Effect of swift heavy ion irradiation on the hardness of chromium nanorods

The present study reports the use of swift heavy ion irradiation as a means to tailor the hardness of chromium nanorod coatings. Arrays of slanted and straight Cr nanorods, 1-2 μm long and 300-500 nm in diameter, were grown by dc magnetron sputter glancing angle deposition on Si(100) substrates patterned with 500 nm diameter polystyrene spheres. The samples were irradiated with 100 MeV Ag+8 ions at three different fluence values of 1013, 5x1013, and 1014 ions/cm2, while maintaining the samples at 80 K temperature. The as-deposited samples exhibit a fibrous structure that smoothens after irradiation. Nanoindentation tests performed on these samples reveal that the hardness of the nanorods increases with fluence. For slanted nanorods, the samples irradiated at maximum fluence show an almost 300% increase in hardness as compared to their pristine counterparts. The corresponding increase in the case of straight nanorods was observed to be 77%. This fluence-dependent hardness in Cr nanorods is explained in terms of an ion-irradiation induced defect formation and a decrease in the grain size, as confirmed by glancing angle x-ray diffraction