BN Films Research Articles

Formation and characterization of BN films with Ti added

Boron nitride films with Ti added (BN:Ti) were prepared by a dual-ion beam sputtering method. The properties of the films were investigated by Fourier transform infrared spectrophotometer (FT-IR), electron spectroscopy for chemical analysis, X-ray diffractometer and the nano-indentation method. The structure of the BN:Ti films changed from the cubic phase to the hexagonal phase at more than 14.8 at.% added Ti. The internal stress and hardness decreased with an increase in the Ti content. With the reduction of the internal stress, the FT-IR absorption bands near 1100 cm −1 related to the cubic boron nitride phase changed to lower wavenumber. Added Ti atoms formed TiB 2 and TiN in the films with a small amount of Ti content, but with increasing Ti content, mainly TiN was formed.

Effects of Electrolytes in a Liquid Thin Layer System

The effects of electrolytes on electrochemical behavior from an oil thin layer interposed between a graphite electrode and an aqueous solution phase were examined. A hydrophobic electroactive species, tetrachloro-1,4-benzoquinone (TCQ), in a benzonitrile (EN) layer was employed to study ion transfer properties across the BN-water interface. Experimental results showed that hydrophobic cations as well as anions could be successfully used as ionic charge carriers. The addition of various salts into either the oil layers or the aqueous solutions offers deeper insight for the electrochemistry of the liquid thin layer system. When aqueous perchloric acid is interfaced with the BN films, the perchlorate ion of tetrahexylammonium perchlorate (THAP) substantially suppresses the dissociated proton concentration in the layer by the common ion effect while there is only a little change in the total acid concentration. Further approach by theoretical calculation makes it possible to quantitatively understand the effect of the electrolytes to the electrochemical responses of TCQ, which were previously reported (Anal. Chem. 73, 337 (2001)).

Structure and composition studies of chemical vapour-deposited BCN fibre coatings.

The composition and structure of boron carbonitride (BCN) films were studied. The films were continuously deposited on fibres by atmospheric pressure CVD. The precursors were ammonia, trimethyl borate and toluene. The composition was determined by photoelectron spectra of boron 1s, nitrogen 1s, carbon 1s and oxygen 1s. By fixing the C 1s peak at 285 eV, the position of the B 1s peak and the N 1s peak in the BCN films was equal to BN films. The C content of the films increases from about 6 at% to 60 at%, leaving the stoichiometric boron/nitrogen ratio as well as the oxygen content below 10 at% unchanged. Generally, the carbon content in the films is lower than predicted by the precursor ratios. Obviously, the insertion of carbon into the film is decreased in the presence of ammonia, which is known to etch carbon. With a decreasing ammonia/toluene ratio, the undesired effect in the reaction is suppressed and the carbon deposition becomes considerable. Transmission electron microscopic studies were performed on cross-sections of the coated fibres. High-resolution images generally show a hexagonal turbostratic structure with different orientation preferences of the atomic lamellae similar to hexagonal turbostratic boron nitride and pyrolytic carbon. When a noticeable carbon concentration (20 at%) is reached, the atomic sheets become uniformly distributed in all directions in space.

Using a PLD BN/AlN composite as an annealing cap for ion implanted SiC

A dual BN/AlN capping layer has been developed for annealing implanted SiC up to a temperature of at least 1700 °C. The AlN is used as a protective layer on SiC because it is chemically inert on the material and can be removed selectively with a warm KOH etch, while the BN layer prevents the AlN from evaporating at temperatures above 1600 °C. Prior to etching off the AlN film, the BN film is ion milled off. The BN film appears to be an excellent cap as the hexagonal phases present, hexagonal (hBN) and turbostratic (tBN), are stable to temperatures in excess of 2000 °C. After annealing, the BN forms a tight seal on top of the AlN in a dense epitaxial h-BN phase, with a t-BN layer forming above the hBN. The tBN layer should be able to accommodate strains caused by lattice mismatch and differences in the thermal coefficients of expansion because it, like graphite, forms strong sp 2 bonds in the basal plane, but contains loosely bonded basal planes that easily slip over each other.

