Motivated by the synthesis of the layered structure CoO2via Li atom deintercalation from LixCoO2, herein, we investigated the electronic structure, lattice dynamics, electron–phonon interaction, and superconductivity of monolayer CoO2 using first-principles calculations. This 2D material was predicted to have a ferromagnetic ground state with a metallic band structure and the total magnetization of 0.83μB. Remarkably, the non-spin polarized calculations show that the monolayer CoO2 possesses phonon-mediated superconductivity at 25–28 K owing to its intermediate to strong electron–phonon coupling (EPC). The rather strong EPC in this compound is mainly driven by the acoustic phonons, making this compound one of the highest-temperature superconductors among the existing 2D materials. Moreover, the CoO2 sheets could be synthesized via exfoliation from bulk CoO2 owing to the relatively small interlayer binding energy while maintaining its stability under normal experimental conditions. Compared to its bulk and bilayer counterparts, monolayer CoO2 was found to have highest EPC.

Molecular orientation techniques are becoming available in the study of elementary chemical processes, in order to highlight those structural and dynamical properties that would be concealed by random rotational motions. Recently successful orientation was achieved for asymmetric-top and chiral molecules of much larger complexity than hitherto. In this work, we report and discuss the correlation between the vectors' photofragment recoil velocity v, transition dipole moment μ, and permanent dipole moment d in a dissociation experiment on hexapole oriented 2-bromobutane, photoinitiated by a linearly polarized laser. The sliced ion images of the Br∗(2P1/2) and Br(2P3/2) photofragments were acquired at 234.0 and 254.1 nm, respectively, by a (2 + 1) resonance-enhanced multiphoton ionization technique. A detailed analysis of the sliced ion images obtained at a tilting angle 45° of laser polarization provides information on the correlation of the three vectors, which are confined by two polar angles α and χ and one azimuthal angle φμd in the recoil frame. The sliced ion images of Br fragments eliminated individually from the enantiomers at 254.1 nm yield an asymmetric factor close to zero; for this reason the photofragment angular distributions do not show significant differences. The elimination of the Br∗ fragment at 234.0 nm is mainly correlated with a parallel transition, giving rise to a large anisotropy parameter of 1.85, and thus can be considered as a single state excitation. The resulting recoil frame angles are optimized to 163° ± 8° and 164° ± 1° for α and χ, respectively, whereas φμd is approaching 0° for the best fit. Since for the present molecule, the three vectors have an only slight spatial arrangement, the photofragment angular distributions of the two enantiomers do not show appreciable differences. Theoretical and computational simulations provide us the basis to state that oriented enantiomers can be discriminated on-the-fly in photodissociation processes even initiated by non-circularly polarized light, provided that the three vectors encountered above have specific three-dimensional arrangements. The fact that Br fragment elimination involves a multi-potential dissociation carries uncertainties in theoretical estimates of the vector direction. Therefore, this work represents a preliminary but significant step on the road to chiral discrimination on-the-fly, which is shown to be best propitiated in molecules where vectors are far from having degenerate mutual angular directions. © 2019 the Owner Societies.

Palladium-copper nanoparticles were placed on activated carbon to give a nanocomposite for electrochemical sensing of riboflavin (vitamin B 2 ). The activated carbon was produced by pyrolysis of natural waste of pistachio nutshells after KOH activation and under a nitrogen atmosphere. The carbons possess a large surface area and micro/meso-porosity. The nanocomposite was characterized by a variety of techniques to confirm structures and morphology. A screen-printed electrode modified with the composite was examined by EIS, CV, DPV, and amperometry. The effects of pH value, scan rate, and stability of the modified electrode were studied. Under optimized conditions, vitamin B 2 displays a well-expressed oxidation peak at −0.15 V (vs. Ag/AgCl) in solutions with a pH value of 7.0. The voltammetric signal increases linearly in the 0.02 to 9 μM concentrations range and a lower detection limit of 7.6 pM. The sensor was successfully applied to the determination of vitamin B 2 even in the presence of other common vitamins and in (spiked) raw milk samples. [Figure not available: see fulltext.]. © 2019, Springer-Verlag GmbH Austria, part of Springer Nature.

