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.
Detection of Lead in Soil with Excimer Laser Fragmentation Fluorescence Spectroscopy
Excimer laser fragmentation fluorescence spectroscopy (ELFFS) is used to monitor lead in soil sample and investigate laser-solid interactions. Pure lead nitrate salt and soil doped with lead nitrate are photolyzed with 193 nm light from an ArF excimer at fluences from 0.4 to 4 J/cm{sup 2}. Lead emission is observed at 357.2, 364.0, 368.3, 373.9 and 405.8 nm. Time-resolved data show the decay time of the lead emission at 405.8 nm grows with increasing fluence, and a plasma is formed above fluences of 2 J/cm{sup 2}, where a strong continuum emission interferes with the analyte signal. Fluences below this threshold allow us to achieve a detection limit of approximately 200 ppm in soil.
Adsorption and Laser-Induced Thermal Desorption of 1,3-Butadiene on HOPG(0001)
The adsorption and UV photochemistry of 1,3-butadiene (CH 2 =CHCH=CH 2 ) on highly oriented pyrolytic graphite (HOPG(0001)) was studied using temperature-programmed desorption (TPD) and electron energy loss spectroscopy (EELS). Butadiene physisorbs on HOPG with the monolayer exhibiting first-order desorption kinetics and a corresponding desorption energy of 32 kJ/mol. The multilayer exhibits zero order desorption kinetics with a desorption energy of 28.5 kJ/mol. Irradiation of the C 4 H 6 /HOPG(0001) adlayer (one and three monolayers (ML) of C 4 H 6 ) with UV photons at 193, 248, and 351 nm and fluences of up to 100 mJ/cm 2 _ pulse resulted in molecular photodesorption. Photodesorption was described by a laser-induced thermal desorption process as supported by simple calculations of the surface temperature rise. The photoprocesses occurring in both 1 and 3 ML C 4 H 6 adlayers on HOPG(0001) were also investigated at incident powers of ≤ 10 mJ/cm 2 _pulse. Under these conditions, there was no detectable photodesorption or condensed phase photochemistry at any of the wavelengths investigated.