Carbon nanomaterials are nevertheless the hottest nanomaterial system in the last two decades, starting with fullerene, followed by carbon nanotubes (CNTs), and recently, graphene, thus covering all the low dimensions. Tremendous progress has been achieved in fundamental research on carbon nanomaterials and their applications in various elds. Soon after the discovery of CNTs, substitutional doping of CNTs with B and N heteroatoms has been found to be possible and feasible (Rubio et al. 1994). Given that B and N are the nearest neighbors of C in the periodic table and that their atomic radii are very similar to that of C, B, and N atoms, they have a reasonable probability of entering the CNT lattices through atomic substitutional doping. e co-doping of C nanotubes/nanosheets with both B and N leads to the formation of a ternary system, which is also known as boron carbonitride (BCN) nanotube/nanosheet. e band gap of CNT depends on chirality and diameter. For graphene, its two linear bands cross at Dirac point, resulting in a zero-band gap semiconductor or semimetal, whereas for hexagonal boron nitride
6.1 Introduction 141 6.2 Syntheses 142
6.2.1 Postsynthetic Substitution Reaction Route 143 6.2.2 Direct Synthesis: Arc Discharge and Laser Ablation 144 6.2.3 Direct Synthesis: CVD Growth 145
6.3 Physical Properties 148 6.3.1 Electronic Property 148
220.127.116.11 B-Doped Graphene 148 18.104.22.168 N-Doped Graphene 150 22.214.171.124 Boron Nitrogen Co-Doped Graphene 156 126.96.36.199 BCN Ternary Nanotubes 158
6.3.2 Luminescence 159 6.3.3 Magnetic Property 162
6.4 Concluding Remarks 168 References 169
(h-BN), it is an insulator with an approximately 5.5 eV band gap. e band gaps of BN nanotubes are similar to those of h-BN, which are independent of chiralities and morphologies. B, C, and N can be atomically mixed together to form various semiconducting hexagonal-layered structures with varying stoichiometries (Figure 6.1). eoretical calculation shows that their band gaps are primarily determined by their chemical compositions and independent of their geometry, which could be further tailored to smartly build interesting nano-heterojunctions. BCN nanostructures have elicited much attention because these ternary systems provide the most feasible method to control the semiconducting properties of graphene or BN.