Plasma-enhanced atomic-layer-deposited HfO2–SiO2 nanolaminates for broadband antireflection coatings

The ellipsometry parameters of the monolayer coatings were measured using a spectroscopic ellipsometer (SE; Horiba Uvisel 2) at an angle of incidence of 70° in the reflection mode. The measurement range was 500–900 nm and the step size was 10 nm. The thickness and n were fitted using the commercial software DeltaPsi2. During the fitting, a three-phase physical model of Si|Coating|Air was established, Sellmeier dispersion oscillators [30] were adopted, and the extinction coefficient was regarded as zero. For comparison, the monolayer thickness was characterized using grazing-incidence X-ray reflectometry (XRR; PANalytical Empyrean). The cross-sectional morphologies of the coatings were characterized using high-resolution transmission electron microscopy (TEM; Thermo Fisher Talos F200X S), and the chemical composition profiles were mapped using energy dispersive spectrometry (EDS; Thermo Fisher Super-X). The reflectance and transmittance spectra in the range of 500–900 nm were measured using a UV–visible (VIS)–near infrared (NIR) spectrometer (Lambda 1050 UV/VIS/NIR; Perkin-Elmer).