Incorporation of Ti in epitaxial Fe 2 TiO 4 thin films
Incorporation of Ti in epitaxial Fe 2 TiO 4 thin films
复制标题
Ti 在外延 Fe 2 TiO 4 薄膜中的掺入
DOI：
10.1088/1361-648x/ac0571
复制
发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Comes, Ryan B
中科院分区：
文献类型：
--
作者：
Kaspar, Tiffany C;Spurgeon, Steven R;Matthews, Bethany E;Bowden, Mark E;Heald, Steve M;Wang, Le;Kelley, Ron;Paudel, Rajendra;Isaacs-Smith, Tamara;Comes, Ryan B
钛磁铁矿(Fe2−xTixO4，x⩽1)是一类具有良好磁性、催化和电输运性质的可还原尖晶石结构氧化物。为了解Fe2 TiO4薄膜在低温沉积过程中的稳定性，采用分子束外延(MBE)技术在2 5 0~375C的温度范围内，在MgO(0 0 1)衬底上制备了Fe2 TiO4外延薄膜。在较低的衬底温度下，Ti2 TiO4的均匀掺入、Fe价态和薄膜的形貌都强烈依赖于氧化条件。较高的氧化条件导致相分离为外延、刻面的Fe3O4和金红石型的二氧化钛；较少的氧化条件导致多晶薄膜表现出钛在薄膜表面的偏析以及混合的Fe价态(Fe3+，Fe2+，Fe0)。在中等氧分压的窄窗口沉积过程中，钛的掺入几乎是均匀的，并有大量的Fe2+。然而，这些薄膜的晶化程度较差，X射线磁性圆二色谱在Fe L边缘没有检测到Fe2+占据尖晶石晶格中的四面体位置。真空退火后，发现有一小部分Fe2+占据了四面体位置。将这些结果与前人的工作进行了比较，结果表明，使用氧化镁衬底的低温沉积条件限制了钛在尖晶石晶格中的掺入。提出了一种利用高衬底温度和低氧分压在热稳定衬底上沉积的分子束外延技术获得化学计量比、结晶良好的Fe2TiO4的途径。
The titanomagnetites (Fe 2− x Ti x O 4, x⩽ 1) are a family of reducible spinel-structure oxides of interest for their favorable magnetic, catalytic, and electrical transport properties. To understand the stability of the system during low temperature deposition, epitaxial thin films of Fe 2 TiO 4 were deposited by molecular beam epitaxy (MBE) on MgO (001) at 250–375 C. The homogeneous incorporation of Ti, Fe valence state, and film morphology were all found to be strongly dependent on the oxidation conditions at the low substrate temperatures employed. More oxidizing conditions led to phase separation into epitaxial, faceted Fe 3 O 4 and rutile TiO 2. Less oxidizing conditions resulted in polycrystalline films that exhibited Ti segregation to the film surface, as well as mixed Fe valence (Fe 3+, Fe 2+, Fe 0). A narrow window of intermediate oxygen partial pressure during deposition yielded nearly homogeneous Ti incorporation and a large fraction of Fe 2+. However, these films were poorly crystallized, and no occupation of tetrahedral sites in the spinel lattice by Fe 2+ was detected by x-ray magnetic circular dichroism at the Fe L-edge. After vacuum annealing, a small fraction of Fe 2+ was found to occupy tetrahedral sites. Comparison of these results with previous work suggests that the low temperature deposition conditions imposed by use of MgO substrates limits the incorporation of Ti into the spinel lattice. This work suggests a path towards obtaining stoichiometric, well-crystallized Fe 2 TiO 4 by MBE by utilizing high substrate temperature and low oxygen partial pressure during deposition on thermally stable substrates.