[en] Both high and low frequency relaxation oscillations have been observed in an argon capacitive discharge connected to a peripheral grounded chamber through a slot with dielectric spacers. The oscillations, observed from time-varying optical emission of the main discharge chamber, show, for example, a high frequency (46 kHz) relaxation oscillation at 100 mTorr, with an absorbed power near the peripheral breakdown, and a low frequency (2.7–3.7 Hz) oscillation, at a higher absorbed power. The high frequency oscillation is found to ignite a plasma in the slot, but usually not in the periphery. The high frequency oscillation is interpreted by using an electromagnetic model of the slot impedance, combined with the circuit analysis of the system including a matching network. The model is further developed by using a parallel connection of variable peripheral capacitance to analyse the low frequency oscillation. The results obtained from the model are in agreement with the experimental observations and indicate that a variety of behaviours are dependent on the matching conditions. (fluids, plasmas and electric discharges)

[en] Based on the first-principles plane wave calculations, we show that Li adsorbed on monolayer and bilayer MoS₂ forming a uniform and stable coverage can serve as a high-capacity hydrogen storage medium, and Li-coated MoS₂ can be recycled by operations at room temperature due to Li having strength binding, big separation and is stable against clustering. The full Li coverage MoS₂ system (2*2 hexagonal MoS₂ supercell) can reach up to eight H₂ molecules on every side, corresponding to the gravimetric density of hydrogen storage up to 4.8 wt% and 2.5 wt% in monolayer and bilayer MoS₂, respectively. The adsorption energies of hydrogen molecules are in the range of 0.10eV/H₂–0.25 eV/H₂, which are acceptable for reversible H₂ adsorption/desorption near ambient temperature. In addition, compared with light metals decorated low dimension carbon-based materials, the sandwiched structure of MoS₂ exhibits the greatly enhanced binding stability of Li atoms as well as slightly decreased Li-Li interaction and thus avoids the problem of metal clustering. It is interesting to note that the Li atom apart from the electrostatic interaction, acts as a bridge of hybridization between the S atoms of MoS₂ and adsorbed H₂ molecules. The encouraging results show that such light metals decorated with MoS₂ have great potential in developing high performance hydrogen storage materials. (paper)

[en] Two-dimensional (2D) semiconductors with desirable bandgaps and high carrier mobility have great potential in electronic and optoelectronic applications. In the present work, 2D M-ScN, H-ScN, and O-ScN are predicted by the swarm-intelligent global structure search method. The low formation energies and high dynamical and thermal stabilities indicate the high feasibility of experimental synthesis of these ScN monolayers. The electronic structure calculations reveal that M-ScN and O-ScN are both direct bandgap semiconductors with the bandgaps of 1.39 and 2.14 eV, respectively, while H-ScN has a large indirect bandgap of 3.21 eV. In addition, both M-ScN and H-ScN exhibit ultra-high electron mobilities (3.09 × 10⁴ cm² V⁻¹ s⁻¹ and 1.22 × 10⁴ cm² V⁻¹ s⁻¹, respectively). More notably, O-ScN is found to be a promising 2D auxetic and ferroelastic material. The values of negative Possion’s ratios and reversible strain of this monolayer are predicted to be −0.27% and 15%, respectively. (paper)

[en] Highlights: • The electrochemical activation of Ni(OH)₂ was investigated. • A wet treatment was proposed to fabricate Ni(OH)₂/Ni foam. • The electrochemical performance of Ni(OH)₂ is mainly determined by activation process. • A high-capacity Ni(OH)₂/Ni electrode was fabricated by combining GCD activation and wet treatment. -- Abstract: Nickel hydroxide (Ni(OH)2), as a representative of highly active materials, has been widely studied and applied in the field of energy storage. However, a typical electrochemical activation process is often required before its practical application. Thus, exploring this key activation process is of great significance for the construction of high-capacity Ni(OH)2 electrodes. In this work, we find that the activation of galvanostatic charge-discharge (GCD) is apparently different from that of cyclic voltammetry (CV). After activation, the composition of Ni(OH)2 deposited on the surface of Ni foam prepared by GCD and CV process is the same, but the morphology is obviously different. The layered porous network Ni(OH)2 nanostructures can be prepared by GCD process, while the spherical stacking nanostructures can be formed by CV process. By combining a wet process, two adhesive Ni(OH)2-coated Ni foam (Ni(OH)2/Ni) electrodes can be successfully fabricated. The results exhibit that the Ni(OH)2/Ni electrode obtained by the GCD process shows super energy storage capacity (2338.9 μA h cm-2 (3402 F g-1)) at a high loading mass of Ni(OH)2, which is almost 1.7 times higher than that of the CV-activated electrode (1380.6 μA h cm-2 (2008 F g-1)).

