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 perform density functional theory simulations to investigate how the electronic and structural properties of PG bilayers can be tuned as a result of substitution doping. Specifically, we observed the emergence of different magnetic properties when boron was used as dopant species. On the other hand, in the case of doping with oxygen, the rupture of bonds in the sp$^2$ planes does not induce a magnetic moment in the material.
In this study we present a theoretical investigation of structural, electronic and mechanical properties of pentagonal monolayers of carbon (p-graphene), boron nitride (p-B$_{2}$N$_{4}$ and p-B$_{4}$N$_{2}$) and silver azide (p-AgN$_{3}$) by performing state-of-the-art first principles calculations. Our total energy calculations suggest feasible formation of monolayer crystal structures composed entirely of pentagons. In addition, electronic band dispersion calculations indicate that while p-graphene and p-AgN$_{3}$ are semiconductors with indirect bandgaps, p-BN structures display metallic be…
Covalent functionalization is a way to tune the electrochemical properties of hexagonal boron nitride (h-BN) monolayers. The wide band gap insulator h-BN may become metallic conductor upon functionalization with strong oxidants, such as fluorosulfonyl radicals ($\cdot$OSO$_2$F), as known since 1978 [N. Bartlett et al., J. Chem. Soc. Chem. Comm. {\bf 5}, 200 (1978)], with electrical conductivity of 1.5 S/cm [C. Shen et al., J. Solid State Chem. {\bf 147}, 74 (1999)] that greatly surpasses commercial cathode material Li$_{x}$CoO$_{2}$ while retaining excellent ionic conductivity. Functionalized …
Aiming to improve fabrication protocols for boron nitride and graphene (h-BNG) lateral heterostructures, we studied the growth of h-BNG thin films on platinum and their behavior in an oxygen environment. We employed a surface science approach based on advanced spectroscopy and imaging techniques to investigate the evolution of surface stoichiometry and chemical intermediates at each reaction step. During oxygen exposure at increasing temperatures, we observed progressive and subsequent intercalation of oxygen, and selective etching of graphene accompanied by the oxidation of boron. Additionall…
So far, no boron fullerenes were synthesized: more compact sp3-bonded clusters are energetically preferred. To circumvent this, metallic clusters have been suggested by Pochet et al. [Phys. Rev. B 83, 081403(R) (2011)] as "seeds" for a possible synthesis which would topologically protect the sp2 sector of the configuration space. In this paper, we identify a basic pentagonal unit which allows a balance between the release of strain and the self-doping rule. We formulate a guiding principle for the stability of boron fullerenes, which takes the form of an isolated filled pentagon rule (IFPR). T…
Preparation sequence controls oxygen partitioning between boron and lithium on tungsten
TheoretiK Consulting（TheoretiK咨询公司）；Department of Nuclear Engineering, The Pennsylvania State University（宾夕法尼亚州立大学核工程系）；Department of Materials Science and Engineering, Monash University（蒙纳士大学材料科学与工程系）；Department of Mechanical Engineering, The Pennsylvania State University（宾夕法尼亚州立大学机械工程系）
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 …
Boron-doped graphene was reported to be the best non-metal doped graphene electrocatalyst for the oxygen reduction reaction (ORR) working at an onset potential of 0.035 V [JACS 136 (2014) 4394]. In the present DFT study, intermediates and transition structures along the possible reaction pathways are determined. Both Langmuir-Hinschelwood and Eley-Rideal mechanisms are discussed. Molecular oxygen binds the positively charged B atom and forms an open shell end-on dioxygen intermediate. The associative path is favoured with respect to the dissociative one. The free energy diagrams along the four…
Spin-polarized first-principles calculations have been performed on zigzag Boron-Nitride Nanoribbons (z-BNNRs) with lines of alternating fused pentagon (P) and heptagon (H) rings (Pentagon-Heptagon-line-defect) at single edge as well as at both edges. The number of line (n) of the Pentagon-Heptagon-defect has been varied from 1 to 8 for 10-zBNNRs. Among the different spin-configurations which we have studied, we find that, the spin-configuration with ferromagnetic ordering at each edge and anti-ferromagnetic ordering across the edges is quite interesting. For this spin-configuration, we find t…
Recently, two-dimensional boron sheets have attracted a lot of attentions owing to their structural polymorphs and outstanding properties. And, due to chemical complexity and electron deficiency of B atoms, the 2D boron sheets are easy affected by the environment. So, exploring novel 2D boron oxides gets highly needed. In this study, we theoretically explored 2D boron oxides structures and their basic properties. We found 2D boron oxides are metals or semimetals, when oxygen concentration is low. More interesting, the B6O1 exhibits Dirac Loop near the Fermi level and the maximum Fermi velocity…
