X-ray scattering characterization of iron oxide nanoparticles Langmuir film on water surface and on a solid substrate

• Monolayer of 10 nm iron oxide nanoparticles is formed by the Langmuir technique.
• Both longitudinal and transverse ordering of the monolayer was revealed by X-ray scattering.
• Change of the nanoparticles packing was found after the deposition on a substrate.

In the present study we compare a structure of a Langmuir film assembled from magnetic iron oxide nanoparticles on water surface and a structure of the same film after its transfer to a solid substrate by the Langmuir-Schaefer method. In contrast to most of related studies, where different techniques are used to characterize the films before and after the deposition, we use the same combination of X-ray reflectometry and Grazing Incidence Small-Angle X-ray scattering. In both cases – on a liquid and on a solid substrate – the film was identified as a well-ordered monolayer of the nanoparticles laterally organized in a two-dimensional hexagonal lattice. However parameters of the lattice were found to be slightly different depending on the type of the substrate. It is also demonstrated that Langmuir-Schaefer technique is the right way for deposition of such kind of the particles on a solid substrate.