The Formation and Structure of Warm Dense Silicon Dioxide

Silicon dioxide is a major constituent of the earth's crust and mantle as well as a common material for optics. X-ray absorption spectroscopy measurements have indicated that warm dense SiO2 is either a semimetal or has a significant metallic component. Ultrafast electron diffraction was performed on amorphous silicon dioxide foils irradiated by femtosecond optical pulses. From the electron diffraction patterns, pair distribution functions were calculated showing a reduction of the Si-O peak. The results are compared with molecular dynamics calculations, which predict structures with broken Si-O bonds. In addition, the time scale for the formation of the warm dense state was observed indicating a non-thermal phase transition.