Mechanical properties of electron irradiated graphene drums using AFM nano-indentation*

The elastic modulus of mono layer graphene synthesized by mechanical exfoliation over micron sized holes in SiO₂ was determined using atomic force microscopy based membrane deflection experiments before and after electron irradiation. The irradiation was done using a scanning electron microscope to dosages of 4.96x10¹⁵ e/cm² and 2.03x10¹⁶ e/cm². The irradiation is thought to induce hydrogenation. Nano-indentation curves were measured before and after irradiation. The experimental curves were fitted to theory to determine the elastic modulus. Prior to irradiation an elastic modulus of 277 N/m was measured, after one irradiation we saw an increase to 430 N/m, after a second irradiation we saw a decrease to 275 N/m. This can be explained by previously reported experimental data and analysis showing increases in elastic modulus for small defect density due to suppression of long wavelength flexural modes.