MICROSTRUCTURAL INVESTIGATION OF DROPLETS IN ARC-EVAPORATED TIN FILMS

The microstructure and composition of macro particles (droplets) in TiN films deposited by arc evaporation on cemented-carbide substrates were investigated using a combination of scanning electron microscopy, cross-sectional transmission electron microscopy (TEM) including lattice resolution TEM, X-ray diffraction (XRD), energy-dispersive X-ray analysis and electron energy loss spectroscopy. The apparent surface number density of droplets, with diameters of 0.1-10 mum, was found to be about 10(7) cm-2. Droplets were incorporated in the film at various distances from the substrate surface. In between the droplets, the TiN films exhibited a dense columnar microstructure. On top of the incorporated droplets, the TiN films grew in a pronounced columnar structure with a column diameter close to the droplet diameter. The core of the droplets consisted of equiaxed grains of an alpha-Ti superstructure containing approximately 3-5 at.% N whereas the rim of the droplets had increasing nitrogen content up to 50 at.%. XRD showed evidence for the presence of Ti2N possibly at the rim of the droplets. Beneath each droplet a large voided region was observed with the shape of a flattened torus as a consequence of droplets being incorporated in the solid state and subsequent shadowing of the Ti flux to the film.