Structural evolution and irradiation hardening studies in a-particles irradiated Mo thin films

This study is an account of the a-radiation-induced effects on the microstructure, topography, and hardness of molybdenum (Mo) thin films deposited over graphite. Mo thin films were deposited on graphite substrate by DC magnetron sputtering. Specimens of sputtered thin films were irradiated with He+ ion of 0.8 MeV and 1.6 MeV with an equivalent dose of 0.0765 and 0.645 DPA, respectively. Radiation effects were studied by scanning electron microscopy, X-ray diffraction, atomic force microscopy, Hall's effect and nano-indentation. The ener-getic a-particles were observed to induce defects and reduce the overall crystallite size. The unirradiated sample depicted compressive residual stress, whereas tensile stress was recorded for the irradiated samples. Besides, the tensile stress increase with an increase in the radiation energy. The irradiated samples had relatively rougher topography. The electrical measurements reaffirmed the finding that the energetic a-particles generate defects that impede the charge carrier's transport. Crystal defects, as well as the reduced crystallite size, were found to promote mechanical hardness, as the nanoindentation hardness increased to 9 % and 26 % for low dose and higher dose irradiated samples respectively.