Energies of graphene nanocones with 1 to 5 pentagonal disclinations are studied on an atomically detailed level. The numerical results are interpreted in terms of three different contributions to the cone energy: the core disclination energy, the bending energy of the cone surface, and the ''line tension'' energy of the cone edge that is related to different coordination of carbon atoms situated at the edge. This continuum description allows for a construction of analytic expressions for the cone energetics and indicates different regimes of cone sizes in which cones with a particular number of disclinations are preferred energywise. An important result of the study is that the energetics of various types of cones profoundly depends upon whether the dangling carbon bonds at the cone basis are saturated by hydrogen atoms or not. This may be of use for explaining the differences in the yields of various cone types in different production processes.
Heterostructures made of stacked 2D materials with different electronic properties are studied for their potential in creating multifunctional devices. Graphene (G) and hexagonal boron nitride (h-BN) van der Waals (vdW) systems have been extensively researched, including recent studies on synthesizing h-BN on graphene/SiC(0001) templates. These studies suggest that h-BN encapsulation could occur in addition to vdW epitaxy. This work presents theoretical research on G/h-BN heterostructures on SiC(0001) with a carbon buffer layer. The results show an energetic preference for h-BN encapsulation b…
Highly energetic ions traversing a two-dimensional material such as graphene produce strong electronic excitations. Electrons excited to energy states above the work function can give rise to secondary electron emission, reducing the amount of energy that remains the graphene after the ion impact. Electrons can either be emitted (kinetic energy transfer) or captured by the passing ion (potential energy transfer). To elucidate this behavior that is absent in three-dimensional materials, we simulate the electron dynamics in graphene during the first femtoseconds after ion impact. We employ two c…
There has been a lot of excitement around the observation of superconductivity in twisted bilayer graphene, associated to flat bands close to the Fermi level. Such correlated electronic states also occur in multilayer rhombohedral stacked graphene (RG), which has been receiving increasing attention in the last years. In both natural and artificial samples however, multilayer stacked Bernal graphene (BG) occurs more frequently, making it desirable to determine what is their relative stability and under which conditions RG might be favored. Here, we study the energetics of BG and RG in bulk and …
Transition metal phthalocyanines (TMPc's) are under intense scrutiny in the field of spintronics, as they may be promising storage devices. The simplicity and cheapness of such molecules increase their commercial potential. There is an active study of how the magnetic moment of the metal centre of such molecules can be changed. Here, we particularly consider the iron phthalocyanine molecule (FePc) on a graphene layer as a substrate. We study how graphene defects (the Stone-Wales defect, B-doping, N-doping, S-doping, and combined B (N, S)-doped Stone-Wales defects) change the FePc electronic st…
Ab initio calculations are performed to study consecutive reconstruction of a zigzag graphene edge. According to the obtained energy profile along the reaction pathway, the first reconstruction step, formation of the first pentagon-heptagon pair, is the slowest one, while the growth of an already nucleated reconstructed edge domain should occur steadily at a much higher rate. Domains merge into one only in 1/4 of cases when they get in contact, while in the rest of the cases, residual defects are left. Structure, energy and magnetic properties of these defects are studied. It is found that spo…
Theoretical investigation on armchair graphene nanoribbons with oxygen-terminated edges
采用基于密度泛函理论的晶体轨道方法研究了不同边缘氧原子比例的扶手椅型石墨烯纳米带。所有的纳米带是积极有利的，虽然弯曲的边缘存在。孤立的边缘氧原子通过引入边缘态而引起电子-金属跃迁，而相邻的边缘氧原子则不能。对于在边缘上具有所有氧原子的石墨烯纳米带，带隙和载流子迁移率两者相对于带宽度交替。载流子迁移率为18%-65%大的石墨烯纳米带与氢终止的边缘。这些值高达103 cm 2 V-1 s-1，对于电子设备来说仍然相当高。晶体轨道分析给出了这一现象的图形解释。
Carbon(C) doped hexagonal boron nitride(hBN) has been experimentally reported in recent years to be a possible catalytic host to oxygen reduction reaction(ORR), as well as a possible ferromagnet at room temperature. Substitution by C in hBN has been also reported to form islands of graphene. In this work, we explore from first principles, the connection between these different aspects of C doped hBN. We find formation of graphene islands covering unequal number of B and N sites in hBN to be energetically plausible. They possess a net non-zero magnetic moment and are also found to be substantia…
We study the dissociative adsorption of methane at the surface of graphene. Free energy profiles, which include activation energies for different steps of the reaction, are computed from constrained ab initio molecular dynamics. At 300 K, the reaction barriers are much lower than experimental bond dissociation energies of gaseous methane, strongly indicating that graphene surface acts as a catalyst of methane decomposition. On the other hand, the barriers are still much higher than on nickel surface. Methane dissociation therefore occurs at a higher rate on nickel than on graphene. This reacti…
