Post-annealing effects on stability of lasered nanostructured ZnO sensors for their usage in monitoring smart greenhouse

Long-term space exploration requires an affordable and continuous provision of food and nutrients that need to be palatable so as not to upset the psycho-physical balance of the crewmembers. Moreover, a proper diet composed of fresh food enriched with key nutrients such as minerals and vitamins can minimize the detrimental effects due to microgravity in terms of bones weakening; in addition, the absence of direct incident light from the sun due to a safety shielding from cosmic rays can cause a significant reduction of vitamin D production in the skin. Smart greenhouses based on aeroponics or hydroponics technologies can represent a valuable solution to genuine food supply. Nevertheless, these structures require an affordable monitoring system able to detect key parameters such as nutrients concentration in the mist, gaseous products/pollutants together with relative humidity and temperature. Flexible, light and low-cost gas sensors based on laser-annealed zinc oxide nanostructures can be implemented for this specific application, using different morphologies within the same material for discriminating the different gases. Unluckily, this active material generally exhibits memory effects and significant drift. In this work, we propose a simple method to dramatically increase the reliability of nanostructured ZnO sensor response to be used at low working temperature (room temperature). The resulting devices exploit the porosity of disordered nanostructures thus monitoring CO, CO2, NOX and other gases present in the greenhouse.