Molecular self-assembly on surfaces of organic conducting salts: Epitaxialmonolayer films of naphthalene on the (001) surface of (TMTSF)(2)PF6

Pristine and naphthalene-adsorbed (001) surfaces of the organic conducting salt (TMTSF)(2)PF6 were examined by scanning tunneling microscopy (STM) to determine the structure of epitaxial monolayer films of naphthalene on the (001) surface. The observed STM images were interpreted by calculating part ial electron density plots of the surface, and for naphthalene-adsorbed sur faces, by carrying out Monte Carlo simulations for the adsorption of a naph thalene molecule on the surface. The STM images recorded for the pristine ( 001) surface correspond to the cation layer of (TMTSF)2PF6, and each circul ar bright spot of the molecular-resolution STM images represents the three hydrogen atoms of the most protruding methyl group of a TMTSF molecule on t he (001) surface. Naphthalene molecules adsorbed on this surface form a pse udomorphic (1 x 1) overlayer structure with respect to the underlying subst rate. The naphthalene overlayer shows mechanical stability against etching by the scanning tip. An identical overlayer structure of naphthalene was ob tained from several different preparation methods. On the cation-layer (001 ) surface naphthalene is adsorbed on each "four-methyl-step'' defined by fo ur methyl groups of two adjacent TMTSF molecules within each TMTSF stack.