Significant improvement in wettability of molten tin and indium on calcium fluoride surface by titanium metalization

Common metals exhibit poor chemical bonding affinity with calcium fluoride (CaF 2 ), which complicates the packaging process for CaF 2 optical windows. To enhance the wettability between metal and CaF 2 , this study adopted physical vapor deposition (PVD) techniques to deposit a titanium (Ti) film ∼ 400 nm in thickness onto the CaF 2 substrate. The wetting characteristics of liquid-phase tin (Sn) and indium (In) on this Ti-coated CaF 2 substrate were evaluated using an improved sessile drop method . After titanium surface metallization , the contact angle of molten tin and indium on the surface of CaF 2 decreased significantly. Microstructures and X-ray diffraction analysis shows that titanium reacts with CaF 2 to form compounds such as CaTiF 5 , CaTiF 6 and TiF 3 . The existence of CaTiF 6 may be the main reason for the improvement of wettability , while the decomposition of CaTiF 6 may be the reason for the dewetting phenomenon in some wetting experiments. This study further clarified the mechanism of titanium as an active element at the solid/liquid interface. • Titanium coating via PVD improves wettability, with angles ∼7° for Sn and ∼15° for In. • CaTiF 6 enhances wetting but can cause dewetting in further reactions. • Wettability is improved by interface precipitates, not titanium adsorption.