https://doi.org/10.1140/epjs/s11734-025-01647-3
Regular Article
Unveiling the charge transfer mechanism at Fe3O4(111)/ZnO(0001) interfaces based on density functional theory calculations
1
School of Materials Science and Engineering, Yancheng Institute of Technology, 224051, Yancheng, China
2
School of Mathematics, Physics and Optoelectronics Engineering, Hubei University of Automotive Technology, 442002, Shiyan, China
a
linshi@ycit.edu.cn
b
qfangzhang@gmail.com
Received:
8
May
2024
Accepted:
24
April
2025
Published online:
13
May
2025
Wide band-gap energy and fast recombination of photogenerated charge carriers limit application of zinc oxide in photocatalyst and photovoltaic devices. To solve these problems, Fe3O4/ZnO (FZ) heterostructures have been synthesized. Structures and electronic properties of FZ interfaces, especially the charge transfer at FZ interfaces, have an important impart on applications of FZ heterostructures. Previous studies found the polarization of Fe ions near FZ interface and considered that this phenomenon caused by strain of FZ interface. Actually, these phenomena can be connected with electronic properties and charge transfer. In this study, density functional theory (DFT) calculations were conducted on the FZ interface to confirm charge transfer and identify the underlying causes of this phenomenon. The investigation also included an analysis of the electronic properties of Fe3O4 bulk and Fe3O4(111) surfaces. It was observed that charge disproportionation (Fe2+/Fe3+) occurred at octahedral interstitial sites in the Fe3O4 bulk phase, allowing for the differentiation of Fe ions based on their structural and electronic characteristics. These findings were consistent across Fe3O4 surface and FZ interface. At calculations about different terminations of Fe3O4(111) surfaces, dangling bands with tendence to get electrons get them from Fe2+, and dangling bands with tendence to lose electrons lose them to Fe3+. At FZ interface, we can find obvious polarization of Fe ions near the interface which was Fe2+ originally. Magnetic moments of these Fe ions are almost the same with Fe3+ at this structure. It can be found that density of states (DOS) of these Fe ions have features of Fe3+ ions. They lose all t2g electrons and change from Fe2+ ions to Fe3+ ions. For the more centrally located Fe2+ ions, polarization also occurs, even though not all spin-down t2g electrons of ions are lost. Based on the charge density difference (CDD) at the interface, the predominant direction of charge transfer is from Fe2+ ions to O ions between Fe3O4 and ZnO, and Fe2+ ions near the interface lose all spin-down electrons at t2g orbitals of them. The charge transfer from Fe2+ ions to O ions at FZ interface is effects of dangling bands of O ions and the difference of electrostatic potential between Fe3O4 and ZnO. The results indicate that the disparity in electrostatic potential and polarization of Fe ions at Fe layers in close proximity to the interface facilitates the separation of photogenerated charge carriers. Effective photogenerated carriers can make this structure show better performance in photocatalyst and photovoltaic devices.
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Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
