RESUMEN
Single crystalline magnetic FeCo nanostars were prepared using an organometallic approach under mild conditions. The fine-tuning of the experimental conditions allowed the direct synthesis of these nano-octopods with body-centered cubic (bcc) structure through a one-pot reaction, contrarily to the seed-mediated growth classically used. The FeCo nanostars consist of 8 tetrahedrons exposing {311} facets, as revealed by high resolution transmission electron microscopy (HRTEM) imaging and electron tomography (ET), and exhibit a high magnetization comparable with the bulk one (Ms = 235 A·m2·kg-1). Complex 3D spin configurations resulting from the competition between dipolar and exchange interactions are revealed by electron holography. This spin structures are stabilized by the high aspect ratio tetrahedral branches of the nanostars, as confirmed by micromagnetic simulations. This illustrates how magnetic properties can be significantly tuned by nanoscale shape control.
RESUMEN
Supported nanocrystals of original shapes are highly desirable for the development of optimized catalysts; however, conventional methods for the preparation of supported catalysts do not allow shape control. In this work, we have synthesized concave platinum nanocubes exposing {110} crystallographic facets at 20 °C. In the presence of a crystallographically oriented Pt(111) support in the reaction medium, the concave nanocubes grow epitaxially on the support, producing macroscopic nanostructured surfaces. Higher reaction temperature produces a mixture of different nanostructures in solution; however, only the nanostructures growing along the 111 direction are obtained on the Pt(111) support. Therefore, the oriented surface acts as a template for a selective immobilization of specific nanostructures out of a mixture, which can be regarded as an "epitaxial resolution" of an inhomogeneous mixture of nanocrystals. Thus, a judicious choice of the support crystallographic orientation may allow the isolation of original nanostructures that cannot be obtained in a pure form.