Nanocrystalline growth and diagnostics of TiC and TiB2 hard coatings by pulsed laser deposition

Abstract

Nanocrystalline coatings of TiC and TiB2 were grown by pulsed laser deposition on Si(100) and on X155 steel at low substrate temperatures ranging from 40 degrees C to 650 degrees C. A pulsed KrF excimer laser was used with the deposition chamber at a base pressure of 10(-6) mbar. The morphology and structure of the films, studied with SEM, XRD, and TEM, showed that nanocrystalline films with a fine morphology of TiC and TiB2 were deposited with a grain size of 10 nm-70 nm at all substrate temperatures. The growth of the polycrystalline coatings possessed a columnar morphology with a [100] preferred orientation. The hardness of the coatings was determined to be 40 GPa and the elastic modulus, 240 GPa. The composition and the kinetics of the plume produced during the pulsed laser deposition of TiC and TiB2 was studied under film growth conditions. The mass analysis of ions of the ejected material was performed by time-of-flight mass spectroscopy (TOF-MS) and showed the presence of Ti+ and C+ during TiC ablation and B+, B-2(+), and Ti+ during TiB2 ablation. The kinetic energies (KE) of the ions depended on the laser fluence which was between 0.5 eV and 340 eV. The kinetic energy and the evolution of the plasma was studied with a streak camera. The velocity of the plasma was of the order of 10(6) cm/sec and was linearly dependent on the energy fluence of the laser. The emission spectroscopy of the plasma plume confirmed the atomic neutral and single excited species of Ti. These results show that coating growth basically occurs by the recombination of the ionic species at the surface of the substrate.