BN Target Research Articles

Auger electron spectroscopy/x-ray photoelectron spectroscopy study of Ti–B–N thin films

Ti–B–N layers have been produced by sputter deposition from a BN target onto which small Ti platelets have been positioned. The Ti–B–N composition has been varied and the films studied by Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS). Quantified chemical state information from the XPS B 1s and N 1s peaks give a thin film phase composition consistent with that predicted from the bulk phase diagram. A method of film composition quantification by AES is proposed, accounting for the Ti L3M2,3M2,3 and N KL2,3L2,3 peak overlap problem. Ti L3M2,3M4,5 peak shape changes have been examined using factor analysis, showing the presence of phases and phase changes in qualitative agreement with the phase diagram. Correlations of the compositional and mechanical testing data show that films of highest hardness are obtained when a composition of approximately TiBN0.5 is obtained, the phase composition being a combination of TiB2 and TiN.

Structure and chemical composition of BN thin films grown by pulsed-laser deposition

BN thin films were produced by pulsed laser deposition from a sintered BN target of the hexagonal structural phase using XeCl excimer laser radiation (λ = 308 nm) or pulsed CO2 laser radiation (λ= 10.6 μm), and varying the process variables (laser fluence, N2 partial pressure, target-substrate distance). Film properties such as chemical composition and crystal structure were studied by ex situ X-ray photoelectron, Auger electron and micro-Raman spectroscopies. Simple thermodynamic arguments are given to explain aspects of material removal from the target and film deposition. Films are generally composed of a fine-grained matrix in which particles 10–15 μm (λ = 308 nm) or 10–100 μm (λ= 10.6 μm) in size are embedded. In addition to BN, the films contain contaminants B2O3, metallic B, and a boron-oxynitride species, with the relative proportions dependent on the lateral position on the film surface. Micro-Raman spectra give evidence of amorphous and hexagonal structural phases of the BN matrix material.

Deposition of boron-nitride films by nitrogen sputtering from a boron-metal target

This contribution deals with reactive growth of boron-nitride films by a rf nitrogen-sputtering process from a boron-metal target; thus nitrogen is functioning both as sputter and reactive gas. Only few and superficial reports of reactive sputter depositions from a metallic boron target in various argon/nitrogen mixtures exist, compared to the number of reports on rf sputtering from a BN target. Nitrogen sputtering of boron-metal has previously not been reported. It was shown by Fourier-transform infrared (FTIR) spectroscopy that the hexagonal structure of BN exclusively was deposited. Sputter rates were measured and showed no dependence on the reactive-gas flow and only a marginal dependence on sputter-gas mixtures containing 20% of krypton, argon, or helium. The reported nitrogen-sputtering process appears to be appropriate for exploration of the key parameters for phase control in BN growth and for additional surface engineering processes such as substrate bias and post-ion bombardment.

Structure and chemical composition of BN thin films grown by pulsed-laser deposition (PLD)

BN thin films are grown on Si(100) substrates in a pulsed-laser deposition (PLD) process using a pulsed CO 2 laser, a hexagonal-phase BN (h-BN) target, and N 2 as processing gas. The effect of RF power coupled to the substrate during PLD is investigated. Films are analysed using optical microscopy and micro-Raman and X-ray photoemission spectroscopies. They are generally composed of a fine-grained matrix in which particles 10–100 μm in size are embedded, with the morphology and chemical composition dependent on the lateral position on the film surface relative to the laser-induced plasma plume from the target. The roughness and contaminant concentration (B 2O 3, elemental B, and boron-oxynitride) are largest nearest the plasma-affected region. The matrix material over the entire film surface exhibits weak, broad spectral structures, indicating an amorphous structure. Certain regions have in addition h-BN Raman peaks that are shifted by up to 15 cm −1 to lower wave numbers relative to crystalline h-BN due to strain built in during deposition. No peaks characteristic of cubic BN or B 2O 3 are found. Positions further from the plasma-affected region show stronger peaks, implying more crystalline order. The highest degree of crystallinity is reached for deposition with RF power applied to the substrate mainly during the laser pulses, as opposed to deposition with power applied between pulses or to deposition without RF power. In general, embedded particles have more intense Raman peaks than the surrounding matrix, comparable in strength to those of the target, suggesting that they arise from material ejection.

