Resumo:
Remote detection of explosive materials has become a priority to ensure airport safety. Explosives are easily hidden in luggage, mail, vehicles, aircraft as well as on people, and contain less and less metal parts making their detection by means of metal detectors highly unreliable. Although there are some analytical techniques available to detect explosives, they involve bulky equipment and take long time to report their results. For this reason, highly sensitive, portable chemical sensors showing fast response to explosive analytes or their fingerprint gases are being developed as an alternative. In the present work, metal-oxide sensors containing cupric oxide as sensing material on top of platinum interdigitated electrodes were constructed onto alumina substrates. The sensing material was obtained following two different processing routes: thermal oxidation of sputtered copper metal and hydrothermal growth from a water solution of copper nitrate, obtaining different morphologies. Sensors were dynamically tested in order to detect hydrogen gas in humid air between room temperature and 400◦ C. Sensors showed responses at testing temperatures as low as 200◦ C. Results indicated that sensing materials with grain sizes close to the space-charge region width have higher sensitivity to the presence of hydrogen gas and show faster response. The sensing mechanism in terms of inter-granular potential barriers was explained as an alternative to the sensing mechanisms found in the literature
