Optical Properties Of Femtosecond Laser Micro-structure Silicon

Arrays of micrometer-sized spikes can be formed on the silicon surface by cumulative irradiation of femtosecond laser pulses in the ambient gases such as SF₆ and N₂.Greatly enhanced light absorption of such surface-structured silicon was observed in the whole measured wavelength range from 0.3 to 16.7μm.For the sample fabricated in SF₆,the light absorption is over 80%, while for the sample prepared in N₂,the light absorption is up to 95%over the wavelength range of 0.3～1.1μm and as high as 75%or more in wavelength range of 8.8～13.3μm,though it is down to about 30%in the wavelength range of 2～7μm.Furthermore,light absorption varies with the height and density of the spikes formed on silicon surface,which indicates that the surface microstructures play an important role in the enhancement of light absorption.The surface-microstructured silicon substrate has been developed as substrate for surface-enhanced Raman scattering(SERS).Large SERS signal(up to 10⁶) was measured with pyridine solution on the substrate of silver nanoparticles coated surface microstrutured silicon.The intensity of Raman signals varies as the heights of the spikes.The optimum spikes height for SERS was found to be between 20 - 25μm.