T. M. Schmidt

Formation energy of native defects in BN nanotubes: an ab initio study

Electronic and structural properties of several charge states of vacancies, antisites and carbon substitutional impurities in a (10, 0) BN nanotube are investigated through density functional theory calculations. The formation energies indicate that neutral and simply charged states occur in the range of allowable electronic chemical potential. For carbon substitutional impurities, the most probable states are, besides the neutrals, the positively charged state for carbon at a boron site (CB+), and the negatively charged state for carbon at a nitrogen site (CN−). The charge compensation between neighbouring pairs of CB+ and CN− defects is suggested to explain the successful experimentally obtained boron carbonitride nanotubes. Vacancies always present high formation energies. The neutral and positively charged states of the nitrogen antisite show low formation energies. The calculated formation energies for all defects studied here can be interpreted as due to two main effects: a tendency to recover the number of electrons of the defect-free BN nanotube and the screening effects due to the perturbative potential of the defects.

Prediction of two-dimensional topological crystalline insulator in PbSe monolayer.

Two-dimensional (2D) topological crystalline insulator, a new class where states are protected by lattice symmetry instead of by time-reversal symmetry, is predicted in PbSe monolayer based on first-principles electronic structure calculations. A combination of strong spin-orbit interaction with quantum confinement effects in PbSe monolayer lead to a topological phase transition with an even number of band inversion momentum space points. We demonstrate that the PbSe nanostructure presents pairs of spin-polarized Dirac cones coming from the monolayer edges, where each Dirac pair presents a unique spin alignment, leading to a quantum spin Hall system. More importantly, due to the quantum confinement this 2D nanostructure presents larger band gap as compared to its parent narrow band gap trivial insulator bulk PbSe, favoring a room-temperature 2D band gap with crystalline-protected Dirac states at the edges, turning this system interesting to combine nontrivial topological states with nanoelectronic and spintronic applications.

Doping of graphene adsorbed on the a-SiO2 surface

We have performed an ab initio theoretical investigation of a graphene sheet adsorbed on amorphous SiO2 surface (G/a-SiO2). We find that graphene adsorbs on the a-SiO2 surface through van der Waals interactions. The inhomogeneous topology of the a-SiO2 clean surface promotes a total charge density displacement on the adsorbed graphene sheet, giving rise to electron-rich as well as hole-rich regions on the graphene. Furthermore, the adsorbed graphene sheet exhibits a net total charge density gain. In this case, the graphene sheet becomes n-type doped, however, no chemical bonds form at the graphene–SiO2 interface. The electronic charge transfer from a-SiO2 to the graphene sheet occurs upon the formation of a partially occupied level lying above the Dirac point. We find that this partially occupied level comes from the three-fold coordinated oxygen atoms in the a-SiO2 substrate.

Spin texture and magnetic anisotropy of Co impurities in Bi2Se3topological insulators

Based upon first-principles methods, we investigate the magnetic anisotropy and the spin-texture of Co adatoms embedded in the topmost Se network of the topological insulator Bi

Bi covered Si(111) surface revisited

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Antioxidant properties of plant extracts: an EPR and DFT comparative study of the reaction with DPPH, TEMPOL and spin trap DMPO

Se

Effects of extended defects on the properties of intrinsic and extrinsic point defects in silicon

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Topological states ruled by stacking faults in Bi2Se3 and Bi2Te3

surface. We find the formation of energetically stable magnetic moment perpendicular to the surface plane, S

An ab initio study of energetic stability and electronic confinement for different structural phases of ZnO nanowires

_z

On the p-type character of Cd-and Zn-doped InAs nanowires

. Our results for the pristine Bi