Interplay between metal nanoparticles and dielectric spacing layers during the growth of Au/Si_3N_4 multilayers

摘要

Competition between ordering and disordering processes during growth of granular Si_3N_4/[Au(t)/Si3N_4]_n thin films by vapor deposition is tracked in a simple, unconventional and nondestructive way by probing the infrared response of the dielectric matrix. Si_3N_4 crystallization occurs as a consequence of the presence of Au nanostructures. The average Si_3N_4 crystalline order is improved upon increasing the thickness t_(Au) of deposited Au per bilayer. On the contrary, crystalline order is destroyed when the number n of bilayers overcomes a threshold value that varies with t. Additional information provided by conventional measurements (x-ray diffraction, visible absorption spectroscopy) and by transmission electron microscopy observations suggests that the Si_3N_4 atomic ordering results from seed-induced crystallization on the Au(111) planes. Disordering is tentatively attributed to roughness accumulation upon stacking, whose magnitude is ruled by the roughness of the first deposited Au granular layer.