Penta-graphene is a quasi-two-dimensional carbon allotrope consisting of a pentagonal lattice in which both sp2 and sp3-like carbons are present. Unlike graphene, penta-graphene exhibits a non-zero bandgap, which opens the possibility of its use in optoelectronic applications. However, as the observed bandgap is large, gap tuning strategies such as doping are required. In this work, density functional theory calculations are used to determine the effects of the different number of line defects of substitutional nitrogen or silicon atoms on the penta-graphene electronic behavior. Our results show that this doping can induce semiconductor, semimetallic, or metallic behavior depending on the doping atom and targeted hybridization (sp2 or $sp3-like carbons). In particular, we observed that nitrogen doping of sp2-like carbons atoms can produce a bandgap modulation between semimetallic and semiconductor behavior. These results show that engineering line defects can be an effective way to tune penta-graphene electronic behavior.
We present a tight-binding parametrization for penta-graphene that correctly describes its electronic band structure and linear optical response. The set of parameters is validated by comparing to ab-initio density functional theory calculations for single-layer penta-graphene, showing a very good global agreement. We apply this parameterization to penta-graphene nanoribbons, achieving an adequate description of quantum-size effects. Additionally, a symmetry-based analysis of the energy band structure and the optical transitions involved in the absorption spectra is introduced, allowing for th…
Carbon allotropes have a large family of materials with varieties of crystal structures and properties and can realize different topological phases. Using first principles calculations, we predict a new two-dimensional (2D) carbon allotrope, namely penta-octa-graphene, which consists of pentagonal and octagonal carbon rings. We find that penta-octa-graphene can host both type-I and type-II Dirac line nodes (DLNs). The band inversion between conduction and valence bands forms the type-I DLNs and the two highest valence bands form the type-II DLNs. We find that the type-I DLNs are robust to the …
Penta-graphene is the name given to a novel puckered monolayer of carbon atoms tightly packed into an inerratic pentagonal network, theoretically, which exhibits excellent thermal and mechanical stability and can be rolled into penta-graphene nanotubes (PGNTs). Herein, we perform the first simulation study of mechanical properties of PGNTs under uniaxial tension. In addition to comparable mechanical properties with that of carbon nanotubes (CNT), it is found that PGNTs possess promising extensibility with typical plastic behavior due to the irreversible pentagon-to-polygon structural transform…
The electronic structure of pentacene decorated with dipole groups (d-pentacene) and adsorbed onto a graphene substrate has been studied within the density functional theory. Three reference configurations have been considered, namely the ideal molecule without distortions, the actual molecule including intramolecular distortions and the molecule adsorbed onto graphene. Calculations show a noticeable charge redistribution within the d-pentacene + graphene system due to molecular distortion, as well as the formation of weak $π$-bonds between the molecule and the substrate. Additionally, the eff…
Penta-graphene (PG) has been identified as a novel 2D material with an intrinsic bandgap, which makes it especially promising for electronics applications. In this work, we use first-principles lattice dynamics and iterative solution of the phonon Boltzmann transport equation (BTE) to determine the thermal conductivity of PG and its more stable derivative - hydrogenated penta-graphene (HPG). As a comparison, we also studied the effect of hydrogenation on graphene thermal conductivity. In contrast to hydrogenation of graphene, which leads to a dramatic decrease in thermal conductivity (from 359…
Studies aimed at designing new allotropic forms of carbon have received much attention. Recently, a new 2D graphene-like allotrope named Pentahexoctite was theoretically proposed. Pentahexoctite has a metallic signature, and its structure consists of continuous 5-6-8 rings of carbon atoms with sp2 hybridization. Here, we carried out fully-atomistic computational simulations, combining reactive (ReaxFF) molecular dynamics (MD) and density functional theory (DFT) methods, to study the elastic properties and fracture patterns of Pentahexoctite monolayer. Results revealed a Young's Modulus of 0.74…
