Diagnostics of carbon nanotubes "zigzag" and "armchair"

by method of electron microdiffraction

I.K.Nasyrov, D.N.Valeeva, Yu.N.Osin, Z.Y.Khalitov

Kazan State Technical University of A.N.Tupolev's name

Institute of Nanotechnologies and Nanomaterials

K.Marx, 10, Kazan, 420111, Russia

 

The purpose of this research is the crystallographicљ description of the possibleљ polytype modifications, connected with mutual shifts of layers, of two basic structural varieties of multilayer circular carbon nanotubes: "armchair" and "zigzag", adaptation of the quantitative theory of diffraction by single nanotube to this case in the application to a method of electron microdiffraction, and also reception of the basic ratio and modeling distributions of diffraction intensity for their diagnostics.

It is supposed, that the cylindrical curvature of crystal space of the multilayer carbon structures can result in formation of ordered (including zero) shifts of layers both along an nanotube's axis (longitudinal shift), as in a case of chrysotile, and in a direction of a circle (azimuthal angular shift). The monoclinic and two-layer orthogonal polytype modifications of circular structures "zigzag" and "armchair" are considered. The expressions for cylindrical coordinates of any atoms of the appropriate structures are resulted.

The developed earlier quantitative theory of diffraction by single nanotube in the application to a method of electron microdiffraction adapts for a considered case. The expressions for profiles of strong and diffuse reflections along the layered lines of single nanotubes and for positions of their maxima are given, the modeling profiles are calculated. It is shown, that diagnostics of polytype modifications of carbon nanotubes "armchair" and "zigzag" and definition of their parameters can be carried out љfrom disposition of reflexes on the layered lines and their relative intensities.

The interpretation of a pattern of electron microdiffraction by single nanotube is carried out.

The analysis of a picture of a single nanotube's part in transmitting electron microscope and its electron microdiffraction pattern has shown, that there is a nanotube, having ~ 15-18 close packed layers, and poorly crystallized 2-nd phase, located on its external surface. The diffraction pattern of nanotube can be indexed in framework of model of monoclinic longitudinal polytype and it is possible to find the longitudinal parameter of a lattice and interlayer shift.

The arch-like reflections of 2-nd phase are indexed in model of single graphen layers fragments. This means that the 2-nd phase is formed by defective external nanotube's layers, radial distance between which has to some degree accidental character.

The results of the analysis allow to speak that nanotubes of such type are rather perspective for use in composite materials as armoring elements as, on the one hand, their basis are the rather large and perfect cylindrical crystals, and, with another, the 2-nd phase provides high density of free carbon bonds on their surfaces.

Thus, the essential difference of the metrics of "armchair" and "zigzag" carbon nanotube's lattices allows reliably diagnosing them in mixes by a method of electron microdiffraction by single nanotube. The given expressions for profiles of intensity allow, basically, carrying out the x-ray quantitative phase analysis of their mixes.