Samples were prepared by implanting Ge ions into high-purity silica. The concentration of Ge at the surface remained essentially zero. It was found that, during initial annealing, the peak Ge concentration shifted toward the surface. The motion of the ions during annealing could be changed by applying a DC electric field. The diffusion of substitutional Ge in silica was described by:

D(cm2/s) = 7250exp[-131(kcal/mol)/RT]

M.V.Minke, K.A.Jackson: Journal of Non-Crystalline Solids, 2005, 351[27-29], 2310-6