Macroscopic nanoparticle assemblies: exploring the structural and magnetic properties of large supercrystals

Abstract In the present work we demonstrate, how the self-assembly of nanoparticles provides a simple and straightforward way to fabricate ordered nanocomposites on length scales of up to 300…1000 µm. We realize this by employing a centrifugation assisted sedimentation technique. We start with magnetic iron oxide nanoparticles (NPs) with an average diameter of 15 nm, which are dispersed in toluene. The particles are coated with an organic shell to prevent unordered agglomeration of particles. After centrifugation and subsequent drying large macroscopic assemblies of NPs are obtained. The characterization of the samples using scanning electron microscopy (SEM), x-ray diffraction (XRD) and small angle x-ray scattering (SAXS) reveals that the samples are NP macro-polycrystals. By variation of the fabrication parameters as e.g. centrifugation speed and temperature we obtain a systematic study on how NP ordering, crystallinity and morphology depend on the fabrication parameters. Moreover, the magnetic properties of the NP macro-polycrystals are studied using superconducting quantum interference device (SQUID) magnetometry.