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arXiv · 2504.10238

A Wide Optical-Gap in Fully $sp^3$-Like Hydrogenated Monolayer Graphene

Alice Apponi·Orlando Castellano·Daniele Paoloni·Domenica Convertino·Neeraj Mishra·Camilla Coletti·Carlo Mariani·Alessandro Ruocco
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Abstract

A comprehensive spectroscopic characterisation of two highly hydrogenated monolayer graphene samples transferred onto nickel grids is reported. With X ray photoemission spectroscopy on the C 1s core-level, a 100$\%$ $sp^3$ profile was observed upon hydrogenation of a more $sp^3$-like initially defected graphene, while a flatter, more $sp^2$-arranged, graphene reached a 62$\%$ $sp^3$ saturation. Low-energy reflection electron energy-loss spectroscopy (EELS) corroborates these findings through the $\pi$-plasmon excitation quenching for the fully $sp^3$ sample and a significant reduction for the partially converted one. The extreme surface sensitivity of low-energy reflection EELS enables extraction of the optical band gap of the hydrogenated layer even on a metallic support, yielding values of 6.3 and 6.2 eV for the two samples. The C--H stretching vibrational mode is also resolved, providing a direct fingerprint of graphene--hydrogen bonding. Finally, valence-band measurements of the $62\%$ saturated sample suggest the coexistence of one-sided and two-sided hydrogenation morphologies.

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Alice Apponi, Orlando Castellano, Daniele Paoloni, Domenica Convertino, Neeraj Mishra, Camilla Coletti, Carlo Mariani, Alessandro Ruocco. 2025-04-14. A Wide Optical-Gap in Fully $sp^3$-Like Hydrogenated Monolayer Graphene. https://arxiv.org/abs/2504.10238

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