Multiferroic and Core-Shell Nanostructures - Advances in Preparations and Novel Properties.

This dissertation reports the research findings in two nanoscience areas: (i) facile methods for the preparation of multiferroic bismuth ferrites nanoparticles and the observation of room temperature magnetoelectric coupling and optically induced magnetic and electric orderings in BiFeO3 (BFO) thin film; (ii) preparation and characterization of core-shell nanomaterials based on conducting polymer as components for shell and core. Controlled cargo release from the core as well as from the shell surface was examined for nanospheres with conjugate polymer shell. An unusual enhanced electric polarization was observed for nanospheres with high-k strontium titanate (STO) nanocrystals embedded in conductive polyaniline (PANI) matrix.Multiferroics represent a class of new materials having potential applications for design and preparation of multifunctional material due to the coupling of their coexisting electric and magnetic orderings. Previously, the syntheses of thin film multiferroic materials involve multi-steps in various high temperatures or specific demanding environment. We discovered that nanocrystal thin film and powder of multiferroic BFO could be prepared using new facile procedures: spin-casting and autoclave methods. The room temperature magnetoelectric coupling in nanocrystal BFO was established using scanning probe microscopy, including magnetic force microscopy (MFM) and Kelvin probe force microscopy (KPFM). Magnetic and electrical orderings induced by irradiation 300 to 560 nm were observed. Thus, the "magnetic-electric-optic" coupling at room temperature was observed for the first time in BFO nanocrystal thin film.Core-shell nanospheres of conducting polymer poly(3, 4-ethylenedioxythiophene), PEDOT, with soft template (1-butyl-3-methyimidazolium hexafluorophosphate, bmimPF6) were prepared using interfacial polymerization on the shell surface of the micelle stabilized by surfactant (Triton X-100). The diameter of nanospheres was controlled by bmimPF6-to-surfacnt ratio. The release of cargo from the core and shell of the spheres was trigged by pH control and observed by photometric measurement. Aspect ratio and crystallinity of PEDOT shell increases in high pH value (above 10). In addition, the interaction of electronic polarization with atomic polarization was studied for coreshell nanosphere of PANI matrix with STO nanoparticles embedded. This nanosystem represents the first encapsulated nanospheres with extensive interfacial interaction within the core due to atomic polarizable isolated nano-domains embedded in an electronic polarizable continuous matrix.