Femtosecond Laser-Induced Nanowelding: Fundamentals and Applications

Abstract

Fundamentals of femtosecond laser pulse and nanoparticles are analyzed by a two-temperature model. Ultrafast surface melting, surface nanoengineering and shock wave impact are evident in the surface of graphite by femtosecond irradiation. The interaction between femtosecond laser pulses and Au/Ag nanoparticles has been investigated. Two effects are identified at different intensities: photofragmentation at rather high intensity (~10 14 W/cm 2 ), nanojoining at low intensity (~10 10 W/cm 2 ). Photofragmentation forms a large number of tiny nanoparticles with an average size of tens of nanometers. Control over irradiation conditions at intensities near 10 10 W/cm 2 results in nanojoining of most of the nanoparticles. This nanojoining is obtained in both liquid solution and in solid state thin films assembled from nanoparticles. 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 as probes for surface enhance Raman spectroscopy.

Femtosecond laser welded nanostructures and plasmonic devices

“…The bonding is evident by the forming of the necking connection between Ag NPs. These joints can be attributed to solid state diffusion because these NPs are expected to melt at a temperature ranging from 673 to 873 K based on the size effect, 29 above the present sintering temperature. The blank area without Ag NPs dramatically increases, probably due to the melting and evaporation of tiny nanoparticles.…”

“…At a fluence larger than the surface damage threshold, 27 electrons are excited, ejected, and thereby weaken the chemical bonds of lattice atoms, resulting in "melting" of surface atoms, which is a nonthermal phenomenon. 5,[27][28][29] This melting also occurs only on the surface to a nanoscale depth without damaging the bulk and, thus, can be used for welding of nanoparticles. 5 …”

Nano brazing of Pt-Ag nanoparticles under femtosecond laser irradiation

“…Second, a melting and epitaxial growth (or solidification) process occurred during femtosecond laser irradiation. For large nanoparticles, only surface melting occurs during femtosecond laser irradiation [19,20]. The Ag nano brazing filler cluster was very small (normally less than 10 nm) due to the lower ablation energy used.…”

“…The Ag nano brazing filler cluster was very small (normally less than 10 nm) due to the lower ablation energy used. If nanoparticles are tiny clusters with limited atoms, they may suddenly display global melting without surface melting, because the effective laser penetration depth was larger than the particle size [19]. After the laser pulse turned off, the Ag nano brazing filler metal solidified and grew epitaxially on the Pt-Ag surface.…”

Joining of Silver Nanowires by Femtosecond Laser Irradiation Method

“…5,7,8) Gold and silver nanoparticles have been reported to be welded by the fs laser induced method. However, it is still lack of experimental data and basic theory of the joining process.…”