Novel nano-structured materials: Preparation by self-assembly techniques and study of physical properties by x-ray analysis and magnetic characterization.

摘要

The properties and characteristics of nano-structured materials can be quite different from the bulk form of the material. By forming nano-particles, electrical and magnetic properties may be tailored or enhanced beyond that of bulk materials. In this work several single and composite nano-phase materials were prepared by chemical or physical methods. Techniques used for characterization include magnetometry, Mössbauer analysis, x-ray diffractometry, x-ray reflectivity, magneto-transport measurements, and microscopy.; Gamma-ferrous oxide/silver nano-composites were prepared by a reverse micelle technique and compared to powders made by mechanical milling. The composites' properties were compared to pure nano-phase γ-Fe₂O ₃ particles and to composites prepared by different techniques to determine changes or enhancements in physical properties. The comparison indicates that the nano-composites' magnetic properties are consistent with the formation of superparamagnetic γ-Fe₂O₃ nanoparticles. The possible conduction mechanisms explaining the presence of negative magnetoresistance are discussed.; Chemically synthesized nano-phase materials were examined for impurity and crystallite size using x-ray diffractometry. Many of the nano-phase materials examined have concentric shell nano-structures with overlapping diffraction patterns. In these cases x-ray diffractometry was used as a screening tool to tune the particular chemical synthesis technique determine the effectiveness of sample annealing on the crystalline structure of the material.; Single and mufti-layered thin films were prepared by magnetron sputtering and pulse laser deposition. Their structures are characterized by x-ray reflectivity for layer thickness, critical angle of reflection, surface roughness and interfacial smearing. Structural factors were determined using Fourier analysis and spectral estimation techniques. Results were compared to transmission electron microscopy examination to determine the most reliable data processing technique.; In addition, the ordering of nano-scale materials have been studied. Two-dimensional arrays of nano-spheres were prepared by spin coating various substrates, and three-dimensional structures of nano-spheres were formed by self-assembly. Both two- and three-dimensional structures were examined for the extent of ordering using optical microscopy or scanning electron microscopy.