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Carbon Allotropes-Based Nanodevices
Published in Shilpi Birla, Neha Singh, Neeraj Kumar Shukla, Nanotechnology, 2022
Sugandha Singhal, Meenal Gupta, Md. Sabir Alam, Md. Noushad Javed, Jamilur R. Ansari
This concludes that the common features that provide fundamental insights toward graphene structural features are Dirac cones and linear carrier dispersion [12]. Regarding carbon pentagons, the well-known isolated pentagon rule (IPR) states that pentagons should be isolated rather than fused, which provides kinetic stability to fullerenes. Synthesis of fullerenes paved the way for further research to stabilize non-IPR fused pentagon-based carbon nanomaterials across various dimensions [17,18]. Singh et al. (2014) reported a stable 2D allotrope named pentahexocite, a continuous sheet of 5, 6, 8 carbon atom rings. The modes of phonon spectra are unstable, giving rise to planar sheet structure. Moreover, it has mechanical stability as that of graphene. The sheet is of metallic character, which has flat dispersive Fermi-level bands owing to the anisotropic properties. The above sheet becomes a precursor for designing and development of CNTs with chiral properties. However, due to the acoustical and optical mode mixing as well as reduced symmetry over graphene, the conductivity is lower than graphene. The nanowires (1D) with 5,8 carbon chains [15] have been put to use in valley-tronic devices [19]. The photonic bandgap has 40 THz value for the pentahexoctite sheet, making it a suitable candidate for nano-electronic devices [20]. On similar lines, Jena et al. (2015) predicted with theoretical calculations a dynamically and mechanically stable 2D allotrope pentagraphene with pentagon rings and a resemblance to Cairo pentagonal tiling. Also, its ability to withstand high temperatures of 1000K proves thermal stability. The mechanical strength is greater than graphene; it has a negative Poisson's ratio and a large bandgap with value 3.25 eV. The semiconducting pentagon-based nanotubes are formed by rolling pentagraphene sheets. The rolled pentagraphene sheets form semiconducting carbon nanotubes, and the stable 3D T12-carbon structure is built by sheet stacking with a large bandgaps are both thermally and dynamically stable. These extensive features of graphene and its derivatives can help in fields of device fabrication in nanomechanics and nano-electronics [16]. Oganov et al.(2015) predicted a low-energy rectangular 2D allotrope, namely phagraphene, consisting of 5-, 6-, and 7-membered carbon rings. The low energy value for phagraphene of –9.03 compared to graphene; -9.23 eV/atom, is due to sp2 bonding. The calculated value for the planar atomic density of phagraphene is 0.37 units, which is similar to graphene, and the plane group is Pmg. The electronic structure suggests that Dirac cones are distorted to reduce external strain without the effect of Fermi velocity. With the help of these structural observations, further research studies on mass-free Dirac fermions for 2D systems and construction of new phases in the artificial lattices of photons [21] were possible. The above examples indicate that pentagon-containing carbon materials possess varied mechanical and electronic properties [18]. These examples indicate that neither the structural features of graphene (among it are hexagon symmetry and bi-lattice backbone) nor sp2 hybridization is a prerequisite for Dirac carrier dispersion.
On the thermal conductivity of the α2-graphyne nanotubes: A molecular dynamics investigation
Published in Mechanics of Advanced Materials and Structures, 2022
After the realization of the graphene by the experiments in 2004 [1], different researches have been conducted to evaluate its physical properties. Due to the considerable physical properties of the graphene, other two-dimensional nanostructures such as pentagraphene [2], phagraphene [3] and the graphynes [4–6] were also investigated looking for the same great characteristics. The latter mentioned nanostructure, i.e. graphyne, is one of the most important structures that due to its applications in different fields such as energy storage [7, 8] and water purifcation [9, 10] have been extensively studied.