Formation of Silicon Nanoporous Structures Induced by Colloidal Gold Nanoparticles in HF/H2O2 Solutions

Abstract

We developed an efficient method for the production of unique porous silicon structures, capable of achieving very small (less than 20 nm diameter) and uniform pore sizes, without the need for an external electrochemical cell or precoating of a discontinuous metal film. The method consists of the immersion of Si into a colloidal suspension of Au nanoparticles (NPs) containing a HF/H2O2 mixture. Gold colloids are known to be stable in neutral aqueous solutions, mainly because of the electrostatic repulsion between nanoparticles that carry the same negative surface charge. In acidic solutions obtained, for example, by addition of HF, however, conventional Au NPs colloids tend to lose their negative charge and to precipitate. A novel colloidal solution avoids NP precipitation upon acidification and thus enables Au NPs adsorption onto the Si surface, which triggers Si etching along definite crystallographic directions. The etching process occurs independently of the Si doping type or doping level. Because of ...