Graphene, thanks to its extraordinary electronic and mechanical properties, is a potential candidate for a number of applications. Being one-atom thick, it is extremely sensitive to the presence of adsorbed atoms and molecules (either physisorbed or chemisorbed on the surface) and, more generally, to defects such as vacancies, holes and/or substitutional dopants. This property, apart from being directly usable, e.g., in molecular sensor devices, can also be employed to tune graphene electronic properties. In this contribution we review that basic features of atomic-scale defects that can be useful for material design[1]. We first focus on isolated ”pz defects” such as atom vacancies or simple adsorbed species covalently bound to carbon atoms, and on the effect they have on graphene electronic structure at the Fermi level through the formation of quasi-localized midgap states [2,3]. These states support an itinerant electron picture which is usually invoked in -conjugated hydrocarbon chemistry to explain the increased reactivity at specific lattice positions (see Fig.1). Therefore, when considering multiple defective structures, we need to take into account the possible effects such states have on sequential defects formation. This is the case, for instance, of adsorption of atomic species which typically occurs under strict kinetic control because of the presence of an energy barrier to sticking. In this context, we show why chemisorption of H atoms cannot occur randomly on the surface, and how preferential sticking mechanisms concur in forming clusters of adsorbed species [4,5]. Next we consider the reverse problem, that is how to engineer graphene electronic properties by arranging defects to form well-ordered structures, e.g. superlattices of nm-sized holes (see e.g. Ref. [6]). With the help of group theoretical arguments and electronic structure calculations, we show how it is possible to open a band-gap in graphene electronic structure without breaking its symmetry [7], namely by superimposing a honeycomb superstructure of defects to the honeycomb structure of graphene (Fig.2). The induced-gaps are comparable in size to those found in nanoribbons at the same length scale and, interestingly, come with novel Dirac cones right close to the gapped region. Similarly, we consider analogous superlattices of N and B substitutional dopants which show either a modified conical or a gapped quasi-conical structure, depending solely on the symmetry of the superlattice [8]. All these possible structures might find important technological applications in the development of novel graphene-based logic transistors, if progress in bottom-up techniques will make atomically- precise-fabrication possible in the near future

The effect of atomic-scale effects on graphene electronic structure / R. Martinazzo, S. Casolo, G.F. Tantardini. ((Intervento presentato al convegno GraphITA tenutosi a Gran Sasso National Laboratories, Assergi, L'Aquila nel 2011.

The effect of atomic-scale effects on graphene electronic structure

R. Martinazzo
Primo
;
S. Casolo
Secondo
;
G.F. Tantardini
Ultimo
2011-05-16

Abstract

Graphene, thanks to its extraordinary electronic and mechanical properties, is a potential candidate for a number of applications. Being one-atom thick, it is extremely sensitive to the presence of adsorbed atoms and molecules (either physisorbed or chemisorbed on the surface) and, more generally, to defects such as vacancies, holes and/or substitutional dopants. This property, apart from being directly usable, e.g., in molecular sensor devices, can also be employed to tune graphene electronic properties. In this contribution we review that basic features of atomic-scale defects that can be useful for material design[1]. We first focus on isolated ”pz defects” such as atom vacancies or simple adsorbed species covalently bound to carbon atoms, and on the effect they have on graphene electronic structure at the Fermi level through the formation of quasi-localized midgap states [2,3]. These states support an itinerant electron picture which is usually invoked in -conjugated hydrocarbon chemistry to explain the increased reactivity at specific lattice positions (see Fig.1). Therefore, when considering multiple defective structures, we need to take into account the possible effects such states have on sequential defects formation. This is the case, for instance, of adsorption of atomic species which typically occurs under strict kinetic control because of the presence of an energy barrier to sticking. In this context, we show why chemisorption of H atoms cannot occur randomly on the surface, and how preferential sticking mechanisms concur in forming clusters of adsorbed species [4,5]. Next we consider the reverse problem, that is how to engineer graphene electronic properties by arranging defects to form well-ordered structures, e.g. superlattices of nm-sized holes (see e.g. Ref. [6]). With the help of group theoretical arguments and electronic structure calculations, we show how it is possible to open a band-gap in graphene electronic structure without breaking its symmetry [7], namely by superimposing a honeycomb superstructure of defects to the honeycomb structure of graphene (Fig.2). The induced-gaps are comparable in size to those found in nanoribbons at the same length scale and, interestingly, come with novel Dirac cones right close to the gapped region. Similarly, we consider analogous superlattices of N and B substitutional dopants which show either a modified conical or a gapped quasi-conical structure, depending solely on the symmetry of the superlattice [8]. All these possible structures might find important technological applications in the development of novel graphene-based logic transistors, if progress in bottom-up techniques will make atomically- precise-fabrication possible in the near future
Settore CHIM/02 - Chimica Fisica
http://graphita.bo.imm.cnr.it/Invited_Keynote/Martinazzo.pdf
The effect of atomic-scale effects on graphene electronic structure / R. Martinazzo, S. Casolo, G.F. Tantardini. ((Intervento presentato al convegno GraphITA tenutosi a Gran Sasso National Laboratories, Assergi, L'Aquila nel 2011.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2434/193512
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