Time-resolved imaging of gas phase nanoparticle synthesis by laser ablation

Abstract

The dynamics of nanoparticle formation, transport, and deposition by pulsed laser ablation of c-Si into 1-10 Torr He and Ar gases are revealed by imaging laser-induced photoluminescence and Rayleigh-scattered light from gas-suspended 1-10 nm SiO x particles. Two sets of dynamic phenomena are presented for times up to 15 s after KrF-laser ablation. Ablation of Si into heavier Ar results in a uniform, stationary plume of nanoparticles, while Si ablation into lighter He results in a turbulent ring of particles which propagates forward at 10 m/s. Nanoparticles unambiguously formed in the gas phase were collected on transmission electron microscope grids for Z-contrast imaging and electron energy loss spectroscopy analysis. The effects of gas flow on nanoparticle formation, photoluminescence, and collection are described.

Photochemical Interaction of Polystyrene Nanospheres with 193 nm Pulsed Laser Light

“…The particle loss is likely due to the production of gas-phase species that are not recovered to particulate matter and/or the formation of particles smaller than 13 nm, which is the smallest particle diameter measured by the SMPS in this work. The typical nucleation time for gas-to-particle conversion is from 50 µs to 1 ms. [24][25][26] Since this time scale is shorter than the time between the laser pulses in multiple shot irradiation (20 ms), every particle experiences successive disintegration and condensation. During these processes, a larger fraction of the particle volume is lost with increasing PAR, resulting in a decrease of the final particle size and the number concentration.…”

Kinetic-energy induced smoothening and delay of epitaxial breakdown in pulsed-laser deposition

“…18,19 The ambient gas opposes rapid expansion of the PLD plume and confines it to a smaller region. As a result the concentration of the ablated species increases leading to a higher probability of cluster nucleation.…”

Laser Interactions in Nanomaterials Synthesis

“…In this case, for times > 200 µs the photoluminescence from small clusters and nanoparticles formed in the plume is used to reveal their position and dynamics. [17] As the images show, a very bright region of photoluminescent clusters is formed behind the leading edge of the plume. These clusters were too small, however, to scatter light sufficiently for RS imaging.…”

“…The movement of the lower portion of the nanoparticle cloud is due to a very weak gas flow in the chamber caused by the gas introduction. [17] introduce trace impurities of oxygen, no PL is observed. Thus, the choice of background gas can significantly affect the propagation of the plume and its chemistry.…”