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Altres ajuts: acords transformatius de la UAB Magneto-ionics refers to the control of magnetic properties of materials through voltage-driven ion motion. To generate effective electric fields, either solid or liquid electrolytes are utilized, which also serve as ion reservoirs. Thin solid electrolytes have difficulties to (i) withstand high electric fields without electric pinholes and (ii) maintain stable ion transport during long-term actuation. In turn, the use of liquid electrolytes can result in poor cyclability, thus limiting their applicability. Here we propose a nanoscale-engineered magneto-ionic architecture (comprising a thin solid electrolyte in contact with a liquid electrolyte), that drastically enhances cyclability while preserving sufficiently high electric fields to trigger ion motion. Specifically, we show that the insertion of a highly nanostructured (amorphous-like) Ta layer (with suitable thickness and electric resistivity) between a magneto-ionic target material (i.e., Co3O4) and the liquid electrolyte, increases magneto-ionic cyclability from < 30 cycles (when no Ta is inserted) to more than 800 cycles. Transmission electron microscopy together with variable energy positron annihilation spectroscopy reveal the crucial role of the generated TaOx interlayer as a solid-electrolyte (i.e., ionic conductor) that improves magneto-ionic endurance by proper tuning of the types of voltage-driven structural defects. The Ta layer is very effective in trapping oxygen and hindering O2- ions from moving into the liquid electrolyte, thus keeping O2- motion mainly restricted between Co3O4 and Ta when voltage of alternating polarity is applied. We demonstrate that this approach provides a suitable strategy to boost magneto-ionics by combining the benefits of solid and liquid electrolytes in a synergetic manner.

Voltage control of magnetism via electric-field-driven ion migration (magneto-ionics) has generated intense interest due to its potential to greatly reduce heat dissipation in a wide range of information technology devices, such as magnetic memories, spintronic systems or artificial neural networks. Among other effects, oxygen ion migration in transition-metal-oxide thin films can lead to the generation or full suppression of controlled amounts of ferromagnetism ('ON-OFF' magnetic transitions) in a non-volatile and fully reversible manner. However, oxygen magneto-ionic rates at room temperature are generally considered too slow for industrial applications. Here, we demonstrate that sub-second ON-OFF transitions in electrolyte-gated paramagnetic cobalt oxide films can be achieved by drastically reducing the film thickness from >200 nm down to 5 nm. Remarkably, cumulative magneto-ionic effects can be generated by applying voltage pulses at frequencies as high as 100 Hz. Neuromorphic-like dynamic effects occur at these frequencies, including potentiation (cumulative magnetization increase), depression (i.e., partial recovery of magnetization with time), threshold activation, and spike time-dependent magnetic plasticity (learning and forgetting capabilities), mimicking many of the biological synapse functions. The systems under investigation show features that could be useful for the design of artificial neural networks whose magnetic properties would be governed with voltage. This journal is, This work has received funding from the European Unions Horizon 2020 Research and Innovation Programme BeMAGIC under the Marie Sklodowska-Curie grant agreement No 861145. Financial support by the European Research Council (SPIN-PORICS 2014-Consolidator Grant, Agreement No. 648454, and MAGIC-SWITCH 2019-Proof of Concept Grant, Agreement No. 875018), the Spanish Government (MAT2017-86357-C3-1-R, PID2020-116844RB-C21), the Generalitat de Catalunya (2017-SGR-292 and 2018-LLAV-00032) and the European Regional Development Fund (MAT2017-86357-C3-1-R and 2018-LLAV-00032) is acknowledged. The authors would like to thank João Lucas (jgbl89@gmail.com) for the illustrations. XAS experiments were performed at BL29-BOREAS beamline at ALBA Synchrotron with the collaboration of ALBA staff. E. M. is a Serra Húnter Fellow.

