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Denis P.A.,Computational Nanotechnology And Laboratorio Of Bioinformatica Y Farmacologia Molecular | Denis P.A.,Centro Interdisciplinario En Nanotecnologia Y Quimica Fisica Of Materiales | Iribarne F.,Computational Nanotechnology And Laboratorio Of Bioinformatica Y Farmacologia Molecular
Journal of Physical Chemistry C | Year: 2011

The covalent functionalization of graphene with nitrene radicals has been investigated employing first principles calculations. Perfect graphene is very reactive against nitrene radicals and the binding energy per NH group is significantly increased when the nitrene groups are agglomerated. For bilayer graphene, we determined that the presence of a second layer does not affect the reactivity of the upper layer from a thermodynamical stand point. High levels of functionalization are needed to open a band gap in nitrene-modified graphene. At the LDA, GGA, LDA+U and HSE06 levels, we did not observe band gap opening even for the addition of one NH group per 32 carbons. This result is in contrast with a recent experimental study that attributed the band gap opening of epitaxial graphene to the adsorption of one nitrene radical per 53 carbon atoms. The small amount of adsorbed nitrene radicals is also in contrast with our results that predicted a large reactivity. We attribute this discrepancy to the large size of trimethylsilane that inhibited the agglomeration of nitrene radicals. Thus, it is possible to control the number of nitrene groups added just by varying the size of the functional group attached to nitrogen. For small functional groups like NH, it is feasible that the synthesis of 100% functionalized graphene is feasible because the binding energy per NH is duplicated with respect to the isolated addition. The addition of NH groups to graphene is more favorable when the functionalized CC bonds are broken. However, the structure with the disrupted CC bonds may prove difficult to synthesize because the break of CC bonds is not favorable at lower levels of functionalization. © 2010 American Chemical Society. Source


Denis P.A.,Computational Nanotechnology | Denis P.A.,Centro Interdisciplinario En Nanotecnologia Y Quimica Fisica Of Materiales
Computational and Theoretical Chemistry | Year: 2011

Bilayer graphene simultaneously doped with two different second-row atoms (aluminum and phosphorus) was investigated employing first-principle density functional calculations (LDA, VDW-DF and M06-L). In agreement with the results obtained for bilayer graphene doped with one type of heteroatom, we found that at 1.56% atomic doping of Al and 1.56% atomic doping of P, the structure with sheets not linked is more stable than that with an Al-P bond. While all methods agreed in predicting the most stable structure, the relative energies of the structural isomers were different at the three levels of theory considered. The electronic properties of doped bilayer graphene showed an unusual variation upon small conformational changes. In effect, metallic, semiconducting and semimetallic properties were observed upon variation of the protruding orientation of the heteroatoms. The electronic properties of bilayer graphene seem to be determined by the layer whose heteroatom protrudes into the interlayer region. When Al protrudes in and P out metallic properties are observed. However, when P protrudes in and Al in a small band gap semiconductor is obtained. This work shows that the electronic properties of bilayer graphene can be more easily tuned than those of monolayer graphene because a small conformational change can induce a metallic to semiconductor transition or vice versa. © 2011 Elsevier B.V.. Source


Denis P.A.,Computational Nanotechnology | Denis P.A.,Centro Interdisciplinario En Nanotecnologia Y Quimica Fisica Of Materiales
Chemical Physics Letters | Year: 2010

The chemical doping of monolayer and bilayer graphene with aluminium, silicon, phosphorus and sulfur was investigated. Si-doped graphene has the lowest formation energy although it is semimetallic. P-doped graphene has a magnetic moment of 1 μB and for 3 at.% of doping the band gap is 0.67 eV. Al-doped graphene is very unstable but it is an attractive material because it is metallic. To reduce the formation energies of the substitutional defects we investigated the formation of interlayer bonds in bilayer graphene. Phosphorus forms the strongest bonds between layers giving particular stability to this material. P-doped bilayer graphene has a gap of 0.43 eV but it is has no magnetic moment. © 2010 Elsevier B.V. All rights reserved. Source


Denis P.A.,Computational Nanotechnology | Denis P.A.,Centro Interdisciplinario En Nanotecnologia Y Quimica Fisica Of Materiales
Chemical Physics Letters | Year: 2011

Herein, we perform a M06-2X/6-311G investigation of the homo and mixed dimers formed between corannulene, sumanene, and pentaindenocorannulene; also, their complexes with C 60 and C 70 were studied. Despite the lower area of sumanene, the interaction of the sumanene-dimer is stronger that of the corannulene-dimer because of CH-π interactions. For mixed-dimers, when the concave and convex sides perfectly match the interactions are similar to those of the homodimers. However, when the concave area is larger than the convex one, CH-π interactions become important and perfect stacking is lost. The interaction between pentaindenocorannulene-C 60 is twice that of corannulene-C 60, and ΔG 298 = -10.8 kcal/mol. Thus, pentaindenocorannulene is a better choice to catch C 60. © 2011 Elsevier B.V. All rights reserved. Source


Denis P.A.,Computational Nanotechnology | Denis P.A.,Centro Interdisciplinario En Nanotecnologia Y Quimica Fisica Of Materiales
Chemical Physics Letters | Year: 2011

Herein, we investigate bilayer graphene doped with second-row atoms using the LDA, M06-L, and VDW-DF functionals. For 2-3 at.% or lower Al and P dopings the structure with a short interlayer distance and without a covalent bond between the heteroatoms is more stable than that with a covalent bond and longer interlayer separation. However, for Si the linked structure is more stable. Doped bilayer-graphene is prone to the attachment of more heteroatoms, as reflected by the large adsorption energies, which decrease in the following order Al > Si > P. We show that it is feasible to tune the electronic properties, and the interlayer-interaction energy varying the type or amount of second row atoms. © 2011 Elsevier B.V. All rights reserved. Source

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