Monolayer Of Nitrogen Research Articles

Thermal rectification in novel two-dimensional hybrid graphene/BCN sheets: A molecular dynamics simulation

The graphene-like monolayer of carbon, boron and nitrogen that maintains the native hexagonal atomic lattice (BCN), is a novel semiconductor with special thermal properties. Herein, with the aid of a non-equilibrium molecular dynamics approach (NEMD), we study phonon thermal rectification in a hybrid system of pure graphene and BCN (G-BCN) in various configurations under a series of positive and negative temperature gradients. We begin by investigating the relation of thermal rectification to sample’s mean temperature, T, and the imposed temperature difference, ΔT, between the two heat baths at its ends. We then move to explore the effect of varying strain levels of our sample on thermal rectification, followed by Kapitza resistance calculations at the G-BCN interface, which shed light on the interface effects on thermal rectification. Our simulation results reveal a BCN-configuration-dependent behavior of thermal rectification. Finally, the underlying mechanism leading to a preferred direction for phonons is studied using phonon density of states (DOS) on both sides of the G-BCN interface.

Boron and carbon in two-dimensional nitrogene structures: Heterodoping, doping, and chemical functionalization

We perform density functional calculations to determine the effects of simultaneous doping with carbon (C) and boron (B) on the electronic properties of nitrogene. Our procedure substitutionally incorporates the two dopants into the nitrogen monolayer. We analyze the relative position between dopants by considering different configurations. Band structure, density of states, band gaps, magnetic stability energies (energy difference between states with total magnetization with spin S=1 and S=0), and energetic stability were examined. The codoped structures exhibit a spin−dependent band gap with a strength of 1.04–2.68 eV, which is reduced compared to that in nitrogene (3.80 eV). The B-C codoped nitrogene incorporated ferromagnetism with well-localized flat bands around the Fermi level. A spin−polarized ground state was exhibited by the systems with a total magnetization of S=1, in which magnetic moments were localized mainly at the C atom and its first neighbors. The systems displayed an antiferromagnetic ordering when the total spin was fixed to S=0. The valence band maximum (VBM) was dominated by spin−up, while the conduction band minimum (CBM) was dominated by spin−down. Dopants placed as second neighbors in the nitrogene structures exhibited the most prominent band gap and magnetic stability.

C[formula omitted]N[formula omitted]: A symmetry-protected semimetal

In this paper, we propose a symmetry-protected semimetal C4N4, which is a two-dimensional carbon–nitrogen monolayer that can be synthesized from the moleculars of 1,3,5,7-Tetrazocine via the dehydrogenation reaction. With the help of first-principle calculations and symmetry analysis, we find the nodal line in the monolayer C4N4 are protected by horizonal mirror symmetry and they originates from the crossing between N-px(y) and C-pz orbitals. An k⋅p model is used to explain the formation of the nodal line. If this material is synthesized on a substrate, the nodal line will transform into multiple isolated Dirac points with the protection of vertical mirror symmetries. The study of the energy band structures of AA- and AB-stacking bulks reveals that there are nodal surfaces in their 3D Brillouin zone. Our research provides a possible experimental routine to synthesize 2D C4N4 and validate the symmetry-protected nature of the nodal line.

XXVI International Symposium Nanophysics and Nanoelectronics", Nizhny Novgorod, March 14-March 17, 2022 Effect of chemical passivation of GaAs(001) surface on anisotropy and orientation of gold nanoclusters formed on it and their plasmons

The principal role of chemical passivation of GaAs surface in the formation on it of oriented anisotropic nanoclusters of gold is discussed. The nanoclusters are fabricated by thermal annealing of a gold film deposited onto GaAs(001) surface passivated as a preliminary by a monolayer of nitrogen or sulfur atoms. These atoms, bonded chemically to gallium atoms of the crystal surface, form a crystal lattice and prevent the chemical interaction of Au with GaAs. As a result of annealing, the arrays of anisotropic (elongated) nanoclusters of chemically pure Au oriented preferably in crystal [110] direction are formed on passivated GaAs(001) surface. The presence of strong anisotropy and orientation of Au clusters on passivated GaAs surfaces is established by the methods of probe diagnostics and of optical reflectance anisotropy spectroscopy and polarized reflection spectroscopy. Using an optical model of plasmonic polarizability of elongated Au spheroids, it is shown that the spectral features observed in polarized reflection originate from anisotropic plasmons of Au nanoclusters polarized mainly in direction [110] of crystal. Keywords: semiconductor surface, nitride passivation, gold nanoclusters, anisotropic plasmons, polarized reflectance.