Magneto-ionics, which deals with the change of magnetic properties through voltage-driven ion migration, is expected to be one of the emerging technologies to develop energy-efficient spintronics. While a precise modulation of magnetism is achieved when voltage is applied, much more uncontrolled is the spontaneous evolution of magneto-ionic systems upon removing the electric stimuli (i.e., post-stimulated behavior). Here, we demonstrate a voltage-controllable N ion accumulation effect at the outer surface of CoN films adjacent to a liquid electrolyte, which allows for the control of magneto-ionic properties both during and after voltage pulse actuation (i.e., stimulated and post-stimulated behavior, respectively). This effect, which takes place when the CoN film thickness is below 50 nm and the voltage pulse frequency is at least 100 Hz, is based on the trade-off between generation (voltage ON) and partial depletion (voltage OFF) of ferromagnetism in CoN by magneto-ionics. This novel effect may open opportunities for new neuromorphic computing functions, such as post-stimulated neural learning under deep sleep., Financial support by the European Research Council (MAGIC-SWITCH 2019-Proof of Concept Grant, Agreement No. 875018), the European Union's Horizon 2020 research and innovation programme (European Training Network, BeMAGIC ETN/ITN Marie Skłodowska-Curie grant No. 861145; and Integrated Infrastructure, RADIATE, grant No. 824096), the Spanish Government (MAT2017-86357-C3-1-R, PID2020-116844RB-C21 and PDC2021-121276-C3), the Generalitat de Catalunya (2017-SGR-292 and 2018-LLAV-00032), the European Regional Development Fund (MAT2017-86357-C3-1-R and 2018-LLAV-00032) and the KU Leuven (BOF program) is acknowledged. A. Q. acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities through the “Severo Ochoa” Programme for Centers of Excellence in R&D (FUNFUTURE CEX2019-000917-S) and the Juan de la Cierva formación contract (FJC2019-039780-I). J. S. thanks the Spanish Fábrica Nacional de Moneda y Timbre (FNMT) for fruitful discussions. The XAS measurements were performed at BL29-BOREAS beamline at ALBA Synchrotron with the collaboration of ALBA staff. We acknowledge service from MiNa Laboratory at IMN, and funding from CM (project S2018/NMT-4291 TEC2SPACE), MINECO (project CSIC13-4E-1794) and EU (FEDER, FSE). E. M. is a Serra Húnter Fellow., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

Magneto-ionics is an emerging actuation mechanism to control the magnetic properties of materials via voltage-driven ion motion. This effect largely relies on the strength and penetration of the induced electric field into the target material, the amount of generated ion transport pathways, and the ionic mobility inside the magnetic media. Optimizing all these factors in a simple way is a huge challenge, although highly desirable for technological applications. Here, we demonstrate that the introduction of suitable transition-metal elements to binary nitride compounds can drastically boost magneto-ionics. More specifically, we show that the attained magneto-ionic effects in CoN films (i.e., saturation magnetization, toggling speeds, and cyclability) can be drastically enhanced through 10% substitution of Co by Mn in the thin-film composition. Incorporation of Mn leads to transformation from nanocrystalline into amorphous-like structures, as well as from metallic to semiconducting behaviors, resulting in an increase of N-ion transport channels. Ab initio calculations reveal a lower energy barrier for CoMn-N compared to Co-N that provides a fundamental understanding of the crucial role of Mn addition in the voltage-driven magnetic effects. These results constitute an important step forward toward enhanced voltage control of magnetism via electric field-driven ion motion., Financial support by the European Research Council (MAGIC-SWITCH 2019-Proof of Concept Grant, agreement no 875018; REMINDS 2021-ERC-Advanced Grant, agreement no 101054687), the European Union’s Horizon 2020 research and innovation program (European Training Network, ETN/ITN Marie Skłodowska-Curie grant no 861145; and Integrated Infrastructure, RADIATE, grant no 824096), the Spanish Government (PID2020-116844RB-C21 and PDC2021-121276-C31), the Generalitat de Catalunya (2017-SGR-292), and the KU Leuven (BOF program) is acknowledged. We acknowledge the technical support from the MiNa Laboratory at IMN in Madrid, who received funding from the CM (project S2018/NMT-4291 TEC2SPACE), MINECO (project CSIC13-4E-1794), and EU (FEDER, FSE). A.Q. acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities through the “Severo Ochoa” Programme for Centers of Excellence in R&D (FUNFUTURE CEX2019-000917-S) and the “Juan de la Cierva─Formación” contract (FJC2019-039780-I). J.S. thanks the Spanish “Fábrica Nacional de Moneda y Timbre” (FNMT) for fruitful discussions. E.M. is a Serra Húnter Fellow., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

