A method was developed to make atom-flat sensors that seamlessly integrate with devices to report on what they perceive. Electronically active 2D materials, touted for their strength, are difficult to move to where they’re needed without destroying them. The new method keeps the materials and their associated circuitry, including electrodes, intact as they’re moved to curved or other smooth surfaces.
The concept was tested by making a 10-nanometer-thick indium selenide photodetector with gold electrodes and placing it onto an optical fiber. Because it was so close, the near-field sensor effectively coupled with an evanescent field — the oscillating electromagnetic wave that rides the surface of the fiber — and accurately detected the flow of information inside. The benefit is that these sensors can now be embedded into such fibers where they can monitor performance without adding weight or hindering the signal flow.
Raw 2D materials are often moved with a layer of polymethyl methacrylate (PMMA), more commonly known as Plexiglas, on top and the new method makes use of that technique. Researchers needed a robust bottom layer that would not only keep the circuit intact during the move but could also be removed before attaching the device to its target. (The PMMA is also removed when the circuit reaches its destination.)
The solution was polydimethylglutarimide (PMGI), which can be used as a device fabrication platform and easily etched away before transfer to the target. PMGI appears to work for any 2D material.
Only passive sensors have been developed but the researchers believe their technique will make active sensors or devices possible for telecommunication, biosensing, plasmonics, and other applications.