Structural changes in soot particles induced by diode laser irradiation

The effects of laser radiation on soot in a vacuum were studied by Raman spectroscopy and transmission electron microscopy. It was found that defective carbon onions could be formed simply by irradiation of focused common diode lasers with intensity much lower (103–106 W/cm2) than those used in the previous work. A modified Melton model was introduced to analyze the formation of onions. The results show a threshold value of laser intensity (5.49 × 103 W/cm2), above which sublimation and rearrangement play a dominant role in the formation of onions. Such onions can also be formed with laser intensities below the threshold since neighboring graphene layers may merge and grow by capturing interstitial carbon atoms. The deposited soot is damage resistant to the diode laser radiation in air due to the rapid formation of carbon onions.