XPS investigations on boron nitride fibre coatings prepared by chemical vapour deposition in comparison to their hydrolytic rate

Investigations on CVD boron nitride films on fibres by means of photoelectron and X-ray spectroscopy resulted in B/N ratios above the stoichiometric value 1 and oxygen contents up to 25 at%. Compared to the hydrolytic rate of the films an apparent dependence was found on the deposition rate and some evidence of the oxygen concentration. CVD fibre coatings exhibit a hexagonal turbostratic structure with extremely small atomic layer plane dimensions, which was proved by transmission electron microscopy. Corresponding to oxygen concentrations in pyrolytic carbon films with similar structure a model is proposed, where the small atomic layers with dimensions of some nanometers cause a relatively high oxygen concentration in the boron nitride films. The oxygen atoms saturate the dangling bonds. Moreover the B/N ratio extents the expected stoichiometric ratio due to the oxygen atoms at nitrogen sites. Received: 15 July 1997 / Revised: 29 January 1998 / Accepted: 2 February 1998     

ESCA investigations on pyrolytic carbon films for fiber coatings

Photoelectron spectroscopy on pyrolytic carbon films revealed a main part of carbon atoms in graphitic planes and a smaller part of functional groups with oxygen bonded to carbon atoms. Oxygen totalled a share of 10 at% and more of the carbon coating. The films with a turbostratic structure consist of nearly parallel oriented atomic layers of hexagonal rings with dimensions in the nanometer scale, which is well known from HREM investigations. The oxygen atoms are proposed to saturate the numerous dangling bonds around these individual atomic planes. The oxygen atoms form double bonds or bridges between carbon atoms. Received: 15 July 1998 / Revised: 28 January 1998 / Accepted: 2 February 1998     

The properties of BCN films formed by ion beam assisted deposition

A study has been made on the formation and the properties of boron carbonnitride (BCN) thin films. The BCN films were produced by ion beam assisted deposition, in which boron and carbon were deposited by electron beam heating and nitrogen was supplied by ion implantation simultaneously. The mechanical properties of BCN films were measured using a ultra micro hardness tester and a friction tester. The atomic ratio and the structure of BCN thin films were estimated by means of X-ray photoelectron spectroscopy, laser Raman spectroscopy and Fourier transform infrared spectroscopy. As preliminary results, it was found that the BCN films are higher in hardness and lower in friction coefficient than diamond-like carbon (DLC) films. The mechanical properties are discussed with the relation of surface composition and structure.     

Influence of the composition of BCN films deposited by reactive magnetron sputtering on their properties

Compounds of the B--C--N system are very promising to produce superhard coatings with good tribological, chemical, and thermal properties. To investigate the influence of the composition of BCN films on their properties, films with five different compositions at nearly constant nitrogen content were deposited on silicon wafers by magnetron sputtering from hexagonal boron nitride and graphite targets operated in RF and DC mode, respectively. The compositions and binding states of the films were determined by XPS. The nitrogen content was found to be almost constant for all films at about a 40 at-%, whereas boron and carbon compositions ranged between 15-35 and 25-50 at-%, respectively. The electronic and bonding structure of the coatings were analyzed by REELS using three different electron beam energies to obtain information at different depths. An increase of the carbon content of the films resulted in a significant shift of the pi-pi* interband transition with respect to the energy loss corresponding to h-BN. The absence of the pi-pi* transition in the energy loss spectra acquired at a beam energy of 1900 eV indicates the existence of a very thin overlayer mostly sp(2) bonded and probably with a distorted hexagonal structure. The position of the bulk plasmon losses corresponded to the hexagonal phase for the overlayer and presented a shift of more than 1.5 eV to the higher energy loss direction for the spectra obtained at 1900 eV beam energy. This shift and the absence of the sp(2)-bond fingerprint induced the possibility of an underlying disordered structure with a majority of sp(3) bonds.     

