In Situ and Real-Time Inspection of Nanoparticle Average Size in Flexible Printed Sensors

Nanoparticles play an integral part for the production of contacts and active sensing layers in the fast-developing printed electronic technology on flexible devices. Unfortunately, all currently available techniques for nanoparticle characterization are limited to ex situ and/or off-line processing. Here, we describe a new approach composed of two complementary parts for in situ and real-time estimation of the nanoparticles' effective diameter on flexible substrates. The first part of the approach is based on measurements of electrical resistance of the device in response to strain, and correlation of the response with the nanoparticles' diameter. The second part takes place only when measuring the electrical resistance is unfeasible. It is based on UV-vis absorption of the device and correlation of the absorption peak with the nanoparticle diameter based on previous calibration data from strain sensitivity. The new approach shows excellent estimations of the nanoparticle diameter (2.5-20 nm) on the substrate with the advantages of being online, in situ, and inexpensive. In addition, the estimated nanoparticle diameter is in excellent agreement with atomic force microscopy (AFM) measurements. These capabilities are expected to improve the process of quality control of the nanoscale-enabled flexible devices, which, until now, has been considered to be one of the most annoying issues that inhibits the commercialization of nanotechnology-based flexible products.