[en] Highlights: • H passivation at the edge greatly enhances the stability of Be_2C nanoribbons. • Stable bare Be_2C nanoribbons are all nonmagnetic semiconductors. • H passivated b-Be_2C-NR with C site terminated edge is half-metallic. • Ground state of H passivated b-Be_2C-NR with C site terminated edge is ferromagnetic. - Abstract: First-principles calculations are carried out to investigate the stability, electronic structure and magnetic properties of Be_2C nanoribbons (Be_2C-NRs) with their ribbon axis along the a and b axes. It is found that except for b-Be_2C-NR with the C site terminated edge, a-Be_2C-NRs and other b-Be_2C-NRs possess good structural stabilities at room temperature. In addition, H passivation enables b-Be_2C-NR with C site terminated edge to stabilize at room temperature by saturating the dangling bonds at edges. Furthermore, stable a-Be_2C-NRs and b-Be_2C-NRs are all nonmagnetic semiconductors and their band gaps are significantly dependent on the edge configuration and the ribbon width. In contrast, H passivated b-Be_2C-NR with C site terminated edge is half-metallic with a magnetic ground state, irrespective of the ribbon width. In particular, H passivated b-Be_2C-NR with C site terminated edge has a strong intra-edge ferromagnetic coupling interaction in the ground state, and an inter-edge ferromagnetic interaction is found in small-width H passivated nanoribbon. The calculated density of states and the spin density distribution show that the p–p hybridization interaction involving polarized electrons is responsible for intra-edge and inter-edge ferromagnetic coupling.

[en] In view of important role of inducing the magnetism in semiconducting transition metal dichalcogenides monolayer, the influences of a series of transition metal and alkaline-earth dopants, including Ca, Sc, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd and In, on the electronic and magnetic properties of semiconducting CrS_2 monolayer are systematically investigated using first-principles calculations. The calculations show that Nb, Mo, Ru and Rh dopants cannot induce the magnetism in doped CrS_2 monolayer, whereas ground states of Ca, Sc, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sr, Y, Zr, Pd, Ag, Cd and In-doped system are magnetic and the stability of magnetic state of V doped system is small. Furthermore the value and the distribution of the magnetic moment induced by dopant not only relate to the number of valence electrons and the occupancy of the d orbitals of dopant, but also depend on the hybridization between dopant and its neighboring S and Cr atoms. Note that it is found that the substitutional doping at the Cr site of CrS_2 monolayer with numerous transition metal and alkaline-earth atoms should be possible under the Cr-poor growth conditions. Overall, the calculated results show high potential for inducing the magnetism in CrS_2 monolayer by doping at the Cr site. - Highlights: • The doping at the Cr site should be possible under the Cr-poor growth conditions. • Ca, Sc, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sr, Y, Zr, Pd, Ag, Cd and In dopants produce magnetism. • Ca, Sc, Ti, V, Zn, Ga, Sr, Y, Zr, Nb, Cd and In dopants result in p-type doping. • Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd and Ag dopants lead to n-type doping

[en] Highlights: • A new PHM with environmental factors and degradation trend as covariates is built. • The complex integrand in reliability function is solved by the Taylor formula. • A real-time updated reliability prediction method is developed based on the PHM. • Numerical study and real case studies show the superiority of the proposed method. Degradation data and lifetime data have been broadly used for assessing product and system reliability. To utilize the two kinds of data simultaneously, the proportional hazard (PH) model with degradation data as a covariate is proposed for reliability analysis. However, most existing works focus on modeling the PH model with degradation state as a covariate, while the degradation trend is ignored, which makes the PH model unable to carry out reliability prediction directly. Confronted with that, a new PH model with the degradation trend and environmental factor as covariates is developed in this paper. The Wiener process is firstly applied to depict the degradation trend, then the degradation trend and temperature are used as covariates to establish the PH model, and a closed-form of the reliability is derived by the Taylor approximation. Based on the degradation data under actual ambient conditions, the real-time updated reliability prediction is provided to guide the health management of products and systems. The simulation study validates that the proposed model outperforms two existing models in terms of Mean Square Error (MSE). Finally, a real-world example of MOSFET is presented to demonstrate the implementation of the proposed method.