XPS investigations of thick,oxygen-containing cubic boron nitride coatings

Cubic boron nitride (c-BN) coatings produced by PVD and PECVD techniques usually exhibit very high compressive stresses and poor adhesion due to intense ion bombardments of the growing surface that are mandatory during the formation of the cubic phase. Our previous investigations indicate, however, that a controlled addition of oxygen during film deposition can lead to a drastic reduction of the detrimental stress, yet having minor effect on the cubic phase content in the resulting low-stress, oxygen-containing c-BN:O coatings (as already confirmed by various analytical methods like X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and electron diffraction, and Fourier transform infra-red spectroscopy (FTIR)). This stress-reduction technique makes possible the deposition of well-adhered, superhard c-BN:O layer about 2 μm thick through magnetron sputtering on top of an adhesion-promoting base layer and via a compositional-graded nucleation process. In the present paper, we report on the atomic bonding structure relating in particular to the incorporated oxygen within such a thick c-BN:O coating using X-ray photoelectron spectroscopy (XPS). The c-BN:O top layer was found to consist of about 49.8 at% boron, 42.2 at% nitrogen, 5.5 at% oxygen, as well as small amounts of carbon (1.4 at%) and argon (1.1 at%). Because of the low oxygen concentration, it was difficult to categorize the bonding state of oxygen according to the XPS spectra of B 1s and N 1s elemental lines. However, the detailed results in terms of the O 1s spectrum strongly indicated that the lattice nitrogen of c-BN was partially replaced by the added oxygen.     

Characterisation of boron nitride fibre coatings with different crystalline order by TEM and XPS

Reinforcement effects in composites are widely influenced by fibre coatings. A detailed understanding of their microstructure and chemical composition is of great interest. Boron nitride films were deposited continuously on fibre rovings of various ceramics in CVD reactors of vertical as well as horizontal position. XPS depth profilings show that the film compositions are close to stoichiometric BN with carbon and oxygen impurities in the range of 10 at%. Cross-sections of separated fibres were investigated by HREM and TEM diffraction. All BN films are hexagonal turbostratic. The (002) layers with an increased distance (about 0.36 nm) showed a mean stacking sequence near to graphite and a characteristic orientation to the fibre in the interface region. We assume the gas flow type and hence the exchange rate of matter and energy determines the film structure in this region. With increasing film thickness the (002) layers fold randomly in all directions or form nanocrystals at elevated temperatures. Received: 7 September 1998 / Revised: 13 January 1999 / Accepted: 5 February 1999     

BCN化合物的合成与表征

以石墨和六方氮化硼(h-BN)粉为原料,利用高能机械球磨和高温高压技术对BCN化合物的形成、结构及相变进行了研究.经120h球磨制备出BCN非晶体.在1400cm^-1附近,BCN非晶有一宽化的强红外吸收峰,在740和1630cm^-1附近观察到弱的红外吸收峰;在1330cm^-1附近观察到一宽化的Raman散射峰.BCN非晶中B_1s的结合能为191.9eV,C_1s的结合能为284.9和286.8eV,N_1s的结合能为398.3和400.5eV.将BCN非晶在4GPa和1473K下退火45min后转化为六方结构的BCN晶体,其晶格常数为a=0.2505nm,c=0.6664nm.其红外光谱特征吸收峰分别出现在1398,1103,1024,925和802cm^-1.Raman散射峰分别出现在1328,1358,1582和1614cm^-1.并对非晶BCN的形成和相转变机制进行了研究.     

