Thin-film conformal fluorescent SU8-phenylenediamine

Abstract

The SU8 polymer is a negative photoresist widely used to produce high-quality coatings, with controllable thicknesses ranging from nanometers to millimeters, depending on fabrication protocols. Apart from conventional use cases in microelectronics and fluidics, SU8 is quite an attractive platform in nanophotonics. This material, being straightforwardly processed by ultraviolet lithography, is transparent to wavelengths longer than 500 nm. However, introducing fluorescent agents within the SU8 matrix remains a challenge owing to its high hydrophobicity. Here, we develop a process, where colorful quantum dots co-participate in the polymerization process by epoxide amination and become a part of a new fluorescent material – SU8-phenylenediamine. Through comprehensive characterization methods, including XPS and ¹H-NMR analyses, we demonstrate that m-PD covalently binds to SU8 epoxy sites with its molecular amine, virtually forming a new material and not just a mixture of two compounds. After characterizing the new strongly fluorescent platform, thin 300 nm films were created on several surfaces, including a conformal coverage of a nanofluidic capillary. This new process provides opportunities to incorporate various functional molecules into optoelectronic devices without the need for multistep deposition and surface functionalization.