[en] This paper reports that the equilibrium structure of NH₂ has been optimized at the QCISD/6-311++G (3df, 3pd) level. The ground-state NH₂ has a bent (C_2v, X²B₁) structure with an angle of 103.0582°. The geometrical structure is in good agreement with the other calculational and experimental results. The harmonic frequencies and the force constants have also been calculated. Based on the group theory and the principle of microscopic reversibility, the dissociation limits of NH₂(C_2v, X²B₁) have been derived. The potential energy surface of NH₂(X²B₁) is reasonable. The contour lines are constructed, the structure and energy of NH₂ reappear on the potential energy surface

[en] Using the time-dependent multilevel approach (TDMA) and B-splines function, we have calculated the five quantum state population transfer of rydberg lithium atoms. We also analyse the influence of the four major parameters of the frequency-chirped laser pulses field on transition. The result shows that the population can be completely transferred to the target state by changing the parameters of the laser pulse and achieve manual controls to a certain degree. (authors)

[en] Highlights: • The P–Co₃Mo₃C/Co/CNFs has a suitable heterogeneous structure for HER. • The P–Co₃Mo₃C/Co/CNFs possesses large active surface and efficient charge transfer. • The P–Co₃Mo₃C/Co/CNFs exhibits remarkable HER performance in alkaline medium. • It has promising application prospect for different water splitting devices. -- Abstract: Exploring high-performance and low-cost electrocatalysts toward hydrogen evolution reaction aimed at generating hydrogen to alleviate the pressure of energy crisis is of extremely urgent. Herein, we report phosphorus-doped Co₃Mo₃C/Co/CNFs (termed P–Co₃Mo₃C/Co/CNFs) hybrid with unique three-dimensional network structure as efficient hydrogen evolution reaction catalyst. Note that the introduction of P can modulate electronic structure of Mo and Co centers to accelerate hydrogen evolution reaction kinetics. The P–Co₃Mo₃C/Co/CNFs exhibits low onset potential of −19 mV and Tafel slope of 64 mV dec⁻¹ in 1 M KOH. It requires overpotential of only 81 mV to afford a current density of 10 mA cm⁻² and presents long-time stability for more than 40 h at current density of ∼10 mA cm⁻² and ∼50 mA cm⁻². More excellently, this facilely prepared P–Co₃Mo₃C/Co/CNFs catalyst reveals promising application prospect in different kinds of water splitting devices. This work highlights an effective approach to perfect hydrogen evolution reaction catalytic performance via phosphorus-doped.

[en] Highlights: • Microplastic at 1 μm promoted growth of Microcystis aeruginosa. • Microplastic aggregated on algal cell surface and induced oxidative stress. • Larger microplastic promoted more microcystins production. Due to increasingly severe microplastic pollution in freshwaters, the interaction between these contaminants and cyanobacteria warrants study. In this study, we expose the freshwater cyanobacterium Microcystis aeruginosa to different sizes (1 μm and 100 nm) of polystyrene (PS) microplastics of 5 mg/L. Results indicate 1 μm microplastics promote algal growth (12.42% ± 0.94%) at 96 h, and have greater potential to aggregate on algal cell surfaces and inhibit photosynthesis. But no significance was observed in 100 nm microplastics treatment on algal growth and photosynthetic activity after 96 h exposure. Especially, 1 μm microplastics increased the content of intracellular microcystins (MCs) (18.42% ±0.33%) after 72 h and inhibit MCs release (23.87% ±8.79%) at 72 h, while 100 nm PS microplastics promote MCs production only at 48 h (14.83% ± 7.07%). Results indicate that smaller size does not necessarily mean greater toxicity, 1 μm microplastics showing more adverse effects than 100 nm microplastics to M. aeruginosa, improving understanding of the toxicity of microplastics in freshwater ecosystems, and challenging the conventionally held belief that smaller microplastics are more toxic.