With rapid advances in flexible electronics and communication devices, flexible dielectric capacitors exhibiting high permittivity, low loss, and large electric-field tunability over a wide frequency range have attracted increasing attention. Here, a large-scale Ba0.67Sr0.33TiO3 (BST) dielectric thin film sandwiched between SrRuO3 (SRO) bottom electrode and Pt top electrode is fabricated on a flexible mica substrate. The mica/SRO/BST/Pt capacitor exhibits a dielectric constant (er′) of more than 1200, a loss tangent [tan(δ)] as low as 0.16, and a tunability of 67% at low frequencies around 10 kHz. Simultaneously, the capacitor can retain an er′ of 540 and a tan(δ) of 0.07 at microwave frequencies, e.g., 18.6 GHz. Moreover, even when the capacitor is bent to a small radius of 5 mm or undergoes 12 000 bending cycles (at 5 mm radius), almost no deterioration in er′, tan(δ), and tunability is observed. The excellent dielectricity and mechanical flexibility and durability endow the mica/SRO/BST/Pt capacitor wi...

Achieving high power conversion efficiencies (PCEs) in ferroelectric photovoltaics (PVs) is a longstanding challenge. Although recently ferroelectric thick films, composite films, and bulk crystals have all been demonstrated to exhibit PCEs >1%, these systems still suffer from severe recombination because of the fundamentally low conductivities of ferroelectrics. Further improvement of PCEs may therefore rely on thickness reduction if the reduced recombination could overcompensate for the loss in light absorption. Here, a PCE of up to 2.49% (under 365-nm ultraviolet illumination) was demonstrated in a 12-nm Pb(Zr0.2Ti0.8)O3 (PZT) ultrathin film. The strategy to realize such a high PCE consists of reducing the film thickness to be comparable with the depletion width, which can simultaneously suppress recombination and lower the series resistance. The basis of our strategy lies in the fact that the PV effect originates from the interfacial Schottky barriers, which is revealed by measuring and modeling the thickness-dependent PV characteristics. In addition, the Schottky barrier parameters (particularly the depletion width) are evaluated by investigating the thickness-dependent ferroelectric, dielectric and conduction properties. Our study therefore provides an effective strategy to obtain high-efficiency ferroelectric PVs and demonstrates the great potential of ferroelectrics for use in ultrathin-film PV devices. An approach to boost the power conversion efficiencies (PCEs) of ferroelectric photovoltaics (PVs) is proposed based on the Schottky barrier effect. This approach leverages the thinning of a ferroelectric film to somewhere close to the depletion width, which can simultaneously suppress the recombination and lower the series resistance. Using this approach, we achieve a PCE up to 2.49% (under 365-nm ultraviolet illumination) in the 12-nm Pb(Zr0.2Ti0.8)O3 ultrathin films. Our study provides insightful guidance on how to design and tailor the ferroelectric films to achieve high PCEs, and also demonstrates the great potential of ferroelectrics for use in ultrathin-film PV devices. Eliminating stray electrical effects in ultra-thin films can help optimize an unconventional solar energy technology. Ferroelectric materials have internal dipoles that spontaneously move photogenerated charges toward external circuits, producing higher power outputs than predicted by theory. Zhen Fan from South China Normal University in Guangzhou and colleagues now report that the dimensions of ferroelectric thin films distinctly affect how efficiently they convert sunlight into electricity. Measurements of solar cells containing lead-zirconium-titanate ferroelectrics with different thicknesses revealed a jump in conversion efficiencies when the film reached a thickness of 12 nanometers. Further analysis showed that this thickness correlates with the solar cell’s ‘depletion width’, a zone formed when metal electrodes contact the film. The electric field in the depletion zone complements the pushing actions of the ferroelectric dipoles, lowering electrical losses compared to thicker ferroelectric films.

