Femtosecond Double Pulses Ablation Materials With Ethanol Assistance And Preparation Of Silicon Nanoparticles

In recent years, micro/nano fabrication based on femtosecond (fs) laser technology hasalready become the hotspot of scientific research. The appearance and development of fslaser pulse train processing technology provides a new efficient tool for ultrafast lasermicro/nano fabrication because of its unique advantages which offer the possibility of highquality, high efficiency, and high precision of material processing. The designing pulsetrains not only can control the electronic excitation/ionization process when processingwith the solid material, but control the chemical reaction process in the femtoseconds scale.Based on previous studies, this study focuses to reveal the interaction mechanism betweenthe fs laser and materials theoretically and experimentally. We fabracate small size anduniformly distribution of silicon (Si) nanoparticles (NPs) using fs double pulses ablation thetarget in solution.The research work of this paper can be summarized as the following three:(1) In air environment, the ablation areas of laser induced surface structures in thecraters oscillate to decrease with pulse delays less than1.0ps when fs laser ablation of thesilicon and Ge. However, in ethanol environment, emergence of ablation enhancementphenomenon when the pulse delay time Δt>200fs under the same experimental conditions,this phenomenon appears when the laser fluence higher than0.4J/cm2processing ofsemiconductors. When the fs double pulses ablation of the metal material, such as Al, thephenomenon of ablation enhancement is not observed when Δt>200fs.（2）Free electrons will be generated due to the dissociation of H-O bond when fslaser ionization of ethanol molecules. Pump-probe techniques show that the completiontime of ionization reaction is about200fs, and combined of electronics-holes tend to bemore likely to occur in the semiconductor material. It is considered that the enhancement ofablation rate mainly attributed to high photon absorption efficiency caused by the increaseof localized transient electron density result from the first sub-pulse ionization of ethanolmolecules before the second sub-pulse arrives. In addition, better surface quality and higherablation rate can be obtained using the designed fs laser pulse train.(3) Si Nps can be obtained using the method of fs laser ablation the target in solution.Traditional fs laser enable produce small particle size NPs under low energy butcompromised by an extremely low production rate. High production rate and small particle size with uniform distribution of Si NPs are obtained using the fs double pulses ablation thesilicon in ethanol when the delay time exceeds200fs. This method can process a variety ofsubstrate materials and the experimental procedure is simple and easy to operate.