We study the energetic stability and the local electronic structure of the general twisted trilayer graphene (TTG) with the top and bottom layers rotated with respect to the middle layer respectively by $θ$ and $θ'$. Approximate supercells of the moiré-of-moiré superlattices with $θ$ and $θ^{\prime}$ within $1^{\circ}\sim 2^{\circ}$ are established to describe the structural and electronic properties of relaxed TTG with the periodic boundary condition. Full relaxation demonstrates that the commensurate TTG with $θ=θ^{\prime}$ has the local minimum total energy ($E_{tol}$) at a fixed $θ$, while…
The atomic structure of nanomaterials is often studied using transmission electron microscopy. In addition to image formation, the energetic electrons may also cause damage while impinging on the sample. In a good conductor such as graphene the damage is limited to the knock-on process caused by elastic electron-nucleus collisions. This process is determined by the kinetic energy an atom needs to be sputtered, ie, its displacement threshold energy. This is typically assumed to have a fixed value for all electron impacts on equivalent atoms within a crystal. Here we show using density functiona…
In this work a systematic approach to the search for all-$sp^2$ bonded carbon allotropes with low density is presented. In particular, we obtain a number of novel energetically stable crystal structures, whose arrangement is closely related to the topology of graphene, by modifying the packing of congruent discs under the condition of local stability. Our procedure starts from an initial parent topology and proceeds to generate daughter architectures derived by lowering the packing factors. Furthermore, we assess both the electronic properties, such as the band structure and the density of sta…
Grain boundaries (GBs), an important constituent of polycrystalline materials, have a wide range of manifestion and significantly affect the properties of materials. Fully understanding the effects of GBs is stalemated due to lack of complete knowledge of their structures and energetics. Here, for the first time, by taking graphene as an example, we propose an analytical energy functional of GBs in angle space. We find that an arbitrary GB can be characterized by a geometric combination of symmetric GBs that follow the principle of uniform distribution of their dislocation cores in straight li…
Two different types of boron-doped graphene/copper interfaces synthesized using two different flow rates of Ar through the bubbler containing the boron source were studied. X-ray photoelectron spectra (XPS) and optically stimulated electron emission (OSEE) measurements have demonstrated that boron-doped graphene coating provides a high corrosion resistivity of Cu-substrate with the light traces of the oxidation of carbon cover. The density functional theory calculations suggest that for the case of substitutional (graphitic) boron-defect only the oxidation near boron impurity is energetically …
An Alternative Strategy to Control the Electronic Properties of Bilayer Graphene: Semi-metal to Metal Transition and a 2D Material with Dirac Cone
AB堆叠的双层石墨烯（BLG）是一种纯半导体，其带隙和性质可以通过各种方法（例如掺杂或施加栅极电压）来调节。在这里，我们展示了一种替代方法来控制BLG的电子特性;在两个单层石墨烯（MLG）之间插入过渡金属原子。对二维MLG、BLG、BLG插层纳米结构材料进行了理论研究，所有材料都是能量稳定的。我们的研究表明，只有MLG和BLG-插入一个钒（V）原子（BLG-1V）材料在K点有一个狄拉克锥。这项研究揭示了一种新的策略，以控制BLG的材料特性，表现出各种行为，包括：金属，半金属，半导体通过改变BLG中的V原子的浓度和自旋排列。在所有情况下，本DFT计算表明，石墨烯中的C原子的2 p $_z$子壳层和V原子的3d $_{yz}$子壳层提供了费米能级附近的电子密度，控制BLG插层材料的材料性质。从而证明了面外原子对BLG中面内电子密度的影响。
In two-dimensional van der Waals (vdWs) materials, the relative twist angle between adjacent layers not only controls their electronic properties, but also determines their stacking energy. This effect makes it much easier to realize energetically favorable configurations of the vdWs materials, for example, Bernal-stacked structure of bilayer graphene. Here we demonstrate that we can controllably tailor adhesive energy landscape of graphene nanostructures on graphene and stabilize the system with tunable twist angle by using a one-dimensional tilt grain boundary (GB). The area ratio with diffe…
Monolayer and multilayer graphene are promising materials for applications such as electronic devices, sensors, energy generation and storage, and medicine. In order to perform large-scale atomistic simulations of the mechanical and thermal behavior of graphene-based devices, accurate interatomic potentials are required. Here, we present a new interatomic potential for multilayer graphene structures referred to as "hNN--Gr$_x$." This hybrid potential employs a neural network to describe short-range interactions and a theoretically-motivated analytical term to model long-range dispersion. The p…
Berry phase plays an important role in determining many physical properties of quantum systems. However, a Berry phase altering energy spectrum of a quantum system is comparatively rare. Here, we report an unusual tunable valley polarized energy spectra induced by continuously tunable Berry phase in Bernal-stacked bilayer graphene quantum dots. In our experiment, the Berry phase of electron orbital states is continuously tuned from about pi to 2pi by perpendicular magnetic fields. When the Berry phase equals pi or 2pi, the electron states in the two inequivalent valleys are energetically degen…
Pristine graphene interacts relatively weakly with Al, which is a specie of importance for novel generations of metal-ion batteries. We employ DFT calculations to explore the possibility of enhancing Al interaction with graphene. We investigate non-doped and N-doped graphene nanoribbons, address the impact of the edge sites, which are always present to some extent in real samples, and N-containing defects on the material's reactivity towards Al. The results are compared to that of pristine graphene. We show that introduction of edges does not affect the energetics of Al adsorption significantl…
