Nitrogen-substituted nanotubes and nanojunctions: Conformation and electronic properties

Abstract

We present a theoretical study on the structural and electronic modifications caused by random nitrogen substitution in carbon tubular and branched nanostructures. Finite cluster calculations with hydrogen saturation of the tube ends were performed. Geometry optimizations were carried out through semiempirical quantum chemical calculations. Densities of states (DOS) were calculated by the density functional theory. The energy associated with nitrogen incorporation was obtained. Some tubular structures undergo a length shortening as a consequence of N substitution. DOS analysis is consistent with the shift of the electronic spectrum to lower energies and a more metallic character of the tubes upon nitrogen doping due to the emergence of nitrogen-induced states close to the conduction band. The defective regions of junctions and bends were built including five-, seven-, and eight-membered rings in the otherwise hexagonal network of carbon bonds. In order to reduce the stress caused by the curvature, a chemical doping through nitrogen substitution is proposed. Results are consistent with the shortening of bonds within the junctions and bends and an increased chemical stability of the defects.

Conformational analysis and electronic structure of chiral carbon and carbon nitride nanotubes

“…As can be observed in Figure 1, before doping the model molecules do not show irregularities along the tube walls. Similar results were already obtained in our early works 28,36 . In these works 28,36 we showed that N-doped zig-zag tubes are more stable (the formation enthalpy decreases) than armchair tubes of similar diameter.…”

“…Similar results were already obtained in our early works 28,36 . In these works 28,36 we showed that N-doped zig-zag tubes are more stable (the formation enthalpy decreases) than armchair tubes of similar diameter. At the same time the stressed small diameter tubes are more easily doped by nitrogen than the large diameter tubes.…”

“…In recent years, various synthesis methods to produce CNx nanotubes have been reported, including chemical vapor deposition (CVD) [12][13][14] 4,[23][24][25][26][27] . In our previous work 15,28 , simulations of a random doping of CNTs showed that substitutional nitrogen on the hexagonal carbon network produces localized distortions on the tube walls. Analyzing nitrogen incorporation energy results for molecules of similar diameter, we conclude that carbon atoms are more easily substituted by nitrogen atoms in zigzag than in armchair nanotubes.…”

Formation of contacts between doped carbon nanotubes and aluminum electrodes

“…Substitutional doping by boron or nitrogen results in metallic CNTs [17][18][19][20] but also introduces new effects that must be considered. The electronic properties of intrinsically metallic CNTs degrade on incorportation of substitutional dopants, 21,22 and in addition, it is difficult to precisely control the doping levels within the CNT giving rise to dopant atom fluctuations 23 which impact on achieving reproducible electronic properties.…”

Comparative study of BxNyCz nanojunctions fragments

“…Emission mechanisms, conduction, and rectification processes are not understood if they are measure from carbon nanostructures. Relationship between morphology and electronic properties show controversial experimental results which difficult the development of new nanodevices based on nanostructures [24][25][26][27][28][29][30] . In this sense, we made a comparative study of the energy involved in the carbon atom substitution in B X N Y C Z nanojunctions fragments to propose some rules about the localization of nitrogen and boron atoms in nanojunctions regions of defects.…”