Recently, the anomalous photovoltaic (PV) effect in BiFeO3 (BFO) thin films, which resulted in open circuit voltages (Voc) considerably larger than the band gap of the material, has generated a revival of the entire field of photoferroelectrics. Here, via temperature-dependent PV studies, we prove that the bulk photovoltaic (BPV) effect, which has been studied in the past for many non-centrosymmetric materials, is at the origin of the anomalous PV effect in BFO films. Moreover, we show that irrespective of the measurement geometry, Voc as high as 50 V can be achieved by controlling the conductivity of domain walls (DW). We also show that photoconductivity of the DW is markedly higher than in the bulk of BFO.

Au/Ag bilayered metal mesh with arrays of nanoholes were devised as a catalyst for metal-assisted chemical etching of silicon. The present metal catalyst allows us not only to overcome drawbacks involved in conventional Ag-based etching processes, but also to fabricate extended arrays of silicon nanowires (SiNWs) with controlled dimension and density. We demonstrate that SiNWs with different morphologies and axial orientations can be prepared from silicon wafers of a given orientation by controlling the etching conditions. We explored a phenomenological model that explains the evolution of the morphology and axial crystal orientation of SiNWs within the framework of the reaction kinetics.

A generic process for the preparation of curved silicon nanowires (SiNWs) with ribbon-like cross sections was developed. The present synthetic approach is based on chemical etching of (100)-oriented silicon wafers in mixture solutions of HF and H(2)O(2) by using patterned thin gold films as catalyst and provides a unique opportunity for the fabrication of extended arrays of zigzag SiNWs, ultrathin straight [111] SiNWs, and curved SiNWs with controlled turning angles. On the basis of our experiments performed under various etching conditions, the factors governing the axial crystal orientation and morphology of SiNWs were systematically analyzed. We proposed a model that explains the formation of the present novel silicon nanostructures during chemical etching of silicon.

A drastic change in the conductivity of strained BiFeO 3 (BFO) films is observed after illuminating them with above-band gap light. This has been termed as persistent photoconductivity. The enhanced conductivity decays exponentially with time. A trapping character of the sub-band levels and their subsequent gradual emptying is proposed as a possible mechanism. KeywordsBiFeO 3 , strain, enhanced conductivity, persistent photoconductivity, thermally stimulated current Strained BiFeO 3 (BFO) has proven to show intriguing properties, many of which are very different from the parent non-strained BFO phase. BFO is generally known to have a

Epidermal electronics are extensively explored as an important platform for future biomedical engineering. Epidermal devices are typically fabricated using high‐cost methods employing complex vacuum microfabrication processes, limiting their widespread potential in wearable electronics. Here, a low‐cost, solution‐based approach using electroconductive reduced graphene oxide (RGO) sheets on elastic and porous poly(dimethylsiloxane) (PDMS) thin films for multifunctional, high‐performance, graphene‐based epidermal bioelectrodes and strain sensors is presented. These devices are fabricated employing simple coatings and direct patterning without using any complicated microfabrication processes. The graphene bioelectrodes show a superior stretchability (up to 150% strain), with mechanical durability up to 5000 cycles of stretching and releasing, and low sheet resistance (1.5 kΩ per square), and the graphene strain sensors exhibit a high sensitivity (a gauge factor of 7 to 173) with a wide sensing range (up to 40% strain). Fully functional applications of dry bioelectrodes in monitoring human electrophysiological signals (i.e., electrocardiogram, electroencephalography, and electromyogram) and highly sensitive strain sensors for precise detection of large‐scale human motions are demonstrated. It is believed that our unique processing capability and multifunctional device platform based on RGO/porous PDMS will pave the way for low‐cost processing and integration of 2D materials for future wearable electronic skin.

Selectively activated inorganic synaptic devices, showing a high on/off ratio, ultrasmall dimensions, low power consumption, and short programming time, are required to emulate the functions of high-capacity and energy-efficient reconfigurable human neural systems combining information storage and processing ( Li et al. Sci. Rep. 2014 , 4 , 4096 ). Here, we demonstrate that such a synaptic device is realized using a Ag/PbZrTiO (PZT)/LaSrMnO (LSMO) ferroelectric tunnel junction (FTJ) with ultrathin PZT (thickness of ∼4 nm). Ag ion migration through the very thin FTJ enables a large on/off ratio (10) and low energy consumption (potentiation energy consumption = ∼22 aJ and depression energy consumption = ∼2.5 pJ). In addition, the simple alignment of the downward polarization in PZT selectively activates the synaptic plasticity of the FTJ and the transition from short-term plasticity to long-term potentiation.

Li-S batteries can potentially deliver high energy density and power, but polysulfide shuttle and lithium dendrite formations on Li metal anode have been the major hurdle. The polysulfide shuttle becomes severe particularly when the areal loading of the active material (sulfur) is increased to deliver the high energy density and the charge/discharge current density is raised to deliver high power. This study reports a novel mechanochemical method to create trenches on the surface of carbon nanotubes (CNTs) in free-standing 3D porous CNT sponges. Unique spiral trenches are created by pressures during the chemical treatment process, providing polysulfide-philic surfaces for cathode and lithiophilic surfaces for anode. The Li-S cells made from manufacturing-friendly sulfur-sandwiched cathodes and lithium-infused anodes using the mechanochemically treated electrodes exhibit a strikingly high areal capacity as high as 13.3 mAh cm −2 , which is only marginally reduced even with a tenfold increase in current density (16 mA cm −2 ), demonstrating both high "cell-level" energy density and power. The outstanding performance can be attributed to the significantly improved reaction kinetics and lowered overpotentials coming from the reduced interfacial resistance and charge transfer resistance at both cathodes and anodes. The trench-wall CNT sponge simultaneously tackles the most critical problems on both the cathodes and anodes of Li-S batteries, and this method can be utilized in designing new electrode materials for energy storage and beyond.to other batteries based on different chemistry due to the unsatisfactory energy density of Li-ion batteries particularly for large-scale applications like transportation and stationary energy storage. [1] On the cathode side, conversion chemistry has shown great promise for replacing the intercalation chemistry of Li-ion batteries. Conversion-type cathode materials like sulfur and oxygen can provide 2567 and 3505 Wh kg −1 , respectively, compared to 387 Wh kg −1 of the intercalation-type LiCoO 2 cathode. [2] In particular, Li-S batteries have attracted rapidly increasing attention and substantial progresses have recently been made to alleviate their inherent problems like lithium polysulfide dissolution and shuttle, insulating nature of the end products, and volume variations of sulfur cathode during cycling. [3] As a result, the specific capacity and cycling performance have been markedly improved when the areal loading of sulfur (active material) is low. The energy density based on the mass of sulfur only (not whole cathode or battery pack) has been good enough to beautify researchers' results, but the low sulfur loading has negated the high-energy-density merit of Li-S batteries, resulting in no improvement in the actual energy density of the "cell" or "battery pack" compared to the Li-ion batteries. To have a high "cell-level" energy density, the areal loading of sulfur needs to be increased to ≈10 mg cm −2 or higher, compared to typical literature values Lithium-Sulfur Batter...

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