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In the present work, a facile one-step hydrothermal synthesis of well-defined stabilized CuO nanopetals and its surface study by advanced nanocharacterization techniques for enhanced optical and catalytic properties has been investigated. Characterization by Transmission electron microscopy (TEM) analysis confirmed existence of high crystalline CuO nanopetals with average length and diameter of 1611.96 nm and 650.50 nm, respectively. The nanopetals are monodispersed with a large surface area, controlled morphology, and demonstrate the nanocrystalline nature with a monoclinic structure. The phase purity of the as-synthesized sample was confirmed by Raman spectroscopy and X-ray diffraction (XRD) patterns. A significantly wide absorption up to 800 nm and increased band gap were observed in CuO nanopetals. The valance band (VB) and conduction band (CB) positions at CuO surface are measured to be of +0.7 and −1.03 eV, respectively, using X-ray photoelectron spectroscopy (XPS), which would be very promising for efficient catalytic properties. Furthermore, the obtained CuO nanopetals in the presence of hydrogen peroxide ( H 2 O 2 ) achieved excellent catalytic activities for degradation of methylene blue (MB) under dark, with degradation rate > 99% after 90 min, which is significantly higher than reported in the literature. The enhanced catalytic activity was referred to the controlled morphology of monodispersed CuO nanopetals, co-operative role of H 2 O 2 and energy band structure. This work contributes to a new approach for extensive application opportunities in environmental improvement.

Electron transfer from valence to conduction band states in semiconductors is the basis of modern electronics. Here, attosecond extreme ultraviolet (XUV) spectroscopy is used to resolve this process in silicon in real time. Electrons injected into the conduction band by few-cycle laser pulses alter the silicon XUV absorption spectrum in sharp steps synchronized with the laser electric field oscillations. The observed ∼450-attosecond step rise time provides an upper limit for the carrier-induced band-gap reduction and the electron-electron scattering time in the conduction band. This electronic response is separated from the subsequent band-gap modifications due to lattice motion, which occurs on a time scale of 60 ± 10 femtoseconds, characteristic of the fastest optical phonon. Quantum dynamical simulations interpret the carrier injection step as light-field–induced electron tunneling.

Experiments showing that electron dynamics can be controlled on attosecond timescales suggest that wide-bandgap semiconductors could be exploited for petahertz signal processing technologies. High-speed photonic and electronic devices at present rely on radiofrequency electric fields to control the physical properties of a semiconductor 1 , which limits their operating speed to terahertz frequencies (10 12  Hz; ref.  2 ). Using the electric field from intense light pulses, however, could extend the operating frequency into the petahertz regime (10 15  Hz; ref.  3 ). Here we demonstrate optical driving at a petahertz frequency in the wide-bandgap semiconductor gallium nitride. Few-cycle near-infrared pulses are shown to induce electric interband polarization though a multiphoton process. Dipole oscillations with a periodicity of 860 as are revealed in the gallium nitride electron and hole system by using the quantum interference between the two transitions from the valence and conduction band states, which are probed by an extremely short isolated attosecond pulse with a coherent broadband spectrum. In principle, this shows that the conductivity of the semiconductor can be manipulated on attosecond timescales, which corresponds to instantaneous light-induced switching from insulator to conductor. The resultant dipole frequency reaches 1.16 PHz, showing the potential for future high-speed signal processing technologies based on wide-bandgap semiconductors.

