Topology Analysis And Two-dimensional Raman Spectra Study Of Nanotubes

Recently, nanotubes have been widely studied in materials area with having special structures and excellent properties. Magnesium Oxide (MgO), which is an oxydum, has been used in so many aspects. Nowadays, subsize MgO has been widely studied, such as MgO nanotubes. Boron nitride nanotubes (BNNTs), which have similar structures and properties as carbon nanotubes (CNTs). However, BNNTs have a more stable band gap which is independent of the tube diameter, length, chirality. There are similar other nanotubes, MgO and BN nanotubes have excellent properties in electricity, mechanics, optics and magnetics. The topology analysis of different structures and diameters of MgO nanotubes using the density functional theory. The topology analysis including the electron density, bond ellipticity, energy density function, localized locator of bond critical point. Then, the Raman spectroscopy of different lengths and diameters armchair BNNTs are analyzed using two-dimensional (2D) synchronous and asynchronous correlation technology. This paper is organized as follows two parts:(1) The topology analysis of zigzag and armchair MgO nanotubes.The structures of zigzag (L=7-17) and armchair (n=3-7) MgO nanotubs using Gaussian03PBE/6-31G(d) level. The electron density, bond ellipticiy, Laplacian of electron density, Lagrangian kinetic energy density, potential energy, local energy density, electron localization function, localized orbital locator of intra-layer and inter-layer bond critical points of these nanotubes using wave function analysis software Multiwfn. The results show that the topology analysis of MgO nanotubes are totally different because of diverse structures, even although there are the same Mg atoms and O atoms in a molecule unit. The electron density of bond critical point is locally depleted. The local energy density tends to a certain value when the diameters of MgO nanotubs increase. The electron localization function is similar the localized orbital locator, both of them indicate the localization of electron kinetic energy. The results of topology analysis are determined by the structure, radius and electron density of nanotubes. (2) The2D Raman spectra analysis of different length and diameter armchair BNNTs.The structure of armchair BN nanotubes with layers (L=7-17) and rings (n=3-7) using Gaussian03B3LYP/6-31G*level. Then, the Raman vibrational situations of BNNTs were analyzed by2D Raman correlation spectra which finished in experiment environment of MATLAB. The results show that the Raman shifts of RBM was influenced by dimensional effect when the diameter of BNNTs is a definite value. But Raman shifts would reach a stable value (489cm-1) when the length constantly increased. The Raman shifts of RBM, which by no means reach a stable value when the length is a certain value, are inversely proportional to the radius of BNNTs. The Raman vibrational mode in range (780-880cm-1) of Raman shift. If there is no size effect, the Raman shifts would tend to two stable values (835cm-1) and (823cm-1) when lengths and diameters increased. There is asynchronous correlation relationship in those Raman spectra.