Stability and Dynamics of Boron Nitride Nanoscrolls
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Stability and Dynamics of Boron Nitride Nanoscrolls Eric Perim* and Douglas S. Galvao Applied Physics Department, State University of Campinas, 13083-459 Campinas, Sao Paulo, Brazil *corresponding author: [email protected] ABSTRACT We report here molecular dynamics results for boron nitride nanoscroll structures (BNNSs) with relation to their stability and formation mechanisms. We show that, similarly to carbon nanoscrolls, BNNSs are stable due to van der Waals interactions among overlapping layers. The energy balance between losses and gains (due to elastic deformations and van der Waals interactions, respectively) when the structure is rolled up leads to the existence of a critical value of the internal scroll diameter where stable or metastable structures can be formed. The mechanisms of scroll formation and stability as a function of their chirality were also investigated. INTRODUCTION Carbon nanoscrolls (CNS) are structures formed by rolling up graphene sheets into scrolllike structures. These structures were first observed in the 1960s [1] by Bacon, more than two decades before the discovery of fullerenes. Despite this early discovery, very few works focused on these structures. Some of them suggested that CNSs are intermediate structures formed during carbon nanotube (CNT) synthesis [2,3]. Only in the 2000s efficient methods to produce CNSs from HOPG (highly oriented pyrolytic graphite) were developed independently by two different research groups [4,5]. Both techniques consisted in exfoliating HOPG in solution and then using either sonication [4] or high temperatures [5] for the graphene sheets to curl into CNSs. These advances in the synthesis of the CNSs motivated some theoretical studies on these structures [2,6,7], which showed that CNSs are stable due to van der Waals interactions among overlapping layers, making it possible to overcome the energy losses of bringing the sheet out of its planar structure. Also, it was showed that CNSs may present giant electro actuation and great radial flexibility [7], properties which may be useful in some technological application, such as hydrogen storage [8,9]. Recently, a new and efficient method to produce large quantities of single-layer CNSs was developed [10]. The method consists of depositing graphene sheets over a SiO2 substrate in a mixture of water and isopropyl alcohol, which leads to the spontaneous curling of the sheets and, consequently, to CNSs. Another important class of nanostructures is boron nitride (BN) materials. BN fullerenes and BN nanotubes do exist [11,12]. By analogy, a natural question is whether BN scrolls (BNNSs) can also exist. Up the present moment no experimental evidences of their existence have been reported. In this work we report a theoretical study on BNNSs structures. Our results suggest they are stable and share some of the interesting mechanical properties exhibited by CNSs [13]. Recently, experimental synthesis of BN monolayers have been achieved [14,15]. We believe that similar methods as the ones used to synthesize CNSs c
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