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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion-assisted pulsed laser deposition has been used to produce films containing (approximately-greater-than)85% sp3-bonded cubic boron nitride (c-BN). By ablating from a target of hexagonal boron nitride (h-BN), BN films have been deposited on heated (50–800 °C) Si(100) surfaces. The growing films are irradiated with ions from a broad beam ion source operated with Ar and N2 source gasses. Successful c-BN synthesis has been confirmed by Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (TEM), selected-area electron diffraction, electron energy-loss spectroscopy, and x-ray diffraction. The films are polycrystalline and show grain sizes up to 300 A(ring). In addition, Rutherford backscattering, elastic recoil detection, and Auger electron spectroscopies have been used to further characterize the samples. The effects of varying ion current density, substrate growth temperature, growth time, and ion energy have been investigated. It is found that stoichiometric films with a high c-BN percentage can be grown between 150 and 500 °C. Below ∼150 °C, the c-BN percentage drops dramatically, and the deposited film is completely resputtered at the current densities and ablation deposition rates used. As the deposition temperature rises above ∼500 °C the c-BN percentage also drops, but less dramatically than at low temperatures.In addition, the IR-active c-BN mode narrows considerably as the deposition temperature increases, suggesting that the c-BN material has fewer defects or larger grain size. It is found that films with a high c-BN percentage are deposited only in a narrow window of ion/atom arrival values that are near unity at beam energies between 800 and 1200 eV. Below this window the deposited films have a low c-BN percentage, and above this window the deposited film is completely resputtered. Using FTIR analysis, it is found that the c-BN percentage in these samples is dependent upon growth time. The initial deposit is essentially all sp2-bonded material and sp3-bonded material forms above this layer. Consistently, cross-section TEM samples reveal this layer to consist of an amorphous BN layer (∼30 A(ring) thick) directly on the Si substrate followed by highly oriented turbostratic BN (∼300 A(ring) thick) and finally the c-BN layer. The h-BN/t-BN interfacial layer is oriented with the 002 basal planes perpendicular to the plane of the substrate. Importantly, the position of the c-BN IR phonon changes with growth time. Initially this mode appears near 1130 cm−1 and decreases with growth time to a constant value of 1085 cm−1. Since in bulk c-BN the IR mode appears at 1065 cm−1, a large compressive stress induced by the ion bombardment is suggested. Possible mechanisms are commented on for the conversion process to c-BN based upon the results.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3567-3571 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We examine the crystallographic texture exhibited by cubic boron nitride (cBN) in thin films grown by ion-assisted deposition. Our analysis indicates that the cBN is preferentially oriented such that individual crystallites have at least one [111] direction lying in the plane of the film but are otherwise randomly oriented about (1) the substrate normal and (2) the in-plane cBN [111] axis. This preferential orientation is consistent with an alignment between the cBN {111} planes and the basal planes of the layer of highly oriented graphitic boron nitride that forms in the initial stages of film growth. ©1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 295-303 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A microstructural study of boron nitride films grown by ion-assisted pulsed laser deposition is presented. Fourier transform infrared spectroscopy, electron-energy-loss spectroscopy, and electron-diffraction measurements indicate that within the ion-irradiated region on the substrate, the film consists of a high fraction of the cubic phase (cBN) with a small amount of the turbostratic phase; outside the irradiated region, only the turbostratic phase is detected. Conventional and high-resolution electron microscopic observations show that the cBN is in the form of twinned crystallites, up to 40 nm in diameter. Particulates, formed by the laser ablation process, reduce the yield of cBN in the irradiated regions by shadowing local areas from the ion beam. The films exhibit a layered structure with an approximately 30-nm-thick layer of oriented turbostratic material forming initially at the silicon substrate followed by the cBN. The observations of oriented turbostratic material and twinned cBN crystallites are discussed in relation to a previously proposed compressive stress-induced mechanism for cBN synthesis by ion-assisted film deposition.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Significant ion irradiation is needed during growth to synthesize cubic boron nitride (cBN) films. This results in large film stresses, which have limited cBN film thicknesses to only a few hundred nm and represents a significant barrier in the development of cBN film technology. Using a new hybrid deposition technique, we have synthesized cubic BN films up to 700 nm (0.7 μm) thick. A compositional and structural analysis of the films using several standard characterization techniques confirms that relatively thick polycrystalline films with a high cBN content were synthesized. Thicker cBN films enable hardness measurements to be undertaken without major substrate effects. Nanoindentation measurements yield hardness values for the cubic BN films up to 60–70 GPa, which are greater than values measured for bulk cBN. The measured elastic modulus was observed to be lower than the bulk, and this can be accounted for by an elastic deformation of the silicon substrate. The mechanical properties of the cubic BN films are discussed with reference to other ultrahard thin films such as diamond and diamondlike carbon. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 2813-2815 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cubic BN(c-BN) films were deposited on cubic SiC (β-SiC) films on Si(100) by ion-assisted pulsed laser deposition. The films were nearly phase pure, with c-BN fractions of up to ∼90% as determined by infrared spectroscopy. Cross-sectional transmission electron microscopy showed that much of the film/substrate interface had a thin amorphous layer next to the β-SiC, followed by hexagonal/turbostratic BN (h-BN/t-BN), and then polycrystalline c-BN, as commonly observed on Si substrates. However, there are also c-BN crystals that extend to within 10 A(ring) of the SiC interface, with no intervening h-BN/t-BN layer. A sharp falloff in c-BN content was observed for substrate temperatures 〈150 °C, and below 100 °C c-BN did not form for any ratio of the ion current flux to the deposition flux. At a different ion-to-substrate angle (20° closer to glancing incidence) the falloff in c-BN content for T〈150 °C was less sharp. The existence of a critical temperature for c-BN formation does not result from a nitrogen deficiency at low temperature since film stoichiometry did not change with temperature. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 466-472 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Conventional and high-resolution transmission electron microscopy are used to characterize the initial stages of AlN thin-film growth. AlN films are deposited by molecular beam epitaxy onto annealed (0001) oriented α-Al2O3 (sapphire) substrates. During the initial stages of film growth (film thickness ∼25 nm) AlN forms islands of varying alignment with the Al2O3 substrate. Some of the AlN islands are well aligned with the [112¯0]AlN(parallel)[101¯0] Al2O3 and (0001)AlN(parallel)(0001)Al2O3, which matches closed-packed planes and directions. Other islands exhibit either an alignment of one set of planes, i.e., grains are aligned with the (11¯01)AlN(parallel)(112¯0) Al2O3, or are misaligned with respect to the Al2O3 substrate. As the AlN film grows in thickness (film thickness ∼100 nm), the film becomes continuous, and the closed-packed planes and directions of the film and substrate are aligned for the majority of the film. Islands of AlN with an alignment other than this predominant orientation disturb the growth near the AlN/Al2O3 interface and create displacements along the [0001] AlN direction in overlying AlN grains. These misaligned AlN grains provide one source for the formation of planar defects in the epitaxial AlN films. The evolution of the AlN film microstructure and the reasons for the observed orientation relationships are discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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