Infrared light absorption of silver film coated on the surface of femtosecond laser microstructured silicon in SF6

Absorptive properties of 100 nm thick silver (Ag) films coated on the surface of microstructured silicon prepared by femtosecond laser pulses irradiation in SF6 were measured in a wavelength range of 1.33-16.7 mu m. Greatly enhanced light absorption of Ag films was observed in the entire measured wavelength range. For sample with 6-8 mu m spikes, the absorptance is approximately 0.9 and essentially unchanged in the wavelength region of 1.33-10 mu m, and decreases slightly when lambda>10 mu m. but keeps higher than 0.75 over the whole measured wavelength range. The infrared absorption is strongly related to the height and density of the spikes. While for the samples without Ag coating, the absorption is much lower than that of the Ag films. Multiple reflection of light between spikes and surface plasmon excitation of nano-particles on the spikes surface may lead to the strongly enhanced infrared absorption in such a wide wavelength range. (C) 2009 Elsevier B.V. All rights reserved.