The effect of ionization on cluster formation in laser ablation plumes

Abstract

Ablation plumes caused by short-pulse laser irradiation provide conditions which are well suited to the formation of nanoclusters. The high saturation ratios and presence of ionization lead to extraordinarily high nucleation rates and small critical radii. We have explored the homogeneous nucleation and heterogeneous growth of condensate from Si targets expanding into a low-pressure He ambient using a Nd:YAG laser with pulse length of 8 ns, wavelength of 532 nm and intensities in the range of 5¥10 7 to 5¥10 9 W/cm 2 . Clusters in the range of 5-50 nm have been produced. In the highly dynamic, non-linear regime of short-pulse laser-matter interactions, plume evolution and condensation processes are strongly coupled and difficult to predict accurately from modeling alone. Both numerical predictions and experimental results were used to quantify the competing effects of ionization and supersaturation. The results suggest a dominant influence of ionization for nearly all intensities above the ablation threshold.

Investigation of the interaction of a laser pulse with a preformed Gaussian Sn plume for an extreme ultraviolet lithography source

“…According to homogeneous nucleation theory, the vapor formation rate can be described as exp͑− 0 / t͒, where 0 is the time for the establishment of significant nucleation, which is much longer than the laser pulse duration. 15 So the cold preplume appears several hundred nanoseconds after the prepulse. However, note that in our experiments, the intensity of the prepulse is controlled just around the threshold intensity for phase explosion, so most of the ablated material is in uniform vapor instead of large size droplets.…”

Spectroscopic characterization of laser-induced tin plasma

“…Laser-induced plasma ͑LIP͒ techniques are also used in space applications such as in chemical sensors for the exploration of Mars and micropropulsion for satellite positioning, as well as in the detection of biological molecules. 3,4 Other important applications of LIP include pulsed laser deposition, 5 nanoparticle and cluster production, 6,7 and laser-induced breakdown spectroscopy ͑LIBS͒. 8 Laser-created plasma characteristics are strongly dependent upon several key parameters, including laser intensity, pulse duration and wavelength, target material and geometry, and the nature and pressure of any ambient gas.…”

Structural properties of Ge nanostructured films synthesized by laser ablation

“…Nanostructured semiconductor films (including, e.g. Si nanostructures with remarkable photoluminescence properties) can be grown with this approach [5][6][7][8][9][10]. However, the structural properties of such nanostructures are still poorly characterized.…”