Highly efficient anti-reflection coating on transparent material surface by a deposition-oxidation two-step process using very high-frequency plasma under atmospheric pressure

Using atmospheric-pressure (AP) helium (He)-based plasma excited by a 150 MHz very high-frequency (VHF) power, the formation of low-refractive-index silicon oxide (SiOx) layers for single-layer quarter-wave anti-reflection (AR) coatings of transparent substrate materials is studied. To effectively lower the refractive index of SiOx layers, a deposition-oxidation two-step process is adopted. Specifically, carbon and hydrogen-containing silicon oxide (SiOCH) films are coated in hexamethyldisiloxane and hydrogen-fed plasma on the substrates with fine polystyrene spheres arranged, and subsequently oxidized in oxygen-fed plasma. During the post-oxidation process, the SiOCH film is transformed into silica (SiO2)-like one and the polystyrene spheres underlying the film is simultaneously oxidized to be removed. As a result, a SiO2-like film with a very low refractive index of 1.23 and with excellent adhesion to the substrate is obtained. It is also demonstrated that the low-refractive-index coating functions well as a quarter-wave AR coating of a glass substrate.