Gallium doped in armchair and zigzag models of boron phosphide nanotubes (BPNTs): A NMR study

The electrical properties and NMR parameters of the pristine and Ga-doped structures of two representative (8, 0) zigzag and (4, 4) armchair of boron phosphide nanotubes (BPNTs) have been investigated. The structural geometries of above nanotubes have been allowed to relax by optimization and then the isotropic and anisotropic chemical shielding parameters (CSI and CSA) of ¹¹B and ³¹P have been calculated based on DFT theory. The results reveal that the influence of Ga-doping was more significant on the geometries of the zigzag model than the armchair one. The difference of band gap energies between the pristine and Ga-doped armchair BPNTs was larger than the zigzag model. Significant differences of NMR parameters of those nuclei directly contributed to the Ga-doping atoms have been observed.     

Ammonia adsorption on the C30B15N15 heterofullerene: DFT study of nuclear magnetic shielding and electric field gradient tensors of N and B nuclei

Ammonia adsorption on the external surface of C₃₀B₁₅N₁₅ heterofullerene was studied using density functional calculations. Three models of the ammonia-attached C₃₀B₁₅N₁₅ together with the perfect model were optimized at the B3LYP/6-31G^? level. The optimization process reveals that dramatic influences occurred for the geometrical structure of C₃₀B₁₅N₁₅ after ammonia adsorption; the B atom relaxes outwardly and consequently the heterofullerene distorts from the spherical form in the adsorption sites. The chemical shielding (CS) tensors and nuclear quadrupole coupling constants of B and N nuclei were calculated at the B3LYP/6-311G^** level. Our calculations reveal that the B atom is chemically bonded to NH₃ molecule. The B atom in the NH₃-attached form has the largest chemical shielding isotropic (CSI) value among the other boron nuclei. The C_Q parameters of B nuclei at the interaction sites are significantly decreased after ammonia adsorption.     

Structural, electronic, and magnetic properties of boron cluster anions doped with aluminum: BnAl- (2≤n≤9)

The geometrical structures, relative stabilities, electronic and magnetic properties of small B n Al (2 ≤ n ≤ 9) clusters are systematically investigated by using the first-principles density functional theory. The results show that the Al atom prefers to reside either on the outer-side or above the surface, but not in the centre of the clusters in all of the most stable B n Al (2 ≤ n ≤ 9) isomers and the one excess electron is strong enough to modify the geometries of some specific sizes of the neutral clusters. All the results of the analysis for the fragmentation energies, the second-order difference of energies, and the highest occupied-lowest unoccupied molecular orbital energy gaps show that B 4 Al and B 8 Al clusters each have a higher relative stability. Especially, the B 8 Al cluster has the most enhanced chemical stability. Furthermore, both the local magnetic moments and the total magnetic moments display a pronounced odd-even oscillation with the number of boron atoms, and the magnetic effects arise mainly from the boron atoms except for the B 7 Al and B 9 Al clusters.     

Atomic and magnetic structures of Fe<Subscript>70</Subscript>Al<Subscript>5</Subscript>B<Subscript>25</Subscript> amorphous alloys

The short-range order around boron, aluminum, and iron atoms in Fe₇₅B₂₅ and Fe₇₀Al₅B₂₅ amorphous alloys has been studied by ¹¹B and ²⁷Al nuclear magnetic resonance at 4.2 K and ⁵⁷Fe Mössbauer spectroscopy at 87 and 295 K. The average magnetic moment of iron atoms μ(Fe) in these alloys has been measured by a vibrating sample magnetometer. It has been revealed that the substitution of aluminum atoms for iron atoms does not disturb μ(Fe) in the Fe₇₀Al₅B₂₅ alloy, gives rise to an additional contribution to the ¹¹B NMR spectrum in the low-frequency range, and shifts maxima of the distribution of hyperfine fields at the ⁵⁷Fe nuclei. In the Fe₇₀Al₅B₂₅ amorphous alloy, the aluminum atoms substitute for iron atoms in the nearest coordination shells of boron and iron atoms. This alloy consists of nanoclusters in which boron and iron atoms have a short-range order of the tetragonal Fe₃B phase type.     

Correlations in 11B NMR spectra of dihalo derivatives of bis(1,2-dicarbollyl)cobalt(III)

In the ¹¹B NMR spectra of dihalo derivatives of bis(dicarbollyl)cobalt(III), we have identified a correlation between the ¹¹B NMR chemical shifts of substituted boron atoms and boron atoms found in other positions on the carborane skeleton. We have observed an increased shielding effect for fluorine atoms (compared with other halogens), manifested in an upfield shift of the ¹¹B NMR signals for antipodal and trans boron atoms. For the fluorine-containing compound Bu₄N⁺ [8,8′-F₂-3,3′-Co(1,2-C₂B₉H₁₀)₂]⁻, we propose the following sequence of electron density transfer: B(8) → {B(6) and B(10)} → B(4, 7). __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 547–549 (cont.), July–August, 2006.     