The novel carbon allotrope with particular and unique 2D arrangement of carbon atoms similar to a Cairo pentagonal tiling, with interplay of $sp^{3}$ and $sp^{2}$ hybridized carbon atoms is called of Penta-graphene (PG). Previous theoretical investigations have shown that PG monolayer is mechanically and thermodynamically stable, possessing also a large band gap of $3.25eV$. This new carbon allotrope with unique carbon atom arrangement in a network (non-coplanar pentagons) is the focus of the theoretical investigations in this work. Using the non-equilibrium molecular dynamics simulations with…
We analyze the symmetry and topological features of a family of materials closely related to penta-graphene, derived from it by adsorption or substitution of different atoms. Our description is based on a novel approach, called topological quantum chemistry, that allows to characterize the topology of the electronic bands, based on the mapping between real and reciprocal space. In particular, by adsorption of alkaline (Li or Na) atoms we obtain a nodal line metal at room temperature, with a continuum of Dirac points around the perimeter of the Brillouin zone. This behavior is also observed in …
Since the discovery of graphene, two-dimensional (2D) materials have paved a new routine for designing high-performance nanoelectronic devices. To facilitate the device applications, there are three key requirements for a material: sizeable band gap, high carrier mobility and robust environmental stability. However, for the hottest 2D materials studied in recent years, graphene is gapless, transition metal dichalcogenides have low carrier mobility, and black phosphorene is environmentally sensitive. So far, these three characteristics can seldom be satisfied in one single material. Therefore, …
The development of high-energy and high-power density supercapacitors (SCs) is critical for enabling next-generation energy storage applications. Nanocarbons are excellent SC electrode materials due to their economic viability, high-surface area, and high stability. Although nanocarbons have high theoretical surface area and hence high double layer capacitance, the net amount of energy stored in nanocarbon-SCs is much below theoretical limits due to two inherent bottlenecks: i) their low quantum capacitance and ii) limited ion-accessible surface area. Here, we demonstrate that defects in graph…
The power of polymorphism in carbon is vividly manifested by the numerous applications of carbon-based nano-materials. Ranging from environmental issues to biomedical applications, it has the potential to address many of today's dire problems. However, an understanding of the mechanism of transformation between carbon allotropes at a microscopic level is crucial for its development into highly desirable materials. In this work we report such a phase transformation between two carbon allotropes, from penta-graphene (a semiconductor) into biphenylene (a metal) under uniaxial loading. Using densi…
The unique properties of graphene offer immense opportunities for applications to many scientific fields, as well as societal needs, beyond our present imagination. One of the important features of graphene is the relatively simple tunability of its electronic structure, an asset which extends the usability of graphene even further beyond present experience. A direct injection of charge carriers into the conduction or valence bands, i.e., doping, represents a viable way of shifting the Fermi level. In particular, the electrochemical doping should be the method of choice, when higher doping lev…
The fabrication of atomically precise structures with designer electronic properties is one of the emerging topics in condensed matter physics. The required level of structural control can either be reached through atomic manipulation using the tip of a scanning tunneling microscope (STM) or by bottom-up chemical synthesis. In this review, we focus on recent progress in constructing novel, atomically precise artificial materials: artificial lattices built through atom manipulation and graphene nanoribbons (GNRs) realized by on-surface synthesis. We summarize the required theoretical background…
Pentagonal Monolayer Crystals of Carbon, Boron Nitride, and Silver Azide
在这项研究中，我们提出了一个五角形单层的碳（p-石墨烯），氮化硼（p-B $_{2}$ N $_{4}$和p-B $_{4}$ N $_{2}$）和叠氮化银（p-AgN $_{3}$）的结构，电子和机械性能的理论研究，通过执行国家的最先进的第一性原理计算。我们的总能量计算表明完全由五边形组成的单层晶体结构的形成是可行的。此外，电子能带色散计算表明，虽然p-石墨烯和p-AgN $_{3}$是具有间接带隙的半导体，但p-BN结构显示出金属行为。我们还研究了单轴应变下四种不同五边形结构的力学性能（面内刚度和泊松比）。发现p-石墨烯具有最高的刚度值，并且发现相应的泊松比为负。类似地，p-B $_{2}$ N $_{4}$和p-B $_{4}$ N $_{2}$具有负泊松比值。另一方面，p-AgN $_{3}$具有大的正泊松比。在动力学稳定性测试的基础上计算的声子谱的这些五边形单层，我们发现，只有p-石墨烯和p-B $_{2}$ N $_{4}$是稳定的，但p-AgN $_{3}$和p-B $_{4}$ N $_{2}$是容易受到振动激发。
