Boron Nitride Target Research Articles

Microtribological properties of B–C–N extremely thin protective films deposited on plasma pretreated magnetic layers

In this paper, we present results of microtribological properties of boron, nitrogen, and carbon (B–C–N) and nitrogen containing carbon (C–N) thin films deposited on CoCrTa magnetic disks. The C–N and B–C–N films of 1- and 3-nm thickness were deposited by complex treatment method, including plasma irradiation and reactive sputter deposition, using hexagonal boron nitride (h-BN) and graphite (C) semicircular targets. Nanoindentation experiments were performed using atomic force microscope (AFM) with a 143.6°, three-side pyramidal diamond tip at the load of 100–200 μN. The surface morphology of these coatings was examined by AFM. The B–C–N film showed superior hardness and microwear resistance in comparison to the C–N film. The 1-nm B–C–N film showed excellent tribological properties due to a gradated composition and interfaces.

Mechanical Properties of Extremely Thin B–C–N Protective Layer Deposited With Helium Addition

With complex treatment, which includes plasma irradiation pretreatment and reactive sputtering treatment, a boron–carbon–nitrogen (B–C–N) film was deposited as an overcoat on a CoCrTa magnetic disk by RF sputtering using two semicircular targets. Nitrogen-containing carbon (C–N) and CN/BN layered films were deposited by controlling the time duration the substrate faced each of the graphite and hexagonal boron nitride (h-BN) targets. The effects of plasma irradiation produced from an argon and nitrogen (N2+Ar) mixed gas as well as a nitrogen and helium (N2+He) mixed gas on the mechanical properties of these films were evaluated in this work. Based on the results obtained in microwear and oscillation scratch tests, it is verified that the wear resistance of the B–C–N film formed in N2+He was improved and this film exhibited a high lubricant performance, with a low friction of µ=0.027, due to He addition.

On the stoichiometry condition for the formation of cubic boron nitride films

The stoichiometry of boron nitride (BN) films, which are deposited with self-bias-assisted radio frequency (rf) magnetron sputtering of a hexagonal boron nitride (hBN) target, has been investigated with Auger electron spectroscopy (AES) and the MCs+-mode of secondary ion mass spectroscopy (MCs+-SIMS) for the sake of a better understanding of the growth mechanism of cubic boron nitride (cBN). The cubic fraction of the films is determined with Fourier-transform infrared spectroscopy (FTIR). It is shown that full stoichiometry of the deposited films is decisive for cBN-growth. A substrate bias voltage can increase the N concentration of a growing film under N-deficient deposition conditions. This effect is shown to be temperature dependent.

The constitution and properties of cubic boron nitride thin films: a comparative study on the influence of bombarding ion energy

Boron nitride thin films were deposited by unbalanced radio frequency magnetron sputtering of a hot-pressed hexagonal boron nitride target in a mixed argon/nitrogen atmosphere of 0.2 Pa. The intensity of ion bombardment during deposition was varied by a direct current substrate bias between 0 and −500 V. Thin films containing more than 85% of the sp 3-bonded cubic phase (c-BN), as confirmed by infrared spectroscopy, were produced in a wide voltage range from −200 to −400 V. The high c-BN content can be maintained even at an appreciably reduced bias of −80 V when a nucleation layer is formed in advance. In that case a decrease of compressive stress as well as an alteration of surface structure of the deposited c-BN films was observed. An analysis in light of electron energy loss spectroscopy indicates moreover the existence of an sp 2-coordinated surface layer with an ion-energy-dependent thickness. The results are discussed within the frame of the subplantation model.

Energy and mass dependence of isotopic enrichment in sputtering

Silver, copper, and boron (from a boron nitride target) were sputtered with xenon ions. The isotopic composition of secondary ions of silver was measured at ion energies ranging from 300 eV to 3 keV and, for copper and boron, at 2.0, 2.5, and 3.0 keV. An ion gun was used to generate the ion beam. The secondary ions were detected at a small emission angle by a quadrupole mass spectrometer. The secondary-ion flux of silver was found to be enriched in heavy isotopes at lower incident-ion energies. The heavy-isotope enrichment was observed to decrease with increasing primary-ion energy. Beyond 500 eV, light isotopes of silver were sputtered preferentially with the enrichment increasing to a constant value of 1.018. The sputtered flux of copper and boron also indicated constant enrichments (1.008 and 1.281 for copper and boron respectively) in light isotopes at high ion energies.

