Synthesis of Si/SiO2 nanoparticles using nanosecond laser ablation of silicate-rich garnet in water

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In summary, successful synthesis of Si/SiO2 NPs is achieved using laser ablation of naturally occurring Pyrope garnet rock. These NPs have cubic structure with an inter-planar distance of 3.0 Åand are nearly spherical in shape with wide size distribution between 7 nm and 75 nm. While exciting the samples at 348 nm, a strong blue luminescence is observed near 430 nm. The observed PL spectrum can be fitted with three Gaussians peaks centered at 420, 433 and 454 nm. The origin of peaks 420 and 433 nm has been attributed to the near interface traps at Si-NPs having a coat of SiOx whereas 454 nm peak is assigned to SiO2 NPs. The presence of SiO2 NPs in all the samples has been further confirmed by the appearance of Raman peak at 462.2 cm1 which has been ascribed to the R line of SiO2 NPs. In addition, time dependent ablation of garnet samples and their optical spectra are also examined revealing that the synthesis of Si NPs is favored over that of SiO2 NPs when the sample is ablated for 20 min in water. Unlike pure targets, the ablation mechanism is not straightforward and may depend on the crystal structure, binding energy, bond strength etc. other than input laser and physical parameters. A detailed study may be required to understand the synthesis process of a selective nanoparticle from the complex composition. To the best of our knowledge, this is the first report of the synthesis of Si NPs by the laser ablation of naturally occurring silicate rocks. This procedure has the potential to be scaled up as low cost method towards the mass synthesis of silicon and other novel NPs for various applications such as electronics and optoelectronics.

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