Showing 1–8 of 8 results for author: Soto, G

Study on the formation and the decomposition of AgN3 and a hypothetical compound ReN3 by using density functional calculations

Authors: G. Soto

Abstract: We present a comparative study between ReN3 and AgN3 by using density functional theory. The ReN3 is a hypothetical compound proposed by us to interpret the Re to Re interplanar spacing of thin films grown by sputtering. Both, the AgN3 as the ReN3, are calculated as positive enthalpy compounds. The enthalpy might give a clue about the spontaneous decomposition of the solid form, but it cannot be i… ▽ More We present a comparative study between ReN3 and AgN3 by using density functional theory. The ReN3 is a hypothetical compound proposed by us to interpret the Re to Re interplanar spacing of thin films grown by sputtering. Both, the AgN3 as the ReN3, are calculated as positive enthalpy compounds. The enthalpy might give a clue about the spontaneous decomposition of the solid form, but it cannot be interpreted as a restriction of its synthesizability. As from the calculated total-energy, we discuss the route for the formation of AgN3 starting from atomic species in aqueous solution. We propose that their synthesizability is conditioned by the energy of free nitrogen atoms, and the kinetics of reaction. We conclude that the intrinsic stability of a certain atomic arrangement depends only of the equilibrium of atomic forces, and not from the energy value associated with that structure. △ Less

Submitted 7 November, 2012; originally announced November 2012.

Comments: 4 figures, 3 tables

Synthesis of ReN3 thin films by magnetron sputtering

Authors: G. Soto, H. Tiznado, W. de la Cruz, A. Reyes

Abstract: Recently was reported a novel compound between rhenium and nitrogen, announced with ReN2 composition. This compound was synthesized by the high temperature and high pressure method. We found that the diffraction peaks of this compound are in agreement with the x-ray pattern of a rhenium-nitrogen film, under the assumption that the film is oriented on the substrate. The film was prepared by reactiv… ▽ More Recently was reported a novel compound between rhenium and nitrogen, announced with ReN2 composition. This compound was synthesized by the high temperature and high pressure method. We found that the diffraction peaks of this compound are in agreement with the x-ray pattern of a rhenium-nitrogen film, under the assumption that the film is oriented on the substrate. The film was prepared by reactive magnetron sputtering, at room temperature, and deposited on a silicon wafer. From the analysis of the diffractograms it could be concluded that both materials share the same structure. By density functional calculation was found that the composition could be ReN3, instead of ReN2, as stated before. The ReN3 fits in the Ama2 (40) orthorhombic space group, and by the existence of N3 anions it should be categorized as an azide; that is, a nitrogen-rich compound. To reach high nitrogen concentrations by sputtering a crucial step is the target-poisoning. Under this regime of deposition is ensured that the compound is formed simultaneously on the substrate and the target. The poisoned target is rarely used because of a reduced sputtering yield, but as shall see, it can be used as a novel synthetic technique. △ Less

Submitted 7 November, 2012; originally announced November 2012.

Comments: 8 figures

Comment on Synthesis of rhenium nitride crystal with MoS2 structure

Authors: Gerardo Soto

Abstract: Kawamura et. al. recently published an article about the synthesis of rhenium nitride with MoS2-type structure [APL 100, 251910(2012)]. We disagree with the composition proposed by Kawamura. The compound synthesized by Kawamura is ReN3, or a compound of similar composition. What Kawamura did is to find the Re atomic positions of a compound where the nitrogen concentration remains unknown. This pap… ▽ More Kawamura et. al. recently published an article about the synthesis of rhenium nitride with MoS2-type structure [APL 100, 251910(2012)]. We disagree with the composition proposed by Kawamura. The compound synthesized by Kawamura is ReN3, or a compound of similar composition. What Kawamura did is to find the Re atomic positions of a compound where the nitrogen concentration remains unknown. This paper was rejected form APL. The reviewer comments (and our reply) are included here. △ Less

Submitted 16 October, 2012; v1 submitted 10 October, 2012; originally announced October 2012.

Fluorine effect in layered oxypnictide LaOFeAs

Authors: A. Reyes-Serrato, D. H. Galvan, G. Soto

Abstract: Theoretical calculations under the scheme of WIEN2k computer package had been performed on the pristine compound LaOFeAs, as well as on LaO1-xFxFeAs. One factor crucial to the manifestation of superconductivity seems to be fluorine doping; hence we search for its effect. Paying close attention to Fe d-orbitals upon doping of F by O, at first, Fe d-orbitals have dz2 symmetry, changing gradually t… ▽ More Theoretical calculations under the scheme of WIEN2k computer package had been performed on the pristine compound LaOFeAs, as well as on LaO1-xFxFeAs. One factor crucial to the manifestation of superconductivity seems to be fluorine doping; hence we search for its effect. Paying close attention to Fe d-orbitals upon doping of F by O, at first, Fe d-orbitals have dz2 symmetry, changing gradually to something akin to dx2-y2 which seems more prone to conductivity than the former one. This issue agree with the accepted results happened in the copper-based high-temperature superconductors. △ Less

Submitted 21 November, 2008; originally announced November 2008.

