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Ab initio computational studies of graphyne-related carbon materials and stoichiometric antiphase boundaries in boron nitride

Speaker: 
Ricardo W. Nunes (UFMG, Brazil)
Date: 
Wed, 11/07/2012 - 2:00pm to 3:00pm
Location: 
S13-M01-11 (Physics Conference Room)
Event Type: 
Seminars

Recent theoretical studies (D. Malko et al., PRL 108, 086804, 2012) have revealed the existence of Dirac-cone electronic spectra in a family of carbon materials known as graphynes. Some of these graphynes share with graphene the underlying hexagonal Bravais lattice but not the honeycomb structure. In our study, we concentrate on the so-called alpha-graphynes, which have a 2D crystal structure where a pair of threefold-coordinated carbon atoms, placed on a honeycomb geometry, are connected through chains of twofold coordinated carbons. We show that such geometries can be used to create hydrocarbons with a Dirac-cone electronic structure near the Fermi level. Furthermore, we propose the existence of low-energy stoichiometric antiphase boundaries (APB - an extended 1D defect) in boron nitride. The periodic unit for this 1D defect consists of a tetragon-octagon pair (a 4-8 unit), which is the armchair version of a zigzag-oriented 1D extended defect, with a periodic unit consisting of two pentagons and an octagon (a 5-5-8 unit), that has been recently observed to form in graphene grown on Ni substrates (J. Lahiri et al., Nature Nanotech. 5, 326, 2010). In our study, we show that in BN the 4-8 unit APB has lower formation than the 5-5-8 defect in most growth conditions, and shows the presence of shallow aceptor and donor defect states.

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