Preparation of thin hard boron nitride films by r.f. magnetron sputtering

Abstract Films (0.1–1 μm) of boron nitride were grown on silicon (111), KCl and quartz by r.f. magnetron sputtering of a BN target in an Ar or Ar-N2 atmosphere. The deposition was carried out at two pressures: 2 × 10−3 and 2 × 10−2 Torr. The compositions and structures of the BN films were determined by electron probe microanalysis, electron diffraction and IR analysis. Films obtained at an argon pressure of 2 × 10−3 Torr had a stoichiometric composition. They were dense and hard and had low carbon and oxygen impurity levels. Films exhibited a high microhardness similar to that for films deposited by ion-assisted methods. Films obtained at an argon pressure of 2 × 10−2 Torr had a small excess of boron and increased impurity levels. They were soft and porous. All films were either amorphous or microcrystalline with a hexagonal structure. Application of a negative bias voltage (60–100 V) to the substrate stabilized the cubic phase that was confirmed by three methods. The deposition conditions for obtaining stoichiometric hard BN films and the applicability of the above-mentioned analysis methods are discussed.

Deposition of Boron Nitride Coatings by Reactive Rf Magnetron Sputtering: Correlation Between Boron and Nitrogen Contents and the Flux of Energetic Ar+ Ions at the Substrate

AbstractThin films of BNxOy have been deposited by rf Reactive Magnetron Sputtering from a BN target in Ar+ plasma (1 Pa) at different substrate bias conditions. The possibility of obtaining dense and hard BN coatings at a target-to-substrate distance larger than the mean free path of the B and N atoms has been investigated.In order to deduce the plasma potential and the ion density near the substrates, the discharge characteristics have been measured by means of an electrostatic probe of the Langmuir type properly coupled to the glow discharge for avoiding the rf interference. From the probe data both flux and energy of the Ar+ ions have been determined and correlated to the net contents of boron and nitrogen as measured by means of the N(d,p) and 11Β(p,α) nuclear reactions. The results of this study show that in the investigated experimental conditions the flux of energetic Ar+ ions at the substrates is insufficient for promoting the formation of cubic BN as confirmed by XRD, FT-IR and nanohardness measurements. The reported data agree with recent literature findings and support the need of monitoring both the bombarding rate and energy of the Ar ions in rf discharges if the c-BN deposition is to be attained in a reproducible manner.

Structure and properties of Ti-B-N coatings

Crystal structure studies on Ti-B-N coatings of various composition show a good agreement with the phase diagram predictions of Novotny and coworkers (1961). Simple considerations lead us to believe that the performance of such coatings can be optimized if they do not contain a soft phase such as Ti or h-BN and if the composition is located in a zone where the phases TiB 2 and TiN coexist in nearly equal parts. The microstructure plays an important role, in particular if the grain size of the coatings is in the nanometre range for Ti-B-N coatings. In this case an inverse Hall-Petch effect leading to a softening of the coating might be observed. Several preparation techniques for the synthesis of suitably composed coatings are presented and discussed. These are, in particular: (a) Ti + implantation into hexagonal BN layers; (b) co-sputter deposition from Ti and BN targets; (c) sputtering from a heterogeneously composed Ti-BN target; and (d) Ti/BN multilayer coating interdiffusion. In spite of ultrahigh hardness and good adhesion to metallic substrates, most tribological tests revealed slightly worse performance than TiN and Ti(Al,N) coatings.

Observation of near-band-gap luminescence from boron nitride films

We report results from cathodoluminescence spectroscopy of boron nitride films grown on Si(100) substrates by ion-source-assisted magnetron sputtering of a hexagonal BN target. Three main peaks are observed in the near-band-gap region for hexagonal boron nitride films at energies of 4.90, 5.31, and 5.50 eV. We also report deep-level emission spectra of predominantly cubic boron nitride films which are correlated with sample growth conditions. In particular we show that the emission intensity, position, and linewidth are strongly dependent on the substrate bias voltage used during sample growth.