Deposition of BN thin films onto Si(1 0 0) substrate by PLD with nanosecond and femtosecond pulses in nitrogen gas background

BN thin films were deposited using pulsed laser deposition (PLD) by irradiating a hot-pressed h-BN target with a fourth harmonic wave of a Nd:YAG laser and a fundamental wave of a Ti:Sapphire laser in a background of nitrogen gas atmosphere without any aid of energetic techniques. Si(1 0 0) wafers with smooth and chemically etched surface were used as substrates. The films were characterized by SEM, XPS and FTIR. It was found that the cubic phase is present only in BN films deposited with UV nanosecond pulses. The absence of cubic phase in BN films deposited by femtosecond ablation is supposed to be due to high laser irradiance which causes the removal of unevaporated material from a soft target such as h-BN.

Preparation of high-pressure phase boron nitride films by physical vapor deposition

The high-pressure phases boron nitride films together with cubic, wurtzic, and explosive high-pressure phases, were successfully deposited on the metal alloy substrates by tuned substrate radio frequency magnetron sputtering. The percentage of cubic boron nitride phase in the film was about 50% as calculated by Fourier transform infrared measurements. Infrared peak position of cubic boron nitride at 1006.3 cm−1, which is close to the stressless state, indicates that the film has very low internal stress. Transition electron microscope micrograph shows that pure cubic boron nitride phase exits on the surface of the film. The growth mechanism of the BN films was also discussed.

Dependence of oriented BN films on Si(100) substrate temperature

Abstract The effects of substrate temperature ( T sub ) of Si(1 0 0) on the orientation of hexagonal Boron Nitride (h-BN) films synthesized using magnetron sputtering and Plasma-Enhanced CVD (PECVD) were studied, respectively. It was observed that higher T sub could result in the growth of (0 0 0 2) oriented h-BN films and improve the crystallinity of the films, in contrast the films with the c -axis basically parallel to the surface at lower ones. A tentative explanation on the mechanism of the orientation characteristic is suggested, under the integration of compressive stress due to ion bombardment and desorption from thermal excitation.

HRTEM observation of BN films segregated on stainless steel SUS304 by low temperature heat treatment

High‐resolution transmission electron microscopy and electron energy‐loss spectroscopy observations were performed for the first time at surface films segregated by low temperature treatment from an amorphous layer made by a co‐sputtering deposition technique. It was confirmed that the layer was hexagonal boron nitride having c‐axis perpendicular to the material surface, presumably explaining its features of low occlusion and adsorption of gases as obtained from other experiments. In situ observation of layer growth under high intensity electron irradiation was also performed and it was observed that the layers grow by changing their bonding with different layers.

Reactivity of different tBN environments serving as reaction sites in cBN film deposition

Experimental observation of cubic boron nitride (cBN) growth on most substrates showed that cBN nucleated and grew on turbostratic boron nitride (tBN) layers. TEM study of BN films deposited by both PVD and CVD methods revealed three major types of tBN environments in the tBN layer [tBN with its (0002) planes parallel to the growth direction (I), perpendicular to the growth direction (II) and with its (0002) planes forming curvatures in random directions (III)]. In accord with these tBN environments observed by TEM, the corresponding structural models were designed via theoretical studies. The theoretical studies used frontier orbital theory based on ab initio Hartee–Fock calculations to compare the reactivity of the tBN environments serving as further reaction sites for the cBN growth. Both B and N were chosen as reactants. The type I tBN showed the highest reactivity, while the type II tBN exhibited the lowest reactivity. The type III tBN yielded different reactivity levels, which varied upon the curvature of the tBN (0002) planes. In terms of analyzing the nucleation sites on tBN planes, possible cBN nucleation mechanisms are also discussed. These results are consistent with the current experimental observations and data previously published.

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.

