Synthesis and properties of epitaxial oxide thin films prepared by polymer assisted deposition

Resumo

The development of physical and chemical methods that allowed structuring materials in the form of nanometer thick films represented an extraordinary scientific and technological achievement. In the 1970's the first high-quality epitaxial thin films were fabricated through the use of sophisticated manufacturing techniques which imply evaporation from a source under high vacuum. Among these methods Pulsed Laser Deposition (PLD), Sputtering, Molecular Beam Epitaxy (MBE), and Atomic Layer Deposition (ALD) are the most relevant. These techniques lead to extraordinary control over the synthesis (stoichiometry, thickness, homogeneity), but require a high vacuum system. The high cost of this technology prevents many research groups the access to these studies. The method used in this thesis, the Polymer Assisted Deposition (PAD), is an affordable method for thin films synthesis, whose quality is in many aspects comparable to those obtained by PLD or Sputtering. These films are obtained by a process respectful with the environment, avoiding the need to use organic solvents or complex synthesis processes. Moreover, it is a scalable method with potential for applications in industrial processes. This thesis describes the most relevant aspects in PAD method as well the process of optimization to obtain high quality epitaxial thin films of multicationic oxides. For this we have analyzed the structure and the behavior of polymers both in solution and under thermal degradation, and it has been determined the degree of retention for different metals in combination with various chelating agents. The synthesis and characterization of thin films have been applied to a set of oxides with different compositions and properties, controlling the thickness, stoichiometry, etc. The effect of growth conditions was studied by comparison with films prepared by classical physical methods. Furthermore, two different materials were combined in the same structure in the form of bilayers with a clear interface between the two individual layers. All this progress over single-crystal substrates was used to deposit functional oxides integrated on silicon at the end of this thesis.