12 research outputs found
Singe ferroelectric and chiral magnetic domain of single-crystalline BiFeO in an electric field
We report polarized neutron scattering and piezoresponse force microscopy
studies of millimeter-sized single crystals of multiferroic BiFeO. The
crystals, grown below the Curie temperature, consist of a single ferroelectric
domain. Two unique electric polarization directions, as well as the populations
of equivalent spiral magnetic domains, can be switched reversibly by an
electric field. A ferroelectric monodomain with a single- single-helicity
spin spiral can be obtained. This level of control, so far unachievable in thin
films, makes single-crystal BiFeO a promising object for multiferroics
research.Comment: 4 figures in separate jpg file
Oxygen-deficient triple perovskites as highly active and durable bifunctional electrocatalysts for oxygen electrode reactions
Highly active and durable bifunctional oxygen electrocatalysts have been of pivotal importance for renewable energy conversion and storage devices, such as unitized regenerative fuel cells and metal-air batteries. Perovskite-based oxygen electrocatalysts have emerged as promising nonprecious metal bifunctional electrocatalysts, yet their catalytic activity and stability still remain to be improved. We report a high-performance oxygen electrocatalyst based on a triple perovskite, Nd1.5Ba1.5CoFeMnO9-delta (NBCFM), which shows superior activity and durability for oxygen electrode reactions to single and double perovskites. When hybridized with nitrogen-doped reduced graphene oxide (N-rGO), the resulting NBCFM/N-rGO catalyst shows further boosted bifunctional oxygen electrode activity (0.698 V), which surpasses that of Pt/C (0.801 V) and Ir/C (0.769 V) catalysts and which, among the perovskite-based electrocatalysts, is the best activity reported to date. The superior catalytic performances of NBCFM could be correlated to its oxygen defect rich structure, lower charge transfer resistance, and smaller hybridization strength between O 2p and Co 3d orbitals
Hybrid photoelectrochemical-rechargeable seawater battery for efficient solar energy storage systems
Eco-friendly harnessing of both ocean chemical energy and solar energy would represent a sustainable solution for future energy conversion/storage systems, but it has been challenging to enhance the energy efficiency of such systems for practical applications. Here, we demonstrate an efficient photoelectrochemical-assisted rechargeable seawater battery. By integrating TiO2 nanostructure-based photoelectrodes with the seawater battery, we achieved significant enhancement of the voltage efficiency during the charging/discharging processes; effective photocharging with the TiO2 photoanode reduced the charging voltage to similar to 2.65 V, while the heated carbon felt (HCF) cathode in the seawater battery exhibited charging/discharging voltages of similar to 3.8 V and similar to 2.9 V, respectively. Such a charging voltage reduction led to a voltage efficiency of similar to 109%. Moreover, interestingly, we found that TiO2 nanostructures showed excellent photoelectrochemical performances in seawater in association with the efficient photocharging. As a result, the utilization of TiO2 nanostructures as photocharging/discharging electrodes provides a feasible strategy to optimize the cell configuration for highly efficient solar seawater batteries
Mechanically driven luminescence in a ZnS:Cu-PDMS composite
The conventional mechanoluminescence (ML) mechanism of phosphors such as SrAl2O4:Eu and ZnS:Mn is known to utilize carrier trapping at shallow traps followed by stress (or strain)-induced detrapping, which leads to activator recombination in association with local piezoelectric fields. However, such a conventional ML mechanism was found to be invalid for the ZnS:Cu-embedded polydimethylsiloxane (PDMS) composite, due to the absence of luminescence with a rigid matrix and a negligibly small value of the piezoelectric coefficient (d33) of the composite. An alternative mechanism, namely, the triboelectricity-induced luminescence has been proposed for the mechanically driven luminescence of a ZnS:Cu-PDMS composite
One-dimensional nanostructured vanadium oxides with single-crystalline structure synthesized by cellulose nanocrystal-template-assisted hydrothermal method for Li-ion battery cathodes
