Carbon structures were fabricated on silicon by focused ion beam-chemical vapor deposition using phenanthrene gas. The current of the 30 keV gallium beam was set at 10.7 pA. The relationship between the step size of the raster scan and the nanoscale structures obtained was investigated. Changes in step size from 4 to 85 nm on scan areas of 300, 500, and 1000 nm(2) caused variations in the depletion and replenishment of adsorbed gas molecules, which in turn caused several nanoscale effects such as delocalization, round edge, slant sidewall, locally variation in deposition rate, discrete structure, and shadow effect in carbon structures. Changes in the deposition rates and surface morphologies of the carbon deposits were observed and discussed. (C) 2010 Elsevier B.V. All rights reserved.