Abstract
We have studied the ferroelectric domains in (001) BiFeO3 (BFO) films patterned into mesas with various aspect ratios, using angle-resolved piezoresponse force microscope (AR-PFM), which can image the in-plane polarization component with an angular resolution of 30°. We observed not only stable polarization variants, but also meta-stable polarization variants, which can reduce the charge accumulated at domain boundaries. We considered the number of neighboring domains that are in contact, in order to analyze the complexity of the ferroelectric domain structure. Comparison of the ferroelectric domains from the patterned and unpatterned regions showed that the elastic relaxation induced by removal of the film surrounding the mesas led to a reduction of the average number of neighboring domains, indicative of a decrease in domain complexity. We also found that the rectangular BFO patterns with high aspect ratio had a simpler domain configuration and enhanced piezoelectric characteristics than square-shaped mesas. Manipulation of the ferroelectric domains by controlling the aspect ratio of the patterned BFO thin film mesas can be useful for nanoelectronic applications.
Highlights
BFO thin films have disadvantages such as high leakage currents, for which oxygen vacancies and the unusual local electronic transport behavior at ferroelectric domain walls are the main cause[17,18,19]
To observe the effect of the elastic relaxation induced by focused ion-beam (FIB) patterning, we imaged the ferroelectric domains of BFO thin films patterned with various aspect ratios
By considering the polarization components determined using vertical PFM (VPFM) (see phase images in Fig. S1(a)), we can determine that the BFO thin film studied here had a uniform downward polarization vector component, and the possible polarization variants for the BFO thin film are restricted to the four stable variants shown by the red arrows of Fig. 1(b)
Summary
BFO thin films have disadvantages such as high leakage currents, for which oxygen vacancies and the unusual local electronic transport behavior at ferroelectric domain walls are the main cause[17,18,19]. Park et al introduced angle-resolved PFM (AR-PFM) which provides clearer information on the in-plane polarization directions than conventional PFM method[23,24,25,26]. This method was extended to study charged domain boundaries and the effect of poling on domain structures[27]. We present direct observation using AR-PFM of domain boundaries and intermediate polarization variants in epitaxially-grown BFO thin films patterned into mesas, and we discuss the correlation between the resulting domain configurations and piezoresponse switching behavior. High aspect ratio of BFO mesas have an ordered domain configuration and enhanced piezoelectric characteristics
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