XXVI Международный симпозиум Нанофизика и наноэлектроника", Нижний Новгород, 14-17 марта 2022 г. Влияние химической пассивации поверхности GaAs(001) на анизотропию и ориентацию образующихся на ней нанокластеров золота и их плазмонов

A principal role of chemical passivation of GaAs surface in the formation of oriented anisotropic on-surface nanoclusters of gold is discussed. The gold nanoclusters are fabricated by thermal annealing of the gold film deposited onto GaAs(001) surface passivated preliminary by an atomic monolayer of nitrogen or sulphur. These atoms forming a crystal lattice are bonded chemically to gallium atoms of the crystal surface to prevent chemical interaction of Au with GaAs. Annealing Au on passivated GaAs(001) surface results in formation of arrays of anisotropic (elongated) nanolusters of chemically pure Au oriented preferably in crystal direction. The presence of strong anisotropy and orientation of Au clusters on passivated GaAs surfaces is established by the methods of probe diagnostics and the optical techniques of reflectance anisotropy spectroscopy and polarized reflection spectroscopy. Within an optical model of plasmon polarizability of elongated Au spheroids, it is shown that the spectral features observed in polarized reflection originate from anisotropic plasmons polarized in Au nanoclusters predominantly in direction on GaAs(001) surface.

Engineering the electronic and magnetic properties of nitrogene monolayer and bilayer by doping: A first-principles study

The (N) nitrogen monolayer (nitrogene) has been predicted to be stable in the buckled hexagonal structure. However the non-magnetic nature and large band-gap may restrict its practical applications. In this paper, the electronic and magnetic properties of the nitrogene monolayer and bilayer doped with carbon (C) and boron (B) are investigated using first-principles calculations. Nitrogene monolayer is a non-magnetic two-dimensional (2D) material with an indirect band-gap of 4.185(6.023) eV determined by the PBE(HSE06) functional. Nitrogene bilayers with different stacking shaps are examined. Results reveal dynamical stability of the AA-, AA′-, and AB-stacked bilayers. Such atomic arrangements depict an energy gap reduction as compared to that of the monolayer. C doping causes strong spin polarization at the vicinities of the Fermi level, giving place to magnetic semiconductor nature. The magnetic properties are produced mainly by the C dopants (0.7 μB), and also proximity induced small contributions on the N atoms (0.07 μB). In contrast, B doping produces non-magnetic materials with band-gap reduction (∼12% and 20.5%) for all considered systems. When the co-doping is treated, the effect on the electronic and magnetic properties can be considered as the combined effects of the separated C doping and B doping. Results presented herein may propose an efficient method to functionalize the nitrogene monolayer and bilayer for practical applications in optoelectronic and spintronic nano devices.

On the electronic structure of a recently synthesized graphene-like BCN monolayer from bis-BN cyclohexane with single-atom vacancies: a DFT study

Since the rising of graphene, boron nitride monolayers have been deeply studied due to their structural similarity with the former. A hexagonal graphene-like boron–carbon–nitrogen (h-BCN) monolayer was synthesized recently using bis-BN cyclohexane (B2N2C2H12) as a precursor molecule. Herein, we investigated the electronic and structural properties of this novel BCN material, in the presence of single-atom (boron, carbon, or nitrogen) vacancies, by employing density functional theory calculations. The stability of these vacancy-endowed structures is verified from cohesion energy calculations. Results showed that a carbon atom vacancy strongly distorts the lattice leading to breaking on its planarity and bond reconstructions. The single-atom vacancies induce the appearance of flat midgap states. A significant degree of charge localization takes place in the vicinity of these defects. It was observed a spontaneous magnetization only for the boron-vacancy case, with a magnetic dipole moment about 0.87 μ B .Our calculations predicted a direct electronic bandgap value of about 1.14 eV. Importantly, this bandgap value is intermediate between gapless graphene and insulating hexagonal boron nitride.

