Hydrogenation: A Simple Approach To Realize Semiconductor-Half-Metal-Metal Transition in Boron Nitride Nanoribbons Wei Chen, † Yafei Li, ‡ Guangtao Yu, § Chen-Zhong Li, | Shengbai B. Zhang, ⊥ Zhen Zhou,* ,‡ and Zhongfang Chen* ,† Department of Chemistry, Institute for Functional Nanomaterials, UniVersity of Puerto Rico, San Juan, Puerto Rico 00931, Institute of New Energy Material Chemistry, Nankai UniVersity, Tianjin 300071, People’s Republic of China, The State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin UniVersity, Changchun 130023, People’s Republic of China, Biomedical Engineering Department, Florida International UniVersity, Miami, Florida 33174, and Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180 Received October 5, 2009; E-mail: zhouzhen@nankai.edu.cn; zhongfangchen@gmail.com Abstract: The intriguing electronic and magnetic properties of fully and partially hydrogenated boron nitride nanoribbons (BNNRs) were investigated by means of first-principles computations. Independent of ribbon width, fully hydrogenated armchair BNNRs are nonmagnetic semiconductors, while the zigzag counterparts are magnetic and metallic. The partially hydrogenated zigzag BNNRs (using hydrogenated BNNRs and pristine BNNRs as building units) exhibit diverse electronic and magnetic properties: they are nonmagnetic semiconductors when the percentage of hydrogenated BNNR blocks is minor, while a semiconductorfhalf- metalfmetal transition occurs, accompanied by a nonmagneticfmagnetic transfer, when the hydrogenated part is dominant. Although the half-metallic property is not robust when the hydrogenation ratio is large, this behavior is sustained for partially hydrogenated zigzag BNNRs with a smaller degree of hydrogenation. Thus, controlling the hydrogenation ratio can precisely modulate the electronic and magnetic properties of zigzag BNNRs, which endows BN nanomaterials many potential applications in the novel integrated functional nanodevices. 1. Introduction Graphene, a two-dimensional (2D) sheet of sp 2 -hybridized carbon, is taking us into the new material revolution, 1-3 because the long-range π-conjugation makes it exhibit extraordinary thermal, mechanical, and electrical properties. 4-9 For example, graphene is the strongest material ever measured, 4 and its ability to conduct electricity is the best among the known materials at room temperature. 6 Stimulated by these outstanding properties, graphene-based materials 10-36 attracted extensive experimental and theoretical investigations. By carving the 2D graphene, one-dimensional (1D) graphene nanoribbons (GNRs) have been realized. 1 Because of the change of dimensionality, GNRs display unusual electronic and mag- netic properties different from graphene. 12-29 Both first- principles computations 17,22,23 and experimental investigations 25,26 revealed a nonzero band gap for GNRs independent of their width and chirality. Zigzag GNRs are magnetic, 20,22 while armchair GNRs are nonmagnetic. Moreover, theoretical studies predict that either electric field 27 or chemical functionalization 28-30 can make GNRs half metals, which have potential application in spintronics. Furthermore, by hydrogenating graphene, 2D graphane (fully hydrogenated graphene) was obtained experimentally 10,31 and can be considered as an electronic insulator. 10 A 2D graphane layer, 32 hydrogenation of graphene with defects, 33,34 and fluorine-substituted graphane 35 were theoretically studied in detail. Besides graphane, the electronic and magnetic properties of partially hydrogenated graphene have also been investi- gated. 36-38 Moreover, 1D graphane nanoribbons can be experi- mentally realized by cutting the 2D graphane, similar to the case of GNRs, or by hydrogenating GNRs, like the formation process from graphene to graphane. 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