ZnO films are grown on c-sapphire substrates by laser molecular beam epitaxy. The band offsets of the ZnO/Al2O3 heterojunction are studied by in situ x-ray photoelectron spectroscopy. The valence band of Al2O3 is found to be 3.59±0.05 eV below that of ZnO. Together with the resulting conduction band offset of 2.04±0.05 eV, this indicates that a type-I staggered band line exists at the ZnO/Al2O3 heterojunction.
Using first-principles calculations, we predict that a single C2H4 or C5H5 molecule can form a stable complex with two rare earth metals such as La, Eu, and Ho. The La2C2H4 complex then absorbs up to sixteen hydrogen molecules, reaching a gravimetric storage capacity of 9.5wt% by adding a rare-earth metal atom, The results show that Eu-4𝑓 electrons have little impact on the hydrogen adsorption. The nature of bonding between Eu and H2 is due to the hybridization of Eu-5𝑑 with the H-1𝑠 orbital.
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