Tungsten imido complexes as precursors to tungsten carbonitride thin films

Thin films of tungsten carbonitride have been formed on glass by low-pressure chemical vapour deposition (LP)CVD at 550 degrees C from four closely related precursors: [W(mu-N(t)Bu)(N(t)Bu)Cl(2)(H(2)N(t)Bu)](2), [W(N(t)Bu)(2)Cl(2)(TMEDA)] (TMEDA = N,N,N',N'-tetramethylethylenediamine), [W(N(t)Bu)(2)Cl(2)(py)(2)] (py = pyridine) and [W(N(t)Bu)(2)Cl(N{SiMe(3)}(2))]. The grey mirror-like films were grown with a nitrogen or ammonia bleed gas. In all cases the chlorine content of the deposited films was less than 1 at% and the oxygen content of the films was lower for those grown using ammonia. Surprisingly, the use of ammonia did not significantly change the carbon content of the resulting films. Despite the coordination environment around the metal being essentially the same and the materials having a comparable volatility, some differences in film quality were observed. The films were uniform, adhesive, abrasion resistant, conformal and hard, being resistant to scratching with a steel scalpel. X-Ray powder diffraction patterns of all the films showed the formation of beta-WN(x)C(y). As a comparison the aerosol-assisted chemical vapour deposition (AA)CVD of [W(mu-N(t)Bu)(N(t)Bu)Cl(2)(H(2)N(t)Bu)](2) was investigated and amorphous tungsten carbonitride films were deposited.     

Metal‐Free Dehydrogenation of N‐Heterocycles by Ternary h‐BCN Nanosheets with Visible Light

An efficient metal‐free catalytic system has been developed based on hexagonal boron carbon nitride (h‐BCN) nanosheets for the dehydrogenation of N‐heterocycles with visible light; hydrogen gas is released in the process, and thus no proton acceptor is needed. This acceptorless dehydrogenation of hydroquinolines, hydroisoquinolines, and indolines to the corresponding aromatic N‐heterocycles occurred in excellent yield under visible‐light irradiation at ambient temperature. With h‐BCN as the photocatalyst and water as the solvent, this environmentally benign protocol shows broad substitution tolerance and high efficiency.     

Electronic structure and magnetic properties of hexagonal and cubic forms of aluminum nitride doped with <Emphasis Type="Italic">sp</Emphasis> impurities (B,C, O)

A comparative study of the band structure and magnetic properties of the hexagonal and cubic modifications of aluminum nitride doped with boron, carbon, and oxygen in the nitrogen sublattice has been performed using the ab initio FLAPW-GGA method. Preliminary conclusions on the comparative chemical activity of these phases are drawn from estimates for the energies of substitution of nitrogen atoms by dopants. It has been shown that the doping with boron and nitrogen leads to transition of hexagonal AlN into a magnetic state with high spin polarization of near-Fermi electrons, but for cubic AlN, this effect is absent.     

X-ray photoelectron study of the effect of the composition of the initial gas phase on changes in the electronic structure of hexagonal boron nitride films obtained by PECVD from borazine

Hexagonal boron nitride films are synthesized by plasma enhanced chemical vapor deposition (PECVD) from a gas mixture of borazine and ammonia or helium on Si(100) substrates. X-ray photoelectron spectroscopy is used to study changes in the electronic structure and chemical composition of the films depending on the composition of the initial gas mixture. It is found that the chemical composition of the samples depends on the gas used. The use of helium results in an excess of boron atoms on the film surface, the appearance of B–B bonds, and a decrease in the contribution of B–N bonds in the hexagonal structure. The preparation of h-BN films close to the stoichiometric composition by PECVD methods with the use of borazine is shown to be possible with the addition of ammonia. Based on the literature data, the binding energies in the B 1s XPS spectra are calculated for different boron environments in the hexagonal lattice.     

Chemical Composition and Structure of Thin Films Produced by Chemical Vapor Deposition