Preparation and characterization of cubic boron nitride and metal boron nitride films*

AbstractBoron nitride has generated much scientific interest due to the outstanding material properties of its cubic modification (c‐BN) which can be compared with those of diamond, and to its metal (M) boron nitride compounds (MBN) which have extraordinary mechanical properties such as high hardness and high elasticity. This paper compares and discusses both of these thin film materials, concentrating in particular on their preparation and their mechanical properties in view of future applications as wear‐resistant coatings.There is a strong indication that the mechanism of c‐BN film formation by commonly used physical vapour deposition (PVD) methods is based on recoil implantation of surface atoms into deeper layers. This process creates considerable compressive stress compromising the production of technologically valuable coatings of c‐BN composition. On the other hand BN‐based transition metal films can be made as hard as or even harder than c‐BN films if suitable preparation methods are applied which promote nanometric grain sizes and a mixed phase composition. This paper discusses: (1) Ti implantation into hexagonal BN layers; and (2) co‐sputter deposition from a Ti and Hf target, respectively, and from a BN target; and (3) Ti/BN multilayer interdiffusion. MBN films show good adhesion to metallic substrates such as HSS steels, and preliminary wear tests with a pin‐on‐disk tribometer indicate promising characteristics.Bonding and chemical composition of the films were investigated by electron spectroscopy for chemical analysis (ESCA)‐Auger spectroscopy, the structure and crystallite size by glancing angle x‐ray diffractometry, and the hardness and elasticity by the nanoindentation technique.

Cathodoluminescence Spectroscopy of Boron Nitride Films

ABSTRACTWe report results from cathodoluminescence spectroscopy of boron nitride films grown on Si (100) substrates by ECR ion source assisted magnetron sputtering of a hexagonal BN target. Three main peaks are observed in the near-bandgap region for hexagonal boron nitride films at energies of 4.90 eV, 5.31 eV, and 5.50 eV. In addition, deep-level emission spectra of predominantly cubic boron nitride films are correlated with sample growth conditions. In particular we show that the emission intensity, position, and linewidth are strongly dependent on the substrate bias voltage used during sample growth.

Spectroscopic studies of BN films deposited by dynamic ion mixing

Boron nitride films were deposited by the dynamic ion mixing (DIM) technique at temperatures 300 K and 820 K on silicon and NaCl single crystalline substrates. The vapour deposition was obtained by ion sputtering using a Kauffman-type ion source. BN films of nearly equiatomic composition were synthesized when a gas mixture 1 3 Ar + 2 3 N 2 (volume fraction) was injected in the ion source to make the ion beam which sputtered the BN target. The growing films were simultaneously bombarded with 160 keV Xe + ions and their microstructural state was determined by transmission electron microscopy (TEM) and infrared spectroscopy (IR). Composition depth profiles analysis was carried out by secondary ion mass spectrometry (SIMS) and the chemical binding states of B and N in the films were investigated by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (XAES). The results indicate that the films produced at 300 K without mixing are amorphous, whereas those produced by DIM exhibit the beginning of crystallization and the turbostratic structure (t-BN) was identified. When the substrate temperature was increased to 820 K, a more crystallized state was obtained, consisting of a mixture of turbostratic and hexagonal BN (h-BN) phases. The observed XPS spectra agree with the binding energy between B and N in BN, but the presence of oxygen was also detected. SIMS and XPS spectra reveal that the films where the turbostratic structure is dominant are unstable and easily decompose during air exposure whereas those of hexagonal structure are very stable. The results are discussed and compared with other studies of BN films prepared by different deposition methods.

Imaging and blackbody emission spectra of particulates generated in the KrF-laser ablation of BN and YBa2Cu3O7−x

Blackbody emission from ejecta following KrF-laser irradiation of YBa2Cu3O7−x (YBCO) and BN targets in vacuum has been observed for the first time using intensified charge-coupled-device (CCD) photography and gated photon counting. Temporally resolved emission spectra from particulates up to 2 cm from the target and from 10 μs to 1.5 ms after the laser pulse are attributed to blackbody radiation. The spectra are used to estimate temperatures between 2200 and 3200 K for ejecta from both BN and YBCO when irradiated at Φ248=3.5 J and 1.5 J cm−2, respectively. The measured cooling of the particles in vacuum is compared to a radiative cooling model.

