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Sub-micrometer patterning of amorphous- and β-phase in a crosslinkable poly(9,9-dioctylfluorene) : dual-wavelength lasing from a mixed-morphology device

Kuehne, A. J. C. and Kaiser, M. and Mackintosh, A. R. and Wallikewitz, B. H. and Hertel, D. and Pethrick, R. A. and Meerholz, K. (2011) Sub-micrometer patterning of amorphous- and β-phase in a crosslinkable poly(9,9-dioctylfluorene) : dual-wavelength lasing from a mixed-morphology device. Advanced Functional Materials, 21 (13). pp. 2564-2570. ISSN 1616-301X

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Abstract

The metastable β-phase morphology, inherent to most polyfluorene homo-polymers, is of interest due to its superior optical and electrical characteristics compared to its amorphous analogue. Here, a polyfluorene with vinyl-ether-functionalized aliphatic side-chains that allow crosslinking is reported. It is demonstrated that the previously induced conformational morphology is preserved in the resulting polyfluorene network, which enables subsequent wet thin-film processing. Electron-beam lithography provides a means for sub-(optical)-wavelength patterning of the crosslinkable polyfluorene films. As a specific demonstration, optically-pumped distributed-feedback (DFB) lasers made from surface-relief gratings in amorphous and β-phase polyfluorene are presented. By backfilling gratings of one morphology by the other, devices are demonstrated that exhibit lasing at two wavelengths with a threshold (<1 μJ cm−2) at least an order of magnitude lower compared with previous data.