Epitaxial growth, structure, and thermoelectric properties of CaMn- and V-based oxides

Sammanfattning: This thesis is focused on physical vapor deposition, epitaxy, and structural characterization of CaMnO3 and VO2. Environmentally friendly and abundant materials are important for energy savings in applications, e.g., thermoelectrics for waste-heat recycling and thermochromic materials for passive indoor-temperature regulation. CaMnO3 is thermoelectric and VO2 is thermochromic at attractive temperatures for waste heat recycling and passive indoor-temperature regulation, respectively. The two material systems in this thesis were grown by reactive magnetron sputtering. A two-step synthesis process was investigated where rock-salt (Ca,Mn)O was grown by sputtering followed by an annealing step to form the perovskite CaMnO3. CaMnO3 was alloyed with Nb with the purpose to enhance the thermoelectric properties by increasing the number of free carriers, resulting in CaMn1-xNbxO3 (x = 0 – 0.10) films. CaMnO3 was grown on Al2O3 and LaAlO3 while VO2 was grown on muscovite (mica), phase-pure films of the metastable B phase and the stable M1 phase could be grown by controlling the gas flow and pressure. The mica substrate is a material with weakly interacting van der Waals layers in the structure that enable van der Waals epitaxy for the stable VO2 film in M1 phase. The thickness effect on electrical properties in the thermochromic region was investigated as well as proving van der Waals epitaxy. This thesis therefore provides an overall contribution to the understanding of film structure and the control thereof and how it affects the properties of the film.