PhD ceremony: A. Morelli, 14.45 uur, Academiegebouw, Broerstraat 5, Groningen
Thesis: Piezoresponse force microscopy of ferroelectric thin films
Promotor(s): prof. J.Th.M. de Hosson
Faculty: Mathematics and Natural Sciences
This thesis focuses on ferroelectric thin film characterization through Piezoresponse Force Microscopy (PFM) technique. During the last decades ferroelectric thin films have emerged as an interesting subject for nanoscale applications such as Micro- and Nano-Electromechanical Systems (MEMS and NEMS), and Ferroelectric Random Access Memories (FeRAM). These important technological applications have given a strong impetus to nanoscale characterization. In this thesis Piezoresponse force microscopy (PFM) has proven to be unique tool, enabling polarization domain dynamics studies and detailed ferroelectric characterization at the nanoscales.
PFM is based on the converse piezoelectric effect, in a way that an alternate electric field induces a vibration on a ferroelectric sample surface. The analysis of such vibration (named piezoresponse) provides the information needed. Nonetheless, the interpretation of the piezoresponse is still under discussion. In fact, adsorbates, clamping effect, background noise, and electrostatic interaction play an important role. In addition, as shown in this thesis, the phase of the piezoresponse varies inversely with the frequency of the modulation voltage, the reason of which is still under investigation.
This thesis demonstrates that the polarization of domains at the nanoscale can be visualized. In particular by piezoelectric constant extrapolation and piezoresponse hysteresis loops, the linearity of the piezoresponse and imprint characteristics of the sample were studied.
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