Stability,electronic and magnetic properties of the Octagraphene-like boron nitride Nanosheets: In silico studies

The characterization of the structural, electronic, and magnetic properties of octagraphene-like boron-nitride: BN (B₃₂N₃₂H₂₄, B₃₇N₂₇H₂₄, and B₂₇N₃₇H₂₄), nanosheets were performed by means of density functional theory all-electron calculations at the HSEh1PBE/GGA level. Orbital 6–311G(d,p) basis sets were used. Non-stoichiometric B₃₇N₂₇H₂₄ and B₂₇N₃₇H₂₄ compositions: rich in boron or nitrogen atoms, forming homonuclear B or N bonds, respectively, were chosen. The obtained results reveal that these BN nanosheets reach structural stability in the anionic form, where semiconductor behaviors are promoted. Indeed, the HOMO-LUMO gap values are: 5.09, 1.48 and 2.53 eV, for stoichiometric and non-stoichiometric models, respectively. Whereas the magnetic moments are coming from the boron atoms in all cases (1.0 bohrs magneton). The rich in boron and nitrogen nanosheets presents high-polarity; either in the gas phase or embedded in aqueous mediums like water. Also appears low chemical reactivity, signifying potential applicability as nanovehicles of pharmaceutical species. The nanosheets rich in boron atoms are promising candidates for the design of nanosensors, because they possess low-work functions, mainly arising from the homonuclear boron bond formation.     

First principles study of native defects in a graphitic BC2N monolayer

Spin polarized density functional theory has been used to investigate the stability and electronic properties of antisites and vacancies in graphitic BC₂N sheets. Likewise as we observed in nanotubes, we found that, in a boron-rich system, a boron atom occupying a carbon site (B_CII) and a carbon atom occupying a nitrogen site (C_N), should present the lower formation energy. However, in a nitrogen-rich system, a nitrogen atom occupying a carbon site (N_CI) and carbon atom occupying boron site (C_B), should present the lowest formation energies. These antisites lead the BC₂N monolayer to exhibit acceptor and donor properties. We also observed that antisites that introduce homogeneous B-B and N-N bonds (B_CI, N_CII, B_N and N_B) give rise to deep electronic levels in the band gap. According to our calculations, vacancies should present higher formation energies than the antisites and we also noticed that for vacancies the reconstruction around the defective site depends on the missing atom and does not follow the same trend as observed for nanotubes. The electronic properties are ruled by the under-coordinated atoms that typically lead the system to present a localized magnetic moment.     

Ab Initio Study of Hydrogen Interaction with Defective BC2N Nanotubes

The spin polarized density functional theory is used to investigate the incorporation of hydrogen adatoms and the interaction between molecular H₂ with antisites and vacancies in both zigzag (4,0) and armchair (3,3) BC₂N nanotubes. We find that the presence of antisites and vacancies increases the binding energy of hydrogen adatoms on the tube surface. In the most stable antisites (C_B, C_N, N_CI and B_CII), the hydrogen adatoms bind preferentially on carbon atoms of the defective site (C_B, and C_N) or closer to it (N_CI and B_CII). For a single adsorbed H, the calculated binding energies show that the H adsorption on a carbon vacancy (V_CII) is the most stable site with a binding energy of ?4.23?eV. The adsorption of a second H atom near the previous one is an exothermic process compared to of a single H₂ molecule physisorbed on the nanotube surface.     

Hydrogen adsorption,structural, electronic,and spectroscopic properties of C32, B16N16, and B8C24 by DFT calculations

We used DFT calculations at B3LYP/6-31G(d) level of theory to investigate the structural, electronic and spectral properties of C₃₂, B₁₆N₁₆, and B₈C₂₄ nanocages. The C₃₂ found as the most stable one and the bond lengths was approximately constant for the considered nanocages. We also found that B₁₆N₁₆ has greater atomic charges than C₃₂ and B₈C₂₄. Very low conductivity and reactivity of B₁₆N₁₆, and higher conductivity and reactivity of B₈C₂₄ and C₃₂ were also revealed in this research. C₃₂ is the best electron donor cage and B₈C₂₄ is the best electron acceptor among the studied fullerenes. Simple infrared spectrum of fullerenes was revealed in which a few spectral regions can be identified as fingerprints of related samples. At last the binding energy of hydrogen molecules with the fullerenes was investigated.     

