ALBERT

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: The time-resolved optical reflectivity (at 633-nm wavelength) of ion-implanted silicon is measured during and immediately after CO2 laser irradiation [λ=10.6 μm, pulse duration (FWHM)=70 ns] as a function of the energy density of the laser. For a heavily doped sample and incident energy densities greater than 2.9 J/cm2, the reflectivity of the probe beam is found to rapidly jump to 70%, which is consistent with the reflectivity of liquid silicon. The high-reflectivity phase lasts for up to 1 μs, indicating a relatively deep molten layer as compared to similar annealing experiments with a visible or ultraviolet laser. The transmittance and reflectance (at 10.6-μm wavelength) of ion-implanted silicon are also reported as a function of the energy density of the CO2 laser. For energy densities slightly exceeding a threshold value, the transmittance (reflectance) of the tailing edge of the pulse is found to greatly decrease (increase). The interpretation of the optical measurements is based on a thermal model in which surface melting occurs for incident energy densities exceeding a threshold value.

Notes: We have grown diamond films on films of cubic boron nitride (cBN). The cBN films were grown on Si(100) substrates using ion-assisted pulsed laser deposition. Fourier transform infrared (FTIR) spectroscopy indicated that the BN films contained ∼75% sp3-bonded cBN. The as-grown cBN films were inserted with no surface pretreatment (e.g., abrading or scratching) into a conventional hot filament diamond reactor. In situ Raman spectroscopy was used to confirm diamond synthesis during growth. The nucleation density of the diamond films was estimated at 1×109/cm2, equivalent to or higher than the best values for scratched silicon substrates. In addition, we found that the cBN films were etched in the diamond reactor; a film thickness (approximately-greater-than)1500 A(ring) was required to prevent total film loss before diamond nucleation occurred. The presence of cBN under the diamond was established using FTIR spectroscopy and Auger electron spectroscopy.

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.