Effects of wavelength and fluence on the graphene nanosheets produced by pulsed laser ablation

In this work, graphene nanosheets and carbon nanoparticles were synthesized by nanosecond pulsed laser ablation in liquid nitrogen using Q-switched Nd:YAG laser. The aim is to investigate the wavelength dependence of carbon nanostructures formation mechanisms using fundamental and second harmonic of Nd:YAG laser irradiations at different laser fluence. Carbon nanoparticles and graphene nanosheets fabricated by pulsed laser ablation show the spherical and transparent sheets morphology, respectively, whereas, those due to the fundamental and second harmonic of Nd:YAG laser undergo fragmental shapes. Furthermore, the production rate of carbon nanoparticles produced at 532 nm is noticeably greater than that at 1064 nm wavelength and it can be due to the strong inverse Bremsstrahlung process at IR region. Raman spectra indicate that the graphene nanosheets produced at 532 nm are multilayer while by increasing the laser fluence and wavelength (1064 nm), bilayer graphene nanosheets are formed.