Ion-beam induced quasi-dynamic continual disorder in Bi-implanted Hongan silica glass

摘要

We have studied optical properties of glassy silicon dioxide (Hongan Silica Glass Store, China) irradiated with 30 keV bismuth ions. A broadening with a low-energy shift of absorption edge was found for the samples treated with 1 x 10(16) - 3 x 10(17) cm(-2) ion fluences. The dose dependences of characteristic Urbach energy and width of the optical gap for direct interband transitions were determined and plotted. Based on the linear-type correlation between Urbach energy and optical gap width, the D/K ratio of deformation potential constants was established as well. The constancy of the D/K ratio for silicon dioxide at different fluences of bismuth ions indicates the proportionality between the values of the optical gap and band tails length, which are associated with the static atomic disorder of SiO2 host-matrix. An explanation of the obtained regularities was given using the quasi dynamic (thermodynamic) approach. It was postulated that structural damage caused by ion-beam treatment determines Boltzmann entropy's magnitude as a combination of system various microstates. The functional dependence of sigma-parameter (disordering effective cross-section) on the ion fluence has been established and proved experimentally.