Mössbauer Investigation of Surface Processing by Pulsed Laser Irradiation in Reactive Atmospheres

Abstract

Irradiations of iron (Armco, Fe > 99.85%) substrates in controlled gaseous atmospheres (nitrogen and methane) have been performed with nanosecond pulses of an excimer laser, leading to the formation of nitride and carbide surface layers, respectively, with different stoichiometry and crystallographic structures. The evolution and abundance of each phase is correlated to the experimental parameters such as the number of laser pulses, the laser fluence and the ambient gas pressure. The capability of CEMS to distinguish the atomic surrounding in combination with its sensitivity to the surface makes it an indispensable tool for a proper investigation and optimisation of such surface treatments. Additional analytical techniques have been used in order to have complementary information. Ion beam analysis (Rutherford backscattering spectrometry and resonant nuclear reaction analysis) was performed to measure the depth profiles of nitrogen and carbon, while X-ray diffraction and Rietveld refinement were employed to characterize the crystallographic morphology of the irradiated samples. The results revealed that under proper experimental conditions, the laser treatment can produce almost homogeneous layers of nitride/carbide, where the composition and the structure are determined only by the parameters of irradiation.