Comments: 6 pages, 1 figure

The Laser Ablation Production of Platinum Nitride and its Possible Structure

Authors: G. Soto, M. G. Moreno-Armenta

Abstract: The synthesis of platinum nitride by the laser ablation method is reported. The spectroscopic results show that nitrogen is in interstitial sites of platinum as N-units, contradicting the accepted configuration for PtN2 where it is as N2-units. To elucidate this point we did density functional calculations to correlate composition with nitrogen sites. For dilute nitrogen concentrations, x < 0.2,… ▽ More The synthesis of platinum nitride by the laser ablation method is reported. The spectroscopic results show that nitrogen is in interstitial sites of platinum as N-units, contradicting the accepted configuration for PtN2 where it is as N2-units. To elucidate this point we did density functional calculations to correlate composition with nitrogen sites. For dilute nitrogen concentrations, x < 0.2, nitrogen would be in six-fold coordinated sites (octahedral interstices) as N-units. For 0.2 < x < 1.5, nitrogen would be in tetrahedral interstices as N-units. Only for x > 1.5 the N2-configuration in octahedral sites is attained. △ Less

Submitted 1 August, 2008; originally announced August 2008.

Comments: 8 pages, 4 figures

Theoretical study on the possibility of bipolar doping of ScN

Authors: G. Soto, M. G. Moreno-Armenta, A. Reyes-Serrato

Abstract: Scandium nitride (ScN) is a semiconducting transition metal nitride for which there are not identified dopants. We present local density functional calculations, in supercell approach, for ScN doped with O and C in N-sites and Ca and Ti in Sc-sites. Small additions of these atoms have the effect of shifting the Fermi level within the electronic band structure. O and Ti bring occupied states in b… ▽ More Scandium nitride (ScN) is a semiconducting transition metal nitride for which there are not identified dopants. We present local density functional calculations, in supercell approach, for ScN doped with O and C in N-sites and Ca and Ti in Sc-sites. Small additions of these atoms have the effect of shifting the Fermi level within the electronic band structure. O and Ti bring occupied states in bottom of conduction band, while C and Ca produces holes in top of valence band. Based on the theory we propose that bipolar doping is possible to scandium nitride. △ Less

Submitted 25 March, 2008; originally announced March 2008.

Comments: 9 pages, 1 figure

First Principles Study on the Formation of Yttrium Nitride in Cubic and Hexagonal Phases

Authors: G. Soto, M. G. Moreno-Armenta, A. Reyes-Serrato

Abstract: We have studied the formation of yttrium nitride in which the Y-atoms were arranged in two common close-packed stacking: The AB-stacking (hcp-symmetry) is the ground state of metallic yttrium; while the ABC-stacking (fcc-symmetry) is the ground state of yttrium nitride. Given the different symmetries between YN and Y, there must be a phase transition (hcp->fcc) as N is incorporated in the Y-latt… ▽ More We have studied the formation of yttrium nitride in which the Y-atoms were arranged in two common close-packed stacking: The AB-stacking (hcp-symmetry) is the ground state of metallic yttrium; while the ABC-stacking (fcc-symmetry) is the ground state of yttrium nitride. Given the different symmetries between YN and Y, there must be a phase transition (hcp->fcc) as N is incorporated in the Y-lattice. By means of first principles calculations we have made a systematical investigation where N was gradually incorporated in octahedral interstices in AB and ABC stacking of Y. We report the heat of formation, bulk modulus, lattice parameter and electronic structure of the resultant nitrides. We found that both metal arrangements are physically achievable. Furthermore, for low nitrogen incorporation the two phases may coexist. However for high nitrogen concentration the cubic phases are favored by a 30 kJ mol-1 margin. These results are important since fcc-YN is semiconducting and could be utilized as active layer in electronic devices. △ Less

Submitted 20 June, 2007; v1 submitted 22 March, 2007; originally announced March 2007.

Comments: One document 18 pages

Beryllium nitride thin film grown by reactive laser ablation

Authors: G. Soto, J. A. Diaz, R. Machorro, A. Reyes-Serrato, W. de la Cruz

Abstract: Beryllium nitride thin films were grown on silicon substrates by laser ablating a beryllium foil in molecular nitrogen ambient. The composition and chemical state were determined with Auger (AES), X-Ray photoelectron (XPS) and energy loss (EELS) spectroscopies. A low absorption coefficient in the visible region, and an optical bandgap of 3.8 eV, determined by reflectance ellipsometry, were obtai… ▽ More Beryllium nitride thin films were grown on silicon substrates by laser ablating a beryllium foil in molecular nitrogen ambient. The composition and chemical state were determined with Auger (AES), X-Ray photoelectron (XPS) and energy loss (EELS) spectroscopies. A low absorption coefficient in the visible region, and an optical bandgap of 3.8 eV, determined by reflectance ellipsometry, were obtained for films grown at nitrogen pressures higher than 25 mTorr. The results show that the reaction of beryllium with nitrogen is very effective using this preparation method, producing high quality films. △ Less

Submitted 23 March, 2001; originally announced March 2001.

Comments: 13 pages, 5 figures. Submitted to Materials Letters