Nanoprofiling of alkali-silicate glasses by thermal poling

• Surface relief fabricated by thermal poling in soda-lime glass can reach ~ 200 nm.
• The depth of the relief saturates at air poling charge density of ~ 200 mC/cm2.
• At the saturation voids and channels directed in the depth of the glass arise.
• Replacing ions in glass by hydrogen is insufficient to provide observed relief.
• Poling results in structural rearrangement and oxygen molecule formation in glass.

Formation of nanoscale surface relief on the anodic surface of an alkali-silicate glass in the course of thermal poling in open anode configuration and related structural/compositional changes in subanodic region of the glass are studied. Surface of poled glass beneath anodic electrode goes down relatively to the unpoled glass area. The depth of the relief increases linearly with the electric charge transferred through the glass in poling till ~ 200 mC/cm2 charge density, when the depth saturates at ~ 190 nm. While the depth-charge dependence is linear, the glass surface keeps initial quality, and the saturation region corresponds to arising voids and channels directed in the depth of the poled glass. Our evaluations show that the volume difference resulting from the replacement of alkaline and alkaline earth ions by hydrogen is insufficient to provide observed relief. Raman scattering measurements evidence that the poling induces rearrangement of the structure of the glass via losing non-bridging oxygen atoms and forming molecular oxygen. This makes the glass very similar to silica one. These processes are mainly responsible for the surface relief formation.