Semiconductor clusters in the sol-gel process: quantized aggregation, gelation, and crystal growth in concentrated zinc oxide colloids

A new synthesis of ZnO wurtzite clusters (crystallite sizes 3-6 nm) is presented. This novel approach, employing ultrasound, allows one to produce relatively highly concentrated 0.1 M Q-ZnO colloids within a few minutes. These colloids remains in a dispersed state for weeks. They can be further concentrated into stable syruplike liquids (molarities of ∼1 M). Under the externe concentration conditions (10 M Q-ZnO colloids) employed, ZnO alcogels are formed, and self-induced crystal growth occurs in the alcogels (sizes ranging between 1 and 5 mm)