Metal-Oxide-Semiconductor Nanostructure/NiO Microparticle Heterojunctions Formed on Metallic Foils for Sensitive...

Chemiresistive metal-oxide-semiconductor (MOS) sensors for routine health and environmental monitoring are required to detect ion species in solutions simply and highly sensitively. In this study, p-p and p-n heterojunctions, formed by using facile processing, were introduced to enhance the detection sensitivity of MOS-based ion sensors. NiO microparticle-bearing CuO _x -, ZnO-, and SnO _x -based ion sensors were thermally and hydrothermally fabricated on metallic foils. On the MOS nanostructures, NiO microparticles affected the sensitivity of chloride, sodium, and calcium ion detection in solutions. The ZnO sensor with high-number density NiO microparticles demonstrated an excellent detection sensitivity of 639 at 30 °C in a 1 ppm chloride ion solution. These results suggest that bulk and surface reactions between the MOS and ionic solutions were enhanced by p-p and p-n heterojunctions, lowering activation energies. MOS/NiO p-p and p-n heterojunctions fabricated using the proposed process on metallic foils could contribute to the practical application of chemiresistive MOS sensors for detecting ionic solutions.