Electronic states of graphene have received much interest for the last two decades or so. The interesting properties of graphene are strongly concerned with its specific electronic structure containing conjugated π system. Therefore, an extensive amount of information about graphene has been collected with significant contributions from theoretical and computational investigations.　We measured the electronic spectra of graphene nanostructures (flakes and platelets) extending into the far-ultraviolet (FUV) region by attenuated total reflection far- and deep-ultraviolet (ATR−FUV−DUV) spectroscopy in the region of 2.76−8.55 eV (450−145 nm). Besides a major absorption of graphene appearing in the DUV region (4.7 eV), we observed a new peak in the FUV region, visible clearly in the case of flakes at 7.5−7.7 eV (165−161 nm) and less pronounced in the spectrum of the platelets at 6.6−6.7 eV (188−185 nm). Quantum chemical calculations were applied to several molecular models incorporating the expected principal structural features of graphene nanostructures. On the basis of the results of time-dependent density functional theory and Zerner’s intermediate neglect of differential overlap (ZINDO) calculations, it was possible to consistently reproduce the experimental spectral variations in terms of both band positions and intensities. The spectral differences result from the differences in the die area, ordering and the number of layers, and structural factors which separate nanoflakes and nanoplatelets. These results provide insights into the probable origins of the spectral variability of graphene nanostructures as well as the molecular orbitals involved in a FUV π−π* transition of graphene nanostructures.

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Yukihiro Ozaki, "ATR-FUV spectroscopy of graphene (Conference Presentation)," Proc. SPIE 11086, UV and Higher Energy Photonics: From Materials to Applications 2019, 1108603 (Presented at SPIE Nanoscience + Engineering: August 11, 2019; Published: 9 September 2019); https://doi.org/10.1117/12.2529067.6083789778001.