| Affiliation: | 1. College of Science, Institute of Materials Physics and Chemistry, Nanjing Forestry University, Nanjing, 210037 P. R. China Institute of Physics and Technology, Ural Federal University, Mira Street 19, Ekaterinburg, 620002 Russia;2. Consiglio Nazionale delle Ricerche (CNR)-Istituto Officina dei Materiali (IOM), Laboratorio TASC in Area Science Park S.S. 14 3. km 163.5, Trieste, 34149 Italy;4. Charles University, V Holesovickaˇch 2, Prague 8, Prague, 18000 Czech Republic;5. Elettra-Sincrotrone S.C.p.A, S.S. 14-km 163.5 in AREA Science Park, Trieste, 34149 Italy;6. Department of Industrial and Information Engineering and Economics, Via G. Gronchi 18, 7 University of L'Aquila, L'Aquila, I-67100 Italy;7. Department of Physics, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan, 70101 Taiwan;8. INSTM and Department of Physical and Chemical Sciences, University of L'Aquila, via Vetoio, L'Aquila, AQ, 67100 Italy |
| Abstract: | Recently, germanium selenide (GeSe) has emerged as a promising van der Waals semiconductor for photovoltaics, solar light harvesting, and water photoelectrolysis cells. Contrary to previous reports claiming perfect ambient stability based on experiments with techniques without surface sensitivity, here, by means of surface-science investigations and density functional theory, it is demonstrated that actually both: i) the surface of bulk crystals; and ii) atomically thin flakes of GeSe are prone to oxidation, with the formation of self-assembled germanium-oxide skin with sub-nanometric thickness. Surface oxidation leads to the decrease of the bandgap of stoichiometric GeSe and GeSe1−x, while bandgap energy increases upon surface oxidation of Ge1−xSe. Remarkably, the formation of a surface oxide skin on GeSe crystals plays a key role in the physicochemical mechanisms ruling photoelectrocatalysis: the underlying van der Waals semiconductor provides electron–hole pairs, while the germanium-oxide skin formed upon oxidation affords the active sites for catalytic reactions. The self-assembled germanium-oxide/germanium-selenide heterostructure with different bandgaps enables the activation of photocatalytic processes by absorption of light of different wavelengths, with inherently superior activity. Finally, it is discovered that, depending on the specific solvent-GeSe interaction, the liquid phase exfoliation of bulk crystals can induce the formation of Se nanowires. |
