Prominent electric properties of BiFeO₃ shells sputtered on ZnO-nanorod cores with LaNiO₃ buffer layers

In this work, template-assisted methods were adopted to grow BiFeO3 (BFO)-nanorod arrays on substrates. Well-aligned ZnO-nanorod arrays (ZNAs) grown hydrothermally were chosen as positive templates. It was found that perovskite BFO could not be radio frequency (RF)-magnetron sputtered directly on a ZNA at elevated temperatures. Only amorphous BFO was obtained. However, polycrystalline BFO shells could be fabricated by RF-magnetron sputtering on ZNA templates by the introduction of LaNiO3 (LNO) buffer layers. The LNO buffer layer deposited on the ZNA by RF-magnetron sputtering was demonstrated to improve the adhesion and crystallization of the sequentially sputtered BFO shells. The electrical properties were evaluated by conductive atomic force microscopy and piezoresponse force microscopy. Bulk-limited Poole-Frenkel emission dominates the conduction of BFO shells at positive bias, while barrier-limited Schottky emission accounts for the conduction at negative bias due to the interface between the Pt/Ir-coated tip and the BFO. The piezoelectric coefficient (d33) was estimated to be ∼32.93 pm V(-1) and a polarization of 133 μC cm(-2) was derived. These values are higher than those reported previously for BFO films.