The electronic and structural properties of BN and BP nano-cages interacting with OCN: A DFT study

The adsorption of OCN⁻ (cyanato anion) on boron nitride (B₁₂N₁₂ and B₁₆N₁₆) and boron phosphide nano-cages (B₁₂P₁₂ and B₁₆P₁₆) in terms of energetic, geometric, and electronic properties are studied using density functional theory calculations. Our study results indicated that the first OCN⁻ strongly prefers to be adsorbed from its N atom upon B atoms of the nano-cages than the O atoms of OCN⁻. These findings have been rationalized using frontier molecular orbitals and total electron density plots. The energy gap of the B₁₂P₁₂ is significantly reduced upon the adsorption of OCN⁻ compared to B₁₂N₁₂, thus leading to the increase in electrical conductance of nano-cage.     

A computational NICS and 13C NMR characterization of the substitution patterns of C70−2x(BN)x fullerenes (x=1–25)

A density functional study has been performed to investigate the electronic and magnetic properties of BN substituted fullerenes C_70?2x(BN)_x (x=1, 2, 3, 6, 9, 12, 15, 17, 19, 21, 23 and 25) based on the NMR parameters and NICS index. The calculated ¹³C chemical shielding (CS) tensors are found to be perturbed at the first and second neighbors of the doped atoms while the other distant carbon atoms not to be influenced significantly. ¹³C Chemical shifts (δ_iso) of the second neighbors of nitrogen and boron are significantly shifted to upfield and downfield (the second neighboring effects), respectively. Besides, chemical shifts are also affected by the curvature of the corresponding sites; for example, the perturbed sites at the caps yield smaller absolute values of chemical shifts than those located at the equator. Nucleus independent chemical shifts (NICS) at the cage centers of heterofullerenes (from ?25.29 to ?8.80) demonstrate that all the substituted species are aromatic, but less than C₇₀ (?27.29). The predicted NICS values may be useful for identification of the heterofullerenes through their endohedral ³He NMR chemical shifts.     

Electron field emission from boron doped microcrystalline diamond

Field emission properties of hot filament chemical vapor deposited boron doped polycrystalline diamond have been studied. Doping level (N_B) of different samples has been varied by the B/C concentration in the gas feed during the growth process and doping saturation has been observed for high B/C ratios. Threshold field (E_th) for electron emission as function of B/C concentration has been measured, and the influences of grain boundaries, doping level and surface morphology on field emission properties have been investigated. Carrier transport through conductive grains and local emission properties of surface sites have been figured out to be two independent limiting effects in respect of field emission. Emitter current densities of 500 nA cm⁻² were obtained using electric fields less than 8 V/μm.     

Doping effect of hydrogen on Al3 cluster

The doping effect of hydrogen atoms on geometric and electronic properties of small aluminum cluster, Al₃, where deviation from the jellium model may occur, is investigated from a first-principle method. It is found that the most favorable sites for H atoms to be bound to Al atoms depend on amount of H atoms. For each cluster, Al–H bond lengths have the smallest values when the H atoms are on the top sites and have the largest values when the H atoms are on face sites, while those corresponding to bridge-site H atoms are of medium value. The doping of H increases the binding energy of the Al₃ cluster. Al₃H₃ and Al₃H₅ are found to have much lower electron affinities, higher ionization potentials and significantly larger HOMO–LUMO gaps than their neighbors, which are typical characteristics of magic clusters. The high stabilities of the Al₃H₃ and Al₃H₅ suggest that they may have a good potential applications in cluster-assembled materials.     

Further study of continuous-wave CO flame chemical laser of the CS2/O2/N2O type

This report describes an experimental examination of the output characteristics of the continuous-wave (cw) carbon monoxide flame chemical laser (FCL) of the CS₂/O₂/N₂O type in case of small CS₂/O₂ reactants ratios (tipically CS₂/O₂≦1/10). A linear burner which gives a homogeneous and stable flame was used during the experimental study. The measurements of temperature distribution in CS₂/O₂ as well as CS₂/O₂/N₂O flames show maximum temperatures of 1040 and 890 K, respectively. The addition of nitrous oxide (N₂O) leads to dramatically enhanced output laser power caused primarily by V?V transfer processes. A chemical efficiency, based on the reaction O+CS→CO^*+S, of 3% was achieved. The spectral composition of the CO FCL of the CS₂/O₂/N₂O type shows lasing in the region from 5.130 to 5.586 μm. Experimental results were obtained with a nondispersive optical cavity.     

