WO 3 nanofibrous backbone scaffolds for enhanced optical absorbance and charge transport in metal oxide (Fe 2 O 3 , BiVO 4 ) semiconductor photoanodes towards solar fuel generation

Producing clean fuel (O2 and H2) using semiconductors through solar driven water splitting process has been considered as a promising technology to mitigate the existing environmental issues. Unlike the conventional single photoabsorbers, heterostructured semiconductors exhibit the merits of improved solar light photon harvesting and rapid charge separation, which are anticipated to result in high quantum yield of solar fuel generation in photoelectrochemical (PEC) cells. In this report, we demonstrate the electrospun derived WO3 backbone fibrous channel as heteropartner to the primary photoabsorber (Fe2O3 and BiVO4) for promoting the electron transport from charge injection point to charge collector as well as photoholes to the electrolyte. We examine structure, optical, photoelectrochemical and charge transfer property of Fe2O3/WO3 and BiVO4/WO3 electrodes. These results were compared with directly coated Fe2O3 and BiVO4 photoabsorber onto conducting substrate without WO3 backbone. The optical results showed that the absorbance and visible light activity of Fe2O3 and BiVO4 is significantly improved by WO3 backbone fibers due to high amount of photo absorber loading. In addition, one dimensional (1-D) WO3 fibers beneficially enhance the optical path length to the photoanode through light scattering mechanism. The electrochemical impedance analysis exhibits WO3 nanofiber backbone reduces charge transfer resistance at Fe2O3 and BiVO4 by rapid charge collection and charge separation compare to backbone-free Fe2O3 and BiVO4. As a result, Fe2O3/WO3 and BiVO4/WO3 fibrous hetero interface structures showed fourfold higher photocurrent generation from PEC cell

Mechanical Properties of Silicon Nanowires

Nanowires have been taken much attention as a nanoscale building block, which can perform the excellent mechanical function as an electromechanical device. Here, we have performed atomic force microscope (AFM)-based nanoindentation experiments of silicon nanowires in order to investigate the mechanical properties of silicon nanowires. It is shown that stiffness of nanowires is well described by Hertz theory and that elastic modulus of silicon nanowires with various diameters from ~100 to ~600 nm is close to that of bulk silicon. This implies that the elastic modulus of silicon nanowires is independent of their diameters if the diameter is larger than 100 nm. This supports that finite size effect (due to surface effect) does not play a role on elastic behavior of silicon nanowires with diameter of >100 nm

Low Frequency Noise Sources and Mechanisms in Two Dimensional Transistors

Beyond graphene, two-dimensional (2D) atomic layered materials have drawn considerable attention as promising semiconductors for future ultrathin layered nano-electronic device applications, transparent/flexible devices and chemical sensors. But, they exhibit high levels of low-frequency due to interfacial scattering (small thickness) and interlayer coupling (large thickness). The sources and mechanisms of low frequency noise should be comprehensive and controlled to fulfill practical applications of two-dimensional transistors. This work seeks to understand the fundamental noise mechanisms of 2D transistors to find ways to reduce the noise level. It also verifies how noise can provide a spectroscopy for analysis of device quality. Most noise analysis tend to apply classical MOSFET models to the noise and electrical transport of 2D transistors, which put together all possible independent noise sources in 2D transistors, ignoring the contact effects. So this could lead to wrong estimation of the noise analysis in 2D transistors. This work demonstrates how the noise components can come from the channel and contact/access regions, all independently adding to the total noise. Each noise source can contribute and may dominate the total noise behavior under the specific gate voltage bias. Herein, the measured noise amplitude in our MoS2 and MoSe2FETs shows a direct crossover from channel- to contact-dominated noise as the gate voltage is increased. The results can be interpreted in terms of a Hooge relationship associated with the channel noise, a transition region, and a saturated high-gate voltage regime whose characteristics are determined by a voltage-independent conductance and noise source associated with the metallurgical contact and the interlayer resistance. The approach for separating channel contributions from those contact/access region allows clear evaluation of the channel noise mechanism and also can be used to explain the qualitative differences in the transition regions between contact- and channel-dominated regimes for various devices

