Molecular Self-Assembly on Surfaces of Organic Conducting Salts:  Epitaxial Monolayer Films of Naphthalene on the (001) Surface of (TMTSF)2PF6

Pristine and naphthalene-adsorbed (001) surfaces of the organic conducting salt (TMTSF)2PF6 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 partial electron density plots of the surface, and for naphthalene-adsorbed surfaces, by carrying out Monte Carlo simulations for the adsorption of a naphthalene molecule on the surface. The STM images recorded for the pristine (001) surface correspond to the cation layer of (TMTSF)2PF6, and each circular bright spot of the molecular-resolution STM images represents the three hydrogen atoms of the most protruding methyl group of a TMTSF molecule on the (001) surface. Naphthalene molecules adsorbed on this surface form a pseudomorphic (1 × 1) overlayer structure with respect to the underlying substrate. The naphthalene overlayer shows mechanical stability against etching by the scanning tip. An identical overlayer structure of naphthalene was obtained from several different preparation methods. On the cation-layer (001) surface naphthalene is adsorbed on each “four-methyl-step” defined by four methyl groups of two adjacent TMTSF molecules within each TMTSF stack.