Although the properties of carbon nanotubes (CNTs) are very well-known and are still extensively studied, a thorough understanding of other carbon-based nanomaterials such as C3N nanotubes (C3NNTs) is still missing. In this article, we used molecular dynamics simulation to investigate the effects of parameters such as chirality, diameter, number of walls, and temperature on the mechanical properties of C3N nanotubes, C3N nanobuds, and C3NNTs with various kinds of defects. We also modeled and tested the corresponding CNTs to validate the results and understand how replacing one C atom of CNT by one N atom affects the properties. Our results demonstrate that the Young\'s modulus of single-walled C3NNTs (SWC3NNTs) increased with diameter, irrespective of the chirality, and was higher in armchair SWC3NNTs than in zigzag ones, unlike double-walled C3NNTs. Besides, adding a second and then a third wall to SWC3NNTs significantly improved their properties. In contrast, the properties of C3N nanobuds produced by attaching an increasing number of C60 fullerenes gradually decreased. Moreover, considering C3NNTs with different types of defects revealed that two-atom vacancies resulted in the greatest reduction of all the properties studied, while Stone-Wales defects had the lowest effect on them.

BACKGROUND: Synthesis, properties, structural peculiarities, and applications of nanobuds and related nanostructures are discussed. In addition, few relevant patents to the topic have been reviewed and cited. According to observed properties and those predicted by DFT calculations, the nanobuds are semiconducting and stable in normal conditions, can accept adatoms and molecules. They contain a relatively chemically inert carbon nanotubes and more active fullerene species and can be compatible with a variety of other materials, in particular polymers. In addition to nanobuds for SWCNTs, the nanobuds with graphene, small fullerenes or metal nanobud-like structures are also known.
METHODS: We have undertaken an extensive search of bibliographic databases for peer-reviewed research literature using a focused review question and inclusion/exclusion criteria. The characteristics of screened papers were described and critically compared.
RESULTS: Thirty-six papers were included in the review, mainly from high-impact international journals. The published articles correspond to the range 2006-2016; the term \"nanobuds\" appeared in 2006 after their discovery. The reports included approaches of the synthesis of carbon nanobuds, their formation mechanism, in situ engineering, different modes of attachment of fullerene on carbon nanotubes, DFT and MD calculations, nanobuds containing small fullerenes and graphene nanobuds, information about related noble metal nanobuds, and applications of carbon nanobuds.
CONCLUSIONS: The findings of this review confirm the importance of novel less-common nanostructures on the basis of carbon for fundamental science, their unusual properties and current and possible applications.