Pulse laser ablation in water fragmentation of amorphous silica in water with optional NaCI spiking

Amorphous SiO2 powders having two kinds of medium range order (MRO) were subjected to pulse laser ablation in water (PLAL) for X-ray diffraction, transmission electron microscopy and spectroscopy characterization. The powders fragmented down to 10-20 nm in size are mainly hydrogenated amorphous phase retaining Si-2nd O but not Si-2nd Si MRO. There are minor co-existing crystallites of beta-cristobalite, H2Si2O5 as well as additional alpha-tridymite and Na2SiO3 when water is spiked with NaCI for PLAL. Na-signature also caused lower vibration frequency of the hydrogenated silica network. The opal-like hydrogenated phase assemblage of amorphous phase, cristobalite and tridymite thus formed have a minimum band gap at ca. 5 eV for potential optoelectronic and catalytic applications in UV range and shed light on natural occurrence in dynamic settings such as meteorite impact and lightening strike on silicate-enrich crustal rocks.