Environmental stability investigation on electron-beam deposited coatings with dense capping layer

The properties of coatings deposited by electron-beam (e-beam) technique can be easily influenced by environmental humidity, causing spectrum shift, residual stress evolution, and wave front errors. HfO2 / SiO2 multilayer coatings with different overcoat layer deposition parameters have been prepared. The optical spectrum shifts induced by atmosphere-vacuum effect are investigated by a spectrometer. The laser resistance is studied and their damage morphologies are characterized by a scanning electron microscope. The surface morphologies and the global mechanical stresses of the films are analyzed by an atomic force microscope and zygo interferometer, respectively. The experimental results demonstrate that by introducing a dense capping SiO2 layer employed with plasma ion assisted deposition, considerable environmental stability of e-beam coatings can be improved due to retarded water vapor transport. A relatively smaller grain size can be obtained as well. Moreover, the laser-induced damage threshold shows no significant difference.