A 3D hybrid of graphitic C 3 N 4 nanoparticle decorated in the assembly of graphene and Co 2 Al layered double hydroxide nanosheets (GR-LDH-C 3 N 4 ) was prepared by simple hydrothermal treatment and subsequent calcination-recovery process. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy clearly demonstrated that the g-C 3 N 4 nanoparticle was successful incorporated into the porous GR-LDH nano-scaffold. Then the conductive composite and chitosan (CTS) were used to immobilize hemoglobin (Hb) on a carbon ionic liquid electrode (CILE) for fabrication of a trichloroacetic acid (TCA) biosensor. The spectroscopic results revealed that the immobilized Hb retained the native catalytic activity and conformation. Electrochemical results indicated that the GR-LDH-C 3 N 4 film possessed the large electroactive surface area and fast heterogeneous electron transfer rate. Due to synergistic effects of three components, CTS/GR-LDH-C 3 N 4 -Hb/CILE gave rise to the excellent direct electrochemistry and electrocatalytic activity toward TCA. This bioelectrode exhibited a wide linear detection range from 0.2 to 36.0 mM with a low detection limit of 0.05 mM (3σ). The Michaelis–Menten constant of the developed bioelectrode was obtained as 3.30 mM. Thus, the 3D porous GR-LDH-C 3 N 4 architecture is a promising material for construction of the third-generation biosensors.

Self-assembly of graphene oxide (GO) and Au nanoparticles (AuNPs) was covalently modified by ionic liquid (IL) containing amino groups to prepare the ternary nanocomposite of IL-GO-AuNPs. UV, IR spectra, X-ray power diffraction and scanning electron microscope confirmed the successful hybridization of these three components, leading to the larger surface area and better dispersity. Then a sensitive 2,4-Dichlorophenol (2,4-DCP) sensor was established based on IL-GO-AuNPs modified glassy carbon electrode. The IL-GO-AuNPs composite gave rise to a desirable access to the electron transfer and electrocatalytic capacity toward the oxidation of 2,4-DCP. Differential pulse voltammetry was employed for the quantitative analysis of 2,4-DCP. The proposed sensor showed a wide linear range from 0.01 to 5 μM with a low detection limit of 3 nM (S/N = 3). The developed sensor was successfully used for the determination of 2,4-DCP in water samples with satisfactory recoveries and stability. The excellent electrocatalytic performance could be attributed to the high conductivity and more active sites of IL-GO-AuNPs.

With rapid advances in flexible electronics and communication devices, flexible dielectric capacitors exhibiting high permittivity, low loss, and large electric-field tunability over a wide frequency range have attracted increasing attention. Here, a large-scale Ba

Resistive switching (RS) memory has stayed at the forefront of next-generation nonvolatile memory technologies. Recently, a novel class of transition metal oxides (TMOs), which exhibit reversible topotactic phase transformation between insulating brownmillerite (BM) phase and conducting perovskite (PV) phase, has emerged as promising candidate materials for RS memories. Nevertheless, the microscopic mechanism of RS in these TMOs is still unclear. Furthermore, RS devices with simultaneously high density and superior memory performance are yet to be reported. Here, using SrFeO

$R\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n$ is of critical concern when a memory device stores data. While ferroelectric diodes continue to emerge as a promising memory technology, their retention behavior and underlying physics have not been well investigated. This paper proposes a theoretical model for retention loss in ferroelectric diodes, combining polarization relaxation kinetics and polarization-controlled Schottky emission. The model describes well the behavior of metal/BiFeO${}_{3}$/La${}_{0.7}$Sr${}_{0.3}$MnO${}_{3}$ diodes, and explains the dependences of retention-loss rate on BiFeO${}_{3}$ thickness and electrode screening. These findings should help to guide the development of reliable ferroelectric memory devices.

