Interest in fullerene-based polymer structures has renewed due to the development of synthesis technologies using thin C60 polymers. Fullerene networks are good semiconductors. In this paper, heterostructure complexes composed of C60 polymer networks on atomically thin dielectric substrates are modeled. Small tensile and compressive deformations make it possible to ensure appropriate placement of monolayer boron nitride with fullerene networks. The choice of a piezoelectric boron nitride substrate was dictated by interest in their applicability in mechanoelectric, photoelectronic, and electro-optical devices with the ability to control their properties. The results we obtained show that C60 polymer/h-BN heterostructures are stable compounds. The van der Waals interaction that arises between them affects their electronic and optical properties.

The formation of diamond in multilayer graphene under a local mechanical stress induced by the indentation of a film is theoretically studied. To describe this effect, the machine learning potential based on the representation of the atomic environment in the form of moment of inertia tensors is parameterized. The results demonstrate that the atomic structure of emerging diamond is determined by both graphene stacking and indenter size, providing an interplay of cubic and hexagonal diamond phases observed in the arising structure. The study also reveals a much lower phase transition pressure for graphene with the AA' stacking as compared to the ABC stacking in the films with a number of layers below hundred.

The atomic and electronic structure of superperiodic vertical hybrid Janus heterostructures based on doped twisted bilayer graphenes were theoretically developed and studied using electronic structure calculations. Regularly opposed superperiodic sublattices of fluorine and aluminum adatoms were used to induce structural charge polarization, and uncompensated spin moments up to 1.05 & mu;B per unit cell, caused by local intense transverse electric fields generated by ferromagnetically aligned spin polarization of entire lattices. It was shown that spin polarization of the heterostructures is mostly determined by partial carbon and fluorine electronic states localized in the vicinity of the Fermi level, whereas superlattices of Al adatoms mostly determine the rate of charge polarization, the symmetry, and intensity of the internal transverse electric field up to -0.018 e2/& ANGS;. It was shown that proposed heterostructures may display advanced electronic spin, entanglement and magnetostriction properties perspective for various spin- and quantum-related applications.

Diamanes are unique 2D carbon materials that can be obtained by the adsorption of light atoms or molecular groups onto the surfaces of bilayer graphene. Modification of the parent bilayers, such as through twisting of the layers and the substitution of one of the layers with BN, leads to drastic changes in the structure and properties of diamane-like materials. Here, we present the results of the DFT modelling of new stable diamane-like films based on twisted Moiré G/BN bilayers. The set of angles at which this structure becomes commensurate was found. We used two commensurate structures with twisted angles of θ = 10.9° and θ = 25.3° with the smallest period as the base for the formation of the diamane-like material. Previous theoretical investigations did not take into account the incommensurability of graphene and boron nitride monolayers when considering diamane-like films. The double-sided hydrogenation or fluorination of Moiré G/BN bilayers and the following interlayer covalent bonding led to the opening of a gap up to 3.1 eV, which was lower than the corresponding values of h-BN and c-BN. The considered G/BN diamane-like films offer great potential in the future for a variety of engineering applications.

The mechanical characteristics of diamond-like films, such as Dn21.8, Dn27.8, and Dn29.4 moiré diamanes, formed by the hydrogenation of graphene layers twisted at an angle of about 30°, and of conventional diamane (Dn) based on bilayer graphene with the AB packing are simulated using the molecular mechanics approach. The elastic moduli of these materials are calculated. It is shown that the elastic constants for moiré diamanes differ noticeably from similar constants of Dn diamane, and their fracture occurs at higher strains than at those for the latter. The responses to forces applied in the plane of the films turn out to be anisotropic for the Dn21.8 and Dn27.8 structures and almost isotropic for Dn29.4. It is shown that the breakthrough for the Dn29.4 membrane under the action of a tip occurs at a larger force than that for the membrane made of the most energetically stable Dn27.8 diamane.

