Facile synthesis of boron nitride coating on carbon nanotubes

Boron nitride (BN) coating on the surface of carbon nanotubes (CNTs) was synthesized by the direct reaction of NaBH₄ and NH₄Cl in the temperature range of 500–600 °C. X-ray diffraction, field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) confirm the formation of BN coating. It is revealed that the BN coating follows the shape of CNTS without damaging the surface of CNTs, and the elements B and N distribute homogenously along the whole CNTs without chemical bonds between carbon and BN layers. Besides, the oxidation resistance of the CNTs improved a lot after being coated with BN.     

Atomic scale study of a MOS structure with an ultra-low energy boron-implanted silicon substrate

In this study, a poly-silicon/oxide on silicon structure was analysed at the atomic scale by atom probe tomography (APT). Before oxidation and poly-silicon deposition, the silicon substrate was implanted with boron (500 eV, 1 × 10¹⁵  at cm^− 2), post-annealed (650 °C, 30 min, N₂) in order to get a high deactivation rate and to form boron clusters. A good agreement was obtained between the APT and secondary ion mass spectrometry analyses, although discrepancies are observed on the concentration profiles. Those discrepancies appear as boron-silicon clusters, lying on the (001) plane, as previously observed in the literature.     

Interaction of carbon,boron and sulphur in superalloys

The interaction of carbon, boron and sulphur atoms was studied through observation of the amount, shape and distribution of carbides, borides and sulphides at grain boundary surfaces in superalloys by means of transmission electron microscopy.

Carbon, boron and sulphur atoms segregate towards grain boundaries and can form compounds there. The increases in tendency to segregate are arranged in the order C, Band S, and the B (or S) may force the C (or B) atoms out of grain boundaries. When B (or S) content was not high, with the C (or B) content being increased, the amount and size of borides (or sulphides) were decreased while the amount and size of carbides (or borides) increased gradually. It is shown that the C (or B) atoms, which segregate towards grain boundaries, can slow down the diffusion speed of the B (or S) atoms at the grain boundaries. The temperature of M₃B₄ precipitation was lower than that for M₂₃B₆ at grain boundaries in the superalloy. It is shown that the interaction of C and B atoms may depend on ageing temperature.     

Synthesis of boron carbide powder from hexagonal boron nitride

We report the synthesis of boron carbide powder via the reaction of hexagonal boron nitride with carbon black. The reaction between hexagonal boron nitride and carbon black completed at 1900 °C for 5 h in vacuum. The particle sizes of the synthesized boron carbide powder were about 100 nm from transmission electron microscopy. The possible reaction mechanism was that hexagonal boron nitride decomposed into elemental boron and nitrogen even when there was no carbon at a relatively low rate, and introduction of carbon into hexagonal boron nitride powder facilitated the decomposition process; the boron from the decomposition of boron nitride reacted with carbon to form boron carbide.     

Catalyst-free synthesis of carbon and boron nitride nanoflakes using RF-magnetron sputtering

Catalyst-free boron nitride (BN) and carbon (C) nanoflakes have been produced by direct radio frequency (RF)-magnetron sputtering on molybdenum and tungsten substrates at or above temperatures of 1000 °C and 800 °C, respectively. Selected-area electron diffraction (SAED) shows that the films are polycrystalline and contain disordered graphite and hexagonal BN. Transmission electron microscopy (TEM) reveals curved or twisted flakes up to several hundred nanometres in length. High resolution transmission electron microscopy (HRTEM) confirms the nanoflake structure to be turbostratic, which is intermediate between an amorphous phase and the ordered layered phases of hexagonal BN or graphite.     

Molecular orbital calculations of hydrogen storage in carbon and boron nitride clusters

Hydrogen gas storage ability in carbon and boron nitride (BN) clusters was investigated by molecular orbital calculations. From single point energy calculations, H₂ molecules would enter from hexagonal rings of C₆₀ and B₃₆N₃₆ clusters and octagonal rings of B₂₄N₂₄ cluster because of lower energy barrier. Chemisorption calculation of hydrogen for BN clusters showed that hydrogen bonding with nitrogen atoms was more stable than that with boron atoms. Stability of H₂ molecules in BN clusters seems to be higher than that of carbon clusters.     

Dissimilar laser brazing of boron nitride and tungsten carbide

Using laser brazing process, we made the dissimilar joint of the boron nitride and tungsten carbide with an excellent functionality. In order to investigate the characteristic of joint, observation and structural analysis of its interface by the electron probe micro-analysis (EPMA) and the scanning acoustic microscopy were performed. The wetting property between h-BN and Ag–Cu–Ti braze was excellent, therefore no gaps were seen between them. Moreover, it was suggested that the Ti element, which is the active ingredient in Ag–Cu–Ti braze, reacted with N in h-BN to generate Ti–N composite phase as an interfacial precipitation and the generation of Ti–N composite phase was affected by the concentration of Ti in Ag–Cu–Ti braze. All fracture was formed in h-BN body near the interface and it seemed that the distribution of shear strength of 1.25%Ti to 1.68%Ti was within the margin of variation of bulk strength of h-BN.     

