Boron nitride (BN) thin films were deposited on monocrystalline Si(100) wafers using electron beam evaporation of boron with simultaneous bombardment by nitrogen and argon ions. The effect of film thickness on the resultant BN phase was investigated using Fourier transform infrared (FTIR) spectroscopy and high resolution transmission electron microscopy (HRTEM). These techniques revealed the consecutive deposition of an initial 20 Å thick layer of amorphous BN, 20–50 Å of hexagonal BN having a layered structure, and a final layer of the polycrystalline cubic phase. The growth sequence of the layers is believed to result primarily from increasing biaxial compressive stresses. Favorable surface and interface energy and crystallographic relationships may also assist in the nucleation of the cubic and the hexagonal phases, respectively. The presence of the amorphous and hexagonal regions explains why there have been no reports of the growth of 100% cubic boron nitride on Si.

Articles you may be interested inGrowth of caxis oriented gallium nitride thin films on an amorphous substrate by the liquidtarget pulsed laser deposition technique Boron nitride (BN) thin films have been grown on [100] oriented single crystal Si, diamond, Cu and Ni substrates by ion beam assisted deposition using electron beam evaporation of boron together with simultaneous bombardment by nitrogen and argon ions. Characterization by Fourier-transform infrared spectroscopy and high-resolution transmission electron microscopy showed that the films on Si and diamond consisted of initial noncubic (amorphous and hexagonal BN) layers, followed by the growth of cubic BN (c-BN). This growth sequence was attributed primarily to increasing compressive intrinsic stress with increased film thickness. Increasing the substrate temperature above 400 °C led to the onset of c-BN at a greater film thickness while increased ion flux resulted in earlier growth of this phase. These results may be explained by the relaxation of the intrinsic stress in the films at higher temperatures due to increased adatom mobility and to increased intrinsic stress in the films resulting from increased ion bombardment. Lower temperatures led to mixed phase growth. A minimum substrate temperature (200-300 °C) is required for nucleation and growth of single phase c-BN by this technique. It is believed that the interstitial Ar observed in Rutherford backscattering spectrometry studies is primarily responsible for the stress generation in the films. A combination of h-BN and c-BN was deposited on Ni; only h-BN was obtained on Cu substrates.

The adsorption and reaction of NO on a model catalyst composed of Rh supported on ceria has been studied. CeO2 films were grown epitaxially by laser ablation onto SrTiO3(001) substrates. X-ray diffraction and transmission electron microscopy indicate the films are single crystalline with (001) orientation. Comparison of experimental and computer simulated ion scattering distributions indicate that an annealed CeO2 surface is well ordered and is composed of both O and Ce terminated domains. Exposures to CO and H2 at various temperatures had little or no effect upon the ceria. Photoemission from the Ce 4d levels exhibits complex features that differ between a sputtered and a fully oxidized surface. NO does not adsorb on the Rh free, fully oxidized surface, but does adsorb upon a sputter reduced surface. The thermally induced conversion from molecular NO to atomic N was measured by both N 1s photoemission and x-ray absorption as a function of Rh coverage to determine substrate effects on Rh surface chemistry. Rh deposited on sputtered ceria is more active for NO decomposition and yields higher N2 desorption temperatures than does Rh on the fully oxidized support.

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AlN and GaN epitaxial heterojunctions on 6H-SiC(0001): Valence band offsets and polarization fields