Amorphous BN Research Articles

Homogeneous and amorphous sputtered sp 3-bonded BN films at RT: a stress, spectroscopic ellipsometry and XPS study

A study of amorphous and homogeneous BN (a-BN) films produced by r.f. magnetron sputtering on c-Si(1 0 0) substrates at room temperature is presented. a-BN films with mixed sp 3- and sp 2-bonded BN, were studied in terms of internal stresses, bonding configuration and composition. The optical properties and the composition of BN films were examined by spectroscopic ellipsometry based on specific criteria such as optical gap; while the presence of sp 3-bonded BN in the films was also identified by high resolution X-ray photoelectron spectroscopy. It was found that the growth mechanism of sputtered BN films is sensitive to bias voltage ( V b). There is an ion energy range (40 V<| V b|<80 V), where sp 3-bonded BN is predominant, providing films with internal compressive stresses approximately 8 GPa. A threshold stress value of 3.5 GPa, the same as for the formation of the c-BN phase, was measured for the formation of the sp 3 bonding in the amorphous network of a-BN films.

Amorphous boron nanoparticles and BN encapsulating boron nano-peanuts prepared by arc-decomposing diborane and nitriding

Amorphous boron nanoparticles were prepared by arc-decomposing diborane, which had ideal morphologies in comparison with that of those fabricated by furnace or laser heating diborane. Peanut-shaped boron nitride encapsulating boron nanocapsules were fabricated by nitridation of amorphous boron nanoparticles. Unique core/void/shell structure of the nanocapsules was observed by using a high-resolution transmission electron microscopy. The mechanism of growing the BN nanocapsules by a catalyst free process was distinctly different from the process of arc discharge or laser heating. The broadening of nonpolar intralayer Raman line of hexagonal BN at about 1370 cm−1 was observed, which was attributed to the small crystal size of BN.

Shock‐Induced Transformations in Hexagonal Boron Nitride by High‐Velocity Thermal Spray

Shock synthesis of cubic BN (c‐BN) was accomplished using high‐velocity thermal spray. Al‐8Si‐20BN (hexagonal BN, h‐BN) composite powders were injected into a high‐energy flame where the particles partially melted and accelerated to impact on steel substrates. The shock wave generated by the sudden impact of the droplets propagated through the underlying deposit, which experienced a polymorphic transition to high‐pressure forms. Transmission electron microscopy revealed that the deposits contained platelike c‐BN embedded in h‐BN. The c‐BN formed with a specific orientation relation, with (0001) h‐BN parallel to (111) c‐BN and [11–20] h‐BN nearly parallel to [2–20] c‐BN. As a result of shock propagation, a number of half‐Frank loops with Burgers vector ½[0001] were introduced and thin (∼3 nm) layers of amorphous BN (a‐BN), parallel to the (0002) plane, were formed. Significant shearing of the (10–10) plane with respect to the c‐axis, delamination, and kink bands were also observed in most of the h‐BN grains. The Hugoniot pressure calculation suggested that the impact pressure was sufficient to trigger the nucleation of c‐BN.

Electron spectroscopic studies of nanocomposite PVD TiAlBN coatings

A range of TiAlBN coatings have been deposited by electron beam evaporation and the optimised composition exhibits a 150% improvement over single phase TiAlN coatings in drilling tests. The coatings have been analysed by core level XPS to investigate the phase composition and bonding. Grain sizes have been determined by TEM. Al substitutes into the TiN phase and the coatings show a phase composition in agreement with that predicted by the (Ti,Al)BN equilibrium phase diagram. The optimum microstructure for wet drilling applications consists of 26 nm (Ti,Al)N grains separated by 3 nm regions of amorphous BN. As the grain size increases, a new B 1s component develops, attributable to B either incorporated into the (Ti,Al)N phase or located at grain boundaries.

