Consideration of diffuse scattering in the analysis of specular neutron reflection at the magnetic fluid-silicon interface

Neutron reflectometry data on the interface between a magnetic fluid (magnetite/sodium oleate/D2O) and silicon are considered with allowance for a background of diffuse scattering from magnetic-fluid nanoparticles adsorbed on the silicon surface. Two ways to subtract the background in selecting the specular reflection curve are analyzed. Based on a comparison of neutron reflectometry and small-angle neutron scattering data, it is concluded that individual nanoparticles rather than their aggregates (which are also present in the liquid phase) are preferably adsorbed on the silicon surface. In addition, free sodium-oleate molecules are adsorbed from the magnetic-fluid bulk.