Pulsed laser deposition of ceramic thin films using different laser sources

Abstract

Sintered targets of Al 2O 3 are removed by CO 2- and excimer laser radiation and deposited as thin films onto steel and silicon substrates. Micro Raman spectroscopy and atomic force microscopy are used to characterize the morphological and structural properties of the films. Mechanical properties are investigated by nanoindentation measurements and a laser-acoustic method, optical properties are studied by ellipsometry. Al 2O 3 films deposited using CO 2-laser radiation show an inhomogeneous surface structure with droplets embedded in a matrix, whereas the films deposited using excimer laser radiation are smooth, which is explained by different material removal mechanisms. The microhardness (i.e. ratio of indentation load to residual area of the indent) of the amorphous matrix structure is ~8 GPa, the crystalline droplets are softer at ~2 GPa. Varying the processing gas pressures in the range of 0.01–0.6 mbar yields a change in the index of refraction of the films, which is close to the bulk value for gas pressures < 0.1 mbar. The decrease of the index of refraction is caused by a lowered film density, correlating with a lowered mean energy of the particles impinging on the substrate, which is calculated. The results show the possibility of scaling-up the pulsed laser deposition process for industrial applications by use of CO 2-laser radiation.