A colloidal solution with SiO2 species of ca.
25 nm size was used as a silica source. Composition
of the reaction mixture was 10SiO2:NaOH:TPABr:800H2O.
Removal of template proceeded in a
flow of dried air by heating at a rate of 0.5 8C/min
to an upper temperature which was between 330 and
550 8C. The sample was kept at this temperature for
24 h. Etching was performed by HF of 0.4–4.0% in
water for 0.5–10 min. Images were done on a scanning
electron microscope JSM-5500LV.
HF etching of as-synthesized wafers containing
TPA resulted in formation of sharp, uniformly wide
slits between neighboring crystals (Fig. 2a). This
could be explained by the presence of an amorphous
silica layer filling these slits before etching. It can be
expected that such amorphous layer would dissolve