Water-Induced Phase Separation Forming Macrostructured Epitaxial Quartz Films on Silicon.

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. [ABSTRACT FROM AUTHOR]