Unpredicted surface termination of α-Fe2O3(0001) film grown by mist chemical vapor deposition
Unpredicted surface termination of α-Fe2O3(0001) film grown by mist chemical vapor deposition
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DOI：
10.1016/j.susc.2017.02.002
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发表时间：
2017-06-01
期刊：
影响因子：
1.9
通讯作者：
Katayama, Mitsuhiro
中科院分区：
文献类型：
--
作者：
Osaka, Shun;Kubo, Osamu;Katayama, Mitsuhiro
我们分析了用雾化学气相沉积（CVD）在c平面蓝宝石衬底上生长α - fe2o3（0001）薄膜的表面结构，CVD是最近发展起来的一种简单、安全、经济的薄膜生长方法。利用共轴碰撞-碰撞离子散射光谱分析发现，雾气相沉积法制备的α - fe2o3（0001）薄膜表面末端的原子层序列为Fe-O-3-Fe-。尽管薄雾CVD过程是在常压空气中进行的，但通过密度泛函理论结合热力学方法预测，这种表面终止会在缺氧环境中形成。在600℃以上的超高真空中退火后，表面结构发生了显著变化。我们发现，在650℃退火后，顶层只有几层转变为Fe3O4(111)，这就是所谓的双相重构。在700℃时完全转变为Fe3O4（111）薄膜，其原子层顺序从顶层开始为Fe-O-4-Fe-3-。
We analyze the surface structure of an alpha-Fe2O3(0001) film grown on a c-plane sapphire substrate by mist chemical vapor deposition (CVD), which has been recently developed as a simple, safe, and cost-effective film growth method. Using coaxial impact-collision ion scattering spectroscopy, we found that the atomic-layer sequence of the surface termination of an alpha-Fe2O3(0001) film grown by mist CVD was Fe-O-3-Fe- from the top layer. This surface termination is predicted to form in an oxygen-poor environment by density functional theory combined with a thermodynamical approach despite that the mist CVD process is performed with atmospheric pressure air. The surface structure markedly changes after annealing above 600 degrees C in ultrahigh vacuum. We found that only a couple of layers from the top layer transform into Fe3O4(111) after 650 degrees C annealing, which would be so-called biphase reconstruction. Complete transformation into a Fe3O4(111) film occurs at 700 degrees C, whose atomic-layer sequence is determined to be Fe-O-4-Fe-3- from the top layer.