Strain controllable band alignment and the interfacial and optical properties of tellurene/GaAs van der Waals heterostructures.

By using first principles calculations, we theoretically investigate the electronic structures and the interfacial and optical properties of the two-dimensional tellurene (Te)-gallium arsenide (GaAs) van der Waals heterostructures (vdWHs), i.e., α-Te/GaAs and γ-Te/GaAs, formed using Te and GaAs monolayers. It has been demonstrated that, the semiconductor-semiconductor contacted α-Te/GaAs vdWH exhibits a type-II band alignment with a direct band gap of 0.28 eV while the metal-semiconductor contacted γ-Te/GaAs vdWH has a p-type Schottky contact with a Schottky barrier height (SBH) of 0.36 eV at the interface. The transition from type-II to type-III band alignment is observed firstly in the α-Te/GaAs vdWH when the in-plane biaxial strain is less than -5.2% and larger than 4.4%, meanwhile, the p-type Schottky contact to Ohmic contact transition may be realized in the γ-Te/GaAs vdWH when the in-plane biaxial strain is less than -2.4%. Finally, the maximum optical absorption coefficients of the α- and γ-Te/GaAs vdWHs have been found to be up to 31% and 29%, respectively, and may be modulated effectively by applying in-plane biaxial strain. The obtained results may be of importance in the design of nanoelectronic devices based on the proposed tellurene/GaAs vdWHs.

Robust photogalvanic effect, full spin polarization and pure spin current in the BiC photodetector by vacancy- and substitution-doping.

The photogalvanic effects (PGEs) in low-dimensional devices have attracted great interests recently. Herein, based on non-equilibrium Green's function combined with density functional theory, we investigated spin-dependent PGE phenomena in the BiC photodetector for the case of linearly polarized light and zero bias. Due to the presence of strong spin-orbital interaction (SOI) and C3v symmetry for the BiC monolayer, the armchair and zigzag BiC photodetectors produce robust spin-dependent PGEs which possess the cos(2θ) and sin(2θ) relations on the photon energies. Especially, the armchair and Bi-vacancy armchair BiC photodetector can produce fully spin polarization, and pure spin current was found in the armchair and zigzag BiC photodetector. Furthermore, after introducing the Bi-vacancy, C-vacancy, Bi-doping and C-doping respectively, corresponding armchair and zigzag BiC photodetector can produce higher spin-dependent PGEs for their Cs symmetry. Moreover, the behaviors of spin-dependent photoresponse are highly anisotropic and can be tuned by the photon energy. This work suggested great potential applications of the BiC monolayer on PGE-driven photodetectors in low energy-consumption optoelectronics and spintronic devices. .

A graphene-like semiconducting BC2P monolayer as a promising material for a Li-ion battery and CO2 adsorbent.

Searching for high-performance anode materials and CO2 adsorption materials are key factors for next-generation renewable energy technologies and mitigation of the greenhouse effect. Herein, we report a novel two-dimensional (2D) BC2P monolayer with great potential as an anode material for lithium-ion batteries (LIBs) and as a material for CO2 adsorption. The adsorption energies of Li atoms and CO2 molecules on the BC2P supercell are negative enough to assure stability and safety under operating conditions. More intriguingly, the BC2P monolayer possesses a very high theoretical capacity of 1018.8 mA g h-1 for LIBs. In addition, the diffusion energy barriers of Li on the BC2P supercell are 0.26 and 0.87 eV, showing good charge/discharge capability, and the electrode potential of Li is beneficial to their performance as an anode material. Moreover, four chemical and three physical adsorption sites were verified, indicating that the CO2 molecule was effectively adsorbed on the BC2P supercell. These desirable properties make the BC2P monolayer a promising 2D material for application in LIBs and for CO2 adsorbents aimed at highly efficient CO2 capture.

Spin-filtering and rectification effects in a Z-shaped boron nitride nanoribbon junction.

