Ph.D. thesis
Thesis title: | Interface and domain engineering in ferroelectric BiFeO3 thin films |
Year: | 2017 |
Promotor: | Prof. dr. ir. M. Huijben / Prof. dr. ing. A.J.H.M. Rijnders |
Date defense: | 31-03-2017 |
BiFeO3 (BFO) is one of the most important multiferroic materials that have seen a significant boost in the academic research in the last decades. Coupling between the ferroelectric and antiferromagnetic order parameters of BFO at room temperature promises a groundbreaking technology for nano-electronic devices. Yet, there is still a need for deeper understanding of BFO thin film growth and its functional properties. Therefore this thesis focuses on interface and domain engineering of BFO thin films.
Chapter 2 describes the study of domain ordering in BFO thin films by using the SrTiO3 (STO) substrate surface termination. Chemical treatment and interval pulsed laser deposition methods are used to obtain TiO2 and SrO terminated STO substrates respectively. Piezoresponse Force Microscopy (PFM) technique is used to reveal the ordering of ferroelectric domain structures of BFO thin films.
Chapter 3 focuses on the BFO thin film growth on orthorhombic TbScO3 substrates. Two orientations of TbScO3 (110)o and (001)o were used in order to investigate the substrate symmetry effects while keeping the strain constant. Structural differences of BFO thin films were revealed by using X-ray Diffraction reciprocal space map measurements and PFM.
Chapter 4 gives a comprehensive overview of conduction mechanisms in oxide materials, especially focusing on the ferroelectric oxides. Subsequently, conduction mechanisms of BFO thin films are studied by varying the electrode and interface configurations. Two types of electrodes, namely La2/3Sr1/3MnO3 and Nb:STO, were used in order to investigate the electrode effects on the conduction properties of BFO thin film stacks. The atomic terminating plane of each electrode is also changed in order to investigate the interface effects deeper. Local conductivity measurements were done by Conductive Atomic Force Microscopy.
Chapter 5 studies the domain wall conductivity in BFO thin films. Firstly, the origin of domain wall conductivity is discussed. Secondly, the effect of polarization changes (i.e. charged domain walls) on domain wall conductivity is given.