Experimental measurements have reported ultra-fast and radius-dependent water transport in carbon nanotubes which are absent in boron nitride nanotubes. Despite considerable effort, the origin of this contrasting (and fascinating) behaviour is not understood. Here, with the aid of machine learning-based molecular dynamics simulations that deliver first-principles accuracy, we investigate water transport in single-wall carbon and boron nitride nanotubes. Our simulations reveal a large, radius-dependent hydrodynamic slippage on both materials with water experiencing indeed a $\approx 5$ times lo…
We report room temperature ferromagnetism in boron-doped ZnO both experimentally and theoretically. The single phase Zn1-xBxO films deposited under high oxygen pressure by pulsed-laser deposition show ferromagnetic behavior at room temperature. The saturation magnetization increases monotonously from 0 to 1.5 emu/cm3 with the increasing of B component x from 0 to 6.8%. The first-principles calculations based on density functional theory demonstrate that the ferromagnetism in B-doped ZnO originates from the induced magnetic moments of oxygen atoms in the nearest neighbor sites to the B-Zn vacan…
We have studied the temperature dependencies of the photoluminescence (PL) intensity of 4.1 eV in microcrystalline powder of hexagonal boron nitride in the range of 7-1100 K. The results obtained have been analyzed within the band model of energy levels of associated donor-acceptor pairs based on impurity (ONCN) complexes. Luminescence enhancement processes at T<200 K and two independent channels of external thermal activation quenching are typical of the observable luminescence mechanisms under direct (4.26 eV) excitations of the samples. It has been shown that, at T>220 K, when directly exci…
We have performed ab initio calculations to systematically investigate electronic properties and magnetism of insulating non-magnetic beryllium monoxide nanotubes induced by non-magnetic sp impurities: boron, carbon and nitrogen. We found that in the presence of these sp impurities, which replace oxygen atoms, the non-magnetic BeO NTs transform into magnetic semiconductors, which acquire magnetization caused by spin splitting of (B,C,N) 2p states located in the forbidden gap of a BeO tube. The magnetic moments of the impurities vary from 0.65 to 1.60. On the contrary, when (B,C,N) dopants subs…
Investigation on oxidation resistance of two-dimensional (2D) materials is critical for many of their applications, because 2D materials could have higher oxidation kinetics than their bulk counterparts due to predominant surface atoms and structural distortions. In this study, the oxidation behavior of high-quality boron nitride (BN) nanosheets of 1-4 layer thick has been examined by heating in air. Atomic force microscopy and Raman spectroscopy analyses reveal that monolayer BN nanosheets can sustain up to 850 °C and the starting temperature of oxygen doping/oxidation of BN nanosheets only s…
The recent emergence of a wide variety of two-dimensional (2D) materials has created new opportunities for device concepts and applications. In particular, the availability of semiconducting transition metal dichalcogenides, in addition to semi-metallic graphene and insulating boron nitride, has enabled the fabrication of all 2D van der Waals heterostructure devices. Furthermore, the concept of van der Waals heterostructures has the potential to be significantly broadened beyond layered solids. For example, molecular and polymeric organic solids, whose surface atoms possess saturated bonds, ar…
In 2015, a new two dimensional (2D) carbon allotrope, called phagraphene, was theoretically proposed. Based on this structure, we propose here a new boron nitride structure called phaBN. It is composed by three types of rings: pentagons, hexagons and heptagons. We investigate the electronic, optical, vibrational and thermodynamic properties of phaBN using first-principles calculations in a density functional theory (DFT) framework. Our calculations revealed that the phaBN has an energy gap of 2.739 eV, which is almost half of the energy gap of the hexagonal boron nitride (h-BN), thus being a s…
We report the effect of air exposure on the electronic properties of pentacene single crystals. Air can diffuse reversibly in and out of the crystals and controls the physical properties. We discern two competing mechanisms that modulate the electronic transport. The presence of oxygen increases the hole conduction, as in dark four O2 molecules introduce one charge carrier. This effect is enhanced by the presence of visible light. Contrarily, water, present in ambient air, is incorporated in the crystal lattice and forms trapping sites for injected charges.
