. Preparation of Gas Sensors with Metal Oxide NWsNanowires of metal oxides were prepared using the techniqueof evaporation-condensation, which exploits the vapor phase-solid (VS) and vapor-liquid-solid (VLS) growth mechanisms.The experimental set-up for the deposition of metal oxidesconsisted in an alumina tubular furnace capable of reachinghigh temperatures (1500° C). This high temperature wasrequired to enable the decomposition of the oxide and topromote evaporation. The temperature gradient within thefurnace and the low pressure in an inert atmosphere allowedcondensation and nucleation of the nanostructures[11].The pressure, the thermal gradient and the gas flow must bestrictly controlled in order to ensure the reproducibility of thesamples among different depositions. During the transient toreach the evaporation temperature and to return back to roomtemperature, the inert gas flow was maintained in the oppositedirection (from the substrate towards the dust), to preventunwanted condensation on the substrate.The temperature of the tubular furnace for zinc oxide wasmaintained at 1200 ° C, and the oxide powder was placed in thecenter of the furnace, where the temperature was the highest.Alumina 2x2mm substrates were catalyzed with platinum priorto the introduction into the oven. The deposition parameters forthe catalyst (deposited by sputtering) were: DC sputteringmode, 50W power and deposition time 2 s. Subsequently, thesubstrates were placed on a sample holder and inserted in alateral zone of the furnace, where the temperature was lower(570 °C). The pressure was decreased to 1 mbar. A 100sccmflow of argon was introduced into the chamber, while a pressurecontroller maintained the pressure at 10mbar. The substrateswere maintained at a temperature of about 570 °C for 5 minutesand then brought back to room temperature