Study of electronic and optical properties of pure and metal decorated boron nitride nanoribbons (B15N14H14-X): first principle calculations

Density functional theory (DFT)/time dependent density functional theory (TDDFT) based calculations were performed for basis sets 6-31G for DFT and 6-31G (d), 6-31G (d,p) and 6-31+G (d,p) for TDDFT calculations on pure boron nitride nanoribbon (BNNR) B₁₅N₁₅H₁₄ and metal decorated B₁₅N₁₄H₁₄-X BNNRs, where X = Ni⁺, Fe⁺, Co, Cr⁺, Cu and Al. The metal doping ratio = 3.45% and the doping site (nitrogen atom), were fixed for all the BNNRs. Electronic properties dipole moment, binding energy and bandgap were determined. Absorption properties in the wavelength range (100–600 nm) were studied, and optical gaps, absorption wavelengths, oscillator strengths and dominant transitions were calculated. The effect of metal doping on the electronic and optical properties was investigated. Single metal doping shifts the electronic gap of pure BNNR from insulating to semiconducting nature. Red shift in the absorption wavelengths from ultraviolet to visible in all the BNNRs was noticed.     

毛刺状竹节结构氮化硼纳米管的合成与生长机理

以非晶硼和氧化镍纳米颗粒为原料,在氨气中1100 oC下合成了毛刺状竹节结构的氮化硼纳米管. 利用X射线衍射和透射电镜研究了氮化硼纳米管的结构和形貌. 竹节结构纳米管表面的毛刺是六方氮化硼的纳米薄片. 提出了一种基于固态硼和气态二氧化硼扩散的毛刺形貌生长机理.     

Exohedral chemical functionalization of C48B6N6 with NH3: Binding energies and electronic structures of C48B6N6–(NH3)n=1−6

Theoretical study of exohedral chemical functionalization of C₄₈B₆N₆ with NH₃ molecules has been investigated using DFT. It was found that NH₃ molecule can be chemically adsorbed on boron sites of C₄₈B₆N₆, with a charge transfer from NH₃ to C₄₈B₆N₆. Adsorption energy and the quantity of electron charge transfer from latest adsorbed ammonia to C₄₈B₆N₆ decreased with increasing in the adsorbed NH₃ molecules. Despite the strong adsorption energies, electronic properties of C₄₈B₆N₆ is preserved after modification(s) with NH₃ molecule(s) and chemical modification of C₄₈B₆N₆ with NH₃ molecules can be viewed as some kind of safe modification.     

UV absorption in metal decorated boron nitride flakes: a theoretical analysis of excited states

The excited states of single metal atom (X = Co, Al and Cu) doped boron nitride flake (MBNF) B₁₅N₁₄H₁₄-X and pristine boron nitride (B₁₅N₁₅H₁₄) are studied by time-dependent density functional theory. The immediate effect of metal doping is a red shift of the onset of absorption from about 220 nm for pristine BNF to above 300 nm for all metal-doped variants with the biggest effect for MBNF-Co, which shows appreciable intensity even above 400 nm. These energy shifts are analysed by detailed wavefunction analysis protocols using visualisation methods, such as the natural transition orbital analysis and electron-hole correlation plots, as well as quantitative analysis of the exciton size and electron-hole populations. The analysis shows that the Co and Cu atoms provide strong contributions to the relevant states whereas the aluminium atom is only involved to a lesser extent.     

Characterization of BCN films synthesized by radiofrequency plasma enhanced chemical vapor deposition

Boron carbonitride (BCN) films have been synthesized on Si(1 0 0) substrate by radio frequency plasma enhanced chemical vapor deposition using tris-(dimethylamino)borane (TDMAB) as a precursor. The deposition was performed at the different RF powers of 400-800 W, at the working pressure of 2×10⁻¹ Torr. The formation of the sp²-bonded BCN phase was confirmed by Fourier transform infrared spectroscopy. X-ray photoelectron spectroscopy measurements showed that B atoms were bonded to C and N atoms to form the BCN atomic hybrid configurations with the chemical compositions of B₅₂C₁₂N₃₆ (sample 1; prepared at the RF power of 400 W), B₅₂C₁₀N₃₈ (sample 2; at 500 W) and B₄₆C₁₈N₃₆ (sample 3; at 800 W), respectively. Near-edge X-ray absorption fine structure (NEXAFS) measurements indicated that B atoms were bonded not only to N atoms but also to C atoms to form various configurations of sp²-BCN atomic hybrids. The polarization dependence of NEXAFS suggested that the predominant hybrid configuration of sp²-BCN films oriented in the direction perpendicular to the Si substrate.     