With an emphasis on remarkable properties, twisted vertical heterostructures have received particular attention in experimental and theoretical works. They have promising unknown effects in science and technology. These twisted systems can be considered a platform for the formation of crystalline film structures. In this paper, we consider one of them, diamond-like crystals with Moire atomic structure formed from twisted two-dimensional hexagonal layers. Analogues of carbon Moire diamanes are nanometer-thick films obtained by both stacking and twisting near 30(degrees) of two functionalized monolayers of nitrides (AlN, BN, GaN), which have already been actually obtained. We study their energetically stable atomic configurations and electronic and elastic properties. The proposed hydrogenated and/or fluorinated (second side, Janus structures) Moire nitridane nanostructures with a twisted angle of 27.8(degrees) possess a wide band gap from 3 to 4 eV. Electronic band structures are characterized by many flattened bands located near the edges of the valence and conduction bands, which tend to be signatures of Moire superlattices. The Moire nitridanes can be used as a base for two-dimensional semiconductors with low-dispersive flattened bands and strong localization of the electronic states, which should increase the probability of their resonant IV characteristics and light excitations. Thus, the circumstance is useful for nano- and optoelectronic resonant devices. In addition, it was found that hydrogenated and fluorinated Moire nitridane and nitride films have some very different elastic responses, which are attractive for mechanoelectric applications.

The dodecagonal graphene quasicrystal (GQC) based on a 30° twisted bigraphene has been well investigated. Recently, the sp3-hybridizated carbon analog, the diamane quasicrystal as a H(F) functionalized GQC was proposed. Here we present a study of a similar sp3-hybridizated boron nitride 3-fold symmetry piezoelectric quasicrystal (BNnQC) based on a 30° twisted hexagonal BN bilayer (BNQC). The analysis of the atomic and electronic structures of its approximants based on 29.4° and 27.8° twisted h-BN bilayers has been carried by using of the density functional theory (DFT). The calculated values of the energy gaps ∼5 eV classify this predicted boron nitride material as a new wide-gap 2D quasicrystal.

We proposed novel carbon nanostructures based on a twisted few-layered graphene with one side passivated by hydrogen or fluorine: Moiré diamones on graphene. The presence of a dangling bond at the bottom layer of diamones leads to the appearance of spin density localization, which can be tuned by the variation of the twist angle with the following formation of Moiré diamones. The spin-polarized nature of electronic density distribution was obtained and discussed in detail on the basis of ab initio calculations. Such a feature makes Moiré diamones a promising key element in the field of controllable spintronic devices.

The electronic and transport properties of new hybrid 2D–1D–2D structures of carbon atoms, which are graphene sheets continuously connected through a fragment of a single-layer carbon nanotube, frequently observed experimentally, are theoretically studied. The evolution of the electronic properties of such systems with “zigzag” carbon nanotubes of various diameters with chirality indices (14, 0), (15, 0), (16, 0), and (18, 0) is studied using the tight coupling method within electron density functional theory. The calculation of the transmission coefficient demonstrates a strong nonlinearity in the behavior of the transport properties of these structures near the Fermi energy as a function of the diameter of carbon nanotubes, which explains discrepancies in the previously obtained experimental data.

We investigated hydrogenated twisted and non-twisted bilayer structures consisting of two hexagonal boron nitride ( h BN) monolayers with interlayer covalent bonds. These structures, named bornitranes, are boron nitride analogues of well-known carbon diamanes. We found that the binding energy of twisted structures was about 0.5 eV/BN higher than that of non-twisted AA’- and AB-stacked h BN layers. According to our calculations, the fully hydrogenated Moiré bornitrane with the 21.8 o twisted angle has a flattened valence band and an indirect band gap of about 2.8 eV. This value is almost twice wider than that for their non-twisted counterparts. The computed Young’s modulus of bornitranes is higher than that for the h BN monolayer. The infrared and Raman spectra of the considered systems were also defined. Spectral fingerprints of the Moiré bornitrane possess many peaks due to the presence of distorted interlayer bonds and are radically different from the spectra of non-twisted systems. Calculated peaks can facilitate experimental detection of the Moiré bornitranes. Investigated structures are novel 2D semiconductors suitable for nanoelectronics and optoelectronics applications.