[en] The probe of flexible molecular conformation is crucial for the electric application of molecular systems. We have developed a theoretical procedure to analyze the couplings of molecular local vibrations with the electron transportation process, which enables us to evaluate the structural fingerprints of some vibrational modes in the inelastic electron tunneling spectroscopy (IETS). Based on a model molecule of Bis-(4-mercaptophenyl)-ether with a flexible center angle, we have revealed and validated a simple mathematical relationship between IETS signals and molecular angles. Our results might open a route to quantitatively measure key geometrical parameters of molecular junctions, which helps to achieve precise control of molecular devices

[en] Highlights: • Li, Na, K, Ca and Fe adsorbed on graphene were tend to form stable structures. • Diffusion occurs very possible on Cu and Ag adsorbed graphene. • The electronic properties of graphene was significantly altered by Fe, Cu and Ag. • We found the WF of Ag + graphene and Fe + graphene were increasing. Based on density functional theory (DFT), we studied the structural and electronic properties of seven different metal atoms adsorbed on graphene (M + graphene). The geometries, adsorption energies, density of states (DOS), band structures, electronic dipole moment, magnetic moment and work function (WF) of M + graphene were calculated. The adsorption energies ΔE indicated that Li, Na, K, Ca and Fe adsorbed on graphene were tending to form stable structures. However, diffusion would occur on Cu and Ag adsorbed on graphene. In addition, the electronic structure near the Fermi level of graphene was significantly affected by Fe (Cu and Ag), compared with Li (Na, K and Ca). The electronic dipole moment and magnetic moment of M + graphene were sensitive to the adsorbed metal atoms. Moreover, we found electropositive (electronegative) adsorption can decrease (increase) the WF of the surface. Specially, the WF of Ag + graphene and Fe + graphene would increase because surface dipole moment make a contribution to electron.

[en] The core-hole excitation spectra—near-edge x-ray absorption spectroscopy (NEXAFS), x-ray emission spectroscopy (XES), and x-ray photoelectron spectroscopy (XPS) shake-up satellites have been simulated at the level of density functional theory for the azafullerene C₅₉N and its derivatives (C₅₉N)⁺, C₅₉HN, (C₅₉N)₂, and C₅₉N–C₆₀, in which the XPS shake-up satellites were simulated using our developed equivalent core hole Kohn-Sham (ECH-KS) density functional theory approach [B. Gao, Z. Wu, and Y. Luo, J. Chem. Phys. 128, 234704 (2008)] which aims for the study of XPS shake-up satellites of large-scale molecules. Our calculated spectra are generally in good agreement with available experimental results that validates the use of the ECH-KS method in the present work. The nitrogen K-edge NEXAFS, XES, and XPS shake-up satellites spectra in general can be used as fingerprints to distinguish the azafullerene C₅₉N and its different derivatives. Meanwhile, different carbon K-edge spectra could also provide detailed information of (local) electronic structures of different molecules. In particular, a peak (at around 284.5 eV) in the carbon K-edge NEXAFS spectrum of the heterodimer C₅₉N–C₆₀ is confirmed to be related to the electron transfer from the C₅₉N part to the C₆₀ part in this charge-transfer complex

[en] Highlights: • Porous rGO/NiCo₂O₄ hybrid nanostructures are fabricated for supercapacitor. • The specific capacity of rGO/NiCo₂O₄ can reach 4.37 F cm⁻² by combining capacitive and faradaic storage mechanisms. • The hybrid nanostructure has good componential and structural reversibility during long-term cycling process. • Our experimental and theoretical results give a suggestion on designing optimal structures for electrode materials. - Abstract: Supercapacitors show ultrafast charging-discharging rates but extremely high powers that can address emerging energy needs, in particular for the high specific power and portable energy conversion/storage devices. Herein, we report a novel hybrid electrode material based on complementary components of NiCo₂O₄ nanowires and reduced graphene oxide (rGO) for high performance supercapacitor application by combining capacitive and faradaic materials and storage mechanisms. The unique heterostructured rGO/NiCo₂O₄ nanostructures exhibit high specific capacitance (up to 4.37 F cm⁻² (1248 F g⁻¹), measured at the current density of 2 mA cm⁻² with loading of active materials 3.5 mg cm⁻²) and excellent cycling stability with capacitance retention of 90% after 2000 charge-discharge cycles as well as high rate capability. Due to the difference of work function, the interfacial polarization not only allow the effective adsorption/desorption of the electrolyte ions at the surface of rGO to improve electrochemical double-layer capacitance (EDLC), but also provide both electrolyte ions storage site and transport pathway to facilitate the Faradaic redox reactions near the surface of NiCo₂O₄. The encouraging results show that such hybrid nanostructure combining capacitive and faradaic materials and storage mechanisms have great potential in developing high performance electrochemical supercapacitors.