Dynamic Spectroscopic Study On The Formation And Growth Process Of Nanoparticle Prepared By Pulse Laser Ablation In Liquids

Pulse Laser Ablation in Liquids(PLAL)provides a non-equilibrium localized extreme conditions with high temperature and high pressure when pulse laser interacts with target immersed in liquids.The metastable nanomaterials prepared by this technique generally exhibit unique characteristics,such as uniform size distribution,uncapped surfaces,high activity and high reactivity.However,the intermediate process of metastable nanoparticles evolving into stable nanocrystals is extremely complex.Monitoring and analysis of this process is a key technical problem to understand the growth kinetics of nanoparticles.To solve this problem,in situ dynamic spectroscopy analysis system was designed and built in this paper to conduct in situ dynamic spectroscopy monitoring and analysis for the process of preparing metastable nanoparticles with PLAL.The detail research contents and results of this paper are given as follows:1.Setup of in-situ dynamic spectral systemThe system includes the preparation system of PLAL,in-situ dynamic spectral system(plasma emission and light absorption,fluorescence,Raman spectroscopy)and imaging system.The preparation system was connected with the in situ spectroscopy system through a multifunctional optical reaction chamber.With this system,the following processes can be in situ dynamically monitored and analyzed:the process of the interaction between pulse laser and materials in liquid phase(including the evolution process of plasma plume and cavitation bubble)and the growth process of metastable nanoparticles.This system provides a key technical support for investigating the preparation and growth process of metastable nanomaterials induced by PLAL.2.In-situ dynamic investigation on the interaction between pulse laser and materials in liquidsThe steady-state and time-resolved plasma emission spectra induced by pulse laser in different media were monitored by using the in-situ dynamic spectrum acquisition system.The evolution of plasma plume,shock wave and cavitation bubble induced by pulse laser in different focusing conditions and different solvents was monitored using in-situ dynamic imaging system.These in dynamic investigations provide direct evidences for understanding the mechanisim of PLAL and a scientific basis for the preparation of nanomaterials by PLAL.3.Growth process investigation of Ag nanoparticles based on dynamic light absorption spectraCombining dynamic light absorption spectra and many ex-situ methods,the investigation on the growth process of small-sized,uniformly dispersed and uncapped Ag nanoparticles prepared by PLAL with different disturbance such as oscillation and inserting a Cu wire(for replacement)was done.The results showed that the uncapped Ag nanoparticles prepared by PLAL are highly active and highly reactive.The size,structure and composition of uncapped Ag nanoparticles changed significatle under the external disturbance.In addition,by further investigation on Ag nanoparticles coated with different polarity surfactant molecules,it was found that the two surfactant molecules enhanced the stability of Ag nanoparticles to different degrees,because the long chain molecules formed a more compact double electric layer structure on the surface of Ag nanoparticles.This work provides important theoretical and experimental support for the optimal preparation of metastable Ag nanoparticles in liquids.4.Phase transition kinetics of Se nanoparticles probed by liquid phase in-situ Raman spectroscopyThe phase transformation process of Se nanoparticles prepared by PLAL in different solvents was investigated by in situ Raman spectroscopy.The results show that the amorphous Se nanoparticles prepared by PLAL in water grew in specific orientation and transformed into trigonal phase with different morphologies and structures after centrifugation and dispersion in three different polar aprotic solvents.The phase transitions of Se were monitored by in-situ Raman spectroscopy in liquid phase,and the intensity of Raman characteristic peak of trigonal Se was analyzed by data fitting.It was found that the intensity of Raman characteristic peak of trigonal Se was a power function of aging time in different solvents,and the phase transition rate was positively correlated with the polarity of solvents.