Porous silicon (PSi) has been recognized as an advantageous material for use in optical biosensors due to its large internal surface area, ability to form multilayer optical structures, and compatibility with standard silicon lithographic techniques. We demonstrate an order of magnitude improvement in small molecule detection sensitivity for on-chip PSi ring resonators and photonic crystal nanobeams compared to the same structures fabricated on silicon-on-insulator wafers. Moreover, we demonstrate that PSi optical structures can be exploited for mobile diagnostics by using a smartphone with no additional functional accessories to detect color changes in the PSi that result from molecule capture.
Precision and chip contamination-free placement of two-dimensional (2D) materials is expected to accelerate both the study of fundamental properties and novel device functionality. Current transfer methods of 2D materials onto an arbitrary substrate deploy wet chemistry and viscoelastic stamping. However, these methods produce a) significant cross contamination of the substrate due to the lack of spatial selectivity b) may not be compatible with chemically sensitive device structures, and c) are challenged with respect to spatial alignment. Here, we demonstrate a novel method of transferring 2D materials resembling the functionality known from printing; utilizing a combination of a sharp micro-stamper and viscoelastic polymer, we show precise placement of individual 2D materials resulting in vanishing cross contamination to the substrate. Our 2D printer-method results in an aerial cross contamination improvement of two to three orders of magnitude relative to state-of-the-art dry and direct transfer methods. Moreover, we find that the 2D material quality is preserved in this transfer method. Testing this 2D material printer on taped-out integrated Silicon photonic chips, we find that the micro-stamper stamping transfer does not physically harm the underneath Silicon nanophotonic structures such as waveguides or micro-ring resonators receiving the 2D material. Such accurate and substrate-benign transfer method for 2D materials could be industrialized for rapid device prototyping due to its high time-reduction, accuracy, and contamination-free process.