<title>Air optical breakdown on silicon as a novel method to fabricate photoluminescent Si-based nanostructures</title>

Abstract

A novel "dry", vacuum-free laser-assisted method for a fabrication of nanostructured Si/SiO x layers on a silicon wafer is demonstrated. This method uses the phenomenon of air optical breakdown to modify a semiconductor surface. Pulsed radiation from a CO 2 laser was focused on a silicon wafer to initiate the optical breakdown in atmospheric pressure air. After several breakdown initiations near the threshold of plasma production, a gray-tint layer was formed under the radiation spot on the silicon surface. The size of the processed area could be controlled by varying the radiation focusing conditions. Properties of the layers were studied by optical and SEM microscopies, XPS, XRD, Specular X-ra Reflectivity and PL spectroscopy. It was found that the layers had the porosity of about 75-80% and contained nanoscale holes and channels. They consisted of silicon nanocrystals embedded in S 2 matrix and exhibited strong photoluminescence (PL) at 1.9-2.0 eV, which could be seen by naked eyes. Possible mechanisms of nanostructur formation and PL origin are discussed. The method can be used for a controlled local patterning of photoluminescent nanostructured materials.