In order to study a magnetic principle of carbon based materials, multiple spin state of zigzag edge modified graphene molecules are analyzed by the first principle density functional theory to select suitable modification element. Radical carbon modified C64H17 shows that the highest spin state is most stable, which arises from two up-spin's tetrahedral molecular orbital configuration at zigzag edge. In contrast, oxygen modified C59O5H17 show the lowest spin state to be most stable due to four spins cancellation at oxygen site. Boron modified C59B5H22 have no π-molecular orbit at boron site t…
We present a first-principles computational study of the thermodynamics of carbon defects in hexagonal boron nitride (hBN). The defects considered are carbon monomers, dimers, trimers, and larger carbon clusters, as well as complexes of carbon with vacancies, antisites, and substitutional oxygen. Our calculations show that monomers ($\text{C}_{\text{B}}$, $\text{C}_{\text{B}}$), dimers, trimers, and $\text{C}_{\text{N}}\text{O}_{\text{N}}$ pairs are the most prevalent species under most growth conditions. Compared to these defects, larger carbon clusters, as well as complexes of carbon with va…
Magnetic tunnel junctions with crystalline MgO tunnel barrier and amorphous CoFeB electrodes received much attention due to their high tunnel magneto resistance ratio at room temperature. One important parameter for achieving high tunnel magneto resistance ratios is to control the boron diffusion from the electrodes especially during post growth annealing. By high resolution transmission electron microscopy and electron energy loss spectroscopy techniques we show that the cap layer material adjacent to the electrodes and the MgO deposition method are crucial to control boron redistribution. It…
First-principles spin-polarized calculations have been performed on passivated Boron-Nitride Nanoribbons (BNNRs) with pentagon-heptagon line-defects (PHLDs) (also called as Stone-Wales line-defects). Two kinds of PHLDs, namely, even-line and odd-line PHLDs, have been added either at one edge or at both edges of BNNRs. Single-edge (with all its different possibilities, for example, for a BNNR with 2-line PHLD at single-edge there are 8 possibilities) as well as both-edge passivations have been considered for all the ribbons in this study by passivating each edge atom with hydrogen atom. Density…
We use ab initio simulations to investigate the properties of a sodium borosilicate glass of composition 3Na_2O-B_2O_3-6SiO_2. We find that the broadening of the first peak in the radial distribution functions g_BO(r) and g_BNa(r) is due to the presence of trigonal and tetrahedral boron units as well as to non-bridging oxygen atoms connected to BO_3 units. In agreement with experimental results we find that the [3]B units involve a significant number of non-bridging oxygens whereas the vast majority of [4]B have only bridging oxygens. We determine the three dimensional distribution of the Na a…
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 …
Point defects in hexagonal boron nitride (hBN) have attracted growing attention as bright single-photon emitters. However, understanding of their atomic structure and radiative properties remains incomplete. Here we study the excited states and radiative lifetimes of over 20 native defects and carbon or oxygen impurities in hBN using ab initio density functional theory and GW plus Bethe-Salpeter equation calculations, generating a large data set of their emission energy, polarization and lifetime. We find a wide variability across quantum emitters, with exciton energies ranging from 0.3 to 4 e…
The role of defects in van der Waals heterostructures made of graphene and hexagonal boron nitride (h-BN) is studied by a combination of ab initio and model calculations. Despite the weak van der Waals interaction between layers, defects residing in h-BN, such as carbon impurities and antisite defects, reveal a hybridization with graphene p$_{\rm z}$ states, leading to midgap state formation. The induced midgap states modify the transport properties of graphene and can be reproduced by means of a simple effective tight-binding model. In contrast to carbon defects, it is found that oxygen defec…
