Resolving material-specific structures within Fe3O 4|γ-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 traditional modeling of a single scattering energy, even for cases in which high scattering contrast naturally exists. Specifically, the material-specific structure of monodispersed Fe3O4|γ-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|γ-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. © 2013 American Chemical Society.This work utilized facilities supported in part by the National Science Foundation under Agreement Nos. DMR-0944772 and DMR-0454672. U.S. Department of Energy Contract No. DE-AC02-06CH11357, and Ames Laboratory Contract No.W-7405-Eng-82. Work was also supported by the Spanish MICINN (MAT2008-01939-E, MAT2010-20616-C02, MAT2010-16407, CSD2009-00013, and CSD2006-00012) and Catalan DGR (2009-SGR-1292 and 2009-SGR-00035). Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. Part of this work was performed on the SIM beamline at the Paul Scherrer Institute, Villigen, Switzerland. The authors thank D. Robinson, P. Ryan, and Z. Islam for their help performing the anomalous X-ray scattering measurements at beamline 6-ID-B of the Advanced Photon Source. The authors also thank A. Fraile-Rodríguez and A. Mayoral for their help during the XAS-XMCD and EELS mapping experiments, respectively. G.S.A. thanks the Knut and Alice Wallenberg (KAW) Foundation (Project 3DEMNATUR) for the partial financial support. M.E. thanks the Generalitat de Catalunya for her Beatriu de Pinós scholarship. M.D.B. was partially supported by an ICREA ACADEMIA award.Peer Reviewe