Use of EELS to study the absorption edge of fused silica

Electron energy loss spectroscopy (EELS) was used to study the absorption edge of various types of fused silica. The relationships between transmission (%T), fictive temperature (Tf), band gap energy (E0), and slope of the Urbach tail (K) were investigated. The trends are in agreement with other published studies and provide initial validation of the new technique. The measured band gap energies, E0, varied very little among the different silicas, and there was no obvious relationship between E0 and either %T or Tf. The slopes of the Urbach tail, K, varied significantly and were related to both %T and structural disorder (influenced by both Tf and F concentration). The observed trends were an increase in transmission with an increase in K, and an increase in K with a decrease in structural disorder. The results of this work support the idea that structural disorder affects transmission near the absorption edge.