Superhard properties of rhodium and iridium boride films

Very recently, the superhard properties of rhenium and ruthenium boride films were reported, this research being inspired by the discovery of the ReB(2) bulk superhardness. In this paper, we report the first successful deposition and characterization of rhodium and iridium boride films, other possible candidates for superhard materials. The films were prepared, applying the pulsed laser deposition technique, and studied by X-ray diffraction, scanning electron and atomic force microscopies, and Vickers microhardness. The refined structural parameters for RhB(1.1) and IrB(1.1) films were obtained. The RhB(1.1) film is characterized by the submicrometer crystallite size, whereas for the IrB(1.1) film, the crystallite size is in the tens of nanometers range, and this latter film presents a slightly preferred orientation along the [004] direction. Both the films exhibit very similar morphology, being composed of dense globular aggregate texture. The RhB(1.1) film presents a homogeneously textured surface with an average roughness of 20-50 nm, whereas the IrB(1.1) film possesses a finer texture with an average roughness of 20-30 nm. The intrinsic hardness of both films lies in the superhardness range: the 1.0 microm thick RhB(1.1) film possesses a hardness of 44 GPa, whereas the 0.4 microm thick IrB(1.1) film has a hardness of 43 GPa.