Cubic boron nitride films deposited by unbalanced RF magnetron sputtering and pulsed DC substrate bias

Boron nitride films were deposited by unbalanced RF magnetron sputtering of a sintered hexagonal boron nitride (h-BN) target in an argon and nitrogen mixture working atmosphere with a pulsed DC bias applied to the substrate. The microstructure of the films was analyzed by reflective Fourier transform infrared (FTIR) spectroscopy. The three main absorption peaks observed on the FTIR spectra, i.e. the two h-BN peaks at approximately 1380 and 780 cm −1, and the cubic phase (c-BN) peak at approximately 1080 cm −1, were used to characterize the film structure. The variation of the FTIR spectra with different deposition parameters, including substrate bias voltage, substrate temperature, working gas composition and RF target power, was systematically investigated. It was observed that there existed a threshold bias voltage above which the c-BN started to form. The c-BN content in the film increased with the increase of the bias voltage. A relatively higher substrate temperature favored the c-BN formation. In the range of the deposition conditions investigated, the highest c-BN content, up to 75%, was obtained in the film deposited at 400 °C under a bias voltage of 150 V in the working atmosphere of N 2 to Ar ratio of 1:5 using RF target power of 800 W.

Boron nitride nanostructures formed by ultra-high-repetition rate laser ablation

High-repetition rate (2×10 5 pulses/s), short-pulse (60 ps) laser was used for the first time for ablation of a hexagonal boron nitride (BN) target at nitrogen pressure of ∼100 Torr in search for the optimum conditions of BN nanostructure formation. High-resolution transmission electron microscopy, electron energy loss spectroscopy, and energy-filtered TEM analysis of the produced nanomaterial revealed a variety of BN nanostructures formed due to the interaction of BN plume with nitrogen ambient. Nanorods, multi-layered nanocages, double-layered ‘nanohorns’, and multi- and single-walled BN nanotubes were discovered in the product. BN nanotubes exhibiting various diameters and numbers of layers, including single-walled nanotubes, were frequently assembled in bundles.

Influence of aluminum additions on phase formation in boron nitride films deposited by magnetron sputtering

Boron nitride (BN) thin films have been deposited by magnetron sputtering of an hexagonal BN (h-BN) target with an additional flux of aluminum provided by a special Al sputtering target. Up to an aluminum percentage of about 1.0 at. % the formation of the cubic BN (c-BN) phase was not influenced by the aluminum addition. An Al content of 1.3 at. % was connected with a remarkable delay in the transition from h-BN to c-BN growth as well as a certain deterioration in the crystal quality. An aluminum flux causing a concentration of 1.5 at. % did prevent the growth of the cubic BN phase completely. The dynamics of impurity incorporation were investigated using secondary ion mass spectrometry measurements. We found that the aluminum electrode plays an important role in the incorporation of hydrogen in the films. In connection with other results it can be concluded that for both h-BN and c-BN strong evidence for substitutional incorporation of aluminum on boron sites exists. Cross-section transmission electron microscopy revealed that the formation of the c-BN phase starts at particular sites (c-BN nuclei) which broaden via a wedge shaped growth up to the point where the c-BN nucleation is completed and a nanocrystalline, pure c-BN layer grows. Hence, the interface between h-BN and c-BN has a jagged shape. This structure of the films h-BN/c-BN was found to be essentially independent of the Al incorporation.

Characterisation of a BN magnetron sputtering process with an additional aluminium sputter electrode

The deposition of boron nitride (BN) films by r.f. magnetron sputtering of a hexagonal BN target with intended additional aluminium incorporation has been studied using various in situ plasma diagnostic techniques. The aluminium flux towards the substrates was supplied by an additional ring-shaped aluminium electrode mounted all around the circular magnetron. Langmuir double probe investigations reveal only little influence of the electrode position and electrostatic potential on the magnetron discharge. The most appropriate electrode position was found to be levelled with the anode of the magnetron. The aluminium density in the gas phase was investigated by laser-induced fluorescence and optical emission spectroscopy (OES) yielding an increase with the square of the electrode power. Moreover, a strong dependence on the Ar–N 2 gas mixture was observed which is explained by nitride formation on the surface. OES measurements also imply a significant hydrogen and boron contamination of the electrode during its power-off phases.

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.

