Ming-Xiu Zhou

Bio: Ming-Xiu Zhou is an academic researcher from Nanjing University. The author has contributed to research in topics: Ferroelectricity & Multiferroics. The author has an hindex of 5, co-authored 6 publications receiving 65 citations.

Local electrical conduction in polycrystalline La-doped BiFeO3 thin films

Abstract: Local electrical conduction behaviors of polycrystalline La-doped BiFeO3 thin films have been investigated by combining conductive atomic force microscopy and piezoelectric force microscopy. Nanoscale current measurements were performed as a function of bias voltage for different crystal grains. Completely distinct conducting processes and resistive switching effects were observed in the grain boundary and grain interior. We have revealed that local electric conduction in a grain is dominated by both the grain boundary and ferroelectric domain, and is closely related to the applied electric field and the as-grown state of the grain. At lower voltages the electrical conduction is dominated by the grain boundary and is associated with the redistribution of oxygen vacancies in the grain boundary under external electric fields. At higher voltages both the grain boundary and ferroelectric domain are responsible for the electrical conduction of grains, and the electrical conduction gradually extends from the grain boundary into the grain interior due to the extension of the ferroelectric domain towards the grain interior. We have also demonstrated that the conduction dominated by the grain boundary exhibits a much small switching voltage, while the conduction of the ferroelectric domain causes a much high switching voltage in the grain interior.

Three-state resistive switching in CoFe2O4/Pb(Zr0.52Ti0.48)O3/ZnO heterostructure

Abstract: The heterostructural film combining multiferroic CoFe2O4/Pb(Zr0.52Ti0.48)O3 bilayer with semiconductor ZnO layer was prepared. Three-state resistive switching was demonstrated by time-dependent current measurements under different stimuli combination of voltage pulse and magnetic bias. The asymmetry diodelike current-voltage, capacitance-voltage, and polarization-voltage loops, which seriously depend on magnetic bias, were observed. We revealed that three-state resistive switching was dominated by the changes in the charge carriers in the heterostructure, which were modulated by the magnetoelectric coupling between ferromagnetic and ferroelectric layers and interface polarization coupling between ferroelectric and semiconductor layers. This work provides promising candidates for developing advanced switchable devices with multifunctional memory.

Local Magnetoelectric Effect in La-Doped BiFeO3 Multiferroic Thin Films Revealed by Magnetic-Field-Assisted Scanning Probe Microscopy.

Abstract: Multiferroic La-doped BiFeO3 thin films have been prepared by a sol-gel plus spin-coating process, and the local magnetoelectric coupling effect has been investigated by the magnetic-field-assisted scanning probe microscopy connected with a ferroelectric analyzer. The local ferroelectric polarization response to external magnetic fields is observed and a so-called optimized magnetic field of ~40 Oe is obtained, at which the ferroelectric polarization reaches the maximum. Moreover, we carry out the magnetic-field-dependent surface conductivity measurements and illustrate the origin of local magnetoresistance in the La-doped BiFeO3 thin films, which is closely related to the local ferroelectric polarization response to external magnetic fields. This work not only provides a useful technique to characterize the local magnetoelectric coupling for a wide range of multiferroic materials but also is significant for deeply understanding the local multiferroic behaviors in the BiFeO3-based systems.

Enhanced Magnetodielectric Effect in Graded CoFe2O4/Pb(Zr0.52Ti0.48)O3 Particulate Composite Films

Abstract: Graded particulate composite films in which ferromagnetic CoFe2O4 nanoparticles are gradedly distributed in the ferroelectric Pb(Zr0.52Ti0.48)O3 matrix along the thickness direction have been prepared on Pt/Ti/SiO2/Si wafers via sol–gel spin-coating method and rapid annealing process. Compared with the homogenous films, the graded ones not only exhibited magnetic anisotropy, but also showed evident increase in both ferroelectric polarization and dielectric tunability. Moreover, great enhancement of magnetodielectric effect was observed in such graded films. We elucidated the origin of enhanced magnetodielectric coupling and attributed it to the combined influence of two factors, that is, the enhanced ferroelectric polarization caused by CoFe2O4 distribution gradient and flexoelectric polarization induced by strain gradient under external magnetic field. This work presents a feasible way to modulate the magnetoelectric coupling in ferromagnetic–ferroelectric composite films for developing high-performance multiferroic materials at nanoscale.

