Room temperature highly toxic NO_2 gas sensors based on rootstock/scion nanowires of SnO_2/ZnO, ZnO/SnO_2, SnO_2/SnO_2 and, ZnO/ZnO

摘要

Grafted structures between SnO_2 and ZnO nanowires were realized in a two-step process of growth. First, the rootstocks of SnO_2 or ZnO nanowires were synthesized by thermal evaporation technique. Second, a thin Au layer was sputter deposited on the sample and synthesis of nanowire scions of ZnO or SnO_2, respectively, on the rootstocks was realized by thermal evaporation technique again. In both growth steps, SnO_2 powder or a mixture of ZnO and carbon powders was use as source materials for the synthesis. Different rootstock/scion combinations of SnO_2/ZnO, ZnO/SnO_2 nanowires (called heterostructures) and ZnO/ZnO, SnO_2/SnO_2 nanowires (called homostructures) were synthesised. The fabricated grafted nanowires were examined by field-emission scanning electron microscope and their compositions were analyzed by energy dispersive spectroscopy and X-ray diffraction analysis. The test results indicate that this type of nanostructure material is very promising for NO_2 gas sensing at ppt level at room temperature. Among the fabricated structures the SnO_2/ZnO nanowires showed the best sensing performance with the high sensitivity and fast response and recovery time. We also discussed the gas sensing mechanism of the fabricated sensors based on the band diagram.