Based on direct space DFT PBE0/6-31G* electronic structure calculations, the structure and properties of nanodiamond islands confined between two finite graphene fragments (NDI-c2G) was proposed and theoretically explored. DFT simulations revealed that fusion of planar aromatic molecules with two parent graphene fragments may form either cubic or hexagonal allotropes of NDI-c2Gs lattices accompanied with formation of local corrugated sp(3) sites with substituted dangling bonds embedded into graphene sublattices. It was shown that at the DFT level of theory, low distortion energies of NDI-c2Gs lattices are comparable or smaller than the energy of van-der-Waals interactions, which allows the NDI-c2G lattices to be stabilized by a support and finally synthe-sized. The Nuclear Independent Chemical Shift calculations, shows that in the vicinity of NDI regions, graphene lattices are estimated to be either low-, or anti-aromatic. Furthermore, the formation of NDI-c2Gs leads to localization of HOMO and LUMO states at different sites of the NDI-c2Gs lattices. The NDI-c2G regions with confined frontier orbitals can be considered as arrays of quantum dots isolated from each other by NDI scattering centres of 3.82 angstrom dimension. The results demonstrates that NDI-c2G should be considered as strongly-correlated entangled hybrid quantum dots which may form extended quantum ensembles with great potential for advanced quantum applications.

The atomic and electronic structures of diamanes, i.e., diamond-like films formed by few-layer moiré graphene with a twist angle θ in 00θ and θ00θ stackings are simulated. Chemical adsorption of light atoms (e.g., hydrogen) or molecules on the surface of such graphene leads to the formation of interlayer bonds and, thus, to the complete sp 3 -hybridization of carbon atoms in structures. Using the available experimental data on the preparation of moiré graphene structures and diamanes based on untwisted bigraphene, a model is proposed for the possible synthesis of such diamanes from twisted three- and four-layer graphene. A hypothetical moiré diamane crystal formed from stacks of similar four-layer graphene is also considered. The stability of three- and four-layer moiré diamanes and the proposed artificial crystal has been demonstrated. The band gap decreases with an increase in the number of initial layers, but the band gap for the crystal is wider because of the higher strain of С–С' bonds, which in the previous cases bond C and H atoms.

Extreme structure and spin states of doped and undoped perforated bigraphenes was studied using DFT simulations. It was found that folded nanopores possess extremely high curvature of 0.34 angstrom(-1). Dramatic structural deformation causes severe changes of the chemical properties of carbon atoms localized at the nanopores converting the folded edges to local oxidative fragments. It was found that asymmetrical coordination of either Li, Ca, or Al to the nanopores is coupled with electron transfer from metal to edge carbon atoms and breakdown of local inversion symmetry. Li-, Ca-, and Al-doped perforated AA bigraphene revealed ferromagnetic spin ordering with magnetic moments of 0.38, 0.14, and 0.32 mu(B)/unit cell, respectively, and spin polarization energy gain of 0.037eV for Ca-doped superlattice. It was shown that ferromagnetic spin ordering of bigraphene nanopores contradicts to the Nagaoka's theorem, which excludes strong electron correlations as a reason of spin polarization. Spontaneous lift of spin degeneracy was interpreted in terms of perturbing intense local electrostatic fields from extra electron charges localized at the nanopore edges, coupled with breakdown of space inversion and local translation invariances. It was shown that spin energy splitting is proportional to the matrix elements calculated on Bloch states with opposite wavevectors and perturbing electrostatic fields. (C) 2022 Elsevier Ltd. All rights reserved.

