In the framework of the nano system integration network of excellence »Nanett« at Fraunhofer ENAS we deal intensively with the use of semiconductor nanocrystals (e.g. CdSe / ZnS particles) for material-integrated sensors. Here quantum dots are used for detection, storage and optical visualization of mechanical (over-) loads, for example at reinforced lightweight components.
Key feature of our concept for material-integrated sensor technology is a double layer consisting of a piezoelectric layer and a semiconductor nanocrystal polymer composite film. The mechanical structure, which has to be monitored, will be covered with this double layer. Application of a mechanical load to the structure leads to an accumulation of charges within the electrodes of the piezoelectric layer. The charges are then transferred to the composite film by charge transport layers and injected into the nanocrystals, causing non-radiative exciton recombination. This results in photoluminescence quenching, which can be detected as local optical contrast. The ‘dark state’ is as long as the additional delocalized charge is stored within the particle. Hence the load state, e. g. an impact, can be stored in the functional layer and can be read later, for example during a safety inspection of the mechanical structure.