C60-like boron carbide and carbon nitride fullerenes: Stability and electronic properties obtained by DFT methods

The structural stability, electronic and magnetic properties of novel boron carbide and carbon nitride fullerenes, of chemical compositions: C₃₆B₂₄ and C₂₄B₃₆ (CBF) and C₃₆N₂₄ and C₂₄N₃₆ (CNF), rich in carbon, boron and nitrogen atoms, were determined by means of density functional theory based-methods. Calculations were done using a exchange–correlation functional developed by Heyd-Scuseria-Ernzerhof, within the generalized gradient approximation (HSEh1PBE-GGA) in concert with 6–311G(d,p) basis sets. The DFT simulation results for the neutrals, cations and anions reveal structural stability for the four chosen compositions. Several spin multiplicities were determined for each system. Although distorted, the located low-lying states preserve the basic fullerene features. In the addressed compositions, the lowest energy structures occur for the anions, which behave as semi-metallic and magnetic nanomaterials. Indeed, they have HOMO-LUMO gaps of 0.55, 0.66, 0.34 and 2.17 eV and 3.0, 5.0, 1.0 and 3.0 magneton bohrs, respectively. These CB and CN hybrid fullerenes show high polarity and low-chemical reactivity. Additionally, they have low-work functions, which is crucial for the design of electronic devices.     

Electronic Structure of Corannulene Monoanion: A Comparative Study with the Neutral and Tetraanionic States

Abstract

Electronic structure of monoanionic corannulene, C₂₀H^- ₁₀, has been studied comparing with those of C₂₀H₁₀ and C₂₀H^4- ₁₀ based on the ab initio molecular orbital calculation at the HF/3-21G level. The difference in geometries and electronic structures among these three corannulene systems and the strength of Jahn-Teller distortion appearing in C₂₀H^- ₁₀ are discussed.     

Morphology and composition of nickel–boron nanolayer coating on boron carbide particles

This work is focused on electroless coating of Ni–B nanolayer on B₄C particle surfaces. The B₄C particles used are approximately 2 μm in average size. Effects of activation agent PdCl₂, complexing agent C₂H₈N₂, and reducing agent NaBH₄ addition rate are studied. The solids loading of B₄C is 0.625 g/L and the concentration of Ni²⁺ ions is 0.004 mol/L in the electroless coating solution. Scanning electron microscopy (SEM) shows that when B₄C:Pd²⁺ molar ratio is 1:0.005, a Ni–B nanolayer with the smallest Ni–B nodule size covers the B₄C particle surfaces. Complexing agent C₂H₈N₂ decreases Ni²⁺ ion release rate. Ni:C₂H₈N₂ ratio of 1:6 is the preferred complexing agent amount for achieving a continuous Ni–B nanolayer. The Ni–B nanolayer formation is also strongly dependent on the rate that Ni²⁺ ions are reduced. Slow Ni²⁺ reduction leads to increased Ni content in the Ni–B nanolayer. When the above three factors are combined at the optimal values for the electroless coating process, well-defined Ni–B nanolayer is obtained. SEM cross section analysis shows the Ni–B nanolayer completely covers the B₄C particles with less than 55 nm thickness.     

Theoretical Study of Decachlorocorannulene and its Congeners C20X10 and C20Z5

Abstract

The electronic structure of C₂₀Cl₁₀ synthesized by arc discharge has been studied using ab initio calculation at MP2/3-21G theory level. Theoretical studies of C₂₀F₁₀ and C₂₀O₅, C₂₀S₅, C₂₀P₅ have been carried out using the same method.     