[en] Monofilament and 37-filamentary Bi-2223 tapes were fabricated by powder in tube (PIT) process. And the mono-filamentary wires were drawn from ϕ12mm to hexagon 1.51 mm with one and three times intermediate annealing, respectively. The influences of different intermediate annealing times on the core density, morphology and transport properties of Bi-2223 wires and tapes were systematically investigated. It was noticed that the density and the Vickers micro-hardness values of superconducting core on the cross-section of one time annealing wires were higher than those of three times annealing wires. Meanwhile, it was observed that the Ag/oxide core interfaces of the wire with one time annealing were more smooth than those of the three times annealing wire. With the intermediate annealing time decreasing from three to one, the critical current density J _c increased from 17.9 kA/cm² to 20.5 kA/cm². And the enhancement of Jc-B properties suggests the improvement of intergrain connections due to the increasing core density. Meanwhile one time annealing procedure was used to Ag-Au sheathed tape, J _c reached 16.3 kA/cm², this value was also higher than those traditional wires in our previous experiments, which suggests that the decreasing of annealing times during drawing process is also effective in AgAu sheath tapes for the enhancement of current capacity. (paper)

[en] In consideration of importance of enhancing the magnetic anisotropy in ferromagnetic two-dimensional materials for their applications in magnetic data storage and spintronic devices, the structural stability and magnetic stability of FeCl₂ monolayer in the 1T phase (1T-FeCl₂ monolayer) under different strains and the influence of strain on magnetic stability and perpendicular magnetic anisotropy (PMA) of the 1T-FeCl₂ monolayer are investigated using first-principles calculations. It is found that 1T-FeCl₂ monolayer under different strains are stable at the room temperature by calculating the phonon dispersion and ab initio molecular dynamics (MD) simulations. Ferromagnetic is always the ground state of the unstrained and strained 1T-FeCl₂ monolayer under different strains and the ferromagnetic stability can be enhanced by applying compressive strain. The magnetic anisotropy energy (MAE) of the unstrained 1T-FeCl₂ monolayer is positive and the magnetization axis is perpendicular to the 1T-FeCl₂ layer. As compressive strain increases, the positive contribution to MAE from SOC interaction between $d_{x^2-y^2}(d_{\mathit{xy}})$ and $d_{\mathit{yz}}(d_{\mathit{xz}})$ states increase, which lead to the MAE of the 1T-FeCl₂ monolayer can be enhanced. On the contrary, the tensile strain can make the MAE of the 1T-FeCl₂ monolayer weaken. Our results show that strain engineering is an effective approach to enhance PMA of 1T-FeCl₂ monolayer.

[en] Highlights: • The Tb doped AlN nanobelts were fabricated using modified arc discharge method. • The Tb doped AlN nanobelts exhibit an intensive green emission. • The Tb doped AlN nanobelts exhibit ferromagnetism at room temperature. Tb doped AlN (AlN:Tb) nanobelts were prepared by in situ doping of Tb using a plasma-assisted arc discharge method. The structure, composition and morphology of the doped nanobelts were studied by means of X-ray diffraction, scanning and transmission electron microscopy and X-ray photoelectron spectroscopy, revealing that Tb ions have been introduced into the lattice of wurtzite-structured AlN nanobelts. The AlN:Tb nanobelts exhibit distinct emission peaks corresponding to intra-4f electron transitions of Tb³⁺ ions, and room temperature ferromagnetism, which make AlN:Tb nanobelts an excellent candidate for applications in future solid light-emitting diodes and spintronic nanodevices.