This paper reports results from studies of the chemical composition and structure of semiconducting, dielectric, and metallic films produced from molecular precursors by the chemical vapor deposition method. A study was made of films of zinc sulfides, mixed copper, cadmium, and zinc sulfides, boron nitride, carbonitride, silicon carbonitride, and iridium films. It is shown that the use of metal compounds with different ligands (zinc and manganese) enables production of zinc sulfide films in which manganese ions are uniformly incorporated into the zinc sulfide crystal lattice to substitute zinc at the lattice sites. For the films of simple and mixed cadmium, copper, and zinc sulfides, the film structure depends on the type of substrate. The thin layers of mixed cadmium and zinc sulfides are asubstitution solution with a hexagonal structure. The thin layers of boron nitride produced from borazine exhibit a nanocrystalline structure and are a mixture of cubic and hexagonal phases. Composite layers were produced from alkylamine boranes and their mixtures with ammonia. Depending on synthesis conditions, the layers are mixtures of hexagonal boron nitride, carbide, and carbonitride or pure boron nitride. Using silyl derivatives of asymmetric dimethylhydrazine containing Si—N and C—N bonds in the starting molecule, we produced silicon carbonitride films whose crystal habit belongs to a tetragonal structure with lattice parameters a = 9.6 and c = 6.4 . The iridium films obtained by thermal decomposition of iridium trisacetylacetonate(III) on quartz substrates in the presence of hydrogen have a polycrystalline structure with crystallite sizes of 50 to 500 . A method for determining grainsize composition was proposed, and grain shapes for the iridium films were analyzed. The influence of substrate temperature on the internal microstructure and growth of the iridium films is demonstrated. At the iridium–substrate interface, a transition layer forms, whose composition depends on the substrate material and deposition conditions.     

Structure,Composition, Mechanical,and Tribological Properties of BCN Films Deposited by Plasma Enhanced Chemical Vapor Deposition

In this work thin BCN films were deposited by plasma enhanced chemical vapor deposition (PECVD) using chloridic precursors. Through adjusting the BCl₃ content in the inlet gas mixture the chemical composition of the deposited films was changed from carbon rich to boron rich. Based on optical emission spectroscopy (OES) measurements, a correlation between film composition and precursor species concentration in the plasma was established. The films were amorphous as detected by grazing incidence X-ray diffraction (GIXRD). The hardness and the elastic modulus have maximal values of 25.5±1.2 and 191±6 GPa, respectively, for the films with a boron concentration of 45.2 at.%. GIXRD data suggest that a depletion in boron content may initiate the formation of graphitic domains in the amorphous matrix. The observed degradation of the mechanical properties is associated with the graphitization. The tribological behavior was studied with a tribometer operated in pin-on-plate configuration at the temperatures 25 and 400°C. The wear mechanisms were discussed with respect to the formation of a boric acid surface layer which was detected by reflection electron energy loss spectroscopy (REELS) analysis.     

Density Functional Theory Study of Aspirin Adsorption on BCN Sheets and their Hydrogen Evolution Reaction Activity: a Comparative Study with Graphene and Hexagonal Boron Nitride

We explored the aspirin adsorption and their hydrogen evolution reaction (HER) activity in waste water of borocarbonitride sheets. Our results indicate that BCN sheets considered here show HER activity and exhibit superior performance regarding adsorption of aspirin in waste water in comparison with graphene and hexagonal boron nitride (h-BN). The drug molecule (aspirin) possesses a strong affinity to BCN, with the order of binding energy on following the order BCN∼h-BN>graphene. Upon drug adsorption, the band gap of h-BN is found to be reduced by up to 33 %, whereas the bandgaps of graphene and BCN remain unaltered that makes BCN a potential candidate for HER in waste water.     

SIMS Profiling and TEM of CVD Films on Multi-Filament Samples

 A suitable fibre coating is essential to obtain optimal fibre-matrix interaction in fibre-strengthened composite materials. Thin films (∼100 nm) of silicon carbide, turbostratic carbon, and boron nitride were deposited by CVD as single or double layers on commercial multi-filament fibres in a continuous process. The fibre material itself may be carbon, alumina, silicon carbide, or a quaternary ceramic of SiCBN. The application of MCs⁺-SIMS enables one to determine the composition (including impurities of H and O) of various fibre coating materials with an accuracy of at least 20% relative. Due to the special geometry of the multi-filament samples the depth resolution of the SIMS depth profiles is limited, nevertheless, layered structures and some details of the interface between coating and fibre can be studied. The depth calibration of the SIMS depth profiles is derived from sputter rates established on flat samples with a composition similar to that of the fibre coating material. However, the obtained film thicknesses are not extremely different from the values derived from TEM on cross sections of coated fibres.     

