2,637 research outputs found
Fe adatoms along Bi lines on H/Si(001): Patterning atomic magnetic chains
The stability, electronic and magnetic properties of Fe atoms adsorbed on the
self-assembled Bi-dimer lines nanostructure on the H/Si(001) surface are
addressed by spin-density functional calculations. Our results show that Fe
adatoms are much more stable on sites closer to the Bi nanolines being able to
form one-dimensional atomic arrays. The most stable structure occurs on a
missing dimer line aside the Bi dimers, which corresponds to an array with
distances between Fe adatoms of about 8 Ang. In this array the irons are
coupled antiferromagnetically with spin magnetic moment of about 1.5 Bohr
magnetons per Fe atom, whereas the coupling exchange interactions is found to
be of 14.4 meV. We also estimate a large magnetic anisotropy energy for the Fe
adatom of about 3 meV/atom. In addition, the electronic band structure of the
Fe array at the most stable structure shows a magnetic half-metal behavior.Comment: 5 pages, 5 figures, accepted in AP
Tellurium vacancy in cadmium telluride revisited: size effects in the electronic properties
The quantum states and thermodynamical properties of the Te vacancy in CdTe
are addressed by first principles calculations, including the supercell size
and quasiparticle corrections. It is shown that the 64-atoms supercell
calculation is not suitable to model the band structure of the isolated Te
vacancy. This problem can be solved with a larger 216-atoms supercell, where
the band structure of the defect seems to be a perturbation of that of the
perfect crystal. It is interesting to note that the Te-vacancy formation energy
calculated with both supercell sizes are close in energy, which is attributed
to error cancelation. We also show that the interplay between supercell size
effects and the band gap underestimation of the generalized gradient
approximation strongly influences the predicted symmetry of some charge states.Comment: 9 pages, 7 figure
Energetics and Electronic Properties of Interstitial Chlorine in CdTe
Indexación: Scopus.We acknowledge support from Chilean funding agency FONDECYT under Grants No. 1170480 (W.O.) and 1171807 (E.M-P.). Powered@NLHPC: This research was partially supported by the supercomputing infrastructure of the NLHPC (ECM-02).The role of interstitial chlorine in the electronic properties of CdTe is addressed by density functional theory calculations including hybrid functionals and large unit cells. The stability and diffusion energy barriers of the impurity are analyzed as a function of the Fermi level position in the band gap. Chlorine is found to be stable in at least five interstitial sites with rather close formation energies, suggesting that they are all probable to be found. In p-type CdTe, the most stable sites are at the center of a CdTe bond and at a split-interstitial configuration, both acting as shallow donors. Whereas in n-type CdTe, it is found at the tetrahedral site surrounded by Cd hosts, acting as a shallow acceptor. We also find that chlorine can induce a deep acceptor level in the bandgap after binding with three Cd host atoms, which can explain the experimentally observed high resistivity in Cl-doped CdTe. The energy barriers for chlorine diffusion in both p-type and n-type CdTe are also discussed. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheimhttps://onlinelibrary.wiley.com/doi/full/10.1002/pssb.20180021
Noncovalent functionalization of carbon nanotubes and graphene with tetraphenylporphyrins: stability and optical properties from ab initio calculations
The stability, electronic and optical properties of single-walled carbon nanotubes (CNTs) and graphene noncovalently functionalized with free-base tetraphenylporphyrin (TPP) molecules is addressed by density functional theory calculations, including corrections to dispersive interactions. We study the TPP physisorption on 42 CNT species, particularly those with chiral indices (n,m), where 5≤n≤12 and 0≤m≤n. Our results show a quite strong π-π interaction between TPP and the CNT surface, with binding energies ranging from 1.1 to 1.8 eV, where higher energies can be associated with increasing CNT diameters. We also find that the TPP optical absorptions would not be affected by the CNT diameter or chirality. Results for the TPP physisorption on graphene show a remarkable stability with binding energy of 3.2 eV, inducing a small redshift on the π-stacked TPP absorption bands. The strong graphene-TPP interaction also induces a charge transfer from TPP to graphene, indicating a n-type doping mechanism without compromising the graphene structure
Endohedral terthiophene in zigzag carbon nanotubes: Density functional calculations
The inclusion and encapsulation of terthiophene (T3) molecules inside zigzag
single-walled carbon nanotubes (CNTs) is addressed by density functional
calculations. We consider the T3 molecule inside five semiconducting CNTs with
diameters ranging from 9.6 to 12.7 Ang. Our results show that the T3 inclusion
process is exothermic for CNTs with diameters larger than 9.5 Ang. The highest
energy gain is found to be of 2 eV, decreasing as the CNT diameter increases.
This notable effect of stabilization is attributed to the positively charged
CNT inner space, as induced by its curvature, which is able to accommodate the
neutral T3 molecule. The band structure of the T3@CNT system shows that T3
preserves its electronic identity inside the CNTs, superimposing their
molecular orbitals onto the empty CNT band structure without hybridization. Our
results predict that the electronic states added by the T3 molecules would give
rise to optical effects and nonradiative relaxation from excited states.Comment: 5 pages, 5 figures, 1 table, accepted in PR
- …