Topological domains in ferroelectric materials have attracted considerable interest owing to their exotic functionalities. In this study, using vector piezoresponse force microscopy (PFM), we observe spontaneous ferroelectric topological domains in...
Nanoscale ring-shaped conduction channels with memristive behavior have been observed in the BiFeO3 (BFO) nanodots prepared by the ion beam etching. At the hillside of each individual nanodot, a ring-shaped conduction channel is formed. Furthermore, the conduction channels exhibit memristive behavior, i.e., their resistances can be continuously tuned by the applied voltages. More specifically, a positive (negative) applied voltage reduces (increases) the resistance, and the resistance continuously varies as the repetition number of voltage scan increases. It is proposed that the surface defects distributed at the hillsides of nanodots may lower the Schottky barriers at the Pt tip/BFO interfaces, thus leading to the formation of ring-shaped conduction channels. The surface defects are formed due to the etching and they may be temporarily stabilized by the topological domain structures of BFO nanodots. In addition, the electron trapping/detrapping at the surface defects may be responsible for the memristive behavior, which is supported by the surface potential measurements. These nanoscale ring-shaped conduction channels with memristive behavior may have potential applications in high-density, low-power memory devices.
Utilizing vector PFM (piezoresponse force microscopy) on high-density nanodot arrays, ferroelectric nanodots and domain structure in nanodot arrays were investigated in the current study. Accordingly, we identified four types of topological domain states based on the measurements of spontaneous polarization vectors vs writing results in nanodots. In addition to convergent and divergent domains with upward and downward polarization, double-center domains and triple-center domains were also identified. In addition, center domains could be reversibly switched under the electric field produced by the biased PFM tip, and their stability could be maintained by compensating the polarization charge with the accumulated charge. These stable topological domain states in discrete nanodots present an opportunity to further investigate their new properties in high-density memory devices.
High-density ferroelectric BiFeO3 (BFO) nanodot arrays were developed through template-assisted tailoring of epitaxial thin films. By combining piezoresponse force microscopy (PFM) and Kelvin probe force microscopy (KPFM) imaging techniques, we found that oxygen vacancies in nanodot arrays can be transported in the presence of an electric field. Besides triple-center domains, quadruple-center domains with different vertical polarizations were also identified. This was confirmed by combining the measurements of the domain switching and polarization vector distribution. The competition between the accumulation of mobile charges, such as oxygen vacancies, on the interface and the geometric constraints of nanodots led to the formation of these topological domain states. These abnormal multi-center topological defect states pave the way for improving the storage density of ferroelectric memory devices.
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