STM-assisted nanostructure formation: field-induced excitation and diffusion of precursor molecules

STM-assisted nanostructure formation using precursor molecules at negative sample bias is controlled by the applied electric field. Sharp nanostructur es are produced from the Cu-I (hfac) (vtms) molecule on the Si(111)-(7 x 7) surface at 300 K. The growth process involves the field-induced surface di ffusion from regions outside the growing nanostructure, which acts to suppl y molecules to the nanostructure growth region under the tip. Molecular dec omposition occurs above a critical electric field under the tip. The growth process starts when the electric field at the sample surface exceeds a cri tical level of similar to 0.2 V Angstrom(-1). Simulations of the growth mec hanism, which involves both the radial diffusion of the precursor species f rom outer sample surface regions and their activation underneath the tip, g ive quantitative agreement with the experimental data. (C) 2000 Published b y Elsevier Science B.V. All rights reserved.