Arndt Björn, Lechner Barbara A J, Bourgund Alexander, Grånäs Elin, Creutzburg Marcus, Krausert Konstantin, Hulva Jan, Parkinson Gareth S, Schmid Michael, Vonk Vedran, Esch Friedrich, Stierle Andreas
Deutsches Elektronen-Synchrotron (DESY), D-22607 Hamburg, Germany.
Department of Chemistry & Catalysis Research Center, Technical University of Munich, D-85748 Garching, Germany.
Phys Chem Chem Phys. 2020 Apr 29;22(16):8336-8343. doi: 10.1039/d0cp00690d.
We present surface X-ray diffraction and fast scanning tunneling microscopy results to elucidate the nature of the surface phase transition on magnetite (001) from a reconstructed to a non-reconstructed surface around 720 K. In situ surface X-ray diffraction at a temperature above the phase transition, at which long-range order is lost, gives evidence that the subsurface cation vacancy reconstruction still exists as a local structural motif, in line with the characteristics of a 2D second-order phase transition. Fast scanning tunneling microscopy results across the phase transition underpin the hypothesis that the reconstruction lifting is initiated by surplus Fe ions occupying subsurface octahedral vacancies. The reversible near-surface iron enrichment and reduction of the surface to stoichiometric composition is further confirmed by in situ low-energy ion scattering, as well as ultraviolet and X-ray photoemission results.
我们展示了表面X射线衍射和快速扫描隧道显微镜的结果，以阐明磁铁矿（001）表面在720K左右从重构表面到非重构表面的相变性质。在高于相变温度（此时长程有序消失）下进行的原位表面X射线衍射表明，次表面阳离子空位重构作为一种局部结构基元仍然存在，这与二维二级相变的特征相符。快速扫描隧道显微镜在相变过程中的结果支持了这样的假设，即重构的解除是由占据次表面八面体空位的多余铁离子引发的。原位低能离子散射以及紫外和X射线光电子能谱结果进一步证实了近表面铁的可逆富集以及表面向化学计量组成的还原。
