Laser ablation of nanoscale particles with 193 nm light
Laser interaction with nanoscale particles is distinct and different from laser-bulk material interaction, where a hot plasma is normally created. Here, we review our studies on 193 nm laser ablation of various nanoscale particles including NaCl, soot, polystyrene, and gold. The 20 ns laser beam with fluences up to 0.3 J/cm 2 irradiates nanoparticles in a gas stream at laser repetition rates from 10 to 100 Hz. The particle size distributions before and after irradiation are measured with a scanning mobility particle sizer (SMPS), and particle morphology is examined with electron microscopy. All the nanomaterials studied exhibit a similar disintegration pattern and similar particle formation characteristics. No broadband emission associated with particle heating or optical breakdown is observed. The nanoparticles formed after irradiation have a smaller mean diameter and an order of magnitude higher number concentration with a more spherical shape compared to the original particles. We use the photon-atom ratio (PAR) to interpret the laser-particle interaction energetics.
The effect of dust on 10.6‐μm laser‐induced air breakdown
Laser‐induced breakdown in very clean air at 10.6 μm is shown to have a threshold of 3 × 109 W/cm2 for large beams and is described well by microwave breakdown theory. Dust particles are shown to lower the threshold by an amount which is greater for larger particles and higher vapor temperatures. There is a minimum in threshold for large particles, which for 200‐nsec pulse length is ≤ 108 W/cm2, corresponding to an energy fluence of 10–20 J/cm2. These results are explained qualitatively by the increase in inverse bremsstrahlung rate caused by exploding particles.
Synthesis of β-FeSi2 nanowires by using silicon nanowire templates
Si nanowires templates were grown by a Cu-catalyzed vapor–liquid–solid process and used for the preparation of β-FeSi2 nanowires on a Si substrate. The silicon nanowires were transformed into β-FeSi2 nanowires by annealing with additional source material containing FeCl2 and Si powder. In contrast to uniform Si nanowire templates along the direction, the synthesized nanowires were deformed irregularly. The electron diffraction pattern of the nanowires synthesized from the template corresponded to that of single-crystalline β-FeSi2 and the longitudinal direction of the nanowire was along the direction. The energy dispersive X-ray fluorescence analysis confirmed that the nanowire contained Fe and Si in an atomic ratio of approximately 1:2. The results confirmed that β-FeSi2 nanowires on a Si substrate were synthesized from the Si nanowire templates.Si nanowires templates were grown by a Cu-catalyzed vapor–liquid–solid process and used for the preparation of β-FeSi2 nanowires on a Si substrate. The silicon nanowires were transformed into β-FeSi2 nanowires by annealing with additional source material containing FeCl2 and Si powder. In contrast to uniform Si nanowire templates along the direction, the synthesized nanowires were deformed irregularly. The electron diffraction pattern of the nanowires synthesized from the template corresponded to that of single-crystalline β-FeSi2 and the longitudinal direction of the nanowire was along the direction. The energy dispersive X-ray fluorescence analysis confirmed that the nanowire contained Fe and Si in an atomic ratio of approximately 1:2. The results confirmed that β-FeSi2 nanowires on a Si substrate were synthesized from the Si nanowire templates.