Nucleation and Growth of Cubic Boron Nitride Films Produced by Ion-Assisted Pulsed Laser Deposition

ABSTRACTWe are studying the boron nitride system by using a pulsed excimer laser to ablate from hexagonal BN (hBN) targets to form cubic BN (cBN) films. We are depositing BN films on heated (25 - 800°C) Si (100) surfaces and are using a broad-beam ion source operated with Ar and N2 source gasses to produce BN films with a high percentage of sp3-bonded cBN. In order to understand and optimize the growth and nucleation of cBN films, parametric studies of the growth parameters have been performed. The best films to date show >85% sp3-bonded BN as determined from Fourier-transform infrared (FTIR) reflection spectroscopy. High resolution transmission electron microscopy (TEM) and selected area electron diffraction confirm the presence of cBN in these samples. The films are polycrystalline and show grain sizes up to 30- 40 nm. We find from both the FTIR and TEM analyses that the cBN content in these films evolves with growth time. Initially, the films are deposited as hBN and the cBN nucleates on this hBN underlayer. Importantly, the position of the cBN IR phonon also changes with growth time. Initially this mode appears near 1130 cm-1 and the position decreases with growth time to a constant value of 1085 cm-1. Since in bulk cBN this IR mode appears at 1065 cm-1, a large compressive stress induced by the ion bombardment is suggested. In addition, we report on the variation in cBN percentage with temperature.

Cubic boron nitride formation on Si (100) substrates at room temperature by pulsed laser deposition

We are studying the boron nitride system by using a pulsed excimer laser to ablate from hexagonal BN(hBN) targets to form BN films. We have deposited BN films on heated (600 °C) and room-temperature silicon (100) surface in an ambient background gas of N2. Fourier transform infrared (FTIR) reflection spectroscopy indicates that the films grown at high temperature have short-range sp2 (hexagonal-like) order, whereas films grown at room temperature are a mixture of sp3-bonded BN and sp2-bonded BN. Electron diffraction confirms the presence of cubic BN (cBN) material in the films grown at low temperature and the corresponding TEM lattice images show a grain size of ∼200 Å. The presence of cBN in the films correlates with laser energy density, with cubic material appearing around 2.4 mJ/cm2. Auger electron spectroscopy (AES) indicates that the films are nitrogen deficient.

Maturing thymocytes in accelerated rejection of cardiac allografts in presensitized rats.

LBNF1 cardiac allografts are rejected within 36 hr in LEW rats sensitized with BN skin grafts 7 days earlier (acute rejection in unmodified hosts = 8 days). We have studied and compared the function and migration patterns of thymocytes one day after engraftment in sensitized recipients, unmodified hosts, and normal naive rats. Thymocytes from animals experiencing accelerated rejection were more mature and functionally active, as shown by a significant elevation in percentage of OX-44+ (CD37+) cells, increased alloreactivity to BN and WF antigens, and proliferative responses to Con A and exogenous IL-2. However, the cells could neither lyse BN targets in vitro nor trigger rejection of otherwise indefinitely functioning test cardiac allografts in immunologically unresponsive T cell-deficient (B) rats after adoptive transfer. The traffic of 111In-labeled thymocytes was then evaluated. The migration index increased significantly during accelerated graft rejection, with thymocytes preferentially circulating in the blood, penetrating peripheral lymph nodes--and, interestingly, migrating back to the thymus. Thus, immunoresponsive and functionally active thymocytes, which lack the ability to recognize primed specific antigen, appear during accelerated rejection of cardiac allografts in sensitized rats. These cells migrate to the periphery, and then return in large numbers to their site of origin, the thymus. Hence, this study describes a novel behavior of thymocytes in the state of host alloreactivity that is distinct from the physiological one in otherwise normal thymus.

The Effects of Substrate Bias and Si Doping on the Properties of Rf Sputtered Bn Films

ABSTRACTThe effect of substrate bias on the properties of rf sputtered boron nitride films on Si and GaAs substrate were investigated. IR transmission and reflectivity of films with different substrate bias were measured with Perkin Elmer 983 IR spectroscopy. From the IR reflectivity data, transverse optical mode(TO) and longitudinal optical mode(LO) frequencies were derived by fitting Kramer-Kronig model. Absorption coefficient was determined from IR transmission data. The resultant TO and LO modes showed that substrate bias caused broadening of reststrahlen band of rf sputtered boron nitride. We also tried to dope boron nitride films with silicon by alternate sputtering of BN and Si targets controlling sputtering time of each target followed by annealing. Electrical resistivity was measured over the temperature range between 175 K to 370 K for both intrinsic and Si-doped boron nitride films. Intrinsic rf sputtered boron nitride showed Little change in resistivity (109 Ω cm - 1011 Ω cm ) over the temperature range studied. While Si doped BN showed linear change in resistivity with increasing temperature and its activation energy was about 0.22 eV. The effect of substrate bias was also investigated by monitoring the XPS core level spectra of both Bis and N Is peaks, respectively. Substrate bias caused the shift of both B ls and N ls peak to higher binding energy. The effect of substrate bias on refractive index was also studied.

