Low-Dimensional Physics of Organic-Inorganic Multilayers

Abstract

This thesis demonstrates the rich low-dimensional physics associated with the class of organic-inorganic hybrid materials based on atomic layers of a metal oxide separated by organic spacer molecules. Hybrid materials based on tungsten oxide and also transition metal tungstates (with manganese, iron, cobalt, nickel and copper) were synthesised and characterised using a variety of techniques. The materials in question represent one example of the huge variety of systems classed as 'organic-inorganic hybrids' and have the potential to combine the high-electron mobility of the metal oxide layers with the propensity for self-assembly of the organic layers. The crystal structures of the compounds were investigated using powder X-ray diffraction and electron diffraction, and compared with structural information obtained using IR, Raman, and extended X-ray absorption fine structure (EXAFS) spectroscopies. This data confirmed the presence of a 2-dimensional layered structure. The electronic properties of the hybrids were studied using optical spectroscopy and confirmed via ab initio calculations. The band gaps of the tungsten oxide hybrids were found to be independent of interlayer spacing, and in all cases were larger than that observed in the three dimensional WO3 'parent' material. For the transition metal tungstate hybrids there appeared to be significant interactions between the organic amines and the transition metal ions within the inorganic layers. The magnetic properties of the hybrids incorporating transition metal ions were also studied in detail. Many of these metal tungstate hybrids display magnetic transitions at low temperatures indicating a crossover from 2-dimensional to 3-dimensional behaviour. This illustrates the importance of the low-dimensional nature of the inorganic layers in these hybrid materials and thus their potential in nano-structural applications.