Multi-diagnostic comparison of femtosecond and nanosecond pulsed laser plasmas

Understanding and fully characterizing highly dynamic and rapidly streaming laser ablation plasmas requires multiple techniques for monitoring effects at different stages. By combining multiple diagnostic methods, it is possible to analyze the broad time window over which these ablation plasmas develop and to learn more about the related physical processes that occur. Two laser sources, an 80 fs Ti:Sapphire laser (780 nm) and a 6 ns Nd:YAG laser (1.06 μm), are used in this work in order to compare pulse duration effects at similar wavelengths. Characteristics of the plasma produced by these two lasers are compared under conditions of comparable ablation flux. Results are presented involving correlation of time-resolved Langmuir probe data and electrostatic energy analysis for aluminum plasmas as a representative investigation for metallic systems. In addition, continuous-wave refractive index laser beam deflection is used to characterize the plasma and hot gas generated from boron nitride targets in terms of their ion and neutral atom densities. A self-similarity plasma expansion model is used to analyze the plumes under various conditions. Fundamental data obtained in this way can be relevant to laser micro-machining, laser induced breakdown spectroscopy, and pulsed laser deposition.

Young’s modulus and density of nanocrystalline cubic boron nitride films determined by dispersion of surface acoustic waves

Cubic boron nitride (c-BN) films of 200–420 nm thickness and high phase purity were deposited on silicon (100) substrates by ion-assisted pulsed laser deposition (IA PLD)from a boron nitride target using a KrF-excimer laser, and by plasma-enhanced physical vapor deposition (PE PVD)with a hollow-cathode arc evaporation device. In order to improve the c-BNfilm adhesion, hexagonal boron nitride (h-BN) films with 25–50 nm thickness were used as buffer layers. The density and Young’s modulus of the c-BNfilms were obtained by investigating the dispersion of surface acoustic waves. In data analysis a two-layer model was applied in order to take the influence of the h-BNlayer into consideration. The values for the density vary from 2.95±0.25 g/cm3to 3.35±0.3 g/cm3, and those for the Young’s modulus from 420±40 GPa to 505±30 GPa. The results are compared with literature values reported for nanocrystalline films, polycrystalline disks and single crystal c-BN.

Synthesis and characterization of cubic boron nitride films: substrate bias and ion flux effects

Cubic boron nitride (c-BN) thin films have been synthesized by radio frequency (RF) magnetron sputtering using a hexagonal boron nitride (h-BN) target. In addition to the substrate bias, the distance between the target and the silicon substrate was found to have a significant effect on the formation and volume fraction of the cubic phase in boron nitride films. The increase in ion energy above a certain threshold, corresponding to a substrate bias of −450 V, led to the reduction of the cubic phase content and produced a non-stoichiometric boron nitride structure characteristic of boron–boron bonding.

Detection of boron nitride radicals by emission spectroscopy in a laser-induced plasma

Several vibrational bands of boron nitride radicals have been observed in a plasma produced by pulsed-laser ablation of a boron nitride target in low-pressure nitrogen or argon atmospheres. Using time- and space-resolved emission spectroscopic measurements with a high dynamic range, the most abundant isotopic species B 11N have been detected. The emission bands in the spectral range from 340 to 380 nm belong to the Δυ =−1, 0, +1 sequences of the triplet system (transition A 3Π–X 3Π). For positive identification, the molecular emission bands have been compared with synthetic spectra obtained by computer simulations. Furthermore, B 10N emission bands have been reproduced by computer simulation using molecular constants which have been deduced from the B 11N constants. Nevertheless, the presence of the lower abundant isotopic radical B 10N was not proved due the noise level which masked the low emission intensity of the B 10N band heads.

XUV spectroscopic studies of plasma plumes produced fromboron, boron carbide and boron nitride targets by a laser

Spectroscopic investigations are made on expanding plasma plumescreated by a 20 ns, 3 J laser pulse impinging perpendicularly onto targetsof boron, boron carbide and boron nitride. The characterization of theplasma plumes is carried out spectroscopically in the wavelength rangefrom 30 to 330 Å, and by taking pinhole pictures at shorter wavelengths.The experimental results are compared with the plasma plume produced fromdifferent targets under the same experimental conditions. The calculatedplasma temperatures are 50 eV and 30 eV at 1 mm from the target in thecases of boron and boron carbide targets, respectively. Electrontemperature measurements were made as a function of laser irradiance,distance from the target surface and time elapsed after the maximum of thelaser pulse.

Electron cyclotron wave resonance plasma assisted deposition of cubic boron nitride thin films

Cubic boron nitride (cBN) thin films have been deposited by sputtering the hexagonal boron nitride (hBN) target with nitrogen ions from a low-pressure plasma source. The electron-cyclotron-wave resonance (ECWR) plasma served both to sputter the hBN target and to simultaneously bombard the growing film. Deposits of over 90% cBN content were obtained with ion energies between 70 and 135 eV. The stoichiometry of the films was warranted by the extremely dense nitrogen ions arriving at the substrate. The frequency of the TO-mode for cBN on the Fourier-transform infrared (FTIR) spectra shifted up only slightly from the bulk value at 1065 cm−1. A maximum thickness of 350 nm for the cBN layer was achieved. A cross-sectional transmission electron microscopy (TEM) image showed that the film grew in the turbostratic boron nitride (tBN), aligned hBN-arrays and cBN sequence. At the hBN–cBN interface, some nanoarches were identified. The corresponding interplanar distances for the hBN (0002) and the cBN (111) planes are 0.321 and 0.212 nm, approximately ideal for the 2:3 lattice matching. Both the high-resolution TEM image and the arc pattern of the (111) reflection from selected-area electron diffraction revealed the textured structure of the cubic phase.