Brillouin light scattering study on the elastic properties of thick sputtered c-BN films

The Brillouin light scattering technique is used to observe thermally excited acoustic phonons in backscattering geometry in a transparent, 1.8 μm thick diode sputtered c-BN film. The Rayleigh mode at the film surface and the quasilongitudinal bulk mode were detected under various angles of light incidence. The angular dependent phase velocity of the bulk wave provides evidence for an elastic anisotropy of the film material. Complete descriptions of the elastic properties are presented, assuming either isotropic or hexagonal film symmetry. The reduction of the film stiffness in comparison to the single crystal and the origin of the elastic anisotropy of c11/c33≈4/5, where c11 and c33 are the respective extensional stiffness constants parallel and perpendicular to the film, is discussed. Both effects are predominantly caused by sp2-bonded material and a structured film growth.

Sub-micron coatings with low friction and wear for micro actuators

This paper deals with the fabrication and characterisation of friction and wear reduced nano-films for micro actuator applications. For this investigation films of diamond-like-carbon (DLC), metal doped Me-DLC, carbon-nitride CN x , boron-nitride BN and alumina Al2O3 films have been applied in the thickness range of 20–500 nm. The hardness of those coatings varied between 10 and 60 GPa. Micromechanical and microtribological properties of nano-coatings have been characterized by a modified scanning probe microscope. Besides this a novel micro tester for abrasive wear measurement of nano coatings was used. Friction of micro-contact areas was measured by use of a pin-on-disc tester. It turned out, that friction was – besides other parameters – dependent on determination method and load. Friction determined at areal DLC/DLC contact zones was generally much higher (μDLC 0.1) than diamond tip versus DLC (∼μ DLC 0.06).

Mechanical performance and growth characteristics of boron nitride films with respect to their optical, compositional properties and density

We present a study of the growth processes of sputtered BN films, deposited on c-Si (001) substrates, at room temperature (RT) by rf magnetron sputtering. Nanoindentation (hardness ∼21 GPa), density (∼2.6 g/cm 3) and roughness by X-ray reflectivity and stress measurements indicated the existence of sp 3-bonded BN with properties similar to those of crystalline BN being superior for optical applications due to their homogeneity offering a single refractive index and smooth surfaces. The growth mechanism of sputtered BN films is sensitive to the Ar partial pressure and the bias voltage applied to the substrate during deposition inducing bombardment of the film with Ar + ions. There is a narrow ion energy window where sp 3-bonded BN is predominant providing dense, hard- and wear-resistant films. The fact that they are produced at RT and they are homogeneous with no gradient refractive index and smooth surfaces are correct for processes, such as optical applications on polymers or soft substrates.

Effect of post-N+ implantation on the microstructure of the interfacial non-cubic BN layers

Plasma source ion implantation has been applied as a post treatment in order to modify the interfacial sp2 bonded layer of the cubic BN (cBN) films. The effect of ion irradiation on the microstructure of the noncubic BN layer was investigated. From HRTEM observation, the thickness of the BN layer of the representative sample was about 100 nm including 15 nm of initially grown non-cubic layer at the interface between a substrate and the cubic layer. At optimal plasma source implantation conditions, an acceleration voltage of 50 keV and an ion dose of 2×1016 ions/cm2, the microstructure of the interfacial non-cubic BN layer was changed. It was noticed that the ion irradiation caused the recrystallization of the amorphous phase and transformed the small crystallites into another phase. The micro-hardness of the complex consisting of a hard and soft layer increased as a result of phase transformations. This was caused by atomic displacements in the initially grown amorphous and hexagonal layers. The atomic displacements calculated by the TAMIX code were in the range of 0.31–0.52 nm per atom within 70–100 nm in depth.

Orientation effects in tBN/cBN interfaces: A transmission electron microscopic study

The orientation between cubic boron nitride (cBN) crystallites and the tBN layers on which they grow was studied using high-resolution transmission electron microscopy. BN films were prepared by radio-frequency magnetron sputtering under conditions leading to the formation of ∼100% cBN films grown on a preceding tBN layer. Two types of orientations were observed: (i) cBN layers grown on the edges of the tBN(0002) planes so that the cBN{111} planes are parallel to the tBN(0002) planes (as reported previously by many authors), (ii) cBN layers grown on curved tBN(0002) planes with no orientation to the tBN planes. The first type of cBN growth is associated with stress leading to delamination of cBN films thicker than 100 nm. The second type is associated with reduced stress enabling the growth of much thicker (∼500 nm) films at a relatively low (450 °C) substrate deposition temperature. These results may be helpful in the fabrication of thick cBN films and improving our understanding of the cBN nucleation process.

