Sequential reactions with amine-terminated monolayers and isolated molecules on H/Si(111)

A simple method for preparing monolayers with terminal amine functionality is demonstrated. A gas-phase photochemical reaction of 1,3-diaminopropane with a H-terminated Si(111) surface results in the molecules covalently attaching to the surface, primarily through the formation of a Si-N bond. These monolayers are characterized by scanning tunneling microscopy (STM) and high-resolution electron energy loss spectroscopy (HREELS). The reactivity of the terminal amine is confirmed by exposing the monolayer to benzaldehyde, resulting in the formation of an imine link and the grafting of phenyl rings onto the surface. For short irradiation times, this reaction leads to the formation of isolated amine groups on an otherwise pristine H-terminated surface. STM and HREELS studies of the benzaldehyde reaction on these low-coverage surfaces (less than 0.005 monolayers) indicate that the reaction is restricted to the reactive amine groups, leaving the remainder of the surface unaffected. This simple approach for a sequential coupling reaction is expected to facilitate attachment of more complex molecules (molecular switches, biomolecules) for single-molecule STM studies.