Vibrational properties and Raman spectra of 2‐D octagon‐structure nitrogen

AbstractWe studied the vibrational properties and Raman spectra of two‐dimensional (2‐D) octagon‐structure nitrogen with density functional theory (DFT). There are 10 Raman active modes whose irreducible representations are A1g, B1g, B2g, and Eg. By calculating Raman tensor of each Raman active mode, we obtained polarization angle‐dependent Raman intensities. The results show that B1g and B2g modes can show polarization angle‐dependent Raman intensities when the incident light wave vector is perpendicular to the plane of the nitrogen monolayer, which is different from some other isotropic 2‐D materials. We also discussed polarization angle‐dependent Raman intensities when the incident light wave vector is parallel to the plane of the monolayer. We found that the Raman spectra have seven peaks when the incident light wave vector is perpendicular to the monolayer, while there are four distinct peaks when the incident light wave vector is parallel to the monolayer. Our results will help experimentalists to identify the existence and orientation of octagon‐structure nitrogen monolayer when they are growing it.

Atomic Layer Epitaxy of III-Nitrides: A Microscopic Model of Homoepitaxial Growth.

We develop a microscopic theoretical model of AlN, GaN, and InN film growth by atomic layer epitaxy. To make the model realistic, we take into account the atomic hydrogen that is created by the hydrogen plasma commonly used in plasma-assisted atomic layer epitaxy. This growth technique relies on separate deposition steps for nitrogen and the group-III cation. Our model addresses the processes that occur after a complete monolayer of nitrogen has formed, that is, the deposition, adsorption, surface diffusion, island nucleation, and island growth of group-III cations. According to our model, the three nitrides grow in a standard and qualitatively similar manner: during a brief nucleation phase, a modest attractive interaction leads to stable island nuclei consisting of just a few atoms. These then grow in place at a nearly constant island density and with an island size distribution which obeys an expected universal scaling relationship that depends only on the critical island size.

First-principles exploration of superconductivity in MXenes.

MXenes are an emerging class of two-dimensional materials, which in their thinnest limit consist of a monolayer of carbon or nitrogen (X) sandwiched between two transition metal (M) layers. We have systematically searched for superconductivity among MXenes for a range of transition metal elements, based on a full first-principles characterization in combination with the Eliashberg formalism. Thus, we identified six superconducting MXenes: three carbides (Mo2C, W2C and Sc2C) and three nitrides (Mo2N, W2N and Ta2N). The highest critical temperature of ∼16 K is found in Mo2N, for which a successful synthesis method has been established [Urbankowski et al., Nanoscale, 2017, 9, 17722-17730]. Moreover, W2N presents a novel case of competing superconducting and charge density wave phases.

High-resolution cross-sectional analysis of the interface between SiC and SiO2 in a MOSFET device via atomic resolution STEM

Transition areas in multilayer assemblies used for electronic structures are of vital importance for the characteristics of the final devices. In this study, the interfacial region between SiC and SiO2 was studied with atomic resolution scanning transmission electron microscopy and electron energy-loss spectroscopy in order to gain insight in the structural morphology and the chemical composition of the interface and the appearance of interfacial layers formed during passivation procedures. The annealing process in an N-rich atmosphere during fabrication of the multilayer stack leads to a (sub-)monolayer of nitrogen at the interface between the bulk material and the oxide that is illustrated and quantified. In addition, closer analysis of the EELS signal reveals a transition region that is 3 nm in width, extending approximately 1 nm further into the SiO2 than the N-peak.

Heat capacity and heat of adsorption at orientational phase transition in nitrogen monolayer on graphite

In this paper, we report a simulation study of the effect of the herringbone orientational phase transition on the isosteric heat of adsorption and the heat capacity of the nitrogen adsorption monolayer on graphite surface. We use the previously proposed regression equations of state for phases with the short- and long-ranged orientational ordering (Ustinov et al. in J Phys Chem C 122:2897–2908, 2018). The proposed approach allows one to give an exhaustive thermodynamic description of the isobaric phase transition without direct estimation of the chemical potential, using only the pVT data obtained in a canonical Monte Carlo simulation. The herringbone orientational phase transition is indicated by a peak in the temperature dependence of the heat capacity. Its height and shape is close to those observed experimentally. In addition, the heat spike is observed on the isosteric heat curves near the transition region. It decreases with increasing temperature and completely disappears at a temperature close to the melting point in the gas-crystal system. A combined analysis of the heat capacity and isosteric heat of adsorption demonstrates that the nitrogen monolayer on graphite surface has similar features inherent in a three-dimensional system and, therefore, the translational and rotational degrees of freedom normal to the surface are involved in the mechanism of the long-to-short-ranged orientational transition.