An Erratum to this paper has been published: https://doi.org/10.1134/S0021364022340033

Here we propose the first two-dimensional carbon quasicrystal made entirely of sp(3) -hybridized atoms, namely diamane quasicrystal. This nanostructure is based on incommensurate lattice of two graphene layers twisted by 30 degrees with respect to each other (well-known graphene quasicrystal) with totally hydrogenated or fluorinated surfaces of bilayer graphene (similar to formation of AB-stacked diamane by means of applying high pressure treatment). We describe in detail the features of atomic structure appearing during the formation of quasicrystal. Thermodynamic stability, electronic and mechanical characteristics in comparison with both periodic approximants and AB-stacked diamanes via DFT and MD methods are studied and discussed. Proposed diamane quasicrystals exhibit unique mechanical properties: they are stiffer and more brittle than AB-stacked diamane. Our study shows that quasicrystalline diamane is a prospective material that opens a new way towards the synthesis of inorganic quasicrystals of various compositions with unique set of physical and chemical properties.

Ultra-thin diamond membranes, diamanes, are one of the most intriguing quasi-2D films, combining unique mechanical, electronic and optical properties. At present, diamanes have been obtained from bi- or few-layer graphene in AA- and AB-stacking by full hydrogenation or fluorination. Here, we study the thermal conductivity of diamanes obtained from bi-layer graphene with twist angle θ between layers forming a Moiré pattern. The combination of DFT calculations and machine learning interatomic potentials makes it possible to perform calculations of the lattice thermal conductivity of such diamanes with twist angles θ of 13.2∘, 21.8∘ and 27.8∘ using the solution of the phonon Boltzmann transport equation. Obtained results show that Moiré diamanes exhibit a wide variety of thermal properties depending on the twist angle, namely a sharp decrease in thermal conductivity from high for "untwisted" diamanes to ultra-low values when the twist angle tends to 30∘, especially for hydrogenated Moiré diamanes. This effect is associated with high anharmonicity and scattering of phonons related to a strong symmetry breaking of the atomic structure of Moiré diamanes compared with untwisted ones.

Diamanes are 2D diamond-like films that are nanometers in thickness. Diamanes can exist as bilayer or multilayer graphene with various modes of stacking and interlayer covalent sp3 bonds. The term “diamane” is used broadly for a variety of diamond-like materials at the nanoscale, from individual diamond clusters to nanocrystal films. A short overview of recent progress in the investigation of diamanes, starting from the first theoretical predictions to practical realization, is presented. The results of both theoretical and experimental studies on diamanes with various atomic structures and types of functionalization are considered. It is shown that diamanes are stronger than graphene and graphane and have wide bandgaps ranging from 3.1 to 4.5 eV depending on the structure. Diamane-like structures have been obtained using different experimental techniques, and their structures have been determined by Raman spectroscopy. The potential applications of these carbon nanostructures are briefly reviewed.

We applied density functional theory to predict the atomic and electronic structures, Raman, and IR spectra of the new diamond-like 2D materials - Moire diamanes (Dns). They are based on the fully hydrogenated or fluorinated twisted bilayer graphenes (tBG) and are formed by interlayer connection. Due to the twisted structure of Moire bilayer, graphene interlayer connection significantly different from the connection of AA- or AB-stacked bilayer that dictates their property features. We consider characteristics of hydrogenated and fluorinated Moire diamanes with the simplest unit cell based on the 21.8 degrees tBG- Dn21.8 and F-Dn21.8, respectively. The calculated band structures of considered twisted diamanes show the band gaps higher than 4 eV exceed the gaps of standard diamanes. The presence of a large number of narrow peaks of densities of states (DOS) connected with flattened minizones provides their applicability in optical and optoelectronic devices. To identify Dn21.8 or F-Dn21.8, we calculate and describe Raman and IR spectral features of both structures, which turned out to be similar. The most active Raman frequencies of these Moire structures are blue-shifted concerning standard AA or AB-stacked diamanes. In contrast to traditionally stacked arrangements, considered twisted diamanes can interact with the light polarized parallel to the film plane.