Effect of Nitrogen Flow Rate on Microstructure and Optical Properties of Ta2O5 Coatings

Ta2O5 coatings were prepared on highly transparent quartz glass and silicon wafer substrates using RF magnetron sputtering technology. Different flow rates (10%, 15%, and 20%) of N2 were introduced during the sputtering process while keeping the total sputtering gas flow rate constant at 40 sccm. The effects of N2 flow rate on the phase structure, micro-morphology, elemental composition, and optical properties of Ta2O5 coatings were investigated. The coatings were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), electron energy spectroscopy (EDS), and spectrophotometry. The results show that the phase composition of the coating is an amorphous structure when the sputtering gases are pure argon and nitrogen-argon mixed gases, respectively. The coating after the passage of N2 is mainly composed of Ta, N, and O, which confirms that the deposited coating is a composite coating of Ta oxide and nitride. The EDS spectrum indicates that the ratio of O to Ta atoms in the composite coating is greater than the stoichiometric value of 2.5. It may be related to the deposition rate of Ta atoms during the preparation process. The optical properties show that the average transmittance of the composite coating is greater than 75% and the maximum light transmission is 78.03%. The transmittance in the visible range of Ta2O5 coatings prepared under nitrogen-argon mixed gas sputtering conditions is greater than that of those prepared under pure argon sputtering conditions. Finally, the coatings optical direct band gap Edg and indirect band gap Eig are obtained.