Boron and carbon nitride thin films for tribological applications

The extraordinary properties of the III-V and IV-V nitride materials make them promising candidates for fabrication of advanced devices not possible with current material systems. BN and CN compounds combine high hardness, high thermal conductivity, high resistivity, chemical resistance, and transmittance from infra-red to ultra-visible wavelengths. Thus, they are the potential semiconductors of choice for high power, high temperature, high radiation and corrosive environments. Furthermore, their tribological characteristics and their superior mechanical strength make them ideal for hard coatings.;Stoichiometric BN thin films. with a hexagonal crytalline order, were successfully deposited, whereas CN thin films were substoichiometric with respect to nitrogen and were amorphous. The BN thin films showed very good thermal stability and encouraging tribological properties: reasonably low friction and a smooth surface.;Electron beam evaporation of boron and carbon combined with two nitrogen sources, generating excited nitrogen species, was used to deposit thin films of BN, CN, and BCN on sapphire and silicon substrates. The vacuum environment of this growth technique allows one to control in situ the surface stoichiometry by means of Auger electron spectroscopy. The influence of the growth parameters (substrate temperature, energy and flux density of the nitrogen species, carbon and boron rate) on the surface stoichiometry as well as the surface stability after annealing was thus studied. The thin films were analyzed by electron energy loss spectroscopy for bulk composition and by transmission electron microscopy for microstructure. As a tribological coating, the surface morphology of the BN and BCN thin films was investigated by scanning electron microscopy and atomic force microscopy (submicron scale).