A Z-shaped junction constructed by a few-nanometer-long armchair-edged boron nitride nanoribbon (ABNNR) sandwiched between two semi-infinite zigzag-edged BNNR electrodes with different hydrogen-passivated edge treatment is proposed, and its spin-dependent electronic transport is studied by ab initio calculations. It is found that a short ABNNR exhibits metallic behavior and can be used as a conduction channel. Interestingly, the spin-filtering and rectification effects exist in the junctions without any edge passivation or with boron-edge passivation. The analysis on the projected density of states and spatial distribution of molecular projected self-consistent Hamiltonian eigenstates gives an insight into the observed results for the system. Our results suggest that a BNNR-based nanodevices with spin-filtering and rectification effects may be synthesized from an hexagonal boron nitride sheet by properly tailoring and edge passivation.

Identification of Preisach Model Parameters Based on an Improved Particle Swarm Optimization Method for Piezoelectric Actuators in Micro-Manufacturing Stages.

The Preisach model is a typical scalar mathematical model used to describe the hysteresis phenomena, and it attracts considerable attention. However, parameter identification for the Preisach model remains a challenging issue. In this paper, an improved particle swarm optimization (IPSO) method is proposed to identify Preisach model parameters. Firstly, the Preisach model is established by introducing a Gaussian-Gaussian distribution function to replace density function. Secondly, the IPSO algorithm is adopted to Fimplement the parameter identification. Finally, the model parameter identification results are compared with the hysteresis loop of the piezoelectric actuator. Compared with the traditional Particle Swarm Optimization (PSO) algorithm, the IPSO algorithm demonstrates faster convergence, less calculation time and higher calculation accuracy. This proposed method provides an efficient approach to model and identify the Preisach hysteresis of piezoelectric actuators.

Symmetry-dependent spin-charge transport and thermopower through a ZSiNR-based FM/normal/FM junction.

We investigate the spin-dependent transport and spin thermopower for a zigzag silicene nanoribbon (ZSiNR) with two ends covered by ferromagnets (FMs) under the modulation of a perpendicular electric field, where we take the 6- and 7-ZSiNR to exemplify the effect of the even- and odd-N ZSiNRs, respectively. By using the nonequilibrium Green's function approach, it is demonstrated that a ZSiNR-based FM/normal/FM junction still shows an interesting symmetry-dependent property although the σ mirror plane is absent for any ZSiNR due to the buckled structure of silicene. The junction with even- or odd-N ZSiNR has very different transport and thermopower behavior, which is attributed to the different parity of π and [Formula: see text] band wavefunctions under the c 2 symmetry operation with respect to the centre axis between two edges, and is linked to the unique symmetry of the band structure for the ribbon. As a result, the magnetoresistance (MR) for the 6-ZSiNR junction with a 100% plateau around zero electron energy is observed, but the plateau is absent for the 7-ZSiNR one. In addition, the spin thermopower also displays the even-odd behaviour. The 6-ZSiNR junction is found to possess superior thermospin performance compared with the 7-ZSiNR one, and its spin thermopower can be improved by one order of magnitude in the absence of an electric field. As the strength of the field increases, the spin thermopower for the 6-ZSiNR junction dramatically decreases, while it notably enhances for the 7-ZSiNR one. Interestingly, the spin thermopower for both junctions is strongly dependent on the strength of magnetisation in FM, and it can be very pronounced with a maximum absolute value of 200 µV K(-1)by the optimisation of the parameters. However, with the increase in temperature, the spin thermopower for the 6-ZSiNR junction decreases, but the situation for the 7-ZSiNR one is opposite. Finally, the spin figure of merit for the 6-ZSiNR junction is found to be four orders of magnitude larger than that for the 7-ZSiNR one. This even-odd effect is common for N-SiNR, and the result can be regarded as an advance in the understanding of the characteristics of silicene and may be valuable for experimentally designing spin valve and heat spintronic devices based on silicene.