Effect of argon flow rate on the optical and structural properties of SiO2/Nb2O5 multilayer thin films

In plasma-assisted reactive magnetron sputtering (PARMS), argon (Ar) flow critically shapes the structural and optical properties of SiO 2 /Nb 2 O 5 multilayer thin films targeted at 530 nm aviation lighting filters. Multilayers were deposited at Ar flows of 50, 75, and 100 sccm. XRD and HRTEM show predominantly amorphous layers with short-range order. XPS reveals increased oxygen deficiency at higher Ar flow, accompanied by partial reduction of Nb 5+ to Nb 4+ . EDXRF indicates a concomitant rise in Nb content. The 50 sccm condition achieves a peak transmittance of 97 % at 530 nm. With increasing Ar flow, the transmission maximum red-shifts and weak absorption features emerge near the bandpass edge. Optical simulations (Essential Macleod) reproduce the red shift when Nb 2 O 5 layer thickness is modestly increased, indicating that over-thickening of high-index layers i.e. NbO x is the primary driver, while vacancy-related sub-gap states associated with Nb 4+ account for the added loss features. These results identify Ar flow as a key process parameter that stoichiometry, oxidation state, and optical thickness, enabling tunable performance of SiO 2 /Nb 2 O 5 bandpass stacks for durable, high-transmittance aviation lighting.