Ion-Assisted Pulsed Laser Deposition of Cubic Boron Nitride on Si (100) Substrates

ABSTRACTWe are studying the boron nitride system by using a pulsed excimer laser to ablate from hexagonal BN (hBN) targets to form cubic BN (cBN) films. We are depositing BN films on heated (400°C) Si (100) surfaces and are using a broad beam ion source operated with Ar and N2source gasses to produce BN films with a high percentage of sp3-bonded cBN. The best films to date show ∼85% sp3-bonded BN as determined from infrared (IR) reflection spectroscopy. High resolution transmission electron microscopy (TEM) and selected area electron diffraction (SAD) confirm the presence of cBN in these samples. The films are polycrystalline and show grain sizes up to 500 Å.

Pulsed Excimer Laser Ablation Deposition of Boron Nitride on Si (100) Substrates

ABSTRACTWe are studying the boron nitride system by using a pulsed excimer laser to ablate from hexagonal BN (hBN) targets to form cubic BN (cBN) films. We are depositing BN films on heated (600°C) silicon (100) surfaces in a flowing (0- 10 sccm) ambient background gas of either NH3 or N2 of varying partial pressure (0–100 m Torr). Infrared (IR) reflection spectroscopy indicates the films have short-range hexagonal order. Some films grown at low laser energy densities have shown the cubic phase in IR transmission. Auger electron spectroscopy (AES) indicates the films are nitrogen deficient, which is linked to changes in the target stoichiometry with increasing laser fluence. Raman spectroscopy on the films shows only a strong background luminescence suggesting a high concentration of defects associated with the nitrogen vacancies. Atomic force microscopy (AFM) of the films shows a surface morphology that roughens as the growth rate increases. In order to improve the film stoichiometry it was necessary to actively enhance the nitrogen content of the films. It was found that bombarding films during growth with ions from an ion gun filled with NH3 gas increased the N/B ratio but did not enhance the cubic phase. RF biasing the substrate gave films which showed both cubic and hexagonal features in IR reflection. High resolution transmission electron microscopy (TEM) confirms the presence of cBN grains of ∼ 200Å size in films grown with an RF bias.

Characterization of boron nitride films prepared by dynamic ion mixing

Films of BN were deposited onto various substrates at temperatures of 300 and 680 K by means of the dynamic ion mixing technique. The depositing atom vapour flux was produced by sputtering a BN target with a beam of Ar + and N + ions of 1.2 keV energy and the growing films were simultaneously bombarded with 160 keV Xe + ions. The microstructural states were characterized by transmission electron microscopy (TEM) and IR spectroscopy. The film densities were also determined from the measurement of the critical angle for total X-ray reflection. The results indicate that the films produced without mixing are amorphous whereas those produced by mixing at 300 K exhibit a beginning of crystallization and at 680 K a more crystallized state is observed. Moreover the presence of the hexagonal phase was identified from both TEM diffraction patterns and IR spectra which exhibit two absorption bands at 780 and 1360 cm −1 characteristic of the hexagonal phase. The irradiation-induced crystallization of the films is discussed in relation to the collision cascade effects, and the damage profiles in the growing films have been calculated.

Fast-Iccd Photography and Gated Photon Counting Measurements of Blackbody Emission from Particulates Generated in The KrF-Laser Ablation of BN and YBCO

ABSTRACTFast intensified CCD photography and gated photon counting following KrF-laser irradiation of YBCO and BN targets reveal the first observations of very weak emission from slow-moving ejecta up to 2 cm from the target and times extending to ∼1.5 ms. Time-of-flight velocities inferred from the emission measurements indicate velocities (v ˜ (0.45−1.2) x 104 cm s−1) comparable to those measured for the large particles which often accompany the pulsed laser deposition process. Gated photon counting is employed to obtain temporally resolved spectra of this weak emission. The spectral shape is characteristic of blackbody emission, which shifts to longer wavelengths as the particles cool during flight in vacuum. Estimates of the temperature of the particles are made based on the emissivity of a perfect blackbody and range from 2200 K to 3200 K for both BN and YBCO when irradiated at Φ248 = 3.5 J cm−2 and 1.5 J cm−2, respectively. The temperature decrease of the particles in vacuum is compared to a radiative cooling model which gives estimates of the initial surface temperature and radii of the particles.