Flexoelectric Thin-Film Photodetectors.

The flexoelectric effect, which manifests itself as a strain-gradient-induced electrical polarization, has triggered great interest due to its ubiquitous existence in crystalline materials without the limitation of lattice symmetry. Here, we propose a flexoelectric photodetector based on a thin-film heterostructure. This prototypical device is demonstrated by epitaxial LaFeO3 thin films grown on LaAlO3 substrates. A giant strain gradient of the order of 106/m is achieved in LaFeO3 thin films, giving rise to an obvious flexoelectric polarization and generating a significant photovoltaic effect in the LaFeO3-based heterostructures with nanosecond response under light illumination. This work not only demonstrates a novel self-powered photodetector different from the traditional interface-type structures, such as the p-n and Schottky junctions but also opens an avenue to design practical flexoelectric devices for nanoelectronics applications.

Spin-Filtering Ferroelectric Tunnel Junctions as Multiferroic Synapses for Neuromorphic Computing.

As nanoelectronic synapses, memristive ferroelectric tunnel junctions (FTJs) have triggered great interest due to the potential applications in neuromorphic computing for emulating biological brains. Here, we demonstrate multiferroic FTJ synapses based on the ferroelectric modulation of spin-filtering BaTiO3/CoFe2O4 composite barriers. Continuous conductance change with an ON/OFF current ratio of ∼54 400% and long-term memory with the spike-timing-dependent plasticity (STDP) of synaptic weight for Hebbian learning are achieved by controlling the polarization switching of BaTiO3. Supervised learning simulations adopting the STDP results as database for weight training are performed on a crossbar neural network and exhibit a high accuracy rate above 97% for recognition. The polarization switching also alters the band alignment of CoFe2O4 barrier relative to the electrodes, giving rise to the change of tunneling magnetoresistance ratio by about 10 times and even the reversal of its sign depending upon the resistance states. These results, especially the electrically switchable spin polarization, provide a new approach toward multiferroic neuromorphic devices with energy-efficient electrical manipulations through potential barrier design. In addition, the availability of spinel ferrite barriers epitaxially grown with ferroelectric oxides also expends the playground of FTJ devices for a broad scope of applications.

The Role of Ferroelectric Polarization in Resistive Memory Properties of Metal/Insulator/Semiconductor Tunnel Junctions: A Comparative Study.

Recently, tunnel junction devices adopting semiconducting Nb:SrTiO3 electrodes have attracted considerable attention for their potential applications in resistive data storage and neuromorphic computing. In this work, we report on a comparative study of Pt/insulator/Nb:SrTiO3 tunnel junctions between ferroelectric BaTiO3 and nonferroelectric SrTiO3 and LaAlO3 barriers to reveal the role of polarization in resistance switching properties. Although hysteretic behaviors appear in current-voltage measurements of all devices regardless of the barrier character, significantly improved current ratios by more than three orders of magnitude are observed in the Pt/BaTiO3/Nb:SrTiO3 tunnel junctions due to the dominance of polarization in modulation of junction barrier profiles between the low and high resistance states. The switchable polarization also gives rise to enhanced resistance retention since the electron diffusion that smears the barrier contrast of the bistable resistance states is suppressed by the polar BaTiO3/Nb:SrTiO3 interface associated with the ferroelectric bound charges. These polarization-induced effects are absent in the nonferroelectric Pt/SrTiO3/Nb:SrTiO3 and Pt/LaAlO3/Nb:SrTiO3 devices in which serious resistance state decay, described by Fick's second law, is observed since there are no switchable interface charges on SrTiO3/Nb:SrTiO3 and LaAlO3/Nb:SrTiO3 to block the electron diffusion. In addition, the Pt/BaTiO3/Nb:SrTiO3 device also exhibits an excellent switching endurance up to ∼4.0 × 106 bipolar cycles. These enhancements indicate the importance of ferroelectric polarization for achieving high-performance resistance switching and suggest that metal/ferroelectric/Nb:SrTiO3 tunnel junctions are promising candidates for nonvolatile memory applications.

Porcine FcγRIIb mediates enhancement of porcine reproductive and respiratory syndrome virus (PRRSV) infection.

Antibody-dependent enhancement (ADE) of virus infection caused by the uptake of virus-antibody complexes by FcγRs is a significant obstacle to the development of effective vaccines to control certain human and animal viral diseases. The activation FcγRs, including FcγRI and FcγRIIa have been shown to mediate ADE infection of virus. In the present paper, we showed that pocine FcγRIIb, an inhibitory FcγR, mediates ADE of PRRSV infection. Stable Marc-145 cell lines expressing poFcγRIIb (Marc-poFcγRII) were established. The relative yield of progeny virus was significantly increased in the presence of sub-neutralization anti-PRRSV antibody. The Fab fragment and normal porcine sera had no effect. Anti-poFcγRII antibody inhibited the enhancement of infection when cells were infected in the presence of anti-PRRSV antibody, but not when cells were infected in the absence of antibody. These results indicate that enhancement of infection in these cells by anti-PRRSV virus antibody is FcγRII-mediated. Identification of the inhibitory FcγR mediating ADE infection should expand our understanding of the mechanisms of pathogenesis for a broad range of infectious diseases and may open many approaches for improvements to the treatment and prevention of such diseases.