Tunable resistive switching behaviour in ferroelectric–ZnO bilayer films

Abstract: Pb(Zr052Ti048)O3/ZnO bilayer films with various ZnO-layer thicknesses were prepared by a sol–gel process, and their phase structures, electric conduction and polarization behaviour were measured The results showed that the preferential crystal orientation of the ZnO layer changed with a change in its thickness The strong dependence of both asymmetric current–voltage and polarization–voltage characteristics on the ZnO-layer thickness was observed The resistance ratio of the high-resistance state (HRS) to the low-resistance state (LRS) increased with increasing ZnO-layer thickness, and a high rectification ratio was obtained in the bilayer film with an optimized ZnO-layer thickness The combined effects of interface polarization coupling and energy band structure on the resistive switching behaviour of the bilayer films were revealed, and the electric conduction mechanisms of the bilayer films at both HRS and LRS were analysed in detail This work presents an effective method to modulate the resistive switching behaviour of ferroelectric–ZnO heterostructures, which is significant in designing high-performance ferroelectric–semiconductor heterostructures for actual applications

Rectifying Current-Voltage Characteristics of BiFeO$_{3}$/Nb-doped SrTiO$_{3}$ Heterojunction

Abstract: Epitaxial c-axis oriented BiFeO3 (BFO) thin films were deposited on (001) Nb-doped SrTiO3 (Nb-STO) substrates by pulsed laser deposition. Introducing Bi vacancies caused the BFO thin film to evolve to a p-type semiconductor and formed a p-n heterojunction with an n-type semiconductor Nb-STO. The current density versus voltage (J-V) and capacitance versus voltage (C-V) characteristics of the heterojunction were investigated. A typical rectifying J-V effect was observed with a large rectifying ratio of 5×104. Reverse C-V characteristics exhibited a linear 1∕C2 versus V plot, from which a built-in potential of 0.6V was deduced. The results show a potential application of BFO/Nb-STO heterojunction for oxide electronics.

Polarization-dependent interfacial coupling modulation of ferroelectric photovoltaic effect in PZT-ZnO heterostructures

Abstract: Recently, ferroelectric perovskite oxides have drawn much attention due to potential applications in the field of solar energy conversion. However, the power conversion efficiency of ferroelectric photovoltaic effect currently reported is far below the expectable value. One of the crucial problems lies in the two back-to-back Schottky barriers, which are formed at the ferroelectric-electrode interfaces and blocking most of photo-generated carriers to reach the outside circuit. Herein, we develop a new approach to enhance the ferroelectric photovoltaic effect by introducing the polarization-dependent interfacial coupling effect. Through inserting a semiconductor ZnO layer with spontaneous polarization into the ferroelectric ITO/PZT/Au film, a p-n junction with strong polarization-dependent interfacial coupling effect is formed. The power conversion efficiency of the heterostructure is improved by nearly two orders of magnitude and the polarization modulation ratio is increased about four times. It is demonstrated that the polarization-dependent interfacial coupling effect can give rise to a great change in band structure of the heterostructure, not only producing an aligned internal electric field but also tuning both depletion layer width and potential barrier height at PZT-ZnO interface. This work provides an efficient way in developing highly efficient ferroelectric-based solar cells and novel optoelectronic memory devices.

High-Performance Photovoltaic Readable Ferroelectric Nonvolatile Memory Based on La-Doped BiFeO3 Films.

Abstract: Epitaxial La0.1Bi0.9FeO3 (LBFO) films with SrRuO3 (SRO) bottom electrodes were fabricated on SrTiO3(001) substrates by magnetron sputtering. The LBFO thin films exhibit strong ferroelectric properties. Nonvolatile reversible resistance switchings and switchable photovoltaic effects controlled by electric field have been observed in Pt/LBFO/SRO heterostructures. With the optimized LBFO film thickness, the observed room temperature pulsed-read resistance switching ratio can reach 105% magnitude by applying ±2.7 V pulse voltages. Besides, the observed ferroelectric switchable photovoltaic effect in the visible wavelength range shows a large tunable open-circuit photovoltage from -75 to -330 mV. The switching mechanisms in resistance and photovoltaic effects are demonstrated to be directly related to the ferroelectric reversal, which can be attributed to the polarization-modulated interfacial barriers and deep trap states.