In the present work, the ultrathin exfoliated Ni 2 Al layered double hydroxide (ELDH) nanosheets were prepared by using l -asparagine as pre-intercalator in aqueous medium. The transmission electron microscopy and atomic force microscopy images displayed that ELDH nanosheets had lost the original hexagon of hydrotalcite with about 200 nm lateral size and less than 3 nm thickness. Then a sensitive electrochemical sensor was fabricated for bisphenol A (BPA) detection based on ELDH modified glassy carbon electrode with aid of film-forming agent chitosan. The proposed sensor showed an efficient electrocatalytic performance on the oxidation of BPA with the enhanced oxidation response and the lowered oxidation overpotential (0.489 V). Differential pulse voltammetry (DPV) was employed for the determination of BPA with a wide linear range from 0.02 to 1.51 μM. The detection limit was calculated as 6.8 nM (S/N = 3). The resultant sensor exhibited good reproducibility, selectivity and acceptable stability due to the contribution of the more active sites and the large surface area from ELDH nanosheets. Additionally, the concentrations of BPA in milk samples were analyzed by this developed method with an acceptable result.

Seed vigor is an index of seed quality that is used to describe the rapid and uniform germination and the establishment of strong seedlings in any environmental conditions. Strong seed vigor in low-temperature germination conditions is particularly important in direct-sowing rice production systems. However, seed vigor has not been selected as an important breeding trait in traditional breeding programs due to its quantitative inherence. In this study, we identified and mapped eight quantitative trait loci (QTLs) for seed vigor by using a recombinant inbred population from a cross between rice (Oryza sativa L. ssp. indica) cultivars ZS97 and MH63. Conditional QTL analysis identified qSV-1, qSV-5b, qSV-6a, qSV-6b, and qSV-11 influenced seedling establishment and that qSV-5a, qSV-5c, and qSV-8 influenced only germination. Of these, qSV-1, qSV-5b, qSV-6a, qSV-6b, and qSV-8 were low-temperature-specific QTLs. Two major-effective QTLs, qSV-1, and qSV-5c were narrowed down to 1.13-Mbp and 400-kbp genomic regions, respectively. The results provide tightly linked DNA markers for the marker-assistant pyramiding of multiple positive alleles for increased seed vigor in both normal and low-temperature germination environments.

Ferroelectric photovoltaic materials have attracted intensive interest due to their intriguing above-bandgap photovoltage, while the low photocurrent limits their further device applications. In this work, both enhanced and tunable photovoltaic effect (PVE) are demonstrated in sandwiched structure of Graphene/tetragonal-like BiFeO3/Ca0.96Ce0.04MnO3 (Graphene/T(-like) BFO/CCMO). The epitaxial BFO film is grown on the CCMO buffered LaAlO3 substrate by pulsed laser deposition and the mechanically exfoliated graphene is transferred directly onto the BFO film as top electrode. The optimized open circuit voltage (Voc) and short circuit current density (Jsc) are measured to be −0.88 V and 2.56 mA/cm2, respectively. Moreover, the photovoltaic response can be modulated by controllable ferroelectric polarization, whereby both the Voc and Jsc show piezoresponse-like hysteresis behaviors against voltage. The notably enhanced PVE is likely a result of the combination effects of large polarization in the T(-like) BFO film, partially unscreened depolarization field, high transmittance and conductivity of the graphene top electrode. This work clearly indicates the potential of Graphene/ferroelectric photovoltaic devices for memory and energy conversion applications.

