Ultrafast dynamics of silver nanoparticle shape transformation studied by femtosecond pulse-pair irradiation

Abstract

Spherical silver nanoparticles embedded in glass were irradiated by pairs of time-delayed laser pulses with equal intensities resulting in delay-dependent nanoparticle shape transformations. The corresponding persistent changes in the surface-plasmon extinction bands are analyzed as a function of time delay and relative polarization of the pulse pairs. We find that the strongest nanoparticle shape changes, i.e., the highest aspect ratios, are achieved when the delay between pulse pairs is less than 3 ps. After 10 ps the dichroism is strongly reduced in the case of pulse pairs having identical polarization and vanishes using pulse pairs with orthogonal polarization. Using an extended two-temperature model, the time dependence of directed and isotropic thermal electron emissions was estimated to decay on a time scale of a few picoseconds. Our results strongly suggest that the electron and following ion emission from the nanoparticles are finished within less than 20 ps, and the directional memory is favorably defined by directed emission of hot electrons interacting with the laser field.

Nanowire formation under femtosecond laser radiation in liquid

“…Stalmashonak and co-workers have also reported that the laser induced shape modification of spherical Ag nanoparticles embedded in soda-lime glass was evoked by the surface plasmon assisted photoelectron emission of the electrons from the metal surface during femtosecond laser irradiation . They have also found that such transformation of the metal nanoparticles in glass, which takes place within a timescale of 1 ns, depends on the applied laser pulse intensity, and suggested that the directional memory is defined by the directed emission of hot electrons interacting with the laser field (Unal et al, 2009). Comparing experimental results with simulation results, the shape of the pre-grown Cu nanoparticle produced by the single laser pulse was defined by the laser polarization.…”

Transformation of silver nanospheres embedded in glass to nanodisks using circularly polarized femtosecond pulses

“…[10][11][12][13][14][15][16][17][18] Depending on applied intensity and number of pulses, this procedure transforms the NPs to either prolate ͑large aspect ratio͒ or oblate spheroids ͑very poor aspect ratio͒, with their symmetry axis being uniformly oriented along to the laser polarization. 15,16 This shape transformation on the nanoscale leads macroscopically to two different regimes of dichroism ͑redshifted SP band observed with light polarized parallel or perpendicular to laser polarization͒.…”

“…At the same time, this finding is a further confirmation for the anticipated mechanism of shape transformations, which has been discussed to get the directional memory of the laserpulse polarization via photoionization and directed electron emission into the glass matrix. 16,17 The samples used for the experiments consist of glass containing spherical silver NPs with a mean radius of about 15Ϯ 3 nm and an average volume fill factor of 10 −3 in a Ϸ2 m thick surface layer; the silver content decreases from the surface into the depth of the glass. Extinction for polarized and unpolarized light is 1.8.…”

Laser-matter interactions, phase changes and diffusion phenomena during laser annealing of plasmonic AlN:Ag templates and their applications in optical encoding

“…1 The LSPR traits are strong light absorption, scattering and light field focusing on the NP surface, and are the keystone of the emerging field of plasmonics [2][3][4][5][6][7][8][9][10][11][12] which promises radical breakthroughs in optical storage and transport of information. Strong intensity laser light, on the other hand, interacts with the metal NPs in many more complex ways, which include the self assembly of particles from individual metal atoms, 13 particle reshaping, [14][15][16][17][18][19][20] melting and recrystallization, 21-25 metal growth, 26 and even structural alteration of the dielectric matrix. 27 This photosensitivity is a property of the composite metallodielectric system and depends on the fine details of both the initial NP/host structure and the laser source.…”