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SiC ceramic micropatterns from polycarbosilanes

: Jang, Y.-S.; Jank, M.; Maier, V.; Durst, K.; Travitzky, N.; Zollfrank, C.


Journal of the European Ceramic Society 30 (2010), Nr.13, S.2773-2779
ISSN: 0955-2219
Fraunhofer IISB ()
microstructure-final; SiC; precursors-organics; optical property; softlithography

Micropattemed SiC ceramics were fabricated from polycarbosilanes applying a softlithographic replication technique. A polydimethylsiloxane mould replicated from a photolithographic microstructured silicon wafer was used as master structure. The polydimethylsiloxane mould was coated with a solution containing a mixture of two different polycarbosilanes in n-octane. After treatment at 200-400 degrees C the cross-linked polycarbosilane films were debonded and pyrolysed at 900 degrees C in nitrogen and subsequently crystallised at temperatures up to 1500 degrees C in argon. The cross-linking and thermal degradation behaviour of the polycarbosilanes was investigated by Fourier-transform infrared spectroscopy, differential scanning calorimetry and thermogravimetric analysis. X-ray diffractrometry showed the expected development of a nanocrystalline beta-SiC (3 nm) as the main phase with increasing temperature. However, traces of alpha-SiO2 derived from the polycarbosilane precursors were also detected by X-ray analysis. Removal of the alpha-SiO2 dioxide with hydrofluoric acid in the pyrolysed samples and subsequent increased the crystallite size to 7 nm. The Young's modulus determined by nanoindentation was increased from 3 GPa after cross-linking to 110 GPa after crystallisation. Scanning electron microscopy revealed, that the initial micropatterns were fully retained in the pyrolysed and crystallised SiC ceramics. The micropatterned cross-linked and crystallised beta-SiC based substrates exhibited light scattering characteristics, which qualify them as promising candidates for diffractive optical elements in microoptical applications.