Evolution of β-SiC in laser-generated plasmas

Abstract

A relevant issue in fusion reactors is to choose materials for plasma facing components such that an acceptable lifetime is guaranteed. Silicon carbide is among the very few materials that appear promising to resist harsh environmental conditions including high thermal loads, strong chemical erosion and severe energetic particle bombardment. Thin films, around 130nm thick, of cubic silicon carbide (β-SiC) were pulsed laser deposited on Si (100) substrates at 1173K, at fluences ranging from 3 to 9Jcm−2. The films deposited at 6Jcm−2 appear the most compact, homogeneous, crack free, with a reduced density of particulate and droplets at the surface. Such films were irradiated by different plasmas, generated by ns and fs laser pulses respectively, corresponding to deposited intensities between 108Wcm−2 and 1018Wcm−2. The compositional, morphological and microstructural evolution of irradiated β-SiC films were investigated by energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), vibrational spectroscopies (IR and Raman) and transmission electron microscopy (TEM). Under both irradiation conditions the films remain well adherent to the substrates, showing thermal and mechanical stability. The samples loose only a minor fraction of carbon. However, all irradiations induce meaningful changes of surface morphology, qualitatively different between the ns and fs pulses. In the former an evident columnar structure develops at the crater edges; in the latter, after a single pulse, a wavy structure was observed whose periodicity is nearly identical to the laser wavelength. Under both kinds of irradiation β-SiC shows meaningful chemical and structural stability in highly energetic, aggressive plasma ambient.