The role of various boron precursor on superconducting properties of MgB2/Fe

The superconducting properties of Fe sheathed MgB₂ wire has been studied as a function of precursor B powder particle size. The in situ processed MgB₂ samples were prepared by means of conventional solid state reaction method with magnesium powder (99.8%, 325 mesh) and three different types of amorphous boron powders (purity; 98.8%, >95% and 91.9%) from two sources, Pavezyum (Turkish supplier) and Sigma Aldrich. The particle sizes of Turkish boron precursor powder were selected between 300 and 800 nm. The structural and magnetic properties of the prepared samples were investigated by means of the X-ray powder diffraction (XRD) and ac susceptibility measurements. The XRD patterns showed that the diffraction peaks for our samples belong to the main phase of the MgB₂ diffraction patterns. The highest critical temperature, T_c = 38.4 K was measured for the MgB₂ sample which was fabricated by using the 98.8% B. The critical current density of this sample was extracted from the magnetization measurements and J_c = 5.4 × 10⁵ A cm⁻² at 5 K and B = 2 T. We found that the sample made by using the 98.8% boron showed almost 2 times higher J_c than that of obtained from 91.9% B powder.     

Atomic-scale analysis of light alloys using atom probe tomography

The present paper reviews recent progress in atomic-scale characterisation of composition and nanostructure of light alloy materials using the technique of atom probe tomography. In particular, the present review will highlight atom-by-atom analysis of solid solution architecture, including solute clustering and short-range order, with reference to current limitations of spatial resolution and detector efficiency of atom probe tomography and methods to address these limitations. This leads to discussion of prediction of mechanical properties by simulation and modelling of the strengthening effect exerted by solute clusters and the role of experimental atom probe data to assist in this process. The unique contribution of atom probe tomography to the study of corrosion and hydrogen embrittlement of light alloys will also be discussed as well as a brief insight into its potential application for the investigation of solute strengthening of twinning in Mg alloys.     

Ab initio modeling study of boron diffusion in silicon

We present investigations of boron diffusion in crystalline silicon using ab initio calculations (W. Windl et al., Phys. Rev. Lett. 83 (1999) 4345). Based on these results, a new mechanism for B diffusion mediated by Si self-interstitials was proposed. Rather than kick-out of B into a mobile channel-interstitial, one- or two-step diffusion mechanisms have been found for the different charge states. The predicted activation energy of 3.5–3.8 eV, migration barrier of 0.4–0.7 eV, and diffusion-length exponent of −0.6 to −0.2 eV are in excellent agreement with experiment. We also present results of ab initio calculations for the structure and energetics of boron-interstitial clusters in Si. We show how these first-principles results can be used to create a physical B diffusion model within a continuum simulator which has strongly enhanced predictive power in comparison to traditional diffusion models.     

Molecular dynamics study on doping defected graphene by boron

Boron doping brings remarkable features and modified properties to graphene. In this study, we used molecular dynamics simulations to investigate the influence of vacancies on the graphene boron doping process. The existence of vacancies increases the boron content of doped graphene sheet. The physical mechanisms behind this phenomenon are discussed. The vacancy concentration of graphene affects the formation energy of boron-vacancy pair, the collision frequency between boron atoms and graphene sheet and also affects the boron atom capture cross section of graphene. We have also investigated the boron doping process for bicrystalline graphene. The results reveal that boron atoms tend to be adsorbed on the grain boundary region. The mechanical properties of the boron doped bicrystalline graphene are enhanced compared with the undoped graphene.     

Effect of the radio-frequency power on the dielectric properties of hydrogen-containing boron carbon nitride films deposited by plasma-assisted chemical vapor deposition using tris(dimethylamino)boron gas

We investigated the properties of boron carbon nitride film containing hydrogen (BCNH film) deposited using tris(dimethylamino)boron as the source gas. The dielectric constant (k) of BCNH film decreases with decreasing radio-frequency plasma power used for deposition, and can be as low as 1.8 at 10 W. Thermal desorption spectroscopy analysis shows that the film contains a large amount of hydrogen. Fourier transform infrared spectroscopy shows an absorption band at 2960 cm−1, attributed to the asymmetrical stretching mode of C-H in the methyl group. It is thought that increasing the number of C-H bonds, which have a low polarizability, can achieve a lower k value.     

An experimental study on ballistic performance of boron carbide tiles

Boron carbide is an attractive candidate for use as armour material because of its lower density combined with high hardness. The ballistic performance of boron carbide tiles were evaluated using standard Depth of Penetration (DOP) test method against hard steel 7.62 mm armour piercing (AP) projectiles. The effect of variation in thickness of tile and the projectile velocity on the ballistic efficiency of the material was studied. It has been found that the differential efficiency factor (DEF) increases with increase in projectile velocity from 600 to 820 m/s. And an insignificant or marginal increase in efficiency was observed for increase in tile thickness from 5.2 mm up to 7.3 mm. The effect of the type of radial confinement on the residual DOP was also studied. It was found that the steel radial confinement produces lower residual DOP values compared to aluminium alloy and with no radial confinement. Results along with photographs have been presented.     

