. When growing on Ag(111) an interesting phase behavior is observed for the first molecular layer of SubPc, At low coverage, below 0.2 monolayer (ML), a 2D lattice gas is present, whereas at medium coverage (on the order of 0.2-0.5 ML), 2D condensed molecular islands are observed in ccexistence with the 2D lattice gas. In these condensed islands, the molecules assemble into a well-ordered honeycomb pattem. At higher coverage (approximately 0.5-0.9 ML) the molecules organize into a 2D hex- agonal close-packed (hcp) pattern, in equilibrium with a dense 2D gas phase. In the honeycomb and in the hcp pattem, individual molecules are imaged with submolecular resolution, giving information on their orientation. For both the honeycomb and hcp patterns, islands win two different orientations of the superstructures with respect to the Ag(111) substrate are observed. In case of the honeycomb pattern, the two superstructures are enantiomorphic. The chirality of these layers originates in the loss of the symmetry of the metal surface upon adsorption of SubPc, while the molecules alone are intrinsically achiral. Based on diffrent photoelectron spectroscopy experiments we conclude that the SubPc molecule is adsorbed on Ag(111) with its Cl atom towards he substrate and that the molecule remains intact. Finally. several aspects of the obscrved 2D con- densed phases and the thermodynamic phase behavior are discussed with respect to the charge distribution and the adsorption physics and chemistry of the SubPc molecules.