We have studied the influence of the end of range defects in silicon created by high energy protons and helium ions on subsequent porous silicon formation. The defect generation rate at the end of range is typically ten times higher than that close to the silicon surface. For low fluence irradiation, only the end-of-range region contains enough defects to prevent anodization whereas the low-defect regions closer to the surface are anodized. By varying the end-of-range depth over small lateral distances, silicon lines with tip radii of nanometers were fabricated for low fluence irradiation. For a high fluence irradiation we demonstrate how porous silicon formation is confined to buried channels by selectively producing regions on the silicon surface with two different ends of ranges. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3533438] All rights reserved.