Multi-functional spintronic devices based on boron- or aluminum-doped silicene nanoribbons

First-principles study of strain on BN-doped arsenene

The effects of B, N, and BN doping of arsenene and different strains on the stability, electronic structure, and optical properties of BN-doped arsenene were investigated using a first-principles approach. It was found that B, N, and BN doping caused the bandgap of arsenene to shift from indirect-direct, and strong charge transfer occurred between arsenene and B, N, and BN, and the transfer between N atoms and arsenene was more intense. The binding energy of the BN-doped arsenene system is always negative at different strains and in a stable state, but the stability of the structure is gradually decreasing. The bandgap of the BN-doped arsenene system shows a trend of decreasing, then increasing, and then decreasing under different tensile and compressive deformations. The only difference is that the tensile deformation continues to increase the bandgap at 2%, while the compressive deformation decreases the bandgap. The p-state electrons of the As atom near the Fermi energy level make the main contribution to the BN-doped arsenene system, and the p-state electrons of the B atom have some contribution. Red shifting occurs at the absorption and reflection peaks for doped systems with tensile deformation of 1% to 5%, and the absorption and reflection peaks for doped systems with compressive deformation of - 1% to - 5%.

Magnetism in Au-Supported Planar Silicene

The adsorption and substitution of transition metal atoms (Fe and Co) on Au-supported planar silicene have been studied by means of first-principles density functional theory calculations. The structural, energetic and magnetic properties have been analyzed. Both dopants favor the same atomic configurations with rather strong binding energies and noticeable charge transfer. The adsorption of Fe and Co atoms do not alter the magnetic properties of Au-supported planar silicene, unless a full layer of adsorbate is completed. In the case of substituted system only Fe is able to produce magnetic ground state. The Fe-doped Au-supported planar silicene is a ferromagnetic structure with local antiferromagnetic ordering. The present study is the very first and promising attempt towards ferromagnetic epitaxial planar silicene and points to the importance of the substrate in structural and magnetic properties of silicene.

Vacancy tuned thermoelectric properties and high spin filtering performance in graphene/silicene heterostructures

The main contribution of this paper is to study the spin caloritronic effects in defected graphene/silicene nanoribbon (GSNR) junctions. Each step-like GSNR is subjected to the ferromagnetic exchange and local external electric fields, and their responses are determined using the nonequilibrium Green's function (NEGF) approach. To further study the thermoelectric (TE) properties of the GSNRs, three defect arrangements of divacancies (DVs) are also considered for a larger system, and their responses are re-evaluated. The results demonstrate that the defected GSNRs with the DVs can provide an almost perfect thermal spin filtering effect (SFE), and spin switching. A negative differential thermoelectric resistance (NDTR) effect and high spin polarization efficiency (SPE) larger than 99.99% are obtained. The system with the DV defects can show a large spin-dependent Seebeck coefficient, equal to S_s ⁓ 1.2 mV/K, which is relatively large and acceptable. Appropriate thermal and electronic properties of the GSNRs can also be obtained by tuning up the DV orientation in the device region. Accordingly, the step-like GSNRs can be employed to produce high efficiency spin caloritronic devices with various features in practical applications.

Largely enhanced thermoelectric effect and pure spin current in silicene-based devices under hydrogen modification

Based on the density functional theory and nonequilibrium Green's function methods, we launch a systematic study of the magnetic properties and thermoelectric effects in silicene-based devices constructed by using zigzag silicene nanoribbons (ZSiNRs). By modulating the adsorption site, it is found that the ground state of ZSiNRs varies from an antiferromagnetic state to a ferromagnetic state. Meanwhile, a spin-degenerate semiconductor evolves into a spin semiconductor. The spin and charge thermoelectric figure of merits have an almost equal value of about 60 in the narrow device, which originates from the spin-dependent conductance dips and high spin-filtering effects. Moreover, a thermally-driven pure spin current in the silicene-based devices is obtained in the absence of the gate voltage, and its magnitude is effectively enhanced as the device width increases. Our results suggest that the silicene-based devices have very good prospects for spin caloritronics.

The half-metallicity and the spin filtering, NDR and spin Seebeck effects in 2D Ag-doped SnSe2 monolayer

Two-dimensional SnSe₂ has become more and more attractive due to the excellent electronic, optoelectronic, and thermoelectric properties. However, the study on magnetic properties is rare. Inspired by the recent experimental synthesis of SnSe₂ monolayer and Ag-doped SnSe₂ thin films, we use the first-principles calculations combined with the nonequilibrium Green's function method to investigate the structural, electronic, magnetic, and spin transport properties of an Ag-doped SnSe₂ monolayer. It is found that the doped system exhibits half-metallic ferromagnetism with the energy gap of about 0.5 eV in the spin-down channel. The spin-polarized transport properties based on Ag-doped SnSe₂ monolayers show an excellent spin filtering effect and a negative differential resistance effect under a bias voltage. Interestingly, under a temperature gradient, the spin Seebeck effect and the temperature-controlled reverse of spin polarization are also observed. These perfect spin transport properties can be understood from the calculated spin-polarized band structure and the spin-polarized transport spectrum. These studies indicate the potential spintronic and spin caloritronic applications for Ag-doped SnSe₂ monolayer.