Local-Wetting-Induced Deformation of Rolled-Up Si/Si-Ge Nanomembranes: A Potential Route for Remote Chemical Sensing

We fabricate curled 3-D objects from semiconductor nanomembranes consisting of single-crystal silicon, which is epitaxially grown on silicon-germanium-on-insulator substrates. The curling is caused by relaxing the strain induced by lattice mismatch between silicon (Si) and germanium (Ge). Depending on the lithographically patterned geometries and their orientation with respect to the crystallographic direction, different shapes of tubes can be realized. Particularly interesting are tubes that are not completely closed, or partially open, whose mechanical response is ultraelastic. We demonstrate that applying acetone on such tubes generates a surface stress imbalance between the Si and Si-Ge layers, resulting in detectable shape changes. This mechanism has potential applications in chemical sensing, where the deformable curled structures act as dynamic-aperture reflector antennas. Our simulation suggests the curvature changes induced in the presence of certain chemical, such as acetone, will lead to distinctive far-field radiation patterns in the terahertz (THz) range.