Space-selective fabrication of light-emitting carbon dots in polymer films using electron-beam-induced chemical reactions

Nanocarbon-based materials have excellent properties, including high electrical conductivity as well as charity-dependent optical absorption and luminescence; therefore, the materials are promising in applications for nanoelectric devices, nanophotonics, and so on. Carbon dots (CDs) are one of the carbon materials recently fabricated. Optical properties of CDs have been reported to be similar to those of polycyclic aromatic hydrocarbons (PAHs). For this reason, the CDs are considered to be composed of PAH. Synthesis of CDs has previously been accomplished through hydrothermal synthesis and microwave irradiation. These methods require a long synthesis time, and the processes involve multiple steps. In this study, we developed a fabrication method of CDs in simple and spatially selective ways, by using radical reactions in an organic polymer film with focused electron-beam irradiation. We investigated various organic polymers as reaction materials and found that polystyrene has a higher efficiency for CD formation than other organic polymers investigated. Absorption, photoluminescence, and Raman scattering properties of the electron-beam-irradiated sample were in good agreement with those reported for the CDs. The technique developed in this study is promising for fabricating light-emitting CDs and photonic crystals in a simple and flexible manner.