Synthesis of Colloidal Crystals of Controllable Thickness through the Langmuir−Blodgett Technique

Colloidal crystals of various thicknesses were obtained using silica particles as basic units and the Langmuir−Blodgett technique as a tool for controlling the thickness. Submicronic silica particles are first synthesized via a sol−gel process and then functionalized with an appropriate coupling agent. After compression at the surface of a Langmuir trough to form a well-organized two-dimensional array, silica particles are transferred onto solid substrates. While repeating the transfer several times, we formed colloidal crystals that were characterized by scanning electron microscopy and UV−visible−NIR spectroscopies. Both techniques show that the sample thickness can be controlled at the layer level whereas the overall crystal quality should be good enough for use in several applications.