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Issue 39, 2015
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Strong optical nonlinearity of the nonstoichiometric silicon carbide

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Enhanced nonlinear refractive indices and absorption coefficients of nonstoichiometric SixC1−x with varying C/Si composition ratios from 0.51 to 1.83 grown by low-temperature plasma-enhanced chemical vapor deposition are demonstrated. When increasing the [CH4]/[CH4 + SiH4] fluence ratio from 70% to 92%, two Raman scattering signals at 795 and 970 cm−1 contributed by transverse and longitudinal optical modes of Si–C bonds are simultaneously enhanced in stoichiometric and C-rich SixC1−x samples, whereas the Si-associated Raman peak at 520 cm−1 decreases with increasing C/Si composition ratio. The C-rich SixC1−x film shows additional Raman scattering peaks at 1330 and 1580 cm−1, which are individually contributed by the diamond-like C–C bonds and the G peak of the graphite-like C–C bonds, respectively. The nonlinear refractive index increases to 1 ± 0.1 × 10−11 cm2 W−1 upon increasing the C/Si composition ratio up to 1.83, which is four orders of magnitude higher than that of bulk SiC. The increased C/Si composition ratio reduces the lattice constant and the effective mass of the SixC1−x film and enhances its nonlinear refractive index effectively. In comparison with the sp3-orbital C–C bond, the sp2-orbital C–C bond in SixC1−x films dominates the enhancement of nonlinear refractive index. By contrast, the nonlinear absorption coefficient changes sign and decreases magnitude when transferring the SixC1−x film from Si-rich to C-rich conditions. This sign reversal is primarily attributed to the conversion in the absorption mechanism from two-photon absorption to nonlinear saturable absorption. Unlike Si–Si bonds which favor two-photon absorption, the sp2-orbital C–C bonds with delocalized π-electrons essentially enhance the saturable absorbance. Hence, a higher nonlinear refractive index and a higher saturable absorption coefficient can be obtained by enriching the sp2-orbital C–C bonds in C-rich SixC1−x films.

Graphical abstract: Strong optical nonlinearity of the nonstoichiometric silicon carbide

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Publication details

The article was received on 16 Jun 2015, accepted on 08 Sep 2015 and first published on 08 Sep 2015

Article type: Paper
DOI: 10.1039/C5TC01791B
Citation: J. Mater. Chem. C, 2015,3, 10164-10176
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    Strong optical nonlinearity of the nonstoichiometric silicon carbide

    C. Cheng, C. Wu, Y. Lin, W. Yan, M. Shih, J. Chang, C. Wu, C. Lee and G. Lin, J. Mater. Chem. C, 2015, 3, 10164
    DOI: 10.1039/C5TC01791B

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