Scanning tunneling microscope assisted nanostructure formation: Two excitation mechanisms for precursor molecules

The scanning tunneling microscope in a near-field emission mode has been em ployed to create nanostructures using the hexafluoroacetylacetonate Cu (I) vinyltrimethylsilane precursor molecule on the Si(111) surface at 300 K. Tw o distinctive mechanisms controlling the nanostructure formation have been delineated. The first process involves excitation of the molecule by the ap plied electric field, and the field induced surface diffusion acts to suppl y molecules to the nanostructure growth region under the tip. The second me chanism involves the dissociation of the molecule by an electron attachment process. The generated nanostructure topology is quite different for each excitation mechanism. Narrow cone-like structures are produced by the elect ric field while broad structures of lower height are produced by the electr on attachment process. Both mechanisms operate simultaneously in the low bi as voltage regime (V < 8 V), with the field activated process dominating. T he electron induced process becomes the governing process at higher voltage s. (C) 1999 American Institute of Physics. [S0021- 8979(99)02321-X].