Direct Imaging of Dopant and Impurity Distributions in 2D MoS2

Molybdenum disulfide (MoS₂) nanosheet is a two-dimensional (2D) material with high electron mobility and with high potential for applications in catalysis and electronics. MoS₂ nanosheets are synthesized using a one-pot wet-chemical synthesis route with and without Re doping. Atom probe tomography reveals that 3.8 at% Re is homogeneously distributed within the Re-doped sheets. Other impurities are also found integrated within the material: light elements including C, N, O, and Na, locally enriched up to 0.1 at%, as well as heavy elements such as V and W. Analysis of the nondoped sample reveals that the W and V likely originate from the Mo precursor. It is shown how wet-chemical synthesis results in an uncontrolled integration of species from the solution that can affect the material's activity. The results of this work are expected to contribute to an improved understanding of the relationships linking composition to properties of 2D transition-metal dichalcogenide materials.     

Laser pulsing of field evaporation in atom probe tomography

The processes by which field evaporation in an atom probe is momentarily stimulated by impingement of a laser beam on a specimen are considered. For metals, the dominant and perhaps only sensible mechanism is energy absorption leading to thermal pulsing, which has been well established. The energy of a laser beam is absorbed in a thin optical skin depth on the surface of the specimen. For materials with a band gap such as semiconductors and dielectrics, it is found that energy absorption in a thin surface layer dominates the process as well and leads to similar thermal pulsing. The relative amount of surface absorption versus volume absorption can strongly influence the heat flow and therefore the mass spectrum of the specimen. Thus it appears for very different reasons that all materials behave similarly in response to laser pulsing in atom probe tomography.     

Effect of functionalization and boron and nitrogen substitution on some properties of carbon nanotubes

Molecular orbital calculations of the ionization potential of single wall carbon nanotubes having donor NH₂ and acceptor NO₂ groups bonded to the side walls and ends and boron and nitrogen substituted for carbon show substantial increases in ionization potential compared to carbon nanotubes with no functional groups and no carbon substitutions. The presence of a carbon vacancy on the side wall also causes a substantial increase in the ionization potential. The effect of tube length on the ionization energy is also calculated. The calculations also suggest that at appropriate levels of boron and nitrogen doping the armchair carbon nanotubes could be high temperature organic ferromagnetic materials.     

Influence of boron on strain hardening behaviour and ductility of low carbon hot rolled steel

The beneficial effect of boron on mechanical properties of low carbon Al-killed steel has been reported in recent past. However, the effect of boron on strain hardening exponent (n) and ductility has not been fully understood. This aspect has been discussed in present work. The results of mill trials with reference to n and ductility with boron added steel are compared to those for commercial grade. The lowering of ‘n’ with increased total elongation in boron bearing steel has been related to the microstructural evolution as a result of boron addition.     

On the current role of atom probe tomography in materials characterization and materials science

Atom probe tomography has without any doubt become a routine technique to analyze the detailed three-dimensional chemistry of materials at the nanoscale. This article provides a general overview of what APT can reliably do today and what it might do tomorrow in terms of material characterization. The recent achievements in the analysis of new materials and new materials structures are first presented allowing some speculation on future possible developments. The ability to provide unique quantitative chemical information to link processing to device performance is then reviewed in the context of the recent nanowire and gate structures analyses. Finally examples of the systematic use of atom probe tomography to explore material behaviors and kinetic processes controlling microstructure evolution are presented.     

Critical assessment 20: on carbon excess in bainitic ferrite

For several decades, the question of carbon supersaturation in bainitic ferrite has attracted the attention of physical metallurgists. Originally, this was associated with excess carbon due to the displacive nature of phase transformation and its subsequent trapping at defects in bainitic ferrite. The development of advanced experimental techniques, such as atom probe tomography and in situ synchrotron and neutron X-ray diffraction, has provided new insights into carbon distribution within bainitic ferrite. Possible explanations for carbon excess in solid solution are discussed, and the pathways for the future advancement of this research question are suggested.     

Large-scale synthesis of BN nanotubes using carbon nanotubes as template

Boron nitride nanotubes (BN-NTs) were synthesized in large scale by the reaction of NaBH₄ and NH₄Cl in the temperature range of 500-600 °C for 10-18 h, where carbon nanotubes (CNTs) were mixed together with the reactants to serve as template. Pure BN-NTs were obtained by oxidizing the product at about 800 °C in air atmosphere. The structure and morphology of the product with a surface area of 106.635 m²/g were characterized by X-ray diffraction, transmission electron microscopy, Fourier transformation infrared spectroscopy, and thermogravimetric analysis. Large scale preparation of BN-NTs could be realized by this simple and effective route.