Graphite Surface Microhardening with Femtosecond Laser Pulses

The effects of direct femtosecond laser processing of a polycrystalline graphite surface are experimentally investigated. The functional graphite surfaces are fabricated at laser intensity of $\sim10^{17}$ W/cm$^2$ in vacuum and then thoroughly analyzed by means of Raman spectroscopy and nanoindentation test. The measured Raman spectra at $257$ nm show presence of an amorphous carbon phase containing $sp^3$ hybridized carbon atoms and a discontinuous nanocrystalline diamond film, while the results of microhardness measurements demonstrate a sixteen-fold increase in microhardness as compared to the unirradiated graphite surface. The modulus of elasticity is found to increase nearly by $3.4$ times.