Half-metallic graphene nanodots

Abstract

A comprehensive first-principles theoretical study of the electronic properties and half-metallic nature of finite rectangular graphene nanoribbons is presented. We identify the bisanthrene isomer of the C28H14 molecule to be the smallest polycyclic aromatic hydrocarbon to present a spin polarized ground state. Even at this quantum dot level, the spins are predicted to be aligned antiferromagnetically at the two zigzag edges of the molecule. As a rule of thumb, we find that zigzag edges that are at least three consecutive units long, will present spin polarization if the width of the system is 1 nm or wider. Room temperature detectability of the magnetic ordering is predicted for molecules with zigzag edges 1 nm and longer. For the longer systems studied, spin wave structures appear in some high spin multiplicity states. Energy gap oscillations with the length of the zigzag edge are observed. The amplitude of these oscillations is found to be smaller than that predicted for infinite ribbons. The half-metallic nature of the ribbons under an external in-plane electric field is found to be preserved even for finite and extremely short systems.

Edge effects in finite elongated graphene nanoribbons

“…Edge effects play a dominant role when considering the electronic and magnetic character of low dimensional elongated systems. This has been shown for systems such as graphene nanoribbons, 4,8,9,10,49,50,51,52,53,54,55,56 carbon nanotubes, 25,27,28,29,30,31,32,33,34,35,36 and other related structures. 53 When considering the study of graphene nanoribbons as candidates for future nanoelectronic devices, it is important to identify the contribution of finite-size effects to the physical properties of the entire system.…”

“…Graphene nanoribbons (GNRs) have been suggested as potential candidates for replacing electronic components and interconnects in future nanoelectronic 1,2,3,4,5,6,7 and nanospintronic 8,9,10 devices. Experiments have revealed the possibility of obtaining a wide range of electronic behavior when studying these systems, ranging from coherent transport 11 suitable for interconnects, to field effect switching capabilities 12 needed for electronic components design.…”

“…The reduced dimension of these quantum dots introduces important physical phenomena such as quantum confinement and edge effects. 10,17,18,19,20,21,22,23 Several theoretical studies have emphasized the importance of such effects when considering the electronic structure, 24,25,26,27,28 electric transport, 29,30,31,32,33 and magnetic 34,35,36 properties of finite carbon nanotubes (CNTs). These effects are expected to be manifested in experiments involving the dielectric screening constants, 26 optical excitations 37 and Raman spectrum 38 of such systems.…”

“…5 The inclusion of short-range exact-exchange in the HSE06 functional makes it suitable to treat electronic localization effects 47,48 which are known to be important in this type of materials. 4,8,9,10,49,50,51,52,53,54,55,56 The DOS was calculated using the following relation:…”

“…magnetic ordering. 4,8,9,10,49,50,51,52,53,54,55,56 In Fig. 4 we show the single particle Kohn-Sham orbitals appearing in the vicinity of the Fermi level of a 6 nm long 04-ACGNR.…”