Correlating Electronic Transport and 1/f Noise in MoSe2 Field-Effect Transistors

Citation: Kwon, J., Prakash, A., Das, S. R., & Janes, D. B. (2018). Correlating Electronic Transport and 1/f Noise in MoSe2 Field-Effect Transistors. Physical Review Applied, 10(6), 064029. https://doi.org/10.1103/PhysRevApplied.10.064029Two-Dimensional Transition Metal Dichalcogenides (2D TMDCs) such as MoS2, MoSe2, WS2, and WSe2 with van der Waal's type interlayer coupling are being widely explored as channel materials in a Schottky Barrier Field Effect Transistor (SB FET) configuration. While their excellent electrostatic control and high on/off ratios have been identified, a clear correlation between electronic transport and the low-frequency noise with different atomic-layer thickness is missing. For multilayer channels in MoS2 FETs, the effects of interlayer-coupling resistance on device conductance and mobility have been studied, but no systematic study has included interlayer effects in consideration of the intrinsic (channel) and extrinsic (total device) noise behavior. Here, we report the 1/f noise properties in MoSe2 FETs with varying channel thicknesses (3–40 atomic layers). Contributions of channel vs access/contact regions are extracted from current-voltage (transport) and 1/f noise measurements. The measured noise amplitude shows a direct crossover from channel- to contact-dominated noise as the gate voltage is increased. The results can be interpreted in terms of a Hooge relationship associated with the channel noise, a transition region, and a saturated high-gate-voltage regime whose characteristics are determined by a voltage-independent conductance and noise source associated with the metallurgical contact and the interlayer resistance. Both the channel Hooge coefficient and the channel/access noise amplitude decrease with increasing channel thickness over the range of 3–15 atomic layers, with the former remaining approximately constant and the latter increasing over a range of 20–40 atomic layers. The analysis can be extended to devices based on other TMDCs

Electrically conductive metal oxide-Assisted multifunctional separator for highly stable Lithium-Metal batteries

Lithium (Li) metal anodes have received intensive attention owing to its high specific capacity and low redox potential. However, chronic issues related to dendritic Li growth have hindered the pragmatic use of Li-metal batteries (LMBs). As one of feasible approaches, depositing a functional material on the separator is an efficient strategy for improving the electrochemical stability of LMBs. In this paper, we report a functionalized separator, comprising a nitrided niobium dioxide (named as n-NbO2) and a polypropylene (PP) separator. It is identified that niobium oxide interact with metallic Li, resulting in redistributing the localized Li ion. The n-NbO2-coated separator with enhanced electrical conductivity promotes Li plating/stripping process, reinforcing the Li ion redistribution effect. Due to these properties, Li-Cu cells with the n-NbO2-coated separator show the most outstanding cycle stability with high Coulombic efficiency (CE) over 200 cycles

Stimuli-Responsive Matrix-Assisted Colorimetric Water Indicator of Polydiacetylene Nanofibers

An alternative signal transduction mechanism of polydiacetylene (PDA) sensors is devised by combining stimuli-responsive polymer hydrogel as a matrix and PDA sensory materials as a signal-generating component. We hypothesized that volumetric expansion of the polymer hydrogel matrix by means of external stimuli can impose stress on the imbedded PDA materials, generating a sensory signal. PDA assembly as a sensory component was ionically linked with the alginate hydrogel in order to transfer the volumetric expansion force of alginate hydrogel efficiently to the sensory PDA molecules. Under the same swelling ratio of alginate hydrogel, alginate gel having embedded 1-dimensional thin PDA nanofibers (???20 nm diameter) presented a sharp color change while 0-dimensional PDA liposome did not give any sensory signal when it was integrated in alginate gel. The results implied that dimensionality is an important design factor to realize stimuli-responsive matrix-driven colorimetric PDA sensory systems; more effective contact points between 1-dimensional PDA nanofibers and the alginate matrix much more effectively transfer the external stress exerted by the volumetric expansion force, and thin PDA nanofibers respond more sensitively to the stress.clos

Unusual Na+ ion intercalation/deintercalation in metal-rich Cu1.8S for Na-ion batteries

A key issue with Na-ion batteries is the development of active materials with stable electrochemical reversibility through the understanding of their sodium storage mechanisms. We report a sodium storage mechanism and properties of a new anode material, digenite Cu1.8S, based on its crystallographic study. It is revealed that copper sulfides (CuxS) can have metal-rich formulas (x ≥ 1.6), due to the unique oxidation state of +1 found in group 11 elements. These phases enable the unit cell to consist of all strong Cu–S bonds and no direct S–S bonds, which are vulnerable to external stress/strain that could result in bond cleavage as well as decomposition. Because of its structural rigidness, the Cu1.8S shows an intercalation/deintercalation reaction mechanism even in a low potential window of 0.1–2.2 V versus Na/Na+ without irreversible phase transformation, which most of the metal sulfides experience through a conversion reaction mechanism. It uptakes, on average, 1.4 Na+ ions per unit cell (∼250 mAh g–1) and exhibits ∼100% retention over 1000 cycles at 2C in a tuned voltage range of 0.5–2.2 V through an overall solid solution reaction with negligible phase separation

