We perform first-principles calculations to investigate the roles of silicon vacancy (VSi) and nitrogen impurity in the magnetic properties of silicon carbide (3C-SiC). High-spin configurations are predicted for the negatively-charged (VSi) defects. The coupling is ferromagnetic between the (VSi) defects at −2e charge state, whereas the (VSi) defects at -e charge state prefer to interact antiferromagnetically. Substituting C with N atoms can manipulate the charge states of (VSi) defects and the magnetic interactions between them. Our work offers a possible route toward high Curie temperature (Tc) ferromagnetism in metal-free 3C-SiC materials.
The geometric, electronic, and magnetic properties of titania nanoribbons (TiO 2 NRs) are investigated with use of first-principles calculations within density-functional theory. The TiO 2 NRs formed by cutting ultrathin TiO 2 nanosheet along armchair and zigzag axes have high energetic stability. Zigzag TiO 2 NRs are more preferable than armchair ones. The electronic structures of TiO 2 NRs highly depend on the growth orientation and the ribbon width. Introducing oxygen vacancy defects into the edges of zigzag TiO 2 NRs under poor oxygen conditions can reduce the band gap and trigger the spin-polarization of edge states. These TiO 2 NRs with well-defined atomic structures, high stability, and tunable electronic properties are expected to have potential applications in solar cells, spintronic devices, and sensors.
We performed density-functional theory calculations to study the energetic stability and the electronic structures of negatively-charged nitrogen-silicon-vacancy center (N-VSi)− in cubic silicon carbide (3C–SiC). We show that the (N-VSi)− center is energetically preferable in n-type 3C–SiC and possesses a stable A32 ground state and doubly degenerated E3 excited states. The (N-VSi)− centers prefer to couple weakly in an antiferromagnetic way, triggered by superexchange between them. Our work indicates that 3C–SiC may be an economical candidate material to achieve a solid state qubit operation beyond diamond.
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