A comparative study on carbon, boron-nitride, boron-phosphide and silicon-carbide nanotubes based on surface electrostat
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ORIGINAL PAPER
A comparative study on carbon, boron-nitride, boron-phosphide and silicon-carbide nanotubes based on surface electrostatic potentials and average local ionization energies Mehdi D. Esrafili & Hadi Behzadi
Received: 14 November 2012 / Accepted: 28 January 2013 / Published online: 14 February 2013 # Springer-Verlag Berlin Heidelberg 2013
Abstract A density functional theory study was carried out to predict the electrostatic potentials as well as average local ionization energies on both the outer and the inner surfaces of carbon, boron-nitride (BN), boron-phosphide (BP) and silicon-carbide (SiC) single-walled nanotubes. For each nanotube, the effect of tube radius on the surface potentials and calculated average local ionization energies was investigated. It is found that SiC and BN nanotubes have much stronger and more variable surface potentials than do carbon and BP nanotubes. For the SiC, BN and BP nanotubes, there are characteristic patterns of positive and negative sites on the outer lateral surfaces. On the other hand, a general feature of all of the systems studied is that stronger potentials are associated with regions of higher curvature. According to the evaluated surface electrostatic potentials, it is concluded that, for the narrowest tubes, the water solubility of BN tubes is slightly greater than that of SiC followed by carbon and BP nanotubes. Keywords Carbon nanotube . Boron-nitride nanotube . Electrostatic potential . DFT . Average local ionization energies
Introduction The discovery of carbon nanotubes (CNTs) by Iijima [1] has set off a tremendous explosion of general interest in these M. D. Esrafili (*) Laboratory of Theoretical Chemistry, Department of Chemistry, University of Maragheh, PO Box: 5513864596, Maragheh, Iran e-mail: [email protected] H. Behzadi Department of Chemistry, Kharazmi University, Mofatteh Avenue, Tehran, Iran
quasi-one-dimensional structures. Subsequent investigations have introduced stable tubular structures other than CNTs where the counterparts of atoms in the third and fifth groups of elements (III–V) have been proposed as proper materials [2–8]. To date, the properties of boron-nitride nanotubes (BNNTs) [9, 10] and boron-phosphide nanotubes (BPNTs) [11–13] have been investigated by numerous experimental and computational methods. It is well-documented that, due to their small covalent radius, carbon, boron and nitrogen atoms can generate considerable strain energy, preventing the formation of the close-packed structures with larger coordination found in clusters of covalent elements with larger radii such as silicon [14]. Consequently, carbon and boron-nitride can form very stable low-dimensional structures with smaller coordination. By contrast, low coordinated structures of Si, graphitic or cage-like, are predicted to be unstable [15, 16]. The possibility exists, however, that substitutional doping of tubular Si structures by a sufficient number of C atoms may render it stable. This is because both C–C and Si–C bonds are known to be stronger t
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