Spectroscopic ellipsometry studies on BN films from IR to vacuum UV energy region

The dielectric function ε(ω) of fully sp3 or sp2 amorphous BN materials, was calculated in the range 0.3–20 eV by applying the appropriate modeling, using one or two Tauc–Lorentz (TL) oscillators, respectively, in the analysis of the measured ε(ω) from 1.5 to 9.5 eV, combining conventional spectroscopic ellipsometry (SE) with synchrotron radiation (SR) SE. The basic characteristics of the electronic transitions occurring in the different types of BN hybridized bonds, such as energy of absorption, broadening, and the fundamental optical gap were deduced. Based on these results we studied composite BN films prepared by magnetron sputtering, and measured by SRSE, and in situ SE in the range 1.5–5.5 eV. The dominant sp2 or sp3 BN character can easily be revealed when the upper limit of the ε(ω) spectrum is confined to 5.5 eV. However, the extension of this limit to 9.5 eV can provide more valuable information on the bonding configuration in BN materials, which are well-correlated to the Fourier Transform IR SE measurements, also presented in this work.

Evaluating the microstructure and performance of nanocomposite PVD TiAlBN coatings

Physical vapour deposition (PVD) TiAlBN coatings can exhibit excellent wear resistance, with optimised coating compositions demonstrating a 150% increase in lifetime compared to standard TiAlN coatings in wet-cutting drill tests. For various TiAlBN compositions deposited by electron-beam evaporation, the stoichiometry and relative phase composition were determined using X-ray photoelectron spectroscopy (XPS) and the microstructure was examined by transmission electron microscopy (TEM). Al was found to substitute for Ti into the cubic TiN structure. In accordance with their position in the Ti(Al)BN phase diagram, all coatings exhibited a three-phase composition of (Ti,Al)N+BN+TiB 2. The TiB 2 content was very small and the microstructure was effectively that of a (Ti,Al)N and BN dual-phase coating. Optimum drilling performance was obtained for a coating with a phase fraction of approximately 90% (Ti,Al)N and 10% BN. The microstructure can be described as nanocrystalline (Ti,Al)N grains separated by an intergranular amorphous BN phase, in which the average (Ti,Al)N grain size and grain separation was determined to be 26 and 3 nm, respectively. The presence of a compliant intergranular phase permits some degree of grain displacement under load, reducing the elastic modulus, leading to greater toughness and wear resistance.

Effect of nitrogen ion implantation on the microstructural transformation of boron film

The structural transformation by nitrogen ion implantation into boron film as a function of film thickness, implant voltage and nitrogen ion dose was systematically investigated. Boron films were deposited on single crystal Si substrates using the electron beam evaporation of pure metallic boron, the thickness being 200, 500, 1000 and 2000 Å, respectively. The films were then nitrogen ion-implanted at 25-, 50- and 75-kV implant voltages applied to substrate, respectively, for a fixed nitrogen ion dose of 3×10 17 cm −2, and at 1×10 17, 2×10 17 and 3×10 17 cm −2 nitrogen ion doses, respectively, for a fixed implant voltage of 50 kV. The nitrogen ion-implanted boron films were characterized by Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). XPS results showed that the nitrogen ion-implanted boron films were nitrogen-deficient. Boron exists in the form of both metallic boron and boron nitride as indicated by XPS B1s bands. FT-IR spectra revealed that amorphous boron nitride (a-BN) or hexagonal boron nitride (h-BN) formed during nitrogen ion implantation into boron films. As implant voltage and nitrogen ion dose increased, amorphous BN was initially formed, while h-BN occurred at greater implant voltage and nitrogen ion dose. The thinner film led to the formation of h-BN at a relatively low implant voltage and nitrogen ion dose.

Production and structural characterization of BN/TiN multilayers

A pulsed excimer laser was used to evaporate targets of boron nitride and titanium nitride in an attempt to produce hard thin films on crystalline silicon substrates. The films were either pure TiN or BN layers, as well as alternating multilayers and mixed layers. Deposition could be assisted by ion bombardment. The films were characterized by Auger electron spectroscopy, Fourier transform infrared spectroscopy (FTIR), and x-ray diffraction. A selection of films was also studied by profilometry in order to determine deposition rate and the type of stress present. The level of stress in TiN films was also a function of the deposition temperature and could be varied with the use of ion bombardment. Amorphous, cubic, and hexagonal BN films were produced and the effect of the stress of the substrate on these layers was investigated. Multilayers were stressed, having alternating layers of nanocrystalline TiN and amorphous BN. Mixtures consisted of nanometer-sized regions of crystalline TiN and sp2 coordinated boron nitride. FTIR spectra and high-resolution transmission electron microscope pictures suggested that in the mixtures, boron nitride planes tended to parallel the surface of the TiN grains. No sign of stress-driven formation of cubic BN was observed in the multilayers nor in the nanosized mixtures, regardless of the stress level present in them; neither was there any sign of titanium borides or other structures that might increase the hardness of the films.

