Thin Ti films (less than or equal to 200 nm) were grown on Si wafers (100) by means of a hollow cathode are evaporation device (HCAED). The layer growth was monitored in situ by monochromatic ellipsometry. Spectroscopic ellipsometry was used to characterize the as-deposited layers. The results obtained by ellipsometry have been compared with other thin film diagnostic techniques, especially with Rutherford backscattering spectroscopy. Modelling of the ellipsometric measurements shows that the film density is strongly influenced by the deposition conditions. The RBS analysis supports the results of ellipsometric studies. There exists a strong relation between the energy of the Ti ions striking the substrate and the layer density. Nucleation is described by a columnar microstructural development during the early stage of the growth. The bulk grows homogeneously beneath a surface roughness layer which is a consequence of incomplete coalescence of the initial nuclei. The surface quality of the substrate influences the early stage of the film growth. If a shutter above the titanium vessel is used, the layer grows inhomogeneously. The density gradients are caused by the increasing evaporation rate because of thermal stabilization of the HCAED after opening the shutter.