Sacrificial Templating : A Route to Europium-II Oxide (EuO) Particles with Arbitrary Shape Prepared Indirectly by Hostile Takeover

Abstract

Shape–property correlations of nanocrystals have recently moved into focus in materials science research. Magnetic properties, for instance, depend strongly on shape. Because crystal morphology is determined by a certain set of lattice planes (hkl) representing the surfaces, the achievable shapes are set by crystallographic symmetry. For instance, for a cubic crystal (90° angles) system it is very hard to realize hexagonal crystal shapes (120° angles). Breaking this paradigm is, thus, highly challenging. Here, we present a synthesis concept suitable for the synthesis of atypical Europium(II) oxide (EuO) particles. EuO is interesting as it is one of few materials known that belong to the class of intrinsic ferromagnetic semiconductors. It is shown that ZnO nanoparticles (rod-like, hexagonal platelets, spherical, and dumbbells) act as a sacrificial template and can be converted to the corresponding EuO particles by preservation of structural features, when treated with Eu-vapor. The transformation proceeds via a Kirkendall mechanism. This new reaction pathway enhances the accessibility of EuO particles tremendously and enables systematic studies on the magnetic shape property relationships of this highly functional metal oxide.