The guided self-assembly of magnetic nanoparticles into two- and three-dimensional nanostructures using patterned substrates

The present thesis provides an original and extensive contribution to the understanding of the self-assembly of magnetic nanoparticles in different dimensions with the help of patterned sapphire substrates and block copolymers. The combination of real space and reciprocal space techniques allows a better understanding of nanostructures with different dimensions, which are formed on the patterned substrates. The first topic covered in the thesis is formation of 2D nanoparticle assemblies by annealing the M-plane sapphire at various temperatures. The procedure is adjusted to obtain patterned substrates that can accommodate the nanoparticles of a given size. The highly-ordered 2D magnetic nanoparticles arrays deposited on patterned sapphire substrates were studied using scanning electron microscopy and grazing incidence x-ray scattering (GISAXS) methods. In addition, a detailed analysis of GISAXS data using the Distorted Wave Born Approximation theory allowed characterizing the samples quantitatively. The second topic is to deal with the self-organization of 3D nanoparticles assemblies over the macroscopic scale, with precise control of the spatial organization of nanoparticles by employing the block copolymers. It was achieved by controlling the morphology of the block copolymer films with a solvent vapor annealing, which proved to be a powerful method. It was demonstrated that the solvent volume, annealing time and drying process had an impact on the final morphology of the nanocomposite film. The influence of those parameters was thoroughly investigated and optimum values were derived. The orientation parameter obtained from GISAXS measurements allows identifying the different stages of the alignment of the block copolymer matrix. Using developed approach, 3D nanoparticles with a long-range order in nanocomposite film can be readily obtained on patterned substrates, which were confirmed by both atomic force microcopy and GISAXS methods. The magnetic interactions between magnetic nanoparticles in nanocomposite film, containing only 8 wt % of nanoparticles were studied with polarized neutron scattering experiments. The qualitative analysis of the grazing incidence neutron scattering and polarized neutron reflectometry data, combined with GISAXS data analysis, unambiguously demonstrated that a weak magnetic scattering from array of magnetic nanoparticles can be detected. The methodology developed in this work exemplifies a key role of polarized neutron scattering techniques in characterization of magnetic inter-particle interactions embedded in complex nanocomposite materials. In conclusion, this work shows how 2D and 3D nanoparticles assemblies can be prepared by using patterned substrates and how preparation parameters affect the resulting nanostructures. The vital role of various scattering methods in qualitative characterization of structural and magnetic properties of nanostructures was emphasized