RESUMEN
Exotic 1D and 2D carbon nanostructures have been grown in the laboratory in the last few years by means of surface-assisted chemical routes. In these processes, the strategical choice of a molecular precursor plays a dominant role in the determination of the synthesized nanocarbon. Further variations of these techniques are able to produce non-benzoidal carbon quantum-dots (QDs). Considering this experimental scenario as motivation, we propose a series of nanoribbon systems based on concatenating recently synthesized carbon QDs containing pentagonal, hexagonal, and heptagonal rings. We use density functional theory (DFT) simulations to reveal their properties can range from metallic to semiconducting depending on the concatenation hierarchy used to form the nanoribbons. This DFT implementation is based on a LCAO approach to describe valence wavefunctions and most of the simulations employ the PBE-GGA functional. Since this functional is known to underestimate band gaps, we also use the B3LYP functional in a plane-wave DFT approach for a selected case for comparison purposes. These systems show a different gap versus width relationship compared to conventional graphene nanoribbons setups and a particular set of carrier mobility values. We further discuss the interplay between the QD's frontier states and the electronic properties of the nanoribbons in light of their structural details.
RESUMEN
The 2D naphthylene-ß structure is a theoretically proposed sp2 nanocarbon allotrope based on the assembly of naphthalene-based molecular building blocks, which features metallic properties. We report that 2D naphthylene-ß structures host a spin-polarized configuration which turns the system into a semiconductor. We analyze this electronic state in terms of the bipartition of the lattice. In addition, we study the electronic properties of nanotubes obtained from the rolling up of 2D naphthylene-ß. We show that they inherit the properties of the parent 2D nanostructure, such as the emergence of spin-polarized configurations. We further rationalize the results in terms of a zone-folding scheme. We also show that the electronic properties can be modulated using an external transverse electric field, including a semiconducting-to-metallic transition for sufficiently large field strength.
RESUMEN
Graphyne nanocarbons are composed of a mixture of sp and sp2 hybridized atoms in different ratios and distributions. In addition to pure hexagonal systems, non-conventional graphynic structures can also accommodate non-hexagonal rings, as proposed recently on the basis of previously studied haeckelites. Here we use computational simulations to investigate the electronic properties emerging from quantum confinement when such 2D systems are cast into different families of nanoribbons. We show that the electronic behavior of these ribbons closely follow those of their 2D counterparts. However, we find that part of these quasi-1D systems become semiconductors due to the emergence of spin-polarized states at their edges. We further investigate how such multiple spin-configurations influence the electronic transport properties of nanojunctions involving these non-conventional graphyne nanoribbons. These findings highlight how details of these graphyne nanoribbons' atomic structure can be used to tune their electronic properties for targeted applications in nanoelectronics.
RESUMEN
Several bottom-up chemical routes have been developed in the last few years to find ways to grow new forms of nanocarbon by devising a strategical selection of molecular precursors. Here, theoretical calculations are performed on 2D nanocarbon allotropes obtained from the fusion of triphenylene-like units through tetragonal rings. This 2D triphenylene structure has a metallic character in a closed shell configuration, but it also features a spin-polarized semiconducting state. The behavior of the electronic properties of the system is investigated when the structure is cast into nanoribbon forms. It is found that to be metallic in the nonpolarized case, the ribbons must be sufficiently wide while narrow 1D systems are semiconducting. A lower threshold width is also needed for the emergence of a spin-polarized semiconducting configuration in these nanoribbons. These behaviors are robust as they do not depend on edge geometry and chirality, thus offering opportunities for their possible applications in nanoscale devices.
RESUMEN
Tripentaphenes are 2D nanocarbon lattices conceptually obtained from the assembly of acepentalene units. In this work, density functional theory is used to investigate their structural, electronic, and vibrational properties. Their bonding configuration is rationalized with a resonance mechanism, which is unique to each of the 2D assemblies. Their formation energies are found to lie within the range of other previously synthesized carbon nanostructures and phonon calculations indicate their dynamical stability. In addition, all studied tripentaphenes are metallic and display different features (e.g., Dirac cone) depending on the details of the atomic structure. The resonance structure also plays an important role in determining the electronic properties as it leads to delocalized electronic states, further highlighting the potential of the structures in nanoelectronics.
