Laser-induced treatment of silicon in air and formation of Si/SiOx photoluminescent nanostructured layers

Two different mechanisms of laser-induced treatment of silicon in atmospheric air are compared. In one, silicon target was ablated by pulsed UV radiation, which led to a formation of microscale spikes under the irradiation spot and a deposition of material around it. The treated material contained silicon nanocrystals and exhibited weak photoluminescence (PL) signals, whose peak position was not uniform over the treated surface and varied from 2.0 to 2.3 eV in different points. In another mechanism, silicon target served to provide first electrons in order to initiate a breakdown in surrounding air by pulsed IR radiation. As a result, a highly porous nanostructured layer was formed under the contact of the target with the breakdown plasma. All points of the layer exhibited only 1.95 eV PL signals, whose intensity was stronger than in the case of the UV ablation by at least an order of magnitude. Possible mechanisms of nanostructure formation and PL origin are discussed.