[en] Thirty-seven-filamentary AgAu-sheathed Bi-2223 tapes were fabricated by a powder-in-tube (PIT) process. And, the round wires (ϕ 1.86 mm) were rolled to 0.35-mm tapes with 12, 7, 5, and 4 rolling passes through flat rolling, respectively. The influences of different rolling passes on the core density, deformation, and transport properties of Bi-2223/AgAu tapes were systematically investigated. It was noticed that after rolling, the Vickers microhardness of the superconducting core and deform homogeneity along both the horizontal and vertical directions on the cross section of seven-pass rolled tape were better than those on the tapes with other passes, which proved the larger core density and uniform deformation with the seven-pass rolling process. Meanwhile for the wires with 12 and 7 passes, the AgAu/superconducting core interfaces were much flatter. With the rolling passes decreasing from 12 to 4, the critical current density (J_c) first increased and then decreased. Due to the better homogeneity and flatter interfaces, J_c reached the maximum value of 17.3 kA/cm² on the seven-pass sample. Meanwhile, the enhancement of current capacities in magnetic field applied parallel to the Bi-2223/AgAu tape surface could also be recognized as the evidence of improving intergrain connections due to the higher density in seven-pass rolled tapes.

[en] In view of important role of inducing and manipulating the magnetism in two-dimensional materials for the development of low-dimensional spintronic devices, the influences of strain on electronic structure and magnetic properties of commonly observed vacancies doped monolayer MoS₂ are investigated using first-principles calculations. It is shown that unstrained V_S, V_S2, and V_MoS3 doped monolayer MoS₂ systems are nonmagnetic, while the ground state of unstrained V_MoS6 doped system is magnetic and the magnetic moment is contributed mainly by six Mo atoms around V_MoS6. In particular, tensile strain can induce magnetic moments in V_S, V_S2, and V_MoS3 doped monolayer MoS₂ due to the breaking of Mo–Mo metallic bonds around the vacancies, while the magnetization induced by V_MoS6 can be effectively manipulated by equibiaxial strain due to the change of Mo–Mo metallic bonds around V_MoS6 under strains

[en] Highlights: ► Electropolishing was used to obtain smooth surfaces on Ni5W substrates for the preparation of YBCO coated conductors without obvious change of the textures of these Ni5 W substrates. ► Combining the phenomena observed during experiments and electropolishing theories, the electropolishing mechanism in this system has been studied, which is different with that on Ni metals due to the additional tungsten. ► In our theory, H₂WO₄, functioning as the viscous film, plays more important role during the electropolishing than NiO in the selective dissolution. - Abstract: The application of NiW substrates for YBCO coated conductor is hindered due to their roughness of surfaces. It was demonstrated that the smooth NiW substrate surfaces can be obtained through electropolishing in a sulfuric acid electrolyte. In this paper, the parameters in the electropolishing process, such as electrolyte temperature, current density and time, are optimized so as to attain the best surface brightness measured by an atomic force microscopy. The e1ectropolishing mechanism was discussed on the film generated during the electropolishing process. The results suggest that the electropolishing behavior of NiW alloy is under mass-transfer control and H₂WO₄ is the governing factor for the film formation mechanism during anodic dissolution.

[en] Using first-principles calculations, we study the geometrical structure, electronic structure and magnetic properties of substitutionally doped blue phosphorene with a series of nonmetallic atoms, including F, Cl, B, N, C, Si and O. The calculated formation energies and molecular dynamics simulations indicate that F, Cl, B, N, C, Si and O doped blue phosphorene are stable. Moreover, the substitutional doping of F, Cl, B and N cannot induce the magnetism in blue phosphorene due to the saturation or pairing of the valence electron of dopant and its neighboring P atoms. In contrast, ground states of C, Si and O doped blue phosphorene are spin-polarized and the magnetic moments induced by a doping atom are all 1.0 μ_B, which is attributed to the appearance of an unpaired valence electron of C and Si and the formation of a nonbonding 3p electron of a neighboring P atom around O. Furthermore, the magnetic coupling between the moments induced by two C, Si and O are found to be long-range anti-ferromagnetic and the origin of the coupling can be attributed to the p–p hybridization interaction involving polarized electrons. - Highlights: • F, Cl, B, N, C, Si and O doped blue phosphorene are stable. • Substitutional doping of C, Si and O can produce the magnetism in blue phosphorene. • Magnetic coupling between two C, Si and O is long-range anti-ferromagnetic.