Torruella Pau, Ruiz-Caridad Alicia, Walls Michael, Roca Alejandro G, López-Ortega Alberto, Blanco-Portals Javier, López-Conesa Lluís, Nogués Josep, Peiró Francesca, Estradé Sònia
Laboratoire de Physique des Solides , Paris-Sud University , Orsay 91405 CEDEX , France.
Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB , Bellaterra , E-08193 Barcelona Spain.
Nano Lett. 2018 Sep 12;18(9):5854-5861. doi: 10.1021/acs.nanolett.8b02524. Epub 2018 Sep 4.
The atomic structure of nanoparticles can be easily determined by transmission electron microscopy. However, obtaining atomic-resolution chemical information about the individual atomic columns is a rather challenging endeavor. Here, crystalline monodispersed spinel FeO/MnO core-shell nanoparticles have been thoroughly characterized in a high-resolution scanning transmission electron microscope. Electron energy-loss spectroscopy (EELS) measurements performed with atomic resolution allow the direct mapping of the Mn/Mn ions in the shell and the Fe/Fe in the core structure. This enables a precise understanding of the core-shell interface and of the cation distribution in the crystalline lattice of the nanoparticles. Considering how the different oxidation states of transition metals are reflected in EELS, two methods of performing a local evaluation of the cation inversion in spinel lattices are introduced. Both methods allow the determination of the inversion parameter in the iron oxide core and manganese oxide shell, as well as detecting spatial variations in this parameter, with atomic resolution. X-ray absorption measurements on the whole sample confirm the presence of cation inversion. These results present a significant advance toward a better correlation of the structural and functional properties of nanostructured spinel oxides.
纳米颗粒的原子结构可通过透射电子显微镜轻松确定。然而，获取有关单个原子列的原子分辨率化学信息是一项颇具挑战性的工作。在此，结晶单分散尖晶石FeO/MnO核壳纳米颗粒已在高分辨率扫描透射电子显微镜中得到充分表征。以原子分辨率进行的电子能量损失谱（EELS）测量能够直接绘制出壳层中的Mn/Mn离子以及核结构中的Fe/Fe。这使得能够精确理解核壳界面以及纳米颗粒晶格中的阳离子分布。考虑到过渡金属的不同氧化态如何在EELS中体现，介绍了两种对尖晶石晶格中阳离子反转进行局部评估的方法。这两种方法都能以原子分辨率确定氧化铁核和氧化锰壳中的反转参数，并检测该参数的空间变化。对整个样品进行的X射线吸收测量证实了阳离子反转的存在。这些结果朝着更好地关联纳米结构尖晶石氧化物的结构和功能特性迈出了重要一步。
