The structure and properties of ion-beam-synthesized boron nitride films

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Abstract
Films containing boron and nitrogen were prepared by electron-beam evaporation of boron and bombardment of the growing film with nitrogen ions of energy up to 1500 eV. Hard films of high transparency (extinction coefficient <0.01) were prepared with nitrogen-to-boron atomic arrival ratios greater than one. The optical constants in the visible part of the spectrum were determined as a function of B-to-N atomic ratio in the film and substrate temperature using optical photometry. Measurements of the optical constants were extended to 40 eV using a Kramers–Kronig analysis of electron-energy-loss spectra. Boron-to-nitrogen atomic arrival rates were determined and show that as ion energy and substrate temperature are increased ion flux must be increased to achieve the same stoichiometry. Film structure was imaged using high-resolution electron microscopy, and the radial distribution function (RDF) was determined. The RDF of stoichiometric films showed that high substrate temperatures increased the size of the ordered regions. The RDF and high-resolution imaging of all films were consistent with the presence of the hexagonal form of BN with substoichiometric films containing amorphous boron as the other constituent. This conclusion is consistent with the analysis derived from the sum rule obtained from the optical constants. No evidence could be found for the cubic form of BN.