Femtosecond Laser Processing Of Graphene Films And Graphene Oxide Films

Femtosecond laser has attracted tremendous research interest for many applications due to its ultrashort pulse duration and extremely high peak intensity.Recently,direct micro/nanostructuring of graphene-based materials has been widely studied with the development of related two-dimensional materials.Femtosecond laser displays prominent superiority in this field.In this work,on the one hand,the femtosecond laser ablation properties of graphene films was investigated.Compared with graphene oxide films and graphite films,the mechanism of the abnormal phenomenon that the ablated area of graphene films remained unchanged with the increasing of pulse number was revealed.On the other hand,based on the theory of electron dynamic control,femtosecond laser double-pulse train which has been reported to hold great advantages in high precision and high quality processing was applied to the reduction of graphene oxide filmsMajor contributions and innovations in this paper are summarized as follows:(1)Femtosecond laser ablation of graphene films prepared by direct filtration was experimentally studied.An abnormal phenomenon was discovered: the ablated area remained unchanged for graphene paper with increasing number of pulses,which was found to be a general feature for a large range of laser fluences.This feature was distinctive from those of other materials irradiated by ultrashort(a few tens of femtoseconds to a few picoseconds)lasers,including metals,semiconductors,polymers,transparent materials,and other graphene-based materials(e.g.single-layer graphene,and graphite).Comparative femtosecond laser ablation experiments were carried out in graphene oxide films and highly oriented pyrolytic graphite,which demonstrated that the non-incubation effect in terms of ablated area was unique to graphene films.(2)A series of characterization techniques were carried out to analyze the ablation threshold fluences,ablation morphologies,micro/nanostructures,chemical compositions and Raman results of the three graphene-based materials mentioned above.Combined the analysis with some previous publications,we attribute the abnormal non-incubation effect of graphene films to: 1)femtosecond laser nonthermal ablation through rolling up of graphene nanoflakes induced by the distinctive multi-level layer-by-layer structures and 2)ultrafast energy relaxation after femtosecond laser irradiation.In addition,the experiments and analysis systematically studied the fundamental ablation properties of graphene films,graphene oxide films and graphite irradiated by femtosecond laser.We anticipate this study might impact on femtosecond laser processing of paper-like graphene materials for multifunctional applications.(3)Femtosecond laser double-pulse train with 76 MHz repetition rates was generated via a Michelson interferometer and applied to the reduction of graphene oxide films.The reduction effect was studied with different delay times between the two subpulses.It indicated that 76 MHz femtosecond laser double-pulse train with a delay time of 3 picosecond was the most effective reduction condition in our experiments,which could further decrease the content of oxygen atoms of around 5% when compared with traditional femtosecond laser single pulse train under the same experimental condition.In addition,the integrity of reduced graphene oxide sheets was perfect and the reduction efficiency is much higher when compared with those reduced by femtosecond laser with 1 KHz repetition rates,which demonstrated the superior reduction effect of femtosecond laser double-pulse train.This study opens up alternative routes for femtosecond laser reduction of graphene oxide materials with better reduction effect.