Two mechanisms of scanning tunneling microscopy assisted nanostructure formation using precursor molecules

Scanning tunneling microscopy has been employed to create nanostructures at both polarities of the applied bias voltage, using the hexafluoroacetylace tonate Cu (I) vinyltrimethylsilane precursor molecule on the Si(111) surfac e at 300 K. Two distinctive mechanisms controlling the formation of nanostr uctures have been delineated. The first mechanism causes the dissociation o f the molecule by an electron attachment process. The second process involv es excitation of the molecule by the applied electric field; here field ind uced surface diffusion acts to supply molecules to the nanostructure, growt h region under the tip. Both mechanisms have a threshold in the range of 2. 5-4.5 V, and while the electron current induced process operates only at po sitive sample bias, the field induced mechanism works at both bias polariti es. Model calculations of the field assisted growth mechanism, which involv es both the radial diffusion of the precursor species from outer surface re gions and their activation underneath the tip, show a very reasonable quant itative agreement with the experimental data. (C) 1999 American Vacuum Soci ety. [S0734-2101(99)09304-5].