Interface engineering of CdS/CZTS(Se) is an important aspect of improving the performance of buffer/absorber heterojunction combination. It has been demonstrated that the crossover phenomenon due to the interface recombination can be drastically eliminated by interface modification. Therefore, in-depth studies across the CdS/CZTS(Se) junction properties, as well as effective optimization processes, are very crucial for achieving high-efficiency CZTSSe solar cells. Here, we present a comprehensive study on the effects of soft-baking (SB) temperature on the junction properties and the corresponding optoelectronic and interface-structural properties. Based on in-depth photoemission studies corroborated with structural and composition analysis, we concluded that interdiffusion and intermixing of CZTSSe and CdS phases occurred on the Cu-poor surface of CZTSSe at elevated SB temperatures, and the interface dipole moments induced by electrostatic potential fluctuation were thus significantly eliminated. In contrast, with low SB temperature, the CdS/CZTSSe heterojunction revealed very sharp interface with very short interdiffusion, forming interface dipole moments and drastically deteriorating device performance. These post thermal treatments also significantly suppress defect energy level of interface measured by admittance spectroscopy from 294 to 109 meV due to CdS/CZTSSe interdiffusion. Meanwhile, the interdiffusion effects on the shift of valence band maximum, conduction band minimum and band offset across the heterojunction of thermally treated CdS/CZTSSe interface are spatially resolved at the atomic scale by measuring the local density of states with cross-sectional scanning tunneling microscopy and spectroscopy. A significant enhancement in the power conversion efficiency from 4.88% to 8.48% is achieved by a facile interface engineering process allowing a sufficient intermixing of CdS/Cd and CZTSSe/Se phases without detrimental recombination centers.

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The present investigation mainly addresses the open circuit voltage (Voc) issue in kesterite based Cu2ZnSn(S,Se)4 solar cells by simply introducing alkali metal fluoride nanolayers (~ several nm NaF, or LiF) to lower the work functions of the front ITO contacts without conventional hole-blocking ZnO layers. Kelvin probe measurements confirmed that the work function of the front ITO decreases from 4.82 to 3.39 and 3.65 eV for NaF and LiF, respectively, resulting in beneficial band alignment for electron collection and/or hole blocking on top electrodes. Moreover, a 10.4% power conversion efficiency (~ 11.5% in the cell effective area) CZTSSe cell with improved Voc of up to 90 mV has been attained. This demonstration may provide a new direction of further boosting the performance of copper chalcogenide based solar cells as well.

Photocatalytic formation of hydrocarbons using solar energy via artificial photosynthesis is a highly desirable renewable-energy source for replacing conventional fossil fuels. Using an l-cysteine-based hydrothermal process, here we synthesize a carbon-doped SnS2 (SnS2-C) metal dichalcogenide nanostructure, which exhibits a highly active and selective photocatalytic conversion of CO2 to hydrocarbons under visible-light. The interstitial carbon doping induced microstrain in the SnS2 lattice, resulting in different photophysical properties as compared with undoped SnS2. This SnS2-C photocatalyst significantly enhances the CO2 reduction activity under visible light, attaining a photochemical quantum efficiency of above 0.7%. The SnS2-C photocatalyst represents an important contribution towards high quantum efficiency artificial photosynthesis based on gas phase photocatalytic CO2 reduction under visible light, where the in situ carbon-doped SnS2 nanostructure improves the stability and the light harvesting and charge separation efficiency, and significantly enhances the photocatalytic activity.

AbstractPorous α-Fe2O3 nanoparticles are directly grown on acid treated carbon cloth (ACC) using a simple hydrothermal method (denoted as ACC-α-Fe2O3) for employment as a flexible and wearable electrochemical electrode. The catalytic activity of ACC-α-Fe2O3 allowing the detection of dopamine (DA) is systematically investigated. The results showed that the ACC-α-Fe2O3 electrode exhibits impressive electrochemical sensitivity, stability and selectivity for the detection of DA. The detection limit determined with the amperometric method appears to be around 50nM with a linear range of 0.074–113μM. The impressive DA sensing ability of the as prepared ACC-α-Fe2O3 electrode is due to the good electrochemical behavior and high electroactive surface area (19.96cm2) of α-Fe2O3 nanoparticles anchored on the highly conductive ACC. It is worth noting that such remarkable sensing properties can be maintained even when the electrode is in a folded configuration.