Layer-number determination in graphene on SiC by reflectance mapping
In short: Graphene attracts much attention due to its exceptional electronic properties for future electronics. Growth of graphene on silicon carbide is a promising method for large-scale device-ready production. A significant parameter characterizing the quality of the grown material is the number of layers. Here we report a simple, handy and affordable optical approach for precise number-of-layers determination of graphene based on the reflected power of a laser beam.
Nowadays graphene, the single layer of graphite, attracts much attention from the research community due to its exceptional electronic properties, which open new horizons in building the electronic components of the future. Growth of graphene on silicon carbide is one of the most promising methods for establishing large-scale device-ready production.
Perhaps the most important parameter characterizing the quality of the grown material is the number of layers. In this article we report a simple, handy and affordable optical approach for precise number-of-layers determination of graphene on SiC based on monitoring the power of the laser beam reflected from the sample (reflectance mapping) in a slightly modified micro-Raman setup.
The sample is scanned under the microscope objective focusing the laser on the sample and a map with precise distribution of the number of graphene layers on the sample surface is obtained (reflectance mapping). The reflectance mapping is compatible with simultaneous Raman mapping, allowing assessment of other properties (e.g., doping, stress) locally via the Raman spectra. We find experimentally that the reflectance of graphene on SiC normalized to the reflectivity of bare substrate (the contrast) increases linearly with ~1.7% per layer for up to 12 layers, in excellent agreement with theory. The wavelength dependence of the contrast in the visible spectrum is investigated using the concept of ideal fermions and compared with existing experimental data for the optical constants of graphene. We argue also that the observed contrast is insensitive to the doping condition of the sample, as well as to the type of sample (graphene on C- or Si-face of 4H or 6H SiC, hydrogen-intercalated graphene). The possibility to extend the precise layer counting to ~50 layers makes reflectivity mapping superior to the commonly used but relatively labour-consuming low-energy electron microscopy (limited to ~10 layers) in quantitative evaluation of graphene on the C-face of SiC. The method is applicable to graphene grown on other insulating or semiconducting substrates.
Details of the research are described in Carbon 77 492 (2014)
- EuroGRAPHENE program of the European Science Foundation (ESF)
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Last updated: 09/05/14