We investigate the influence of impurities and vacancies in the formation of magnetic moment in CaB6 using full potential ab initio band structure calculations. CaB6 is found to be a band insulator with a band gap of about 0.2 eV. The calculated results indicate that carbon and oxygen substitution in boron sublattice, usually expected as impurity in low purity borons, do not play significant role in the local moment formation. Boron vacancy in the boron sublattice, on the other hand, leads to the formation of an impurity band in the vicinity of the Fermi level, which exhibit finite exchange sp…
Boron suboxide B6O, the hardest known oxide, has an R-3m crystal structure (α-B6O) that can be described as an oxygen-intercalated structure of α-boron, or, equivalently, as a cubic close packing of B12 icosahedra with two oxygen atoms occupying all octahedral voids in it. Here we show a new ground state of this compound at ambient conditions, Cmcm-B6O (\b{eta}-B6O), which in all quantum-mechanical treatments that we tested (GGA, LDA, and hybrid functional HSE06) comes out to be slightly but consistently more stable. Increasing pressure and temperature further stabilize it with respect to the …
Based on variable components global optimization algorithm, we predict a stable two-dimensional (2D) phase of boron phosphide with 1:5 stoichiometry, i.e. boron pentaphosphide (BP_5) monolayer, which has a lower formation energy than that of the commonly believed graphitic phase (g-BP). BP_5 monolayer is a multiferroic material with coupled ferroelasticity and ferroelectricity. The predicted reversible strain is up to 41.41%, which is the largest among all reported ferroelastic materials. Due to the non-centrosymmetric structure and electronegativity differences between boron and phosphorus at…
Charge transfer from a metal substrate stabilizes honeycomb borophene, whose electron deficit would otherwise spoil the hexagonal order of a $π$-bonded 2D atomic network. However, the coupling between the substrate and the boron overlayer may result in the formation of strong chemical bonds that would compromise the electronic properties of the overlayer. In this paper we present a theoretical study, based on state-of-the-art density-functional and genetic-optimization techniques, of the electronic and structural properties of borophene grown on Al(111), with emphasis on the impact of oxygen o…
Hexagonal boron nitride (h-BN) is well-established as a requisite support, encapsulant and barrier for 2D material technologies, but also recently as an active material for applications ranging from hyperbolic metasurfaces to room temperature single-photon sources. Cost-effective, scalable and high quality growth techniques for h-BN layers are critically required. We utilise widely-available iron foils for the catalytic chemical vapour deposition (CVD) of h BN and report on the significant role of bulk dissolved species in h-BN CVD, and specifically, the balance between dissolved oxygen and ca…
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…
From Amorphous to Amorphous-Crystalline Mixed-Phase Boron Nitride: Evolution of the Thermal and Elastic Properties
Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST（加泰罗尼亚纳米科学与纳米技术研究所）；Faculty of Physics, Autonomous University of Barcelona（巴塞罗那自治大学物理系）；Universite Claude Bernard Lyon 1, CNRS, LMI, UMR 5615（里昂第一大学）；Faculty of Physics and Astronomy, Adam Mickiewicz University（亚当密茨凯维奇大学物理与天文学院）；International Iberian Nanotechnology Laboratory（伊比利亚纳米技术国际实验室）；ICREA（加泰罗尼亚高级研究院）
Since two-dimensional boron sheet (borophene) synthesized on Ag substrates in 2015, research on borophene has grown fast in the fields of condensed matter physics, chemistry, material science, and nanotechnology. Due to the unique physical and chemical properties, borophene has various potential applications. In this review, we summarize the progress on borophene with a particular emphasis on the recent advances. First, we introduce the phases of borophene by experimental synthesis and theoretical predictions. Then, the physical and chemical properties, such as mechanical, thermal, electronic,…
