Raman investigation of ion irradiated TiC and ZrC

Single crystals of transition metal carbides from group IV, TiC_1-x and ZrC_1-x, have been irradiated at room temperature (RT) with 1.2 MeV gold ions for various fluences in the range 2 x 10¹⁴ -3 x 10¹⁶ ions/cm² and polycrystals for fluences between 2 x 10¹³ and 4 x 10¹⁵ ions/cm². The irradiated samples were characterized by micro Raman spectroscopy. For this purpose, the evolution of main parameters of Raman spectra for both types of samples (band positions, shifts, and intensities, and optical over acoustical band area ratios) versus ion fluence are reported, and discussed. All acoustic and optical bands increase and broaden with fluence. Yet no amorphization is achieved under the highest fluence for both carbides. From the lowest fluence up to 10¹⁵ ions/cm², point defects like interstitials and vacancies are created. The increasing number of carbon vacancies involves a local variation in stoichiometry accompanied by carbon release. For fluence above 10¹⁵ ions/cm², extended defects like dislocation loops appear, as seen by TEM observations. (authors)