Freindl Kinga, Wojas Joanna, Kwiatek Natalia, Korecki Józef, Spiridis Nika
Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, 30-239 Kraków, Poland.
J Chem Phys. 2020 Feb 7;152(5):054701. doi: 10.1063/1.5136322.
We studied magnetite-hematite-magnetite transformations in an ultrathin epitaxial film on Pt(111) using surface sensitive and bulk sensitive methods. At initial oxidation stages at elevated temperature (810 K), a 5-nm thick magnetite FeO(111) film became non-stoichiometric toward maghemite and then showed the first signs of hematite phase formation under an oxygen exposure of 3 × 10 L. Finally, under 2 × 10 L, the film fully transformed to hematite α-FeO(0001), maintaining a high single-crystal quality. A comparison of the conversion electron Mössbauer spectra and low energy electron diffraction pattern showed that at intermediate oxidation stages, hematite dominated at the surface, whereas a spinel phase was still observed in the deeper layers. The magnetite-hematite conversion was fully reversed by annealing under ultra-high vacuum at temperatures exceeding 600 K, and despite a change in morphology, the magnetite film preserved the original crystal structure and orientation.
我们使用表面敏感和体敏感方法研究了Pt(111)上超薄外延膜中的磁铁矿-赤铁矿-磁铁矿转变。在高温（810 K）的初始氧化阶段，5纳米厚的磁铁矿FeO(111)膜变得对磁赤铁矿非化学计量，然后在3×10 L的氧气暴露下显示出赤铁矿相形成的最初迹象。最后，在2×10 L的氧气暴露下，该膜完全转变为赤铁矿α-FeO(0001)，保持了高单晶质量。转换电子穆斯堡尔谱和低能电子衍射图案的比较表明，在中间氧化阶段，赤铁矿在表面占主导，而在较深层仍观察到尖晶石相。通过在超过600 K的温度下在超高真空下退火，磁铁矿-赤铁矿转变完全逆转，并且尽管形态发生了变化，但磁铁矿膜保留了原始的晶体结构和取向。