Influence of nitriding gases on the growth of boron nitride nanotubes

Boron nitride (BN) nanotubes of different sizes and tubular structures exhibit very different mechanical and chemical properties, as well as different applications. BN nanotubes of different sizes and nanostructures have been produced in different nitriding gases in a milling and annealing process, in which elemental boron powder was first milled in NH₃ for 150 h and subsequently annealed at 1,200 °C for 6 h. The influence of nitriding gases was investigated by using N₂, NH₃, N₂–H₂ mixture gases. A relatively slow nitriding reaction in NH₃ gas leaded to a 2D growth of BN (002) basal planes and the formation of thin BN nanotubes without the help of metal catalysts. Fast nitriding reactions occurred in N₂ or N₂–H₂ mixture gases, catalyzed by metal particles, resulted in 3D crystal growth and the formation of many large cylindrical and bamboo tubes.     

Gas-liquid detonation synthesis of CNTs@Fe/Fe3C composites and their application as electrode materials for double-layer capacitors

Abstract

The carbon nanotubes doping with Fe and Fe₃C nanocrystal (CNTs@Fe/Fe₃C) are successfully synthesized by the gas-liquid detonation (GLD) decomposition of CH₄, O₂, C₁₀H₁₀Fe and C₁₀H₈. The composition and structural properties of the as-obtained composites were investigated by XRD, TEM, XPS and Raman spectroscopy. The obtained composites were also applied to the electric double-layer capacitor. The results showed that the specific capacitance of CNTs@Fe/Fe₃C can reach 125?F·g^?1 at the current density of 100?mA·g^?1 and after 10000 cycles the capacitance retention is 93.1% at a current density of 2?A·g^?1.     

Mixed-State Specific Heat of the Type-II Superconductor Nb0.77Zr0.23 in Magnetic Fields up toB c2

In order to document the behavior of the mean-field mixed-state specific heat of an isotropic. strongly type-II superconductor (i.e., with a large value of the Ginzburg parameterk), and to provide a basis for comparison with high-temperature superconductors, we measured the specific heatC of the alloy Nb_0.77Zr_0.23 withT _c = 10.8K, B _c2 (0) = 7.9T, in magnetic fieldsB = 0, 0.2, 1.0, 12, 2.0, 2.4. 3.0, 3.3. 4.0. 4.4, 4.8, 5.2, 6.0. 6.6, 7.2 and 10 T. The values of the upper critical fieldB _c2 ( T), thermodynamic critical fieldB _c (T), Ginzburg parameterk(T), and coefficient γ(B) = lim_{T0(C(T. B)/T)} are derived from the specific heat data and found to be in agreement with the GLAG theory in the dirty limit. The behavior of the mixed-state specific heat is analyzed in terms ofC _el /T,∂(C _el /T)/∂B, and∂(C _el /T)/∂T vs. Tcurves, whereC _el is the electronic contribution to the specific heat.     

A MODEL STUDY OF NARROW NANOTUBES RELATED TO C36, C32, C20, AND C16: SEMIEMPIRICAL AND NONEMPIRICAL TREATMENTS

ABSTRACT

Very recently, narrow nanotubes have been observed with diameters of 5 or even 4?Å. In this report we perform calculations of narrow model nanotubes capped by fragments of D _2d and D _6h C₃₆ fullerene cages or by fragments of C₃₂ and C₁₆ quasi-fullerene cages with two four-membered rings, or finally by a fragment of dodecahedral C₂₀. The computations can reproduce the observed diameters of the narrow nanotubes. The results also indicate that fragments of C₃₂, used as caps instead of C₃₆, can lead to quite competitive energetics. Thus, a novel possibility that some of the narrow nanotubes can contain four-membered rings at their tips is suggested.     