Nucleation of boron-nitrogen on transition metal surface: A first-principles investigation

Boron nitrogen (BN) monolayer has attracted considerable attention because of their successful incorporation with graphene based nanodevices. However, many important aspects of the growth mechanisms are still not well explored. Using density functional theory (DFT) calculations, we found that Cu(111) surface is more suitable to be used as a substrate to grow BN monolayer compared with Ni(111) surface. Moreover, we explored that one-dimensional (1D) BN chain configuration is dominant to the two-dimensional (2D) BN ring formation from one pair to five BN pairs deposited on Cu(111) surface. Energetically stable structure transformation of BN monolayer from 1D BN chain to 2D BN ring occurs when the number of pairs is n>5. It is suggested that, as the number of BN pairs increases the energetically stable structures achieve.

Inorganic graphenylene as a promising novel boron nitrogen membrane for hydrogen purification: a computational study

A novel boron nitrogen monolayer named as inorganic graphenylene (IGP) was proposed for H2 purification, and its stability was confirmed by the calculated cohesive energy and phonon dispersion spectrum. Using the density function theory (DFT) calculations and molecular dynamic (MD) simulations, we found that the IGP membrane can fulfill the requirements of both the high H2 permeance (~10−3 mol/m2 s Pa) and high H2 selectivities (>107) over H2O, CO2, N2, CO, and CH4 at 300 K. Excitingly, the MD results matched well with the DFT calculations including the selectivity, permeance as well as the adsorption properties of different gases.

(Invited) New Functionalities of 2-Dimensional Materials: Graphene, Doped-Graphene, Tough Fibers and Beyond

This talk will first provide an overview of different defects in 2-Dimensional materials including graphene and Chalcogenides. In particular, we will focus on: 1) defining the dimensionalities and atomic structures of defects; 2) pathways to generating structural defects during and after synthesis and, 3) the effects of having defects on the physico-chemical properties and applications. We will then discuss the synthesis of large-area, high-quality monolayers of nitrogen-, boron- and silicon-doped graphene sheets on Cu foils using ambient-pressure chemical vapor deposition (AP-CVD). Scanning tunneling microscopy (STM) and spectroscopy (STS) demonstrate that defects in doped graphenes arrange in different geometrical configurations exhibiting different electronic and chemical properties. Interestingly, these doped layers can be used as efficient molecular sensors and electronic devices. In this context, Graphene enhanced Raman spectroscopy will be introduced and it will explained that by doping graphene with Nitrogen, the Fermi level (EF) of graphene shifts, and if this shift aligns with the lower unoccupied molecular orbital (LUMO) of a molecule, charge transfer would be enhanced, thus significantly amplifying the molecule's vibrational Raman modes. Concentrations as low as 10-11 mol/L of different dye molecules can be detected using GERS. Finally, we will discuss the controlled synthesis and assembly of chalcogenide monolayers on different substrates. The electronic performance of monolayers of MoS2, WS2 and hetero-systems operating under flexural strain will also be presented. Our findings demonstrates that it is now possible to use chalcogenide layers for the fabrication of flexible electronic devices, however, defect control is required to tailor their performance. Finally, we will talk about the transformation of graphite into graphene oxide (GO). This material could be used in the fabrication of robust and super-tough films and fibers, as well as 3-Dimensional graphene foams; all exhibiting fascinating mechanical, and electronic properties. These GO materials could also be incorporated in ceramics and polymers, and recent exciting progress in these areas will be introduced.

Two-dimensional honeycomb (A7) and zigzag sheet (ZS) type nitrogen monolayers. A first principles study of structural, electronic, spectral, and mechanical properties

Two single-bonded 2D nitrogen allotropes of the honeycomb (A7) and zigzag sheet (ZS) topology have been calculated using density functional theory (DFT). The optical (vibrational, absorption, nuclear magnetic resonance), thermodynamic and elastic properties of the A7 and ZS sheets have been calculated for the first time. The band structure calculation have revealed a semiconducting nature of the ZS sheet with a direct gap of 1.246eV, while the A7 monolayer behaves as an insulator with an indirect gap of 3.842eV. Phonon dispersion calculations have justified these structures as vibrationally stable 2D materials. The IR spectroscopy completely failed in the characterization of the studied materials, while the Raman spectroscopy can be effectively applied for the experimental spectral identification. The absorption spectra demonstrate complete opacity of the A7 and ZS monolayers to the UV irradiation only above ca. 9 and 6eV, respectively. Thus, the studied materials are expected to be transparent to the visible light. The electron arrangement of the nitrogen nuclei in the studied polynitrogen sheets is denser compared to the N2 molecule which follows from the calculation of the values of magnetic shielding tensors. The elastic constants reveal a robust mechanical stability of the studied 2D nitrogen allotropes. The Young moduli values are only twice as lower than that of the graphene molecule.

