Diffusion of gallium in quartz and bulk-fused silica

Abstract

Articles you may be interested inHigh-tone bulk acoustic resonators on sapphire, crystal quartz, fused silica, and silicon substrates Diffusion ofGa into quartz (crystal Si0 2 ) and bulk-fused silica (amorphous Si0 2 ) was studied by neutron activation analysis. Slow and fast diffusion of Ga was observed in bulk-fused silica, while in quartz only slow diffusion was observed. The difference in the diffusion mechanisms is discussed on the basis of the difference in porosity of the two materials. In the bulk-fused silica, which has a lower density of2.20 g cm -3, there are two regions with high and low densities. The higher density region is composed of cristobalite, which has the maximum distance between atomic strings of (at most) 6 A. The lower density region is composed ofa random network ofSi and ° atoms, and in the network there exist many microchannels, an average diameter and the real density of which are estimated to be 17 A and 7.5 X lOll cm -2, respectively. These microchannels act as the high-speed diffusion paths, while the cristobalite region is the slow diffusion path. In quartz which has a density of2.65 g cm -3, the widest interatomic spacing perpendicular to c axis is about 5 A and only the slow (bulk) diffusion can occur. The discrepancy in the diffusion coefficients ofGa reported previously by Grove and Wagner can be explained by the present model.

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“…The recrystallization of the amorphous layer and supersaturation provide the driving force for diffusion to the surface. While our own SiO 2 films were already amorphous before implantation, the recovery of local order in the SiO 2 from implant damage may play a role in the surface diffusion of Ga. Gas-phase studies of Ga diffusion in quartz and much more porous bulk-fused silica indicate that microchannels enhance the diffusion of Ga as well . Damage from the Ga implantation process almost certainly results in the SiO 2 structure becoming more porous and open, possibly offering low-resistance, fast-diffusion pathways which may affect the rate and directional preference of Ga diffusion.…”

“…While our own SiO 2 films were already amorphous before implantation, the recovery of local order in the SiO 2 from implant damage may play a role in the surface diffusion of Ga. Gas-phase studies of Ga diffusion in quartz and much more porous bulk-fused silica indicate that microchannels enhance the diffusion of Ga as well. 18 Damage from the Ga implantation process almost certainly results in the SiO 2 structure becoming more porous and open, possibly offering low-resistance, fast-diffusion pathways which may affect the rate and directional preference of Ga diffusion. Also of interest is that Ohkubo et al observed MnO micrometersized surface precipitates crystalgraphically aligned with the Al 2 O 3 substrate after annealing Mn implanted Al 2 O 3 in oxygen.…”