Resistive switching (RS) memory has stayed at the forefront of next-generation nonvolatile memory technologies. Recently, a novel class of transition metal oxides (TMOs), which exhibit reversible topotactic phase transformation between insulating brownmillerite (BM) phase and conducting perovskite (PV) phase, has emerged as promising candidate materials for RS memories. Nevertheless, the microscopic mechanism of RS in these TMOs is still unclear. Furthermore, RS devices with simultaneously high density and superior memory performance are yet to be reported. Here, using SrFeOx as a model system, it is directly observed that PV SrFeO3 nanofilaments are formed and extend almost through the BM SrFeO2.5 matrix in the ON state and are ruptured in the OFF state, unambiguously revealing a filamentary RS mechanism. The nanofilaments are ≈10 nm in diameter, enabling to downscale Au/SrFeOx /SrRuO3 RS devices to the 100 nm range for the first time. These nanodevices exhibit good performance including ON/OFF ratio as high as ≈104 , retention time over 105 s, and endurance up to 107 cycles. This study significantly advances the understanding of the RS mechanism in TMOs exhibiting topotactic phase transformation, and it also demonstrates the potential of these materials for use in high-density RS memories.

The polarization imprint along with the photovoltaic (PV) effect has been studied in Pt/Pb(Zr0.3Ti0.7)O3/SrRuO3 ferroelectric capacitors. It is shown that the positive DC poling induces the imprint with a downward direction whereas the negative DC poling suppresses the imprint (i.e., rejuvenation). In the polarization up state, the imprinted capacitor exhibits degraded PV properties compared with the rejuvenated one. This may be because the imprint reduces the number of upward domains, thus lowering the driving force for the PV effect. In the polarization down state, however, the rejuvenated capacitor enters the imprinted state spontaneously. This rejuvenation-to-imprint transition can be further aggravated by applying positive voltages and ultraviolet illumination. It is proposed that the domain pinning/depinning, which are associated with the oxygen vacancies and trapped electrons modulated by polarization, voltage, and illumination, may be responsible for the polarization imprint and rejuvenation. Our ...

We have comparatively studied the dielectric, ferroelectric, conduction, and photovoltaic properties of Ti/BaTiO3 (BTO)/SrRuO3 (SRO) and Pt/BTO/SRO capacitors. The resistive switching (RS) is observed in the Pt/BTO/SRO capacitor while it is absent in the Ti/BTO/SRO capacitor, which may be attributed to the interfacial layer existing between Pt and BTO and the Ti/BTO Ohmic interface, respectively. Further analyses on the conduction mechanisms suggest that the RS may be caused by the opening/closing of conduction paths in the Pt/BTO interfacial layer, whereas the polarization is ruled out as the origin of RS because of the inconsistency between the RS switching voltages and coercive voltages. On the other hand, it is observed that the photovoltaic effects (PVEs) in both Ti/BTO/SRO and Pt/BTO/SRO capacitors are electrically unswitchable and the open-circuit voltages of the two capacitors are similar in magnitude, implying that the PVE is driven by an internal bias field rather than the polarization-induced f...

Seed vigor is an index of seed quality that is used to describe the rapid and uniform germination and the establishment of strong seedlings in any environmental conditions. Strong seed vigor in low-temperature germination conditions is particularly important in direct-sowing rice production systems. However, seed vigor has not been selected as an important breeding trait in traditional breeding programs due to its quantitative inherence. In this study, we identified and mapped eight quantitative trait loci (QTLs) for seed vigor by using a recombinant inbred population from a cross between rice (Oryza sativa L. ssp. indica) cultivars ZS97 and MH63. Conditional QTL analysis identified qSV-1, qSV-5b, qSV-6a, qSV-6b, and qSV-11 influenced seedling establishment and that qSV-5a, qSV-5c, and qSV-8 influenced only germination. Of these, qSV-1, qSV-5b, qSV-6a, qSV-6b, and qSV-8 were low-temperature-specific QTLs. Two major-effective QTLs, qSV-1, and qSV-5c were narrowed down to 1.13-Mbp and 400-kbp genomic regions, respectively. The results provide tightly linked DNA markers for the marker-assistant pyramiding of multiple positive alleles for increased seed vigor in both normal and low-temperature germination environments.