Penta-graphene (PG) is a carbon allotrope that has recently attracted the attention of the materials science community due to its interesting properties for renewable energy applications. Although unstable in its pure form, it has been shown that functionalization may stabilize its structure. A question that arises is whether its outstanding electronic properties could also be further improved using such a procedure. As PG bilayers present both sp$^2$ and sp$^3$ carbon planes, it consists of a flexible candidate for functionalization tuning of electromagnetic properties. In this work, we perfo…
For two-dimensional (2D) materials, a pure large out-of-plane piezoelectric response, compatible with the nowadays bottom/top gate technologies, is highly desired. In this work, the piezoelectric properties of penta-graphene (CCC) monolayer are studied with pure out-of-plane piezoelectric effect by density functional theory (DFT). However, the $d_{36}$ is very small, and only -0.065 pm/V. Two strategies are proposed to enhance piezoelectric properties of CCC monolayer. Firstly, both biaxial and uniaxial strains are applied, but the enhancement is very small, and at -2\% biaxial (-4\% uniaxial)…
Electric field enhances the electronic and diffusion properties of penta-graphene nanoribbons for application in lithium-ion batteries: a first-principles study
A quasi-2D semiconductor carbon allotrope called tetrahexcarbon, also named tetragraphene, was recently proposed featuring an unusual structure combining squared and hexagonal rings. Mechanical and electronic properties of tetragraphene have been predicted based on first-principles Density Functional Theory (DFT) calculations. However, a comprehensive study of its mechanical behavior under different temperatures is still lacking. In this work, using fully atomistic reactive molecular dynamics (MD) simulations, we investigate the mechanical properties of monolayer tetragraphene under tensile st…
The electronic and optical properties of graphene can be precisely tuned by generating deterministic arrangements of strain features. In this paper, we report the formation of widespread and controlled buckling delamination of monolayer graphene deposited on hexagonal boron-nitride promoted by a significant squeezing of the graphene flake and induced by polymeric micro-actuators. The flexibility of this method offers a promising technique to create arbitrary buckling geometries and arrays of wrinkles which could also be subjected to iterative folding-unfolding cycles. Further development of th…
Two-dimensional (2D) lattices composed exclusively of pentagons represent an exceptional structure of materials correlated to the famous pentagonal tiling problem in mathematics, but their $π$-conjugation and the related electronic properties have never been reported. Here, we propose a tight-binding (TB) model for a 2D Cairo pentagonal lattice and demonstrate that $p$-$d$ $π$-conjugation in the unique framework leads to intriguing properties, such as an intrinsic direct band gap, ultra-high carrier mobility and even slant Dirac cones. On the basis of first-principles calculations, we predict …
Electronic properties of graphene nano-flakes: Energy gap, permanent dipole, termination effect and Raman spectroscopy
采用密度泛函理论研究了不同边缘钝化处理的石墨烯纳米片的电子性质。考虑用F和H原子钝化：C $_{N_c}$ X $_{N_x}$（X=F或H）。我们用$10<N_c<56$研究了GNF，并将我们自己限制在最低能量配置。我们发现：i）最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）之间的能量差$Δ$随着$N_c$而减小，ii）拓扑缺陷（五边形和七边形）打破了GNF的对称性并增强了电极化的强度，iii）双层GNF的相互作用可以通过偶极-偶极相互作用来理解，发现偶极-偶极相互作用对GNF的相对取向敏感，iv）永久偶极子取决于边缘终止原子，而能隙与之无关，以及v）GNF中七边形和五边形缺陷的存在导致自旋上电子和自旋下电子的能量之间的最大差异，与F钝化的GNF相比，H钝化的GNF的差异更大。我们的研究清楚地显示了几何形状、尺寸、终止方式和双层结构对小石墨烯纳米纤维电子性质的影响，揭示了石墨烯纳米薄片的重要特征，这些特征可以用拉曼光谱来检测。
We elaborate that single-layer graphene with periodic vacancies can have a band structure containing nodal lines or nodal loops, opening the possibility of graphene-based electronic or spintronic devices with novel functionalities. The principle is that by removing carbon atoms such that the lattice becomes nonsymmorphic, every two sublattices in the unit cell will map to each other under glide plane operation. This mapping yields degenerate eigenvalues for the glide plane operation, which guarantees that the energy bands must stick together pairwise at a boundary of the Brillouin zone. Moving…
Tunnel-Barrier-Engineered Ultrafast Demagnetization and Spin Transport in Graphene-Based Heterostructures
S. N. Bose National Center for Basic Sciences（S.N. 玻色基础科学国家中心）；Indian Institute of Science Education and Research Kolkata（加尔各答印度科学与教育研究所）；Uppsala University（乌普萨拉大学）