HighlightsHigh conduction band inorganic layers are manufactured via simple but efficient methodology.The multilayered nanocomposite possesses an outstanding breakdown strength of 611 MV m−1 and an excellent discharged energy density of 14.3 J cm−3, which are 119% and 177% of the randomly dispersed nanocomposite (515 MV m−1, and 8.1 J cm−3).The current work offers a new paradigm for design and production of high energy density flexible dielectric films.Dielectric polymer nanocomposites are considered as one of the most promising candidates for high-power-density electrical energy storage applications. Inorganic nanofillers with high insulation property are frequently introduced into fluoropolymer to improve its breakdown strength and energy storage capability. Normally, inorganic nanofillers are thought to introducing traps into polymer matrix to suppress leakage current. However, how these nanofillers effect the leakage current is still unclear. Meanwhile, high dopant (> 5 vol%) is prerequisite for distinctly improved energy storage performance, which severely deteriorates the processing and mechanical property of polymer nanocomposites, hence brings high technical complication and cost. Herein, boron nitride nanosheet (BNNS) layers are utilized for substantially improving the electrical energy storage capability of polyvinylidene fluoride (PVDF) nanocomposite. Results reveal that the high conduction band minimum of BNNS produces energy barrier at the interface of adjacent layers, preventing the electron in PVDF from passing through inorganic layers, leading to suppressed leakage current and superior breakdown strength. Accompanied by improved Young’s modulus (from 1.2 GPa of PVDF to 1.6 GPa of nanocomposite), significantly boosted discharged energy density (14.3 J cm−3) and charge–discharge efficiency (75%) are realized in multilayered nanocomposites, which are 340 and 300% of PVDF (4.2 J cm−3, 25%). More importantly, thus remarkably boosted energy storage performance is accomplished by marginal BNNS. This work offers a new paradigm for developing dielectric nanocomposites with advanced energy storage performance.

Using a one-dimensional solar cell capacitance simulator (SCAPS-1D), the initial simulation study is carried out by using inorganic Pb-free RbGeI 3 -based perovskite layer along with 2,2′,7,7′- tetrakis [N, N-di4-methoxyphenylamino]-9,9′-spirobifluorene (Spiro-OMeTAD) as a hole transport layer (HTL) and titanium dioxide (TiO 2 ) as an electron transport layer (ETL), which shows a device efficiency of 13.11%. In addition, we investigated the impact of the conduction band offset (CBO) between the ETL and absorber layer, and the valence band offset (VBO) between the absorber and HTL. Band offsets play a critical role in carrier recombination at the interfaces, which determines the open-circuit voltage (Voc). Our study found that extremely negative and positive band offsets lead to reduced PV performance. The optimum position of CBO with respect to the perovskite layer is found to be − 0.2 to − 0.1 eV, while the optimum position of VBO is found to be − 0.1 to 0.0 eV. When ETL is replaced by ZnSe and HTL by CuSCN, the device shows an improved power conversion efficiency (PCE) of 15.82%, as predicted by band offset engineering. The effect of thickness and defect density of perovskite layer, back contact work function, series resistance, shunt resistance, and temperature on the performance of perovskite solar cell (PSC) has been analyzed. The optimized device exhibited a PCE of 17.93%, fill factor (FF) of 74.96%. Thus, the proposed simulation study promotes RbGeI 3 as a promising candidate for the absorbing layer and provides significant insight that will help to find out the suitable ETL and HTL combination.

For further uptake in the solar cell industry, n-ZnO/p-Si single heterojunction solar cell has attracted much attention of the research community in recent years. This paper reports the influence of bandgap and/or electron affinity tuning of zinc oxide on the performance of n-ZnO/p-Si single heterojunction photovoltaic cell using PC1D simulations. The simulation results reveal that the open circuit voltage and fill factor can be improved significantly by optimizing valence-band and conduction-band off-sets by engineering the bandgap and electron affinity of zinc oxide. An overall conversion efficiency of more than 20.3% can be achieved without additional cost or any change in device structure. It has been found that the improvement in efficiency is mainly due to reduction in conduction band offset that has a significant influence on minority carrier current.

