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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.

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.

Notes: 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 A(ring). 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.