We propose a tunable optical setup to engineer topologically nontrivial flat bands in twisted bilayer graphene under circularly polarized light. Using both analytical and numerical calculations, we demonstrate that nearly flat bands can be engineered at small twist angles near the magic angles of the static system. The flatness and the gaps between these bands can be tuned optically by varying laser frequency and amplitude. We study the effects of interlayer hopping variations on Floquet flat bands and find that lattice relaxation favors their formation. Furthermore, we find that, once formed,…
By using the density functional theory (DFT) combined with the molecular dynamics (MD) simulations, structural and electronic properties of mono-vacancy (MV) defect in Möbius strip formed from graphene are investigated. Two kinds of MV are observed depending on the local structures around defects. At static condition, in the curved areas of Möbius strip, MV has the configuration of one pentagon and one nonagon ring (59-type), which is similar to that of carbon nanotubes and graphene. the most stable MV appear in the twisted areas and has a profile of two pentagon and two hexagon rings (5566-ty…
The concept of alloy engineering has emerged as a viable technique towards tuning the bandgap as well as engineering the defect levels in two-dimensional transition metal dichalcognides (TMDC). Possibility to synthesize these ultrathin TMDC materials through chemical route has opened realistic possibilities to fabricate hybrid multi-functional devices. By synthesizing nanosheets with different composites of MoS$_{2x}$Se$_{2(1-x)}$ (x = 0 to 1) using simple chemical methods, we systematically investigate the photo response properties of three terminal hybrid devices by decorating large area gra…
The search for new materials is a very intense task in many technological areas. In 2015, a new variant of graphene was proposed, the pentagraphene, which was followed by the propose of a pentagonal boron nitride structure called penta-BN$_2$. Based on these structures, we investigated the electronic, magnetic, and optical properties of penta-BN$_2$ nanoribbons (p-BNNRs) considering four different kinds of edges, carefully closing the valence shells with H atoms to prevent dangling bonds. To achieve this goal, we used first-principles calculations in a density functional theory framework. Our …
Using the first-principles calculations based on density functional theory, we systematically investigate the strain-engineering (tensile and compressive strain) electronic, mechanical and transport properties of monolayer penta-SiC$_2$. By applying an in-plane tensile or compressive strain, it is easy to modulate the electronic band structure of monolayer penta-SiC$_2$, which subsequently changes the effective mass of carriers. Furthermore, the obtained electronic properties are predicted to change from indirectly semiconducting to metallic. More interestingly, at room temperature, uniaxial s…
The method for production of atomic chains by heating of graphene nanoribbons (GNRs) is proposed and studied by molecular dynamics simulations. The Brenner potential is revised to adequately describe formation of atomic chains, edges and vacancy migration in graphene. A fundamentally different behavior is observed for zigzag-edge GNRs with 3 and 4 atomic rows (3 and 4-ZGNRs) at 2500 K: formation of triple, double and single carbon chains with the length of hundreds of atoms in 3-ZGNRs and edge reconstruction with only short chains and GNR width reduction in 4-ZGNRs. The chain formation mechani…
2D ferroelectrics with robust polarization down to atomic thicknesses provide novel building blocks for functional heterostructures. Experimental reports, however, remain scarce because of the requirement of a layered polar crystal. Here, we demonstrate a rational design approach to engineering 2D ferroelectrics from a non-ferroelectric parent compound via employing van der Waals assembly. Parallel-stacked bilayer boron nitride is shown to exhibit out-of-plane electric polarization that reverses depending on the stacking order. The polarization switching is probed via the resistance of an adja…
Silicon is one of the most frequently used chemical elements of the periodic table in nanotechnology. Two-dimensional (2D) silicene, a silicon analog of graphene, has been readily obtained to make field-effect transistors since 2015. Recently, as new members of the silicene family, penta-silicene and its nanoribbon have been experimentally grown on Ag(110) surface with exotic electronic properties. However, the thermoelectric performance of penta-silicene has not been so far studied that would hinder its potential applications of electric generation from waste heat and solid-state Peltier cool…
