| Summary: | Thin-film n-n nanoheterostructures of SnO<sub>2</sub>/TiO<sub>2</sub>, highly sensitive to NO<sub>2</sub>, were obtained in a two-step process: (i) magnetron sputtering, MS followed by (ii) Langmuir-Blodgett, L–B, technique. Thick (200 nm) SnO<sub>2</sub> base layers were deposited by MS and subsequently overcoated with a thin and discontinuous TiO<sub>2</sub> film by means of L–B. Rutile nanopowder spread over the ethanol/chloroform/water formed a suspension, which was used as a source in L–B method. The morphology, crystallographic and electronic properties of the prepared sensors were studied by scanning electron microscopy, SEM, x-ray diffraction, XRD in glancing incidence geometry, GID, x-ray photoemission spectroscopy, XPS, and uv-vis-nir spectrophotometry, respectively. It was found that amorphous SnO<sub>2</sub> films responded to relatively low concentrations of NO<sub>2</sub> of about 200 ppb. A change of more than two orders of magnitude in the electrical resistivity upon exposure to NO<sub>2</sub> was further enhanced in SnO<sub>2</sub>/TiO<sub>2</sub> n-n nanoheterostructures. The best sensor responses R<sub>NO2</sub>/R<sub>0</sub> were obtained at the lowest operating temperatures of about 120 °C, which is typical for nanomaterials. Response (recovery) times to 400 ppb NO<sub>2</sub> were determined as a function of the operating temperature and indicated a significant decrease from 62 (42) s at 123 <b>°</b>C to 12 (19) s at 385 <b>°</b>C A much smaller sensitivity to H<sub>2</sub> was observed, which might be advantageous for selective detection of nitrogen oxides. The influence of humidity on the NO<sub>2</sub> response was demonstrated to be significantly below 150 <b>°</b>C and systematically decreased upon increase in the operating temperature up to 400 <b>°</b>C.
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