Graphene-like Boron-Carbon-Nitrogen Monolayers.

A strategy to synthesize a 2D graphenic but ternary monolayer containing atoms of carbon, nitrogen, and boron, h-BCN, is presented. The synthesis utilizes bis-BN cyclohexane, B2N2C2H12, as a precursor molecule and relies on thermally induced dehydrogenation of the precursor molecules and the formation of an epitaxial monolayer on Ir(111) through covalent bond formation. The lattice mismatch between the film and substrate causes a strain-driven periodic buckling of the film. The structure of the film and its corrugated morphology is discussed based on comprehensive data from molecular-resolved scanning tunneling microscopy imaging, X-ray photoelectron spectroscopy, low-energy electron diffraction, and density functional theory. First-principles calculations further predict a direct electronic band gap that is intermediate between gapless graphene and insulating h-BN.

Structural and electronic properties of arsenic nitrogen monolayer

We present our first-principles calculations of a new two-dimensional material, arsenic nitrogen monolayer. The structural, electronic, and mechanical properties are investigated in detail by means of density functional theory computations. The calculated binding energy and the phonon spectra demonstrate that the AsN can form stable monolayer in puckered honeycomb structure. It is a semiconductor with indirect band gap of 0.73 eV, and displays highly anisotropic mechanical properties. Strain has obvious influence on the electronic properties of AsN monolayer. It is found that in the armchair direction, a moderate compression strain (−12%) can trigger an indirect to direct band gap transition and a tensile strain of 18% can make the AsN becoming a stable metal. In the zigzag direction, a rather smaller strain than armchair direction (12% for compression and 8% for stretch) can induce the indirect band gap to metal transition.

Band Gap Engineering of Two-Dimensional Nitrogene.

In our previous study, we have predicted the novel two-dimensional honeycomb monolayers of pnictogen. In particular, the structure and properties of the honeycomb monolayer of nitrogen, which we call nitrogene, are very unusual. In this paper, we make an in-depth investigation of its electronic structure. We find that the band structure of nitrogene can be engineered in several ways: controlling the stacking of monolayers, application of biaxial tensile strain, and application of perpendicular electric field. The band gap of nitrogene is found to decrease with the increasing number of layers. The perpendicular electric field can also reduce the band gap when it is larger than 0.18 V/Å, and the gap closes at 0.35 V/Å. A nearly linear dependence of the gap on the electric field is found during the process. Application of biaxial strain can decrease the band gap as well, and eventually closes the gap. After the gap-closing, we find six inequivalent Dirac points in the Brillouin zone under the strain between 17% and 28%, and the nitrogene monolayer becomes a Dirac semimetal. These findings suggest that the electronic structure of nitrogene can be modified by several techniques, which makes it a promising candidate for electronic devices.

(Invited) Defect Engineering in 2-Dimensional Materials: From Theory to Applications

This talk will first provide an overview of different defects in 2-Dimensional materials such as graphene and Chalcogenides. In particular, we will focus on: 1) defining the dimensionalities and atomic structures of defects; 2) pathways to generating structural defects during and after synthesis and, 3) the effects of having defects on the physico-chemical properties and applications. We will then discuss the synthesis of large-area, high-quality monolayers of nitrogen-, boron- and silicon-doped graphene sheets on Cu foils using ambient-pressure chemical vapor deposition (AP-CVD). Scanning tunneling microscopy (STM) and spectroscopy (STS) demonstrate that defects in doped graphenes arrange in different geometrical configurations exhibiting different electronic and chemical properties. Interestingly, these doped layers could be used as efficient molecular sensors and electronic devices. Finally, we will discuss the controlled synthesis and assembly of chalcogenide monolayers on different substrates. The electronic performance of monolayers of MoS2, WS2 and hetero-systems operating under flexural strain will also be presented. Our findings demonstrates that it is now possible to use chalcogenide layers for the fabrication of flexible electronic devices, however, defect control is required to tailor their performance.