Soft-Chemistry-Based Routes to Epitaxial [alpha]-Quartz Thin Films with Tunable Textures

Quartz is used industrially as an abrasive, as an inert glassy material, or for high-quality crystals in microelectronics. It is also valued for its piezoelectronic properties. However, it is hard to grow quartz as a patterned material or to integrate it into nanostructured devices. Carretero-Genevrier et al. (p. 827; see the Perspective by Brinker and Clem) have developed a method for preparing oriented epitaxial thin films of polycrystalline α-quartz on single-crystal silicon substrates using ambient pressure and temperatures below 1000°C. Different processing conditions can be used to fabricate quartz films with a variety of pore sizes or as a dense nonporous α-quartz film. [PUBLICATION ABSTRACT] Piezoelectric nanostructured quartz films of high resonance frequencies are needed for microelectronic devices; however, synthesis methods have been frustrated by the inhomogeneous crystal growth, crystal twinning, and loss of nanofeatures upon crystallization. We report the epitaxial growth of nanostructured polycrystalline quartz films on silicon [Si(100)] substrates via the solution deposition and gelation of amorphous silica thin films, followed by thermal treatment. Key to the process is the combined use of either a strontium (Sr2+) or barium (Ba2+) catalyst with an amphiphilic molecular template. The silica nanostructure constructed by cooperative self-assembly permits homogeneous distribution of the cations, which are responsible for the crystallization of quartz. The low mismatch between the silicon and α-quartz cell parameters selects this particular polymorph, inducing epitaxial growth. [PUBLICATION ABSTRACT]