Due to its unique physical and chemical properties, graphene is being considered as a promising material for energy conversion and storage applications. Introduction of functional groups and dopants on/in graphene is a useful strategy for tuning its properties. In order to fully exploit its potential, atomic-level understanding of its interaction with species of importance for such applications is required. We present a DFT study of the interaction of sodium atoms with epoxy-graphene and analyze how this interaction is affected upon doping with boron and nitrogen. We demonstrate how the dopant…
The influence of the oxygen segregation into Mg-B-O inclusions (which are oxygen enriched as compared to the matrix material) and the formation of boron enriched phases (with near MgB12 composition) in MgB2 structure on pinning in magnesium diboride and the effect of SiC and Ti alloying on the formation of structural inhomogenities in MgB2 are discussed. A nanostructural material of near theoretical density (2.7 g/cm3) based on MgB2-SiC (10 wt. percents of 200-800 nm SiC was added), which is characterized by high jc (1000000 A/cm2 in 1 T - 100000 A/cm2 in 3.5 T at 20 K and 100000 A/cm2 at 35 K…
Density functional theory (DFT) can be quite advantageous in advancing the field of catalysis because of the microscopic insights it provides, and thus can guide experimental searches of novel catalysts. Several recent works have demonstrated that low-dimensional materials can be very efficient catalysts. Graphene quantum dots (GQDs) have gained much attention in past years due to their unique properties like low toxicity, chemical inertness, biocompatibility, crystallinity, etc. These properties of GQDs which are due to quantum confinement and edge effects facilitate their applications in var…
Ultrathin black phosphorus, or phosphorene, is the second known elementary two-dimensional material that can be exfoliated from a bulk van der Waals crystal. Unlike graphene it is a semiconductor with a sizeable band gap and its excellent electronic properties make it attractive for applications in transistor, logic, and optoelectronic devices. However, it is also the first widely investigated two dimensional electronic material to undergo degradation upon exposure to ambient air. Therefore a passivation method is required to study the intrinsic material properties, understand how oxidation af…
The influence of the mechanical strain and chemical substitution on the magnetic anisotropy energy (MAE) of Cr$_2$O$_3$ is studied using first-principles calculations. Dzyaloshinskii-Moriya interaction contributes substantially to MAE by inducing spin canting when the antiferromagnetic order parameter is not aligned with the hexagonal axis. Nearly cubic crystal field results in a very small MAE in pure Cr$_2$O$_3$ at zero strain, which is incorrectly predicted to be negative (in-plane) on account of spin canting. The MAE is strongly modified by epitaxial strain, which tunes the crystal-field s…
Room-temperature ferrimagnetism was discovered for the anti-site-disordered perovskite Ca2MnOsO6 with Tc = 305 K. Ca2MnOsO6 crystallizes into an orthorhombic structure with a space group of Pnma, in which Mn and Os share the oxygen-coordinated-octahedral site at an equal ratio without a noticeable ordered arrangement. The material is electrically semiconducting with variable-range-hopping behavior. X-ray absorption spectroscopy confirmed the trivalent state of the Mn and the pentavalent state of the Os. X-ray magnetic circular dichroism spectroscopy reveals that the Mn and Os magnetic moments …
Ulsan National Institute of Science and Technology (UNIST)（蔚山科学技术院）；IBS-CMCM（韩国基础科学研究所碳材料创新中心）；Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST)（蔚山科学技术院化学系）；OLA Battery Innovation Center, OLA Cell Technologies（奥拉电池创新中心，奥拉电池技术公司）；Department of Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST)（蔚山科学技术院材料科学与工程系）；School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST)（蔚山科学技术院能源与化学工程学院）
