Freestanding ultra-thin silica

Silica (SiOx) thin films are promising for a wide range of applications, including catalysis, separation technology, biomedicine, or transparent super-hydrophilic films. Here, we present a study demonstrating a unique way of producing ultra-thin, freestanding silica films via silicon etching. This method utilizes silicon wafers with thermally oxidized surfaces and two common inorganic elements (sulfur and tellurium), which leads to high-rate chemical etching of the Si substrate, leaving behind freestanding silica layers. Thermodynamic calculations of the tellurium–silicon–sulfur (Te–Si–S) ternary phase diagram suggest that the removal of the Si substrate from the silica layers is due to chemical reactions that result in liquid/vapor formation of Si–S and Si–Te phases. Importantly, the chemical and physical properties of the silica film post-etch are comparable to those of the starting material. The process described here provides a route to produce large area, flexible glass substrates with widely tunable thicknesses from tens to thousands of nanometers.