Resolving Material-Specific Structures within Fe3O4/gamma-Mn2O3 Core/Shell Nanoparticles Using Anomalous Small-Angle X-ray Scattering

Abstract

Here it is demonstrated that multiple-energy, anomalous small angle X-ray scattering (ASAXS) provides significant enhancement in sensitivity to internal material boundaries of layered nanoparticles compared with the raditional modeling of a single scattering energy, even for cases in which high scattering contrast naturally exists. Specifically, the material-specific structure of monodispersed Fe3O4/gamma-Mn2O3 core/shell nanoparticles is determined, and the contribution of each component to the total scattering profile is identified with unprecedented clarity. We show that Fe3O4/gamma -Mn2O3 core/shell nanoparticles with a diameter of 8.2 ( 0.2) nm consist of a core with a composition near Fe3O4 surrounded by a (MnxFe1_x)3O4 shell with a graded composition, ranging from x~0.40 at the inner shell toward x~0.46 at the surface. Evaluation of the scattering contribution arising from the interference between material-specific layers additionally reveals the presence of Fe3O4 cores without a coating shell. Finally, it is found that the material-specific scattering profile shapes and chemical compositions extracted by this method are independent of the original input chemical compositions used in the analysis, revealing multiple-energy ASAXS as a powerful tool for determining internal nanostructured morphology even if the exact composition of the individual layers is not known a priori.