Atomic-Scale Dynamic Deformation Behavior of BN Thin Films

ABSTRACTDeformation behavior of the BN film was dynamically observed by high-resolution transmission electron microscopy. BN thin films were deposited on a narrow edge of Si flakes, using inductively coupled plasma-enhanced chemical vapor deposition. High-resolution observation of the sample revealed that the BN film was possibly deposited on the edge of the Si thinned to less than 10 nm in thickness, whose morphology varied depending on the thickness of the Si edge. Intriguing mechanical properties of the BN films, especially relating their dynamic behavior, were clearly verified by the high-resolution observation with piezo-ceramic tube for three-axis positioning of an indenter.

Plasma-Enhanced Chemical Vapor Deposition of High Quality Cubic BN Films with an Intermediate Layer of Turbostratic BN Thinner than 3 nm

ABSTRACTCubic boron nitride (cBN) thin films were deposited on silicon wafers by low-pressure inductively coupled plasma-enhanced chemical vapor deposition (ICP-CVD). By using special substrate pre-treatment processes including positive biasing treatment in H2 plasma or 1200 K pre-heating in H2 atmosphere followed by an N2 plasma treatment, turbostratic BN (tBN) intermediate layer was revealed to directly grow on Si substrates without an initial amorphous layer. The thickness of the tBN transition layer can be reduced to less than 3 nm.

Processing and Characterization of CVD c-BN Films and c-BN/Diamond Bilayers

ABSTRACTThe paper reports the syntheses of c-BN films by the reaction of B2H6 and NH3 in the hydrogen and argon mixture using microwave plasma-assisted chemical vapor deposition (MPCVD). The effects of NH3/B2H6 ratios, hydrogen addition, pulsed-DC substrate-bias voltage and diamond as bufferlayer on the formation of c-BN were investigated. As-grown films are characterized by FTIR, grazing-incidence XRD, and SEM. The NH3/ B2H6 = 3 was selected to obtain a better crystallized BN films with moderate deposition rate. When the hydrogen content was at 85 vol.% in the gas mixture and the substrate bias at −200 V, the maximum c-BN content about 65 % was obtained. However, the film was easily cracked in a few hours. The film deposited at lower substrate biasing of −100 V could preserve for a few days without peeling off, although it had lower c-BN content about 40 %. Nanocrystalline diamond film, deposited from 1 vol.% CH4/Ar plasma, as bufferlayer can promote the heteroepitaxial growth of c-BN, resulting in 80 % c-BN content. The c-BN/diamond bilayer were adherent with a total thickness of 1.2 μm.

Atomic layer deposition of BN thin films

Boron nitride has for the first time been deposited from gaseous BBr 3 and NH 3 by means of atomic layer deposition. The deposition temperatures were 400 and 750 °C, and the total pressure was 10 torr. The BN films, deposited on silica substrates, showed a turbostratic structure with a c-axis of 0.70 nm at a deposition temperature of 750 °C as determined by X-ray diffraction. The films deposited at 400 °C were significantly less ordered. The film density was obtained by means of X-ray reflectivity, and it was found to be 1.65–1.70 and 1.90–1.95 g cm −3 for the films deposited at 400 and 750 °C, respectively. Furthermore, the films were, regardless of deposition temperature, fully transparent and very smooth. The surface roughness was 0.3–0.5 nm as measured by optical interferometry.

Multilayered BN Coatings Processed by a Continuous LPCVD Treatment onto Hi-Nicalon Fibers

Boron nitride coatings were deposited onto SiC fibers by means of continuous low-pressure chemical vapor deposition (LPCVD) treatment from BF3/NH3 mixtures. This process lies in unrolling the fiber in the reactor axis. The relationships between the processing parameters and the structure of the BN deposits are presented. Thanks to a temperature gradient present in the reactor, multilayered BN films can be performed by stacking successive isotropic and anisotropic sublayers. Tensile tests show that when the temperature profile is well adapted, the SiC fibers are not damaged by the LPCVD treatment.