Fullerane,the Hydrogenated C60 Fullerene: Properties and Astrochemical Considerations

Abstract

Hydrogenated C₆₀ fullerene, C₆₀H₃₆ was prepared in different solvents using Zn/HCl as reducing agents. The structure of C₆₀H₃₆ was confirmed both by electronic and FT‐IR spectroscopy and the purity of the reaction product was checked by HPLC analysis. It has been confirmed that C₆₀H₃₆ is not stable in air, especially in presence of light which enhances the oxidation. The oxidation of C₆₀H₃₆ was studied by FT‐IR spectroscopy and by differential scanning calorimetry (DSC) in air; the formation of hydroxyl groups on the fullerene cage and ketonic groups (involving cage breakdown) have been detected. Furthermore, the action of O₃ on C₆₀H₃₆ was investigated and it has been found that O₃ exerts practically the same effect of air but causing an enhanced cage breakdown. The thermal stability of C₆₀H₃₆ was checked by a thermogravimetric analysis (TGA) coupled with a differential thermal analysis (DTA) under N₂ flow. The vaporization of C₆₀H₃₆ occurs at very high temperature: the DTA trace has shown an endothermic peak at 540°C (at a heating rate of 20°C/min). C₆₀H₃₆ shows an electronic absorption spectrum with a maximum at about 217 nm and it is able to match both in position and in half width the peak at 217.5 nm observed in the spectrum of the interstellar extinction of light which was attributed to hydrogenated, radiation processed and thermally annealed carbon dust. Similarly, the absorption spectrum of C₆₀H₃₆ is able to match several infrared emission bands (called UIBs) detected from certain astrophysical objects like the protoplanetary nebulae (PPNe). It is proposed that hydrogenated fullerenes can be used as model compounds in the laboratory simulation studies of interstellar carbon dust.     

Characterization of Fullerenes Obtained from Boron Nitrite Containing Graphite Electrodes: Electronic Structure of C60-X-YBXNY and Deformed C60

Abstract

The electronic structure of C₆₀ molecules with carbon substituted by other elements such as boron or nitrogen has been calculated for molecules in the singlet state with even number of electrons. Therefore, in the case of boron and nitrogen substituents, calculations have been performed for ionized molecules. The results obtained from our density functional calculations prove than in the C_60-x-yB_xN_y molecules both HOMO and LUMO levels are split due to the lower symmetry of the molecule Influence of deformation of C₆₀ molecules on electronic states, which is interesting because fullerenes may undergo deformation in solvate crystals, is also shown These C₅₉B and C₅₉N, as well as C₅₈BN molecules are of special interest because samples containing such species can be prepared The Electron Spin Resonance (ESR) in those samples differs from the results obtained in pure C₆₀ samples, it consists of several lines which are very sensitive to the temperature.     

Growth and microstructures of carbon nanotube films prepared by microwave plasma enhanced chemical vapor deposition process

Well-aligned carbon nanotubes (CNTs) were grown on iron coated silicon substrates by microwave plasma enhanced chemical vapor deposition. Effect of plasma composition on the growth and microstructures of CNTs were investigated by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and optical emission spectroscopy. Morphology and microstructure of nanotubes were found to be strongly dependent on the plasma composition. Aligned bamboo-shaped nanotubes consisting of regular cone shaped compartments were observed for C₂H₂/NH₃/N₂ and C₂H₂/NH₃/H₂ gas mixtures. Randomly oriented or no nanotubes growth were observed in C₂H₂/H₂ and C₂H₂/N₂ gas mixtures respectively. CNTs grown in nitrogen rich plasma had more frequent short compartments while compartment length increased with decreasing nitrogen concentration in the plasma. Raman spectroscopy of CNTs samples revealed that CNTs prepared in nitrogen rich plasma had higher degree of disorder than those in low nitrogen or nitrogen free plasma. In-situ optical emission spectroscopy investigations showed that CN and H radicals play very important role in both the growth and microstructure of CNTs. Microstructure of CNTs has been correlated as a function of CN radical concentration in the plasma. It is suggested that presence of nitrogen in the plasma enhances the bulk diffusion of carbon through the iron catalyst particles which causes compartment formation. Based on our experimental observations, growth model of nanotubes under different plasma composition has been suggested using base growth mechanism.     

