Building block analysis of 2D amorphous networks reveals medium range correlation

The random network theory has been the long-accepted structural model for silica glasses. Now, a large bilayer silica sheet that was recently imaged with STM in atomic resolution provides the opportunity for real space structure analysis. General patterns in the formation of amorphous structures may be identified by looking at larger building blocks beyond single rings. Assessments of ring arrangements around each Si atom and ring neighborhoods are compared against uncorrelated structure predictions. A theoretical model of a two-dimensional silica network is investigated in parallel. Significant deviations of the observed structures from the uncorrelated prediction correspond qualitatively with a simple geometric approximation for bond angle frustration.