Femtosecond Laser-Induced Nanowelding: Fundamentals and Applications

摘要

Fundamentals of femtosecond laser pulse and nanoparticles are analyzed by a two-temperature model. Ultrafastsurface melting, surface nanoengineering and shock wave impact are evident in the surface of graphite by femtosecondirradiation. The interaction between femtosecond laser pulses and Au/Ag nanoparticles has been investigated. Two effectsare identified at different intensities: photofragmentation at rather high intensity (~ 1014 W/cm2), nanojoining at lowintensity (~ 1010W/cm2). Photofragmentation forms a large number of tiny nanoparticles with an average size of tens ofnanometers. Control over irradiation conditions at intensities near 1010 W/cm2 results in nanojoining of most of thenanoparticles. This nanojoining is obtained in both liquid solution and in solid state thin films assembled fromnanoparticles. Nanojoining mechanism is further studied by joining Ag nanoparticles encapsulated by a polymer shell.Nonthermal melting is investigated. Nanojoined Au nanoparticles are expected to have numerous applications, such asprobes for surface enhance Raman spectroscopy.