Localized polymerization using single photon photoinitiators in two-photon process for fabricating subwavelength structures

•Single Photon photoinitiators as two-photon dye for polymerization.•Subwavelength lithography using single photon photoinitiators.•Fabrication of complex 2D and 3D structures with subwavelength size features.

Localized polymerization in subwavelength volumes using two photon dyes has now become a well-established method for fabrication of nano structures. Unfortunately, the two photon absorption dyes used in such process are not only expensive but also proprietary. Lucirin TPO-L is an inexpensive, easily available single photon photoinitiator and has been used extensively for single photon absorption of UV light for polymerization. These polymerization volumes however are not localized and extend to micron size resolution having limited applications. We have exploited high quantum yield of radicals of Lucirin TPO-L for absorption of two photons to achieve localized polymerization in subwavelength volumes, much below the diffraction limit. Critical concentration (10 wt%) of Lucirin TPO-L in acrylate (Sartomer) was found optimal to achieve subwavelength localized polymerization and has been demonstrated by fabricating 2D/3D complex nanostructures and functional devices such as variable polymeric gratings using two photon processes. Systematic studies on influence of Lucirin TPO-L concentration on two photon polymerization of Sartomer show that resolution of the fabricated structures critically depends on loading of Lucirin TPO-L. This is expected to unleash the true potential of two photon polymerization for fabrication of complex polymeric nano devices at a larger scale.

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