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27 September 2012 Infrared transmission spectroscopy of CVD graphene on Si
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We report transmission spectroscopy results from the mid- to far-infrared on graphene, grown by chemical vapor deposition (CVD) on Cu. Similar results have been reported by several groups and their substrates of choice were thermal Si dioxide, quartz, or SiC, where strong phonon absorption results in transmission blocking bands in midinfrared. Silicon wafers (thickness ~ 500 μm), on the other hand, have transmission extending out to about 100 cm-1 when the doping level is low. Therefore, we choose to use Si wafers as the carrier substrates for transferred CVD graphene. The complex refractive index of the Si substrate is measured by infrared spectroscopic ellipsometry. As a result, continuous spectra (without blocking bands) in the range of 400 to 4000 cm-1 are obtained and they are modeled by free carrier absorption (the Drude model) and interband transitions (considering the Pauli blocking.) From these, the carrier density, carrier mobility, sheet resistivity, intraband scattering rate, and graphene layer number can be inferred. In the far-infrared range, the absorption is dominated by the intraband free carrier absorption and it mainly results from the interband transition in the mid-infrared range. Having continuous spectra using the Si substrates gives us the advantage to model the whole spectral region (from far-infrared to mid-infrared) accurately.
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Shin Mou, Steve S. Kim, Kuei-Hsien Chen, Li-Chyong Chen, Rajesh R Naik, Gail J. Brown, and W. C. Mitchel "Infrared transmission spectroscopy of CVD graphene on Si", Proc. SPIE 8462, Carbon Nanotubes, Graphene, and Associated Devices V, 84620H (27 September 2012);

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