A DROP IN THE INFRARED (LAMBDA=9.2 MU-M) OPTICAL REFLECTANCE OF AL THIN-FILMS DEPOSITED ON SIO2 GLASS SUBSTRATE

We have measured infrared (lambda = 9.2 mu m) optical reflectance of u ltrathin Al films deposited on SiO2 glass substrate. The film thicknes s ranges 5 similar to 112 Angstrom, and the incident light was p-polar ized with near-normal incident angle (theta(1) = 7 degrees). Among oth er effects, we have observed that the reflectance dropped down from th e value for bare glass substrate when the film thickness was in 30 sim ilar to 80 Angstrom. We have done a calculation for the reflectance. T he numerical results provide a theoretical explanation of the drop: th ere exists a red shift as well as a broadening of the enhanced reflect ion peak in the infrared spectrum when the film thickness increases.