Role of Vacancies in Zigzag Graphene Nanoribbons: An Ab Initio Study Khaldoun Tarawneh 1, a , Nabil Al-Aqtash 2, b 1 Princess Sumaya University for Technology, Amman 11941, Jordan 2 University of Nebraska at Omaha, Omaha, NE 68182, USA a khaldoun@psut.edu.jo (corresponding author), b nalaqtash@unomaha.edu [Submitted: November 4, 2013; revised: December 15, 2013; accepted: December 29, 2013] Keywords: Density functional calculations, ZGNR, single vacancy, double vacancies. ABSTRACT We have studied the effects of vacancies on the structural, electronic and magnetic properties of zigzag-edged graphene nanoribbons (ZGNRs). Our calculations were carried out using an ab initio density functional pseudopotential computational method combined with the generalized gradient approximation for the exchange-correlation functional. The equilibrium geometries, electronic charge spin density distributions, electronic band structures, and magnetic moments were examined in the presence of single vacancy and double vacancies. Structural optimization showed that vacancies induce substantial structural changes in ZGNRs. We found that introducing vacancies into ZGNR changes the spatial distribution of neighbor atoms, particularly those located around the vacancies. Our calculations showed that the vacancies have significant effect on the magnetization of ZGNR. The calculations showed that the changes in the structural geometry, the electronic structure and the magnetization of ZGNR depend on the location of the vacancies with respect to the ribbon edges. These results suggest that vacancy defects can be used to modify the electronic and the magnetic properties of ZGNR. INTRODUCTION Two-dimensional graphene has motivated extensive studies due to its novel properties, including high electron mobility [1], like massless Dirac fermions behavior [2], high electrical conductivity [3], quantum Hall effect at room temperature [4], and high elasticity [5]. One way of controlling the electronic properties of graphene explores the idea of producing quasi-one- dimensional graphene nanoribbons (GNRs), which have even more interesting electronic and magnetic properties depending on their structural parameters, such as width and atomic geometry of their edges [6-9]. GNRs can be divided into two types depending on the edge termination, including zigzag-edged graphene nanoribbons (ZGNRs) and armchair-edged graphene nanoribbons (AGNRs). Several recent theoretical studies have revealed that ZGNRs exhibit a spin-polarized semiconducting ground state with opposite spin orientations at two edges [8,10] which can lead to unusual behaviors such as a half metallic state and giant magnetoresistance effect [11]. These unique properties coupled with the experimental developments make the ZGNRs particularly promising for future potential applications, such as in catalysis [12], spintronics [13], quantum dots [14], and band selective filters [15]. It is demonstrated that the electronic energy bands of different spin polarizations for the ZGNRs are degenerate. This degeneracy can be broken by different methods, such as vacancy [16, 17], doping [18, 19], topological defects [20], chemical functionalization [21], torsional deformation [22], and by imposing an external electric field across the transverse ZGNRs direction [8]. Vacancy is studied extensively because of its strong perturbations on the electronic states of GNR, and it can lead to larger magnetization in the ZGNRs. However, the interaction of the vacancy with the edge state of the ribbon has not been investigated in detail for the ZGNRs. It would be highly motivating to explore this interaction in case of multivacancies at different sublattices, i.e., sub A and sub B, with different spin directions. Journal of Nano Research Vol. 27 (2014) pp 65-73 Online available since 2014/Mar/24 at www.scientific.net © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/JNanoR.27.65 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 193.188.67.34-24/03/14,14:05:17)