Synthesis of high refractive index polymer films via sulfur chemical vapor deposition (sCVD) for optical applications

Abstract

High refractive index polymer (HRIP) thin films have attracted significant research interest as essential components in advanced optical devices owing to outstanding mechanical flexibility, light weight, and high processability compared to inorganic materials. Precise control of refractive index (RI) and thickness in a wide range is crucial for their practical application, however, the low molar refraction of most organic functional groups limits RI of polymer within the range of 1.4 to 1.6. Recently, high sulfur content polymer (HSCP) have emerged as a promising solution, which successffully achieved high RI above 1.8. However, some limitations hinder their versatile optical applications such as difficulty in manufacturing thin film form, poor environmental stability and absorption in visible and infrared (IR) range. In this thesis, a novel one-step synthesis process, sulfur chemical vapor deposition (sCVD), was developed to synthesis new HRIPs with outstanding optical, thermal and mechanical properties. The sCVD process inhibited the formation of long polysulfide chains, allowing to firstly develop the HSCP films with high RI and high transmittance in the visible range. Furthermore, the sCVD process used vaporized reactant, eliminating the miscibility issues associated with molten elemental sulfur, allowing to use various comonomers for synthesis of HSCPs. Due to advantages of the sCVD process, we successfully developed an ultra-high RI (> 1.97) HSCP by introducing high sulfur content without phase separation and using divinyl benzene with high molar refraction as comonomer. Moreover, the novel HSCP with high RI, IR transmittance, and thermal stability was developed by using hexavinyl disiloxane, which is transparent in the infrared (IR) and multiple functionalities. Attributed from the outstanding properties of the HSCP synthesized through the sCVD process, high-performance and thermally stable IR polarizer was achieved using developed HSCP as spacer layer. In conclusion, this thesis has achieved the development of sCVD process firstly using vapor sulfurand we utilized the sCVD process to synthesize the outstanding HRIP materials with highly desirable properties for various applications.