Publications

@proceedings{autreto2013dynamics,

title = {On the Dynamics of Graphdiyne Hydrogenation},

author = {Autreto, PA and de Sousa, JM and Galvao, DS},

url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8915680&fileId=S1946427413006088},

year  = {2013},

date = {2013-01-01},

journal = {MRS Proceedings},

volume = {1549},

pages = {59--64},

publisher = {Cambridge University Press},

abstract = {Graphene is a two-dimensional (2D) hexagonal array of carbon atoms in sp2-hybridized states. Graphene presents unique and exceptional electronic, thermal and mechanical properties. However, in its pristine state graphene is a gapless semiconductor, which poses some limitations to its use in some transistor electronics. Because of this there is a renewed interest in other possible two-dimensional carbon-based structures similar to graphene. Examples of this are graphynes and graphdiynes, which are two-dimensional structures, composed of carbon atoms in sp2 and sp-hybridized states. Graphdiynes (benzenoid rings connecting two acetylenic groups) were recently synthesized and they can be intrinsically nonzero gap systems. These systems can be easily hydrogenated and the amount of hydrogenation can be used to tune the band gap value. In this work we have investigated, through fully atomistic molecular dynamics simulations with reactive force field (ReaxFF), the structural and dynamics aspects of the hydrogenation mechanisms of graphdiyne membranes. Our results showed that depending on whether the atoms are in the benzenoid rings or as part of the acetylenic groups, the rates of hydrogenation are quite distinct and change in time in a very complex pattern. Initially, the most probable sites to be hydrogenated are the carbon atoms forming the triple bonds, as expected. But as the amount of hydrogenation increases in time this changes and then the carbon atoms forming single bonds become the preferential sites. The formation of correlated domains observed in hydrogenated graphene is no longer observed in the case of graphdiynes. We have also carried out ab initio DFT calculations for model structures in order to test the reliability of ReaxFF calculations.},

keywords = {},

pubstate = {published},

tppubtype = {proceedings}

}

@proceedings{machado2013graphyne,

title = {Graphyne Oxidation: Insights From a Reactive Molecular Dynamics Investigation},

author = {Machado, LD and Autreto, PAS and Galvao, DS},

url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8963025&fileId=S194642741300941X},

year  = {2013},

date = {2013-01-01},

journal = {MRS Proceedings},

volume = {1549},

pages = {53--58},

publisher = {Cambridge University Press},

abstract = {Graphyne is a generic name for a family of carbon allotrope two-dimensional structures where sp2 (single and double bonds) and sp (triple bonds) hybridized states coexists. They exhibit very interesting electronic and mechanical properties sharing some of the unique graphene characteristics. Similarly to graphene, the graphyne electronic properties can be modified by chemical functionalization, such as; hydrogenation, fluorination and oxidation. Oxidation is of particular interest since it can produce significant structural damages.

In this work we have investigated, through fully atomistic reactive molecular dynamics simulations, the dynamics and structural changes of the oxidation of single-layer graphyne membranes at room temperature. We have considered α, β, and γ-graphyne structures. Our results showed that the oxidation reactions are strongly site dependent and that the sp-hybridized carbon atoms are the preferential sites to chemical attacks. Our results also showed that the effectiveness of the oxidation (estimated from the number of oxygen atoms covalently bonded to carbon atoms) follows the α, β, γ-graphyne structure ordering. These differences can be explained by the fact that for α-graphyne structures the oxidation reactions occur in two steps: first, the oxygen atoms are trapped at the center of the large polygonal rings and then they react with the carbon atoms composing of the triple bonds. The small rings of γ-graphyne structures prevent these reactions to occur. The effectiveness of β-graphyne oxidation is between the α- and γ-graphynes.},

keywords = {},

pubstate = {published},

tppubtype = {proceedings}

}

@proceedings{autreto2013dynamics,

title = {On the Dynamics of Graphdiyne Hydrogenation},

author = {Autreto, PA and de Sousa, JM and Galvao, DS},

url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8915680&fileId=S1946427413006088},

year  = {2013},

date = {2013-01-01},

journal = {MRS Proceedings},

volume = {1549},

pages = {59--64},

publisher = {Cambridge University Press},

abstract = {Graphene is a two-dimensional (2D) hexagonal array of carbon atoms in sp2-hybridized states. Graphene presents unique and exceptional electronic, thermal and mechanical properties. However, in its pristine state graphene is a gapless semiconductor, which poses some limitations to its use in some transistor electronics. Because of this there is a renewed interest in other possible two-dimensional carbon-based structures similar to graphene. Examples of this are graphynes and graphdiynes, which are two-dimensional structures, composed of carbon atoms in sp2 and sp-hybridized states. Graphdiynes (benzenoid rings connecting two acetylenic groups) were recently synthesized and they can be intrinsically nonzero gap systems. These systems can be easily hydrogenated and the amount of hydrogenation can be used to tune the band gap value. In this work we have investigated, through fully atomistic molecular dynamics simulations with reactive force field (ReaxFF), the structural and dynamics aspects of the hydrogenation mechanisms of graphdiyne membranes. Our results showed that depending on whether the atoms are in the benzenoid rings or as part of the acetylenic groups, the rates of hydrogenation are quite distinct and change in time in a very complex pattern. Initially, the most probable sites to be hydrogenated are the carbon atoms forming the triple bonds, as expected. But as the amount of hydrogenation increases in time this changes and then the carbon atoms forming single bonds become the preferential sites. The formation of correlated domains observed in hydrogenated graphene is no longer observed in the case of graphdiynes. We have also carried out ab initio DFT calculations for model structures in order to test the reliability of ReaxFF calculations.},

keywords = {Graphdyine, Graphynes, Hydrogenation, Molecular Dynamics},

pubstate = {published},

tppubtype = {proceedings}

}

@proceedings{machado2013graphyne,

title = {Graphyne Oxidation: Insights From a Reactive Molecular Dynamics Investigation},

author = {Machado, LD and Autreto, PAS and Galvao, DS},

url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8963025&fileId=S194642741300941X},

year  = {2013},

date = {2013-01-01},

journal = {MRS Proceedings},

volume = {1549},

pages = {53--58},

publisher = {Cambridge University Press},

abstract = {Graphyne is a generic name for a family of carbon allotrope two-dimensional structures where sp2 (single and double bonds) and sp (triple bonds) hybridized states coexists. They exhibit very interesting electronic and mechanical properties sharing some of the unique graphene characteristics. Similarly to graphene, the graphyne electronic properties can be modified by chemical functionalization, such as; hydrogenation, fluorination and oxidation. Oxidation is of particular interest since it can produce significant structural damages.

In this work we have investigated, through fully atomistic reactive molecular dynamics simulations, the dynamics and structural changes of the oxidation of single-layer graphyne membranes at room temperature. We have considered α, β, and γ-graphyne structures. Our results showed that the oxidation reactions are strongly site dependent and that the sp-hybridized carbon atoms are the preferential sites to chemical attacks. Our results also showed that the effectiveness of the oxidation (estimated from the number of oxygen atoms covalently bonded to carbon atoms) follows the α, β, γ-graphyne structure ordering. These differences can be explained by the fact that for α-graphyne structures the oxidation reactions occur in two steps: first, the oxygen atoms are trapped at the center of the large polygonal rings and then they react with the carbon atoms composing of the triple bonds. The small rings of γ-graphyne structures prevent these reactions to occur. The effectiveness of β-graphyne oxidation is between the α- and γ-graphynes.},

keywords = {Graphdyine, Graphyne, Molecular Dynamics, Oxidation},

pubstate = {published},

tppubtype = {proceedings}

}