Topographic studies using scanning probes have found that graphene surfaces are often covered by micron-scale domains of periodic stripes with a 4 nm pitch. These stripes have been variously interpreted as structural ripples or as self-assembled adsorbates. We show that the stripe domains are optically anisotropic by imaging them using a polarization-contrast technique. Optical spectra between 1.1 and 2.8 eV reveal that the anisotropy in the in-plane dielectric function is predominantly real, reaching 0.6 for an assumed layer thickness of 0.3 nm. The spectra are incompatible with a rippled graphene sheet but would be quantitatively explained by the self-assembly of chainlike organic molecules into nanoscale stripes.

中文翻译：

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石墨烯上自组装环境吸附物的光学成像和光谱表征

使用扫描探针的地形研究发现，石墨烯表面通常被间距为4 nm的周期性条纹的微米级区域覆盖。这些条纹已被不同地解释为结构波纹或自组装的吸附物。我们通过使用极化对比技术对条带域进行成像来显示条带域在光学上是各向异性的。在1.1和2.8 eV之间的光谱表明，平面介电函数中的各向异性主要是真实的，对于0.3 nm的假定层厚度，其各向异性达到0.6。光谱与波纹石墨烯片不兼容，但可以通过将链状有机分子自组装成纳米级条纹来定量解释。