Cellulose nanocrystals (CNCs) have emerged as a promising templating material due to unique features, such as high surface area, surface hydroxyl groups and rod-like shape, which allow for sustainable nanoscale control of advanced functional materials. Especially, such high surface functionality and specific morphology can be imparted on the resultant nanomaterials with beneficial properties during templating. Here, we present synthesis of one-dimensional (1D) nanostructured vanadium oxides, such as VO2(B) and V2O5·nH2O nanobelts, with single- crystalline structure by hydrothermal treatment using CNCs as a sacrificial template. Importantly, the single-crystal vanadium oxide nanobelts exhibit the enhanced electrochemical performance of Li ion batteries with high specific capacity (> 300mAh/g) and long lifespan (> 244mAh/g at 50 cycles) compared to the polycrystalline nanoflakes counterpart. Furthermore, we suggest that during hydrothermal treatment the sacrificial CNC template-derived carbon is beneficial for electron transfer in cathode materials. Thus, we demonstrate that the utilization of CNC templating to develop novel single-crystalline oxide cathode nanomaterials can provide a fruitful pathway for extraordinary electrochemical performance of next-generation alkaline batteries. © 2023, The Author(s), under exclusive licence to Springer Nature B.V.FALS
Enhanced electrocatalytic activity via phase transitions in strongly correlated SrRuO3 thin films
Transition metal oxides have been extensively studied and utilized as efficient catalysts. However, the strongly correlated behavior which often results in intriguing emergent phenomena in these materials has been mostly overlooked in understanding the electrochemical activities. Here, we demonstrate a close correlation between the phase transitions and oxygen evolution reaction (OER) in strongly correlated SrRuO3. By systematically introducing Ru-O vacancies into the single-crystalline SrRuO3 epitaxial thin films, we induced a phase transition in crystalline symmetry which resulted in the corresponding modification of the electronic structure. The modified electronic structure significantly affects the electrochemical activities, so a 30% decrease in the overpotential for the OER activity was achieved. Our study suggests that a substantial enhancement in the OER activity can be realized even within single material systems, by rational design and engineering of their crystal and electronic structures. © The Royal Society of Chemistry 20171881sciescopu
Power efficient transistors with low subthreshold swing using abrupt switching devices
With the rapid development of transparent integrated circuits, transistors with extremely low subthreshold swing (SS) is becoming a necessary requirement. Here, we fabricated three transparent device structures that show abrupt electrical switching and make their series connection to the source terminal of the conventional field effect transistors (FET) to lower the SS value. Firstly, we demonstrate an environment friendly, disposable, and transparent conductive bridge random access memory (CBRAM) device composed of a cellulose nanocrystals active layer. Our CBRAM consists of a silver (Ag) electrochemically active top electrode and a cellulose nanocrystals-based switching layer on the FTO coated glass substrate. Devices with CBRAM can enable FET with an ultra-steep slope that is SS < 0.24 mV/dec and has a significantly high on/off ratio (-10(5)) by switching the Ag metallic filament between on and off. Niobium oxide (NbO2) based threshold switching devices and zinc oxide (ZnO) based flexible Schottky diodes that show electrical breakdown were also stacked with FET, which gave SS values < 0.74 mV/dec and < 5.20 mV/dec, respectively. Comparatively, a nano-watt transistor called filament transistor (FET + CBRAM stack) can significantly improve the SS slope value with the lowest leakage current (-nA) and a record low turn on-voltage (-0.2 V) with a set power of only-197 nW compared to the other series stack, which thereby attracts the attention of low power operations. © 2022 Elsevier Ltd. All rights reserved.FALS
Study of Graphene-based 2D-Heterostructure Device Fabricated by All-Dry Transfer Process
We developed a technique for transferring
graphene and hexagonal boron nitride (hBN) in dry conditions for fabrication
of van der Waals heterostructures. The graphene layer was encapsulated
between two hBN layers so that it was kept intact during fabrication
of the device. For comparison, we also fabricated the devices containing
graphene on SiO<sub>2</sub>/Si wafer and graphene on hBN. Electrical
properties of the devices were investigated at room temperature. The
mobility of the graphene on SiO<sub>2</sub> devices and graphene on
hBN devices were 15 000 and 37 000 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, respectively, while the mobility
of the sandwich structure device reached the highest value of ∼100 000
cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, at room
temperature. The electrical measurements of the samples were carried
out in air and vacuum environments. We found that the electrical properties
of the encapsulated graphene devices remained at a similar level both
in a vacuum and in air, whereas the properties of the graphene without
encapsulation were influenced by the external environment