Superhard Nanocrystalline Composites with Hardness of Diamond

We summarize briefly our recently published concept for the design of novel, superhard nanocomposite materials. The fairly general validity of this design concept was documented by the preparation of a number of nanocomposites consisting of nanocrystalline transition metal nitrides and amorphous Si3N4 or BN of different chemical composition the hardness of which reached 40 to 60 GPa. More recently, we succeeded in preparation of nc-TiN/a- & nc-TiSix (x ≈︂ 2) with hardness of 80 to 105 GPa.

Superhard Nanocrystalline Composites with Hardness of Diamond

We summarize briefly our recently published concept for the design of novel, superhard nanocomposite materials. The fairly general validity of this design concept was documented by the preparation of a number of nanocomposites consisting of nanocrystalline transition metal nitrides and amorphous Si3N4 or BN of different chemical composition the hardness of which reached 40 to 60 GPa. More recently, we succeeded in preparation of nc-TiN/a- & nc-TiSix (x ≈︂ 2) with hardness of 80 to 105 GPa.

Synthesis of amorphous boron nitride from the molecular precursor ammonia-monochloroborane

Ammonia-monochloroborane, NH3BH2Cl, has been synthesized from the reaction of ammonia-borane with HCl in Et2O. Decomposition of the solid under NH3 to 600 °C produced amorphous BN in 97% yield. The 11B magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectrum of the amorphous BN is indicative of boron in the same environment as in hexagonal BN. Subsequent pyrolysis of the amorphous BN to 1000 °C produced turbostratic BN. Pyrolysis of NH3BH2Cl under vacuum to 1100 °C led to the formation of turbostratic BN as confirmed by x-ray diffraction (XRD) analysis. Gas evolution during this pyrolysis confirmed that the precursor loses H2 and HCl.

Structure, mechanical and tribological properties of sputtered TiAlBN thin films

TiAlBN films were produced by simultaneously sputtering from TiAl and TiB 2 targets in Ar/N 2 mixtures at a substrate temperature of 150 °C. The goal of this investigation was to study the influence of the nitrogen content (0‐40 at.%) on two sets of four coatings with B/Al ratios of approximately 1 and 5. All coatings showed very dense structures and were mainly found to be only partially crystalline. Evidence of Al, AlN, Ti, TiB 2 , TiN and BN bonding was observed in the XPS spectra, and correlation of the compositional and mechanical data showed that film hardness and elastic modulus decreased with the presence of a ‘‘soft’’ phase (Al, Ti or amorphous BN ). Hardness and elastic modulus values of up to 25 and 250 GPa, respectively, were found for TiAl 0.3 B 1.7 coatings. Coatings with a similar elastic modulus to that of the steel substrate showed the best adhesion. Friction coeYcient values between approximately 0.5 and 0.7 were recorded in sliding wear experiments against SAE52100 and WC/6%Co balls. Although friction coeYcients could not be correlated to the amorphous BN contents, it was noted that low combined ball and disc wear rates were found for coatings containing large amounts of BN. Coatings with B/Al ~5 and elastic moduli of 290 GPa showed two orders of magnitude better sliding wear resistance against WC/6%Co balls compared to commercially available TiN. © 1999 Published by Elsevier Science S.A. All rights reserved.

Microstructural studies of boron nitride films deposited by microwave plasma-assisted chemical vapor deposition by using trimethyl borazine precursor

Thin films of cubic boron nitride (c-BN) were synthesized using an organometallic precursor trimethylborazine (TMB) which contains both boron and nitrogen in 1 : 1 stoichiometric ratio. The films were deposited at different temperatures ranging from 300 to 500 °C at a pressure of 2 Torr and at 360 W microwave power, using N2 as carrier gas. The deposited films were characterized by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and scanning electron microscopy (SEM), which reveal the presence of amorphous BN and crystalline c-BN in varying proportions. The x-ray diffraction pattern of the deposited films showed a strongest peak at 2θ = 57.1° where the interplanar distance value, d = 2.06 Å, agreed well with the (111) crystallographic orientation of c-BN phase.

