Thermal and laser induced sintering in Pt nanoparticles studied by conventional and synchrotron x-ray diffraction*

The thermal and laser induced sintering behavior of 5 -- 6 nm Pt nanoparticles self- assembled into 50 nm diameter spherical aggregates has been studied by conventional and synchrotron-based x-ray diffraction (XRD) measurements. In the first instance, the aggregated Pt nanoparticles were solution annealed at temperatures between 120 and 215 $^{\circ}$C over time periods from 10's to 100's of minutes. In each case the linewidth of the conventionally measured diffraction pattern consisted of a single component which systematically narrowed suggesting an increase in the size of the as-prepared nanoparticles. In a second set of experiments, the aggregated Pt nanoparticles were exposed to about 10,000 laser pulses, each with a duration of about 1 ps and an energy density of 250 mJ/cm$^{2}$. XRD spectra were acquired after each 100 lasers pulses corresponding to 100 ps of sample irradiation. A narrow line component was observed in the diffraction pattern after the first 100 laser pulses and dominated the lineshape after a few thousand laser pulses. These measurements reflect the effects of long term, low temperature atomic transport in comparison with high energy, short time transport.