Wydział Chemii

Krzysztof B. Beć

Yusuke Morisawa

Kenta Kobashi

Justyna Grabska

Ichiro Tanabe

Yukihiro Ozaki

2018

Journal of Physical Chemistry C

122

28998-29008

10.1021/acs.jpcc.8b08089

Naukowa

Angielski

Artykuł

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). The major absorption of graphene appears in the DUV region (4.7 eV), as already reported; however, 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). Graphene flakes (thickness 1–2 nm; sub-micrometers of side dimension) and nanoplatelets (thickness 6–8 nm; several micrometers of side dimension) give notably different ATR absorbance spectra in the spectral region studied. This discrepancy is reduced upon applying mechanical pressure on the samples. These observations can evidence that the morphology as well as electronic structure of graphene can be manifested in the FUV–DUV region. 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.

http://dx.doi.org/10.1021/acs.jpcc.8b08089

https://www.acs.org/content/acs/en.html