SnO/TiO Thin Film n-n Heterostructures of Improved Sensitivity to NO.

Thin-film n-n nanoheterostructures of SnO/TiO, highly sensitive to NO, were obtained in a two-step process: (i) magnetron sputtering, MS followed by (ii) Langmuir-Blodgett, L-B, technique. Thick (200 nm) SnO base layers were deposited by MS and subsequently overcoated with a thin and discontinuous TiO 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 films responded to relatively low concentrations of NO of about 200 ppb. A change of more than two orders of magnitude in the electrical resistivity upon exposure to NO was further enhanced in SnO/TiO n-n nanoheterostructures. The best sensor responses R/R were obtained at the lowest operating temperatures of about 120 °C, which is typical for nanomaterials. Response (recovery) times to 400 ppb NO were determined as a function of the operating temperature and indicated a significant decrease from 62 (42) s at 123 °C to 12 (19) s at 385 °C A much smaller sensitivity to H was observed, which might be advantageous for selective detection of nitrogen oxides. The influence of humidity on the NO response was demonstrated to be significantly below 150 °C and systematically decreased upon increase in the operating temperature up to 400 °C.