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A first principles investigation of the electronic properties of narrow silicon carbon nanoribbons (SiC NRs) having zigzag-shaped edges passivated by hydrogen is presented. It is found that the zigzag SiC NRs exhibit interesting behavior. When an external transverse electric field is applied, the zigzag SiC NRs are converted to ferromagnetic metal from magnetic semiconductor. Interestingly, the magnetization direction depends on the field direction; i.e., the field direction is reversed, and the magnetization direction inverses. Thus, the ZSiC NRs may be utilized for spintronic devices by rendering the enhanced magnetization and changing the spin orientation.

Based on density functional theory and nonequilibrium Green's function method, we systematically investigated the hydrogenated effects on the stability, electronic and magnetic properties, as well as electronic spin transport property of an N chains zigzag silicon carbide nanoribbon (N-ZSiC NR). Our calculated results indicate that by controlling the hydrogen content of the environment, one can get three types of stable edge hydrogenated ZSiC NRs. They are: (a) each edge Si and C atom bonded with one hydrogen atom (N-ZSiC-1H1H), (b) each edge Si atom bonded with two H atoms and each edge C bonded with one H atom (N-ZSiC-2H1H), and (c) each edge Si and C atom bonded with two H atoms (N-ZSiC-2H2H). It was unexpectedly found that N-ZSiC-1H1H NR, which has been studied theoretically to a large extent, is stable only at extremely low ultravacuum pressures. Under more standard conditions, the most stable edge hydrogenated structure is N-SiC-2H2H NR. More interestingly, when N # 4, the N-ZSiC-2H2H NR is a nonmagnetic semiconductor, while when 5 # N # 7, it is a ferrimagnetic ferromagnetic semiconductor. When N $ 8, the N-SiC-2H2H NR turns into a ferrimagnetic half-metallic. As regards the N-ZSiC-2H1H NR, when N # 12, it is a ferromagnetic semiconductor, while when N $ 13, it becomes a ferromagnetic half-metallic. These results manifest that by controlling the hydrogen content of the environment and the temperature, as well as the ribbon width N, one can precisely modulate the electronic and magnetic properties of N-ZSiC NRs, which endows ZSiC NRs with many potential applications in spintronics and nanodevices.

By means of first-principles calculations we predict that it is possible to manipulate the magnetization and magnetization direction in narrow zigzag silicon carbon nanoribbons (ZSiC NRs) by carrier (hole and electron) doping. Without doping, the ground state of the ZSiC NRs wider than 0.6 nm is ferrimagnetic with local magnetic moments at the edge atoms C and Si that are passivated by the hydrogen atoms, and their orientations are parallel at each zigzag edge and are antiparallel between the two edges. Consequently, the magnetic moment per cell of the ZSiC NR is almost zero. It is found that the hole doping enhances the local magnetic moment at the edge C atoms, but weakens the local magnetic moment at the edge Si atoms. As a result, the ZSiC NR is magnetized, and the magnetization direction conforms to the local magnetic moment at the edge C atoms. In contrast, the electron doping weakens the local magnetic moment at the edge C atoms, while it enhances the local magnetic moment at the edge Si atoms. As a result, the ZSiC NR is also magnetized, and the magnetization direction conforms to the local magnetic moment at the edge Si atoms. Thus, the magnetization direction of the ZSiC NRs depends on the type of carrier doping.

Two-dimensional van der Waals (vdW) heterojunctions have been regarded as promising candidates for photocatalytic water splitting and solar energy conversion. Here, we propose a two-dimensional GeC/GaN vdW heterostructure, where the GaN monolayer and the GeC monolayer are stacked. The binding energy, phonon spectrum, and elastic constants demonstrate this material’s high dynamic and mechanical stability. Most notably, the GW band structure, GW + Bethe–Salpeter equation (BSE) optical absorption spectrum, and the band alignment of the density functional theory (DFT) scheme and empirical formula reveal that the GeC/GaN vdW heterostructures have a dramatically high optical absorption coefficient (∼105 cm–1) in the visible region and a suitable band edge with sufficiently large kinetic overpotentials of the hydrogen evolution reaction (ΔE c ≥ 1.945 eV) and the oxygen evolution reaction (ΔE v ≥ 1.244 eV). Photogenerated electrons and holes aggregate on the GeC monolayer and GaN monolayer surfaces, respectively, which could make this heterojunction a promising candidate for photocatalytic water splitting and solar energy conversion.

The edge reconstruction effect of the zigzag silicon carbide nanoribbons (zz SiC NRs) to a stable line of alternatively fused seven and five membered rings without and with H passivation have been studied using first principles density functional theory (DFT). The both side's edges of the pristine SiC are respectively terminated by Si and C atoms and are called the Si-edge and the C-edge, respectively. In the un-passivated systems, the C-edge reconstructed (Crc) could effectively lower the edge energy of the system, while the Si-edge reconstructed (Sirc) could raise the edge energy of the system. Thus, the Crc edge is the best edge for the edge reconstruction of the system, while the both edge reconstructed (brc) system is the metastability. Moreover, the brc system has a nonmagnetic metallic state, whereas the Crc system, as well as Sirc system, has a ferromagnetic metallic state. The edge reconstructed destroys the magnetic moment of the corresponding edge atoms. The magnetic moment arises from the unreconstructed zigzag edges. The pristine zz edge system has a ferrimagnetic metallic state. However, in the H-passivated systems, the unreconstructed zigzag edge (zz-H) is the best edge. The Crc-H system is the metastability. The Sirc-H system has only slightly higher energy than the Crc-H system, whereas the brc-H system of the pristine SiC NR has the highest edge energy. Thus, the H passivation would prevent the occurrence of edge reconstruction. Moreover, H passivation induces a metal-semiconductor transition in the zz and brc SiC NRs. Additionally, except for brc-H system which has non-magnetic semiconducting state, the zz-H, Crc-H, and Sirc-H systems have the magnetic state.

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