BORON-CARBON-NITROGEN THIN SOLID FILMS GROWN BY ION BEAM ASSISTED DEPOSITION (IBAD)

R. Cago, J. Jiménez, J. M. Albella.

Instituto Ciencia de Materiales, CSIC. Cantoblanco. 28049 Madrid (España)

In the last decades there has been a growing interest in the production of new materials for hard coating applications. In this context, diamond and cubic boron nitride (c-BN) are the hardest materials known. However, crystalline diamond requires of severe conditions to be grown and the roughness of its surface avoids the use of this material in optical applications or in systems with high friction. In addition, c-BN present high mechanical stress, which limits the thickness and the lifetime of the coating. Therefore, new materials with less sever deposition conditions or better properties are the subject of intense research. Thin BCN films offer great potential, as they are easy to grow in amorphous form and they are expected to have properties between c-BN and diamond. In this presentation we will report our activities on amorphous carbon (a-C), carbon nitride (a-CNx) and boron carbon nitride (BCN) thin films deposited by ion beam assisted (Ar+,N2+) evaporation of graphite or boron carbide (B4C). The films have been characterized by IR, XANES and Raman spectroscopy and nanoidentation measurements have been related with the chemical structure, In all cases, the production of cubic phase (sp3 bonding) needs of momentum transfer, which is supplied by the assistance of ion beam bombardment. We have found that a-C films with up to 40% sp3 bonding can be grown at selected values of energy and ion to carbon ratios, where the momentum transfer is maximized. The CNx films show a hexagonal structure and nitrogen content around 25% at. With the addition of nitrogen we have doubled the hardness of the films, which has been related with the spectroscopic features observed in the N1s XANES edge. The structure of the BCN films is similar to that of h-BN, with a low carbon concentration (<20%). By the assistance with only nitrogen ions, the cubic phase is observed for high values of assisting voltage (>1keV). However, when Ar+ are added to the ion beam the cubic phase is present for voltages around 0.5 KeV, as the momentum transfer is increased.