Total scattering applied to the study of nanomaterials

Abstract

Total scattering can be used to study crystalline materials, whose structure presents a periodic arrangement of atoms, as well as disordered materials, such as liquids, glasses or nanomaterials. This thesis work reports three experimental case studies in which different analysis methods were chosen as appropriate on a case-by-case basis. This study demonstrates that total scattering combined with modelling and complementary experimental techniques can guide the understanding of the structure of complex nanostructures. X-ray and neutron total scattering data were collected on multi-walled carbon nanotubes continuously filled with iron and analysed using the program PDFgui for refinement of the pair distribution function and molecular dynamics simulations using the program DL_Poly_4. The analyses show that the iron core is mainly composed of ��-Fe and confirms the dependence of the local ordering on the orientation of the crystallographic axes of iron with respect to the nanowire axis. Prussian blue (Fe4[Fe(CN)6]3 · ��H2O) was synthesised in bulk and nanoparticulate phases using deuterated chemicals; the amount of D2O and H2O in the pores and vacancies, as well as polyvinylpyrrolidone remaining in the nanoparticle samples, were estimated, using an ad hoc modelling procedure of the first few peaks in the neutron PDF function. Models of the structure were refined using the programs PDFgui and RMCProfile. In the last case, a 50Å supercell of the bulk structure with randomly distributed stoichiometric vacancies and D2O and H2O molecules occupying both the pores and the vacancies was used as starting atomic configuration. The CaO/CaCO3 family of materials consists of a series of samples that have undergone carbonation and/or calcination. The X-ray and neutron pair distribution function data were compared to the theoretical PDF of the CaO and CaCO3 phase, generated using the program GULP, that produces PDF functions based on the spectrum of phonon frequencies of the material. The analysis shows that the carbonation is almost completed already after 2 minutes of carbonation and the structure remains stable under further carbonation.