Paper SE-TuA8
Effect of Swift Heavy Ion Irradiation on the Hardness of Chromium Nanorods

Tuesday, October 16, 2007, 4:00 pm, Room 617

This presentation discusses the use of ion irradiation to controllably tailor the hardness of Cr columnar thin films. Regular arrays of slanted Cr rods, 2 µm long and 250 nm wide, were grown by glancing angle dc magnetron sputter deposition on patterned Si(100) substrates. The patterns consist of 500-nm-diameter polystyrene spheres that self-assemble to form hexagonal close-packed monolayers. The Cr rod arrays were irradiated with 100 MeV Ag⁺⁸ ions at three different fluences of 10¹³, 5x10¹³ and 10¹⁴ ions/cm², while maintaining the sample at a constant temperature of 80K. The ion-irradiation induced defect formation is dominated by electronic energy losses, with a very small contribution (approximately 0.5%) from the nuclear energy losses and negligible Ag-implantation. The average nanohardness of pristine Cr rods, as determined using a Berkovich diamond tip attached to an atomic force microscope, was found to be 0.6 GPa. Irradiation of the rods with 10¹³ ions/cm² does not lead to a measurable change in the hardness. However, for the fluence of 10¹⁴ ions/cm², the hardness increases to about 4 GPa, leading to an about eight-fold increase. The fluence-dependent hardness in these Cr rods is attributed to the ion-irradiation induced defect formation that may lead to dislocation pinning which is particularly effective due to the nanoscale dimensions of the Cr rods. These results are very promising as they demonstrate the use of swift heavy ion irradiation to tune the hardness of nanorod coatings.