Partial Dehydration in Hydrated Tungsten Oxide Nanoplates Leads to Excellent and Robust Bifunctional Oxygen Reduction and Hydrogen Evolution Reactions in Acidic Media

The development of efficient, low-cost, and stable bifunctional catalysts is necessary for renewable energy storage and conversion, but it remains a challenge. Herein, we first report a novel strategy to develop WO3 center dot nH(2)O (n = 0.33, 1.00, or 2.00) as a highly active and durable bifunctional catalyst for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) in acidic media by controlling the degree of hydration. The content of solvated water molecules in WO3 center dot nH(2)O can be precisely controlled by selectively using ethylenediaminetetraacetic acid or DL-malic acid for room-temperature precipitation synthesis. Structural flexibility associated with water solvation in WO3 center dot nH(2)O leads to excellent bifunctional catalytic activity as well as durability in acidic media. The bifunctional catalytic mechanism of WO3 center dot nH(2)O is mainly attributed to spontaneous partial dehydration during electrolysis, resulting in simultaneous formation of active phases for HER and ORR, respectively

Enhancing Solar Light-Driven Photocatalytic Activity of Mesoporous Carbon–TiO2 Hybrid Films via Upconversion Coupling

Solar energy conversion has emerged as an attractive pathway in the decomposition of hazardous organic pollutants. Herein, tridoped β-NaYF4:Yb3+,Tm3+,Gd3+ upconversion (UC) nanorods were embedded in a carbon-doped mesostructured TiO2 hybrid film using triblock copolymer P123 acting as a mesoporous template and carbon source. The photoactivity of our novel material was reflected in the degradation of nitrobenzene, as a representative organic waste. The broad-band absorption of our rationally designed UC nanorod-embedded C-doped TiO2 in the UV to NIR range unveiled a remarkable increase in nitrobenzene degradation (83%) within 3 h compared with pristine TiO2 (50%) upon light irradiation. These results establish for the first time a synergetic bridge between the effects of a creative photon trapping TiO2 architecture, improved NIR light-harvesting efficiency upon UC nanorod incorporation, and a simultaneous decrease in the band gap energy and increased visible light absorption by C-doping of the oxide lattice. The resulting nanostructure was believed to favor efficient charge and energy transfer between the photocatalyst components and to reduce charge recombination. Our novel hybrid nanostructure and its underlined synthesis strategy reflect a promising route to improve solar energy utilization in environmental remediation and in a wide range of photocatalytic applications, e.g., water splitting, CO2 reutilization, and production of fuels

Dexmedetomidine-Induced Contraction Involves CPI-17 Phosphorylation in Isolated Rat Aortas

Dexmedetomidine, a highly selective α-2 adrenoceptor agonist, produces vasoconstriction, which leads to transiently increased blood pressure. The goal of this study was to investigate specific protein kinases and the associated cellular signal pathways responsible for the increased calcium sensitization induced by dexmedetomidine in isolated rat aortas, with a particular focus on phosphorylation-dependent inhibitory protein of myosin phosphatase (CPI-17). The effect of Y-27632 and chelerythrine on the dexmedetomidine-induced intracellular calcium concentration ([Ca2+]i) and tension were assessed using fura-2-loaded aortic strips. The effects of rauwolscine, Y-27632, chelerythrine, and ML-7 hydrochloride on the dexmedetomidine-induced phosphorylation of CPI-17 or of the 20-kDa regulatory light chain of myosin (MLC20) were investigated in rat aortic vascular smooth muscle cells. The effects of rauwolscine, Y-27632, and chelerythrine on the membrane translocation of Rho-kinase and protein kinase C (PKC) phosphorylation induced by dexmedetomidine were assessed. Y-27632 and chelerythrine each reduced the slopes of the [Ca2+]i-tension curves of dexmedetomidine-induced contraction, and Y-27632 more strongly reduced these slopes than did chelerythrine. Rauwolscine, Y-27632, chelerythrine, and ML-7 hydrochloride attenuated the dexmedetomidine-induced phosphorylation of CPI-17 and MLC20. Taken together, these results suggest that dexmedetomidine-induced contraction involves calcium sensitization, which appears to be mediated by CPI-17 phosphorylation via Rho-kinase or PKC