OPTICAL-ABSORPTION IN GOLD CAUSED BY A ANTIGRANULOCYTES DIELECTRIC OVERLAYER

Light can be used to excite surface plasmons if there are proper mechanisms for coupling with those surface plasmons. This coupling can usually be achieved via surface roughness or evanescent waves in attenuated total-reflection experiments. In the present work, we report evidence of the possibility of having a resonant optical absorption when a granular dielectric layer is deposited on a metallic surface. Very thin films of MgF2 of mass thickness up to 8 nm have been used as a discontinuous overcoat on Au films of 100 nm thickness. Reflectivity measurements with p-polarized light incident at 40-degrees show a resonant-type absorption near 520 nm when the dielectric layer is added to the Au surface. As the MgF2 film grows thicker and becomes continuous this absorption feature is no longer prominent. To account for this phenomenon, an effective-medium theory is used to describe the optical behavior of the coated Au surface. By including mirror-image effects in the dipole approximation, basic features of experimental measurements can be reproduced.