Influence of oxygen on the formation of cubic boron nitride by r.f. magnetron sputtering

Formation of cubic boron nitride by r.f. magnetron sputtering has been studied with O₂ addition to the common working gas Ar/N₂. The chemical and the phase composition were determined with Auger electron spectroscopy sputter depth profiling and Fourier transform infrared spectroscopy. The result shows that oxygen hinders the formation of cBN in sufficient nitrogen-supply, but facilitates the growth of cBN in insufficient nitrogen-supply. With insufficient nitrogen-supply, there exists an optimal oxygen-supply in the working gas that promoted the establishment of the stoichiometric condition in the growing film. O-concentration in the film increases with oxygen-supply in the working gas. cBN forms only when the oxygen concentration is below 5% and c_N/c_B (ratio of concentration of nitrogen atoms and boron atoms) is 1 in the film.     

A novel high-voltage light punch-through carrier stored trench bipolar transistor with buried p-layer

A novel high-voltage light punch-through(LPT) carrier stored trench bipolar transistor(CSTBT) with buried p-layer(BP) is proposed in this paper.Since the negative charges in the BP layer modulate the bulk electric field distribution,the electric field peaks both at the junction of the p base/n-type carrier stored(N-CS) layer and the corners of the trench gates are reduced,and new electric field peaks appear at the junction of the BP layer/N drift region.As a result,the overall electric field in the N drift region is enhanced and the proposed structure improves the breakdown voltage(BV) significantly compared with the LPT CSTBT.Furthermore,the proposed structure breaks the limitation of the doping concentration of the N-CS layer(NN CS) to the BV,and hence a higher NN CS can be used for the proposed LPT BP-CSTBT structure and a lower on-state voltage drop(Vce(sat)) can be obtained with almost constant BV.The results show that with a BP layer doping concentration of NBP = 7 × 1015 cm-3,a thickness of LBP = 2.5 μm,and a width of WBP = 5 μm,the BV of the proposed LPT BP-CSTBT increases from 1859 V to 1862 V,with NN CS increasing from 5 × 1015 cm-3 to 2.5 × 1016 cm-3.However,with the same N-drift region thickness of 150 μm and NN CS,the BV of the CSTBT decreases from 1598 V to 247 V.Meanwhile,the Vce(sat) of the proposed LPT BP-CSTBT structure decreases from 1.78 V to 1.45 V with NN CS increasing from 5 × 1015 cm-3 to 2.5 × 1016 cm-3.     

等离子体增强化学气相沉积法制备立方氮化硼薄膜过程中的表面生长机理

利用感应耦合等离子体增强化学气相沉积法以Ar，He，N₂和B₂H₆为反应气体制备了高纯立方氮化硼薄膜.用四极质谱仪对等离子体状况进行了系统的分析，发现B₂H₆完全被电离而N₂只是部分被电离.H₂和过量的N₂在等离子体中生成大量中性的H原子和活化的N^*₂，它们与表面的相互作用严重地阻碍了立方 关键词： 立方氮化硼薄膜 等离子体 质谱     

Photo-induced site-specific nitridation of plasma-deposited B10C2Hx films: A new pathway toward post-deposition doping of semiconducting boron carbides

We show that dopant impurities can be introduced in a controlled, site-specific manner into pre-deposited semiconducting boron carbide films. B―N bond formation has been characterized by X-ray photoelectron spectroscopy for semiconducting B₁₀C₂H_x films exposed to vacuum ultraviolet photons in the presence of NH₃. Core level photoemission data indicate that B―NH₂ bonds are formed at B sites bonded to other boron atoms (B―B), and not at boron atoms adjacent to carbon atoms (B―C) or at carbon atom sites. Nitridation obeys diffusion-limited kinetics. These results indicate that dopant species can be introduced in a controlled, site-specific manner into pre-deposited boron carbide films, as opposed to currently required dopant incorporation during the deposition process.     

A computational NMR study of nitrogen substitutional impurity in the armchair BeO nanotube

The properties of nitrogen doped model of (5, 5) armchair beryllium monoxide nanotubes (BeONTs) have been investigated by density functional theory (DFT) and chemical shift parameters were calculated. A BeONT consisting of 60 Be, 60 atoms of O, and having a length of 1.67 nm was considered and each end of the nanotube was capped by 10 hydrogen atoms. The calculated results indicate that by replacing an O atom by N atom (N_O-doping), the chemical shift (CS) parameters of ⁹Be and ¹⁷O atoms are un-affected but replacing a Be atom with N (N_Be-doping) affects the CS parameters of O atoms. These results imply that role of nitrogen as an electron acceptor is more significant in the structure for which it dopes a Be atom.