Publicaciones: Modelización y Simulación

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21

Aug 2017

Development of spontaneous magnetism and half-metallicity in monolayer MoS2

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Half-metallic behavior and ferromagnetism are predicted in strained MoS2 with different light elements adsorbed using density functional theory. We find that strain increases the density of states at the Fermi energy for Y doping (Y = H, Li, and F) at the S sites and strain-driven magnetism develops in agreement with the Stoner mean field model. Strain-driven magnetism requires less strain (3%) for H doping as compared with F and Li doping. No saturation of the spin-magnetic moment is observed in Li-doped MoS2 due to less charge transfer from the Mo d electrons and the added atoms do not significantly increase the Spin–orbit coupling. Half-metallic ferromagnetism is predicted in H and F-doped MoS2. Fixed magnetic moments calculations are also performed, and the DFT computed data is fitted with the Landau mean field theory to investigate the emergence of spontaneous magnetism in Y-doped MoS2. We predict spontaneous magnetism in systems with large (small) mag netic moments for H/F (Li) atoms. The large (small) magnetic moments are atttributed to the electronegativity difference between S and Y atoms. These results suggest that H and F adsorbed monolayer MoS2 is a good candidate for spin-based electronic devices.

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05

Sep 2016

Low variability of single-molecule conductance assisted by bulky metal–molecule contacts

Posted by / in Publicaciones 2016, Publicaciones Modelizacion 2016, Publicaciones: Modelización y Simulación, Últimas Publicaciones CINN / No comments yet

A detailed study of the trimethylsilylethynyl moiety, –C[triple bond, length as m-dash]CSiMe3 (TMSE), as an anchoring group in metal-molecule-metal junctions, using a combination of experiment and density functional theory is presented. It is shown that the TMSE anchoring group provides improved control over the molecule–substrate arrangement within metal|molecule|metal junctions, with the steric bulk of the methyl groups limiting the number of highly transmissive binding sites at the electrode surface, resulting in a single sharp peak in the conductance histograms recorded by both the in situ break junction and I(s) STM techniques. As a consequence of the low accessibility of the TMSE group to surface binding configurations of measurable conductance, only about 10% of gold break junction formation cycles result in the clear formation of molecular junctions in the experimental histograms. The DFT-computed transmission characteristics of junctions formed from the TMSE-contacted oligo(phenylene)ethynylene (OPE)-based molecules described here are dominated by tunneling effects through the highest-occupied molecular orbitals (HOMOs). This gives rise to similar conductance characteristics in these TMSE-contacted systems as found in low conductance-type junctions based on comparably structured OPE-derivatives with amine-contacts that also conduct through HOMO-based channels.

 

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11

May 2016

On determining defects identity in carbon nanotubes using charge probes

Posted by / in Publicaciones 2016, Publicaciones Modelizacion 2016, Publicaciones: Modelización y Simulación, Últimas Publicaciones CINN / No comments yet

A metallic carbon nanotube with point-like defects under influence of a local potential due to a point charge probe is theoretically studied. A combination of density functional theory and the Landauer–Büttiker formalism is used to compute the electronic conductance in the zero-voltage limit. From a collection of the results obtained by varying the probe position around different defects the conductance maps are created. The analysis of the conductance maps allows us to formulate conditions under which several point-like defects (the Stone–Wales defect, a simple carbon vacancy, hydrogen-passivated vacancies) can be distinguished and identified in experiments with the help of scanning probe microscopy.

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