Department of Electrical and Computer Engineering, McGill University, 3480 University Street, Montreal, QC, H3A 2A7, Canada.
Nanotechnology. 2010 Jul 23;21(29):295709. doi: 10.1088/0957-4484/21/29/295709. Epub 2010 Jul 5.
The optical reflection contrast and optical transmission contrast of graphitic films on glass ranging in thickness from a monolayer to the limit of bulk graphite have been experimentally measured. For samples with more than 10 graphene layers where optical contrast quantization becomes difficult to observe, atomic force microscopy was used to measure the sample thickness. The visible optical reflection and transmission of thin graphitic films is found to depend strongly on the real component of the optical conductance per graphene layer, and comparatively weakly on the imaginary component of optical conductance. This observation in part explains the significant variation in the refractive index of graphene and graphite reported in the literature to date. Spectroscopic measurements reveal a strong dispersion in the optical conductance of even a 10 layer film, consistent with an imaginary conductance arising from virtual transitions at the band edges of the pi and sigma bands at the M and Gamma points, respectively.
我们实验测量了厚度从单层到块状石墨极限的玻璃上石墨薄膜的光学反射对比度和光学透过对比度。对于超过 10 层石墨烯的样品，由于光学对比度量化变得难以观察，我们使用原子力显微镜测量了样品厚度。我们发现，薄石墨薄膜的可见光反射和透射强烈依赖于每一层石墨烯的光学电导的实部，而相对较弱地依赖于光学电导的虚部。这一观察结果部分解释了迄今为止文献中报道的石墨烯和石墨折射率的显著变化。光谱测量显示，即使是 10 层薄膜的光学电导也有很强的色散，这与来自于 M 和 Gamma 点的 pi 和 sigma 带边缘的虚拟跃迁的虚电导一致。