Microstructure and nanomechanical properties of cubic boron nitride films prepared by bias sputter deposition

Nanoindentations, using a triangular based cube-corner shaped diamond tip, were tried to study the mechanical properties of cubic boron nitride ( cBN) films. Since the cBN film has a layered structure consisting of an initial sp 2-bonded BN (amorphous BN and turbostratic BN) layer and a sp 3-bonded BN ( cBN) layer, which was previously studied by cross-sectional transmission electron microscopy (TEM), cBN films in different growth stages were prepared for the measurements. Hardness and elastic modulus were evaluated as a function of the penetration depth from the obtained loading-unloading curves using a method described by Oliver et al. The maximum hardness and elastic modulus of a 110-nm thick cBN film (including an approximately 50-nm thick initial layer) were approximately 10 and 3 times, respectively, larger than the values evaluated for a silicon wafer substrate. The dependence of the evaluated hardness and the elastic modulus on film thickness and penetration depth can be explained in terms of the layered structure of the cBN film, i.e. soft initial sp 2-bonded BN layer with low elastic modulus, and hard cBN layer with high elastic modulus.

Boron Nitride Obtained from Molecular Precursors: Aminoboranes Used as a BN Source for Coatings, Matrix, and Si3N4–BN Composite Ceramic Preparation

Aminoboranes, pure or partially converted into aminoborazines using thermal or aminolysis polymerization, have been used as boron nitride precursors. An amorphous BN preceramic is obtained when pyrolysed up to 1000°C that can be stabilized using further annealing up to 1400°C or crystallized into h-BN above 1700°C. These molecular precursors have been used to prepare carbon fiber/BN matrix microcomposites to get an efficient BN coating on graphite and as a BN source in Si3N4/BN composite ceramic. The properties of these new types of samples have been compared with those obtained by classical processes. The boron nitride obtained from these precursors is a good sintering agent during the hot-pressing of the samples. However, the crystallinity of BN, even sintered up to 1800°C, remains poor. In fact, most of the mechanical properties of the composite ceramic (density, porosity, hardness) are clearly improved and the aminoboranes can be considered as convenient boron nitride sources and helpful sintering agents in hot-pressing technology.

Deposition of cubic boron nitride layers — characterisation of substrate–layer interface

Cubic boron nitride (c-BN) layers were deposited on (111)-oriented silicon and high-speed steel substrates in a hollow cathode arc evaporation device. The films have a maximum cubic phase content of about 95%. Film growth processes were studied ex situ in dependence on duration of deposition by Fourier transform infrared (FTIR) transmission spectroscopy. Structure of the films was investigated by high resolution transmission electron microscopy (HRTEM) and transmission electron diffraction (TED). c-BN content, ratio of the in-plane vibration (1380 cm −1) to the out-of-plane vibration (780 cm −1) of hexagonal BN, the half-width of the phonon structures and the stress in the films are determined from infrared spectra. On silicon the growth sequence amorphous BN (a-BN)–hexagonal BN (h-BN)–c-BN was observed by the measuring techniques used. An in-situ FTIR reflectance spectrometer was set up in order to monitor growth processes on line. In-situ reflectance measurements on silicon and high-speed steel substrates reveal differences in the growth processes. In contrast to silicon it has been observed that on high-speed steel h-BN and c-BN grow simultaneously.

Growth mechanism of cubic boron nitride thin films by ion beam assist sputter deposition