A Response Surface Model to Predict and Experimentally Tune the Chemical,Magnetic and Optoelectronic Properties of Oxygen-Doped Boron Nitride**

Porous boron nitride (BN), a combination of hexagonal, turbostratic and amorphous BN, has emerged as a new platform photocatalyst. Yet, this material lacks photoactivity under visible light. Theoretical studies predict that tuning the oxygen content in oxygen-doped BN (BNO) could lower the band gap. This is yet to be verified experimentally. We present herein a systematic experimental route to simultaneously tune BNO's chemical, magnetic and optoelectronic properties using a multivariate synthesis parameter space. We report deep visible range band gaps (1.50–2.90 eV) and tuning of the oxygen (2–14 at.%) and specific paramagnetic OB₃ contents (7–294 a.u. g⁻¹). Through designing a response surface via a design of experiments (DOE) process, we have identified synthesis parameters influencing BNO's chemical, magnetic and optoelectronic properties. We also present model prediction equations relating these properties to the synthesis parameter space that we have validated experimentally. This methodology can help tailor and optimise BN materials for heterogeneous photocatalysis.     

Direct Solvothermal Synthesis of B/N‐Doped Graphene

Heteroatom‐doping into graphitic networks has been utilized for opening the band gap of graphene. However, boron‐doping into the graphitic framework is extremely limited, whereas nitrogen‐doping is relatively feasible. Herein, boron/nitrogen co‐doped graphene (BCN‐graphene) is directly synthesized from the reaction of CCl₄, BBr₃, and N₂ in the presence of potassium. The resultant BCN‐graphene has boron and nitrogen contents of 2.38 and 2.66 atom %, respectively, and displays good dispersion stability in N‐methyl‐2‐pyrrolidone, allowing for solution casting fabrication of a field‐effect transistor. The device displays an on/off ratio of 10.7 with an optical band gap of 3.3 eV. Considering the scalability of the production method and the benefits of solution processability, BCN‐graphene has high potential for many practical applications.     

Fabrication of crystallized boron films by laser ablation

Polycrystalline β-rhombohedral boron films mixed with amorphous boron phase have been successfully fabricated on quartz substrates using pulsed laser ablation in a quartz glass tube chamber placed in an electric furnace. The crystallinity of the films strongly depended on the temperature of the furnace and the pressure of background argon gas. High temperature and high pressure in the chamber were suitable for crystallized boron film preparation. The best crystalline films (without B₂O₃ phase formation) were obtained at 1000°C, 100 Pa. XPS measurements demonstrated that the major contaminants were carbon and oxygen, and the atomic ratio of oxygen to boron was 0.05 under the preparation conditions of well-crystallized films. The surface roughness of the films decreased by lowering laser energy to 150 mJ/pulse under the same pressure and temperature conditions.     

Raman spectroscopy of C-, BN-, SiC-layers deposited on multifilament substrates

The analytic characterisation of various layers and layer systems on fibrous materials are presented. The layers, deposited by an isothermal CVD process, consisting mainly of pyrolytic carbon, hexagonal boron nitride and silicon carbide were characterised by different analytical methods, especially by Raman spectroscopy [1]. The surface enhanced Raman spectroscopy (SERS) was used first time for the investigation of boron nitride (BN) coatings on fibres.     

Facile Green Synthesis of BCN Nanosheets as High‐Performance Electrode Material for Electrochemical Energy Storage

Two‐dimensional hexagonal boron carbon nitride (BCN) nanosheets (NSs) were synthesized by new approach in which a mixture of glucose and an adduct of boric acid (H₃BO₃) and urea (NH₂CONH₂) is heated at 900 °C. The method is green, scalable and gives a high yield of BCN NSs with average size of about 1 μm and thickness of about 13 nm. Structural characterization of the as‐synthesized material was carried out by several techniques, and its energy‐storage properties were evaluated electrochemically. The material showed excellent capacitive behaviour with a specific capacitance as high as 244 F g^?1 at a current density of 1 A g^?1. The material retains up to 96 % of its initial capacity after 3000 cycles at a current density of 5 A g^?1.