Effect of different atmospheres on the electrical stabilization of NiO films

Sputtered nickel oxide (NiO) films have a wide range of applications including their use in transparent conductive anodes for organic light-emitting diodes (OLEDs) where stable electrical properties are essential. Unfortunately, NiO films show electrical aging phenomenon in air. In the present experiments, the phenomenon of aging was investigated in different atmospheres including H₂, CO, O₂, CO₂, N₂, and Ar together with varying the humidity. It was found that NiO films were relatively stable in Ar but very unstable in H₂, CO and humid argon atmospheres. The aging rate increased rapidly as the humidity was increased from 2 to 20 relative humidity (RH) and became constant from 20 to 40 RH.     

Nanocrystallized steel surface by micro-shot peening for catalyst-free carbon nanotube growth

Nanocrystallized steel surface by micro-shot peening (MSP) were applied to carbon nanotube growth in this study. Micro-shot peening treatment severely deformed steel surface and nanocrystallized surface layer was formed by the plastic deformation. The grain sizes of the nanocrystallized layer were 10-30 nm after 300 s of MSP treatment. On the nanocrystallized surface, carbon nanotubes were formed with thermal chemical vapour deposition without catalysts. Before carbon nanotube growth, the nanocrystallized steel surface was reduced with H₂/N₂ gas at 600 °C. The carbon nanotube growth was performed at 600 °C with C₂H₂ gas carried by H₂/N₂ gas. The carbon nanotubes formed on the nano-structured surface was multi-walled carbon nanotube and the diameter was 10-20 nm. The reduction process before carbon nanotube growth was essential to form carbon nanotubes on the nanocrystallized surface with MSP.     

High-pressure behavior of the crystal structure of the fullerene molecular complex with ferrocene C60·{Fe(C5H5)2}2

Abstract

The crystal structure of the molecular complex C₆₀·{Fe(C₅H₅)₂}₂ was studied by single crystal X-ray diffraction (XRD) analysis at pressures up to 5?GPa using the diamond anvil cell (DAC) technique. The XRD data and subsequent structural analysis clearly show that there is no pressure-induced polymerization in fullerene layers in pressure range studied. The reciprocal unit cell volume V₀/V is a smooth and monotonous function of pressure and fits well to the Murnaghan equation of state (V₀/V) ^B'=?{1?+?P·(B'/B₀)}, where V₀ is the volume at ambient pressure, B₀=8.7?GPa and B'=10.5 are the bulk modulus and its derivative, respectively. Pressure dependence of the shortest distance between the C₅H₅ ring of the ferrocene molecule and the center of the nearest fullerene molecule is linear, while the slope changes at 2.2?GPa indicating on the intermolecular interactions crossover. Other relevant parameter, the Fe-C bond lengths of ferrocene, sensitive to iron charge state, gradually increases. This peculiarity can a sign of pressure-induced partial charge transfer between the donor ferrocene and acceptor fullerene molecules.     

Kinetics of Plutonium(IV) Reduction with 3,3'-Bis(diaziridinyl) in HNO3 Solution

3,3'-Bis(diaziridinyl), H₂N₂C₂H₂N₂H₂, is oxidized with Pu(IV) ions in excess of reductant to bis(diazirinyl), N₂C₂H₂N₂, and in excess of oxidant, to nitrogen and acetic acid. The reaction rate in the HNO₃ solution at a constant ionic strength is described by the equation -d[Pu(IV)]/dt = k[Pu(IV)]²× [H₂N₂C₂H₂N₂H₂]^{1 . 7}[H⁺]^{- 3}, where k = 28400±1400 mol^{0 . 3} l^{- 0 . 3} min^{- 1} at 35°C. The activation energy of the reaction amounts to 126±11 kJ mol^{- 1}.