Cubic boron nitride (c-BN) thin films were successfully grown on Si(100) substrates by dual ion beam sputter deposition and the growth mechanism was studied with angle resolved in situ x-ray photoelectron spectroscopy (XPS) analysis. Boron was sputter deposited by 1 keV argon ions from a boron target and simultaneously bombarded with low energy nitrogen and argon ions mixture. Through Fourier transform infrared absorption spectroscopy (FTIR) and in situ XPS experiment, the optimum conditions for the c-BN growth such as the substrate temperature, the assist ion current density and the ion energy were determined to be 460 °C, 60 μA/cm2 and 350 eV, respectively. Angle resolved in situ XPS analysis showed that the 1.2±0.2 nm surface layer of the c-BN film is always in the hexagonal boron nitride (h-BN) phase, which clearly shows that c-BN phase grows by the transformation from the initially formed h-BN phase by low energy ion bombardment. Cross-sectional high resolution transmission electron microscopy (TEM) images show that the BN thin films on Si has a sequential layered structure which consists of an initial amorphous BN (a-BN) layer (∼4 nm), a transitional h-BN layer (∼5 nm), and a main c-BN layer. The transformation of the h-BN to the c-BN phase and the unusual sequential layered structure were discussed in view of the compressive stress model.

Laser Heating of Boron Nitride and Graphite in a Diamond Anvil Cell

ABSTRACTCubic, hexagonal BN, and graphite were heated with the aid of cw CO2 or pulsed YAG laser in a diamond anvil cell at pressures up to 35 GPa. The recovered samples were analyzed by high resolution and scanning electron microscopy, micro-Raman, and X-ray diffraction using synchrotron radiation. Melting of hBN and cBN was achieved. Microcrystals of hBN or cBN were grown from the fluid of BN in nitrogen or argon. Analysis of the hBN-cBN transitions in dependence on pressure showed that the hBN-cBN-liquid triple point is located at 9 GPa. In the transient region between the two phases in the same sample amorphous BN was found revealing the microscopic mechanism of diffusion-like first-order transitions. BN nanotubes growing from an amorphous state at the surface of the crystals were discovered. Under nanosecond pulse laser heating graphite transforms to a diamond-like structure. Spherical droplets and nanocrystals were condensed from the ablated carbon. A compound of nitrogen with carbon was found.

Microstructure of BN:C films deposited on Si substrates by reactive sputtering from a B 4C target

The microstructure and composition of boron nitride:carbon (BN:C) thin films prepared by reactive r.f. diode sputtering of a B 4C target in mixed Ar and N 2 discharges were determined by high-resolution electron microscopy, electron diffraction, infrared spectroscopy, electron probe microanalysis, and X-ray photoelectron spectroscopy. Films were prepared with three characteristic phase compositions; cubic BN:C (c-BN), turbostratic BN:C (t-BN), and phase mixture of c-BN and t-BN on Si(001) substrates. While keeping the B/N ratio close to unity, phase structures were mainly correlated to the energy and flux of impinging (Ar + + N 2 +) ions towards the negatively d.c. biased substrate. At a constant ion flux, substrate biases of 500 V yielded c-BN films while biases lower than 300 V resulted in t-BN. Films prepared with the same ion flux and with biases between 300 and 500 V consisted of c-BN and t-BN phase mixtures. The film phase evolution in c-BN films was from an initial amorphous BN:C (a-BN) layer, over a highly oriented t-BN layer with the c axis parallel to the film surface, to a c-BN layer exhibiting (110) prefered orientation. Films consisting of c-BN and t-BN phase mixtures were non-textured nano- to sub-microcrystalline. The c-BN layers/grains showed twinning on the c-BN(111) lattice planes. As-deposited films contained as much as 5–15 at.% of C with mainly CC and BC bonds. The film C content decreased with increasing volume fraction of c-BN.

金属粉の製造および評価試験 機械的合金化したＴｉ‐ｈＢＮ粉末中のＢの状態分析

BK X-ray spectra from mechanically alloyed (MA) Ti-hBN powders were measured precisely using an electron probe microanalyzer (EPMA), in order to investigate the reaction progress of this system. Their spectra features were discussed in comparison with mechanically ground (MG) hBN oowders.At the early stage of MA, the main BK band at 6.9nm was almost unchanged, while 6.5nm satellite peak intensity was increased. From the result of milling of hBN alone, it was considered that hBN was changed into amorphous BN (aBN) in consequence of refinement, but B state of this aBN was still remained as same as that of hBN. BK spectra of 144ks MA powder was clearly different from that of TiB2, in spite of the observation of TiB2 by X-ray diffraction measurement. This spectrum was in good agreement with the combined spectrum with aBN and TiB2 spectrum. In conclusion the excess of B was remained still as aBN after 144ks MA.