X‑ray Absorption Spectroscopic Studies of the Penetrability of Hollow Iron Oxide Nanoparticles by Galvanic Exchange Reactions

Hollow Fe oxide nanoparticles have many applications in catalysis, drug delivery, and energy storage. Hollow Fe oxide shells can also be used for preventing the sintering of catalytically active cores and for magnetic recovery of bimetallic nanoparticles. However, more studies are required under real reaction conditions on the availability of the interior surface or active cores in hollow nanoparticles. Herein, we introduce a simple approach to study the penetrability of hollow Fe oxide shells by attempting galvanic exchange reactions between the remaining Fe(0) core within the hollow Fe oxide shell and Pd­(II) salts. First, <i>in situ</i> high-temperature Fe K-edge XANES was used to monitor the formation of hollow Fe oxide nanoparticles from Fe nanoparticles. Core-void-shell Fe-Fe oxide nanoparticle intermediates were captured at different time intervals and then reacted with Pd­(II). The reduction of Pd­(II) was characterized by <i>in situ</i> Pd L₃-edge XANES spectra. The results show that the core-void-shell nanoparticles had Fe₃O₄ shells, which were found to be impenetrable to Pd­(II) salts when the thickness of the shell was more than 2 nm. However, the core could be accessed using a high-temperature etching strategy for the shell, which then allowed for galvanic reactions with Pd

Supplementary document for a-Si/SiO₂ nanolaminates for tuning the complex refractive index and band gap in optical interference coatings - 6851994.pdf

Full transmittance and reflectance spectr

Correlation of Interface Impurities and Chemical Gradients with High Magnetoelectric Coupling Strength in Multiferroic BiFeO₃–BaTiO₃ Superlattices

The detailed understanding of magnetoelectric (ME) coupling in multiferroic oxide heterostructures is still a challenge. In particular, very little is known to date concerning the impact of the chemical interface structure and unwanted impurities that may be buried within short-period multiferroic BiFeO₃–BaTiO₃ superlattices during growth. Here, we demonstrate how trace impurities and elemental concentration gradients contribute to high ME voltage coefficients in thin-film superlattices, which are built from 15 double layers of BiFeO₃–BaTiO₃. Surprisingly, the highest ME voltage coefficient of 55 V cm^–1 Oe^–1 at 300 K was measured for a superlattice with a few atomic percent of Ba and Ti that diffused into the nominally 5 nm thin BiFeO₃ layers, according to analytical transmission electron microscopy. In addition, highly sensitive enhancements of the cation signals were observed in depth profiles by secondary ion mass spectrometry at the interfaces of BaTiO₃ and BiFeO₃. As these interface features correlate with the ME performance of the samples, they point to the importance of charge effects at the interfaces, that is, to a possible charge mediation of ME coupling in oxide superlattices. The challenge is to provide cleaner materials and processes, as well as a well-defined control of the chemical interface structure, to push forward the application of oxide superlattices in multiferroic ME devices