Optical breakdown processing: Influence of the ambient gas on the properties of the nanostructured Si-based layers formed

Porous nanostructured layers, exhibiting 2-2.2 eV photoluminescent (PL) emission, have been formed on silicon surfaces by the production of optical breakdown in different gases (air, Ar-2, He,N-2, O-2), maintained at atmospheric pressure. We found a significant influence of the ambient gas characteristics on the morphological and chemical properties of the layers produced, as well as on the PL efficiency. Gases with relatively low ionization potentials (air, N-2,O-2) were found to better support the optical discharge and to provide the strongest plasma-related heating of the substrate material. This led to considerable microstructural and composition modifications, which gave rise to the maximization of PL emissions. In particular, for O-2, with the lowest ionization potential, we observed local plasma-provoked melting of the target surface and the disappearance of the porous structure of the layer. We also found a clear correlation between the PL properties of the layers, subsequent to fabrication, as well as after prolonged aging, and the presence of different oxygen-containing compounds. The structures produced are of importance for optoelectronics and biosensing applications. (C) 2004 American Institute of Physics.