Templating an organic layer with the Si(111)-7×7surface reconstruction using steric constraints

Abstract

We demonstrate that the Si(111)-$7\ifmmode\times\else\texttimes\fi{}7$ surface reconstruction can be used to template an ordered array of 1,3,5-methyl benzene molecules that are uniformly distributed over both the faulted and the unfaulted halves of the $7\ifmmode\times\else\texttimes\fi{}7$ unit cell by covalent attachment in vacuo. An intermolecular steric interaction, which hinders nearest-neighbor adsorption, is shown to play an important role in the formation of the ordered array. The stable equilibrium structure is shown to be one where the molecules are located at the corner of the half unit cells maximizing the intermolecular separation. In addition to the intermolecular steric interaction, there is an interaction between the molecule and the surface that plays a important role in reducing disorder in the array. Moreover, as the coverage is increased, there is a switch in site preference, from edge to corner, that mitigates the effect of the intermolecular interaction. To investigate this system we used scanning tunneling microscopy to study site occupancy as a function of coverage, ab initio total energy calculation to study the stability of the attachment sites, and Monte Carlo modeling to examine the emergence of translational order in the overlayer. The switch in site preference from edge to corner is faithfully reproduced by the kinetic Monte Carlo model when an interaction term is included.