Water-Induced Phase Separation forming Macrostructured Epitaxial Quartz Films on Silicon
Glenna L. Drisko, Adrian Carretero-Genevrier,* Martí Gich, Jaume Gàzquez, Djawhar Ferrah, David Grosso, Cédric Boissière, Juan Rodriguez-Carvajal, and Clément Sanchez*.
Adv. Funct. Mater.
Quartz has been widely used as a bulk material in optics, the microelectronic industry, and sensors. The nanostructuring and direct integration of oriented quartz crystals onto a semiconductor platform has proven to be challenging. However, here, a new approach is presented to integrate epitaxial quartz films with macroperforations within the range of 500 nm and 1 μm using chemical solution deposition. This method constitutes an appealing approach to develop piezoelectric mass sensors with enhanced resonance frequencies due to the thickness reduction. Perforated quartz films on (100)-silicon are prepared from amorphous silica films deposited via dip-coating and doped with metal cations that catalyze quartz crystallization. The metal cations are also active in the formation of the macroperforations, which arise due to a phase separation mechanism. Cationic surfactant–anion–metal cation assemblies stabilize droplets of water, creating an indentation in the hydrophilic silica matrix which remains after solvent evaporation. Many cations induce phase separation, including Li+, Na+, Sr2+, Mn2+, Fe2+/Fe3+, Ca2+, Ce3+ and La3+ but only the Sr2+ and Ca2+ cations in this series induce the epitaxial growth of α-quartz films under the conditions studied. The combination of sol–gel chemistry and epitaxial growth opens new opportunities for the integration of patterned quartz on silicon.