Spectral characteristics of laser-induced plasma generated on porous silicon produced by metal-assisted etching

Porous silicon (Si) produced by metal-assisted etching using nanoparticles (Si nanohole array with straight pores) has potential as a sample loading substrate of laser-induced breakdown spectroscopy (LIBS). In this work, we investigated the characteristics of laser-induced plasma generated on the porous Si with different pore depths (pore depth: approximately 180, 320, and 990 nm) from spectroscopic aspects. The intensity of Si I line was enhanced by using the porous Si instead of a flat Si, it increased with increasing the pore depth of porous Si, and its enhancement factor reached 45 (pore depth: approximately 990 nm). The atomic excitation temperature and atomic number density increased with increasing the pore depth, whereas the intensity ratio of Si II line to Si I line and the intensity of nitrogen I line decreased. These results provide an insight into the plasma formation on nanomaterials.