[en] In this study, AlGaN/GaN high-electron-mobility transistors (HEMTs) were grown on a GaN template and GaN substrate under the same growth conditions. It was observed that, in the HEMT structure grown on the GaN substrate, mobility decreased because of an increase in the two-dimensional electron-gas (2DEG) density; the origin of these redundant electrons was studied. The 2DEG density decreased with decreasing temperature, this phenomenon closely related to unintentionally induced shallow donors with ionization energy calculated to be around 67.8 meV. After Ⅴ/Ⅲ ratio regulation, the 2DEG density returned to a normal level; this combined with photoluminescence, confirmed for the first time that the abnormal increase of 2DEG density in HEMT structure grown on the GaN substrate is associated with nitrogen vacancies. Therefore, increasing the Ⅴ/Ⅲ ratio is beneficial for obtaining higher mobility by returning the 2DEG density to a normal level. (author)

[en] Electrical properties of In_xAl_1-xN/AlN/GaN structure are investigated by solving coupled Schroedinger and Poisson equations self-consistently. The variations in internal polarizations in In_xAl_1-xN with indium contents are studied and the total polarization is zero when the indium content is 0.41. Our calculations show that the two-dimensional electron gas (2DEG) sheet density will decrease with increasing indium content. There is a critical thickness for AlN. The 2DEG sheet density will increase with In_xAl_1-xN thickness when the AlN thickness is less than the critical value. However, once the AlN thickness becomes greater than the critical value, the 2DEG sheet density will decrease with increasing barrier thickness. The critical value of AlN is 2.8 nm for the lattice-matched In_0.18Al_0.82N/AlN/GaN structure. Our calculations also show that the critical value decreases with increasing indium content.

[en] Using the time-dependent multilevel approach (TDMA), the properties of high excited Rydberg lithium atom have been obtained in the microwave field. The population transfer of lithium atom are studied on numerical calculation, quantum states are controlled and manipulated by microwave field. It shows that the population can be completely transferred to the target state by changing the chirped rate and field amplitude. (authors)

[en] Highlights: • KMnO₄ was first employed to efficiently remove SDM in aquatic environment. • The oligomers of SDM during KMnO₄ oxidation process were first discovered. • Effect of common substances in aquatic environment on removal process was studied. • Theoretical calculation was combined to the laboratory investigation. -- Abstract: The excess sulfadimethoxine (SDM) in the environment could lead to antibiotic resistance by microorganisms and may do harm to many aquatic organisms. In this work, the removal of SDM by potassium permanganate (KMnO₄) was comprehensively studied. The influence of various factors, including the pH, oxidant doses, and temperature, on SDM removal were investigated. The optimal reaction conditions were determined to be pH 5.0, T = 25 °C and [KMnO₄]₀ = 200 μmol L⁻¹. Anions (Cl⁻, SO₄²⁻, HCO₃²⁻, and NO₃⁻) and cations (K⁺, Ca²⁺, Mg²⁺, and NH₄⁺) had no significant influence on the removal of SDM. However, H₂PO₄⁻ improved the efficiency of SDM removal by KMnO₄. Humic acid (0–10 mg L⁻¹) promoted the removal of SDM, which was attributed to the generation of in situ MnO₂. Meanwhile, the degradation of SDM in various water matrices was studied, and the removal order was ultrapure water > Jiuxiang river water ≈ synthetic water > secondary clarifier effluent. According to ten intermediate products identified and a frontier electron densities (FED) calculation, several pathways were proposed that involve the oxidation of amidogen, the cleavage of CS and SN bonds, and an oligomerization reaction. The predicted toxicity assessment indicated that most of the degradation products were not harmful to aquatic organisms except SDM dimers (connection by HNNH), suggesting that byproducts, such as dimers, formed during the oxidation of SDM and other sulfonamides should be taken into consideration. In sum, KMnO₄ has the potential to remove SDM from the aquatic environment.

[en] Using the time-dependent multilevel approach and the B-spline technique, populations of Rydberg lithium atoms in chirped microwave pulses are demonstrated. Firstly the populations of two energy levels are controlled by the microwave pulse parameters. Secondly the atoms experience the consequence 70s-71p-72s-73p-74s in a microwave field using optimized microwave field parameters. It is shown that the coherent control of the population transfer in the microwave field from the initial to the target states can be accomplished by optimizing the microwave field parameters. (authors)

[en] Current collapses were studied, which were observed in AlGaN/GaN high electron mobility transistors (HEMTs) with and without InGaN back barrier (BB) as a result of short-term bias stress. More serious drain current collapses were observed in InGaN BB AlGaN/GaN HEMTs compared with the traditional HEMTs. The results indicate that the defects and surface states induced by the InGaN BB layer may enhance the current collapse. The surface states may be the primary mechanism of the origination of current collapse in AlGaN/GaN HEMTs for short-term direct current stress. (semiconductor devices)