Investigations of laser-produced plasmas from boron nitride targets

The interaction of 20 ns, 3 J laser pulses with solid boron nitridetargets is studied spectroscopically in the wavelength range from 30 to 300 Å,and by taking pinhole pictures at short wavelengths. The experiments werecarried out for different angles of incidence of the laser beam and as afunction of the depth of the hole in the target. Typical temperatures are from22 to 45 eV. It is observed that the heating of the plasma occurs at the bottomof the hole and that the hole is along the axis of the direction of the laserbeam.

Synthesis and characterization of boron carbon nitride films by radio frequency magnetron sputtering

Boron carbon nitride (BCN) films were deposited on silicon substrates by radio frequency (r.f.) (13.56 MHz) magnetron sputtering from hexagonal boron nitride (h-BN) and graphite targets in an Ar–N 2 gas mixture of a constant pressure of 1.0 Pa. During deposition, the substrates were maintained at a temperature of 400°C and negatively biased using a pulsed voltage with a frequency of 330 kHz. Different analysis techniques such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD) and scanning Auger electron microscopy (SAM) were used for characterization. In addition, the mechanical and tribological properties of the films were investigated by nano-indentation and micro-scratching. The carbon concentration in the films could be adjusted by the coverage area of a graphite sheet on the h-BN target, and decreased with increasing bias voltage. It was found that the ternary compound films within the B–C–N composition triangle possessed a less ordered structure. BN, BC and CN chemical bonds were established in the films, and no phase separation of graphite and h-BN occurred. At zero bias voltage, amorphous BC 2N films with atomically smooth surface could be obtained, and the microfriction coefficient was 0.11 under a normal load of 1000 μN. Hardness as determined by nano-indentation was usually in the range of 10–30 GPa, whereas the Young’s modulus was within 100–200 GPa.

Properties of ion-assisted pulsed laser deposited H-BN/C-BN layer systems

Boron nitride films were prepared by pulsed laser ablation from a boron nitride target using a KrF-excimer laser, where the growing films were deposited in nitrogen atmosphere or bombarded by a nitrogen/argon ion beam. Films deposited at ion-to-arriving-target-atom ( I/ A) ratios at the substrate below 0.5 (l-BN) are hexagonal. Nucleation of the cubic phase (c-BN) takes place exclusively with ion bombardment at I/ A ratios above 1.0, which may be reduced down to 0.6 after the completion of the nucleation process. The adhesion of c-BN films is improved significantly using l-BN films as intermediate layers. Up to 400-nm thick c-BN films have been investigated by cross-section transmission electron microscopy (TEM). The l-BN layers show a strong preferred orientation with the c-axis parallel to the substrate surface. The crystallites of the nearly phase pure c-BN layers show strong 〈110〉 preferred orientation. The Vickers microhardness of l-BN films is in the range of 25–5 GPa and the compressive stresses in the range of 2–16 GPa. The compressive stresses of 400-nm thick c-BN films were in the range of 4–6 GPa.

Characterization of pulsed laser deposited h-BN films and h-BN/c-BN layer systems

Boron nitride films were prepared by pulsed laser ablation from a boron nitride target using a KrF-excimer laser, where the growing films were deposited in nitrogen atmosphere or bombarded by a nitrogen/argon ion beam. Films deposited at high growth rates or weak ion bombardment are hexagonal with turbostratic microstructure (called here l-BN) and show high adhesive strength to silicon and stainless steel substrates. By using them as intermediate layers, the adhesion of pure cubic boron nitride films (c-BN) can significantly be improved. l-BN films and l-BN/h-BN/c-BN layer systems have been investigated by in situ ellipsometry and cross-section transmission electron microscopy. The mechanical properties, i.e. stress and hardness, of those films and layer systems are presented. l-BN films deposited at high laser energy densities may have compressive stresses as high as 16 GPa. Their Vickers microhardness is in the range of 25–5.4 GPa depending on substrate temperature and ion bombardment. The compressive stresses of 400 nm thick adherent c-BN films were estimated to be 4.5 GPa.