Direct observation of ferroelectric field effect and oxygen vacancy screening at ferroelectric-metal interface

Scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) studies of ferroelectric–metal interfaces revealed two distinct polarization charge screening mechanisms, with oxygen vacancies compensating negative charge and electrons compensating positive charge. The findings suggest that dynamics of oxygen vacancies can be major determinants of interface functionality in oxide multilayers, opening a pathway for completely new electronic device concepts.

The interface between metallic oxide lanthanum strontium manganite (LSMO) and ferroelectric bismuth ferrite (BFO) was studied by STEM for both polarization orientations. The images showed local lattice expansion for negative-interface polarization charge, but not for positive. In the region where local lattice expansion was observed, EELS spectra indicate oxygen depletion as well as oxidation state changes for constituent metals, suggesting that the negative polarization charge was compensated by positively charged oxygen vacancies. For the interface with positive polarization charge, none of these phenomena were seen, suggesting purely electronic compensation. First principles calculations were consistent with oxygen vacancies causing local lattice expansion in BFO, while mesoscopic Ginzburg-Landau modeling helped explain additional observed phenomena, such as formation of exclusion layers.
 

Young-Min Kim, Anna Morozovska, Eugene Eliseev, Mark P. Oxley, Rohan Mishra, Sverre M. Selbach, Tor Grande, S. T. Pantelides, Sergei V. Kalinin and Albina Y. Borisevich, “Direct observation of ferroelectric field effect and vacancy-controlled screening at the BiFeO₃/La_xSr_1-xMnO₃ interface,” Nature Materials (2014). http://dx.doi.org/10.1038/nmat4058

 

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