In order to mitigate the current global energy and environmental challenges associated with the use of fossil fuels, there is a need for better energy alternatives such as the inexhaustible solar energy. Of great interest is the design and fabrication of low-cost photovoltaic devices which are the epitome of efficient solar energy harvesting. Herein, we report inexpensive hole transport layer (HTL)-free dye-sensitized solar cell architecture with robust photovoltaic (PV) performance. In the proposed solar cell model, expensive hole transport layers, CuI, CuSCN, Spiro-OMeTAD, and PEDOT:PSS, are not required, but instead, a metallic layer is used for dye regeneration. A thorough analysis of the effect of series and shunt resistances, conduction band offset, Schottky barriers, working temperature, the metal work function of the back contact, and the electron affinities of the electron transport layers (ETLs) on the performance of the proposed solar cell is presented. The Solar Capacitance Simulator (SCAPS-1D) is used to perform the numerical simulations of the proposed solar cell design. The study focused on modeling HTL-free dye-sensitized solar cells with the configuration: FTO/ETL/N719 dye/Au. The performance of two ETLs—ZnOS and TiO 2 are critically examined. The optimized model cell performance for the FTO/ZnOS/N719 dye/Au architecture gave an optimal power conversion efficiency (PCE) of 11.54%, 62.71% as the fill factor (FF), short circuit current (Jsc) of 18.50 mAcm −2 , and an open-circuit voltage (Voc) of 0.99 V. On the other hand, the cell architecture FTO/TiO 2 /N719 dye/Au gave an optimized performance of 10.22% as the PCE, 63.58% as the FF, a Voc of 0.97 V, and 16.50 mAcm −2 as the Jsc. Based on these results, ZnOS is a suitable ETL material that has better PV performance of the solar cell device under consideration. ZnOS is earth-abundant, has a tunable band gap, is less toxic, and is, therefore, a promising candidate to replace TiO 2 ETL in future designs and manufacture of HTL-free DSSCs for commercial production.

Biological ion channels are protein nanotubes embedded in, and passing through, the bilipid membranes of cells. Physiologically, they are of crucial importance in that they allow ions to pass into and out of cells, fast and efficiently, though in a highly selective way. Here we show that the conduction and selectivity of calcium/sodium ion channels can be described in terms of ionic Coulomb blockade in a simplified electrostatic and Brownian dynamics model of the channel. The Coulomb blockade phenomenon arises from the discreteness of electrical charge, the strong electrostatic interaction, and an electrostatic exclusion principle. The model predicts a periodic pattern of Ca2+ conduction versus the fixed charge Qf at the selectivity filter (conduction bands) with a period equal to the ionic charge. It thus provides provisional explanations of some observed and modelled conduction and valence selectivity phenomena, including the anomalous mole fraction effect and the calcium conduction bands. Ionic Coulomb blockade and resonant conduction are similar to electronic Coulomb blockade and resonant tunnelling in quantum dots. The same considerations may also be applicable to other kinds of channel, as well as to charged artificial nanopores.

We investigate the temperature dependence of the resistivity and Hall coefficient for heavily Al-doped p-type 4H-SiC epilayers with Al concentrations (C_Al) of > 2E19 cm^−3, which are substrates for the collectors of insulated-gate bipolar transistors. The signs of the measured Hall co- efficients (R_H) changed from positive to negative at low temperatures. For epilayers with C_Al values of < 3E19 cm^−3, a negative R_H was observed in the hopping conduction region. In contrast, for epilayers with C_Al values of > 3E19 cm^−3, a negative R_H was observed in not only the hopping conduction region but also the band conduction region, which is a striking feature because the movement of free holes in the valence band should make R_H positive. For an epilayer with C_Al of 1.8E20 cm^−3, the sign of R_H clearly changed three times in the band conduction region. Moreover, the activation energies of the temperature-dependent R_H values were similar to those of the temperature-dependent resistivity in the corresponding temperature ranges, irrespective of the conduction mechanisms (band and hopping conduction).

Copper antimony selenium (CuSbSe2) is considered a promising candidate for manufacturing flexible thin film solar cells. However, inappropriate band offset deteriorates the properties of CuSbSe2 solar cell devices. In this work, the effects of Cd1−xZnxS and ZnOyS1−y buffer layers on the performance of CuSbSe2 solar cells were studied with SCAPS simulation. The preliminary structure was designed, and the influence of Zn/(Zn + Cd) ratio, O/(O + S) ratio, thickness, and donor density of Cd1−xZnxS and ZnOyS1−y buffer layers on the performance of the solar cell was then investigated. The conduction band offset (CBO) of the interface between buffer layer and absorber layer was optimized. Efficiency values of 7.81% and 10.26% were obtained for the CuSbSe2 devices with Zn/(Zn + Cd) = 0.5 and O/(O + S) = 0.6, and the thickness of Cd1−xZnxS and ZnOyS1−y buffer layers was 20 nm and 30 nm, respectively.