Here, we show that the aerosol assisted chemical vapor deposition process is suitable for growing single crystalline tungsten oxide nanowires loaded with nickel oxide nanoparticles.

The properties of multi-wall carbon nanotubes decorated with iridium oxide nanoparticles (IrO_x-MWCNTs) are studied to detect harmful gases such as nitrogen dioxide and ammonia. IrO_x nanoparticles were synthetized using a two-step method, based on a hydrolysis and acid condensation growth mechanism. The metal oxide nanoparticles obtained were employed for decorating the sidewalls of carbon nanotubes. Iridium-oxide nanoparticle decorated carbon nanotube material showed higher and more stable responses towards NH₃ and NO₂ than bare carbon nanotubes under different experimental conditions, establishing the optimal operating temperatures and estimating the limits of detection and quantification. Furthermore, the nanomaterials employed were studied using different morphological and compositional characterization techniques and a gas sensing mechanism is proposed.

Indium oxide octahedral nanopowders were obtained from an ionic precursor compound after an oxidation process conducted under a low-oxygen atmosphere. This method was found to produce contamination-free indium oxide nanomaterial with very similar morphological and crystalline properties to the one produced by vapor-phase transport, but at significantly lower temperatures and higher yield. The as-synthesized indium oxide was mixed to an organic vehicle and microdrop deposited to form a film bridging the interdigitated silver electrodes patterned on top of a flexible, polyimide (Kapton^®), substrate. The gas sensing properties of the flexible chemoresistors towards ammonia vapors, hydrogen, and nitrogen dioxide were investigated. It was found that these sensors were remarkably sensitive to nitrogen dioxide at a low operating temperature of 150 °C. These results are consistent with the performance of vapor-phase transport synthesized indium oxide octahedra sensors on rigid, ceramic substrates. Therefore, the results presented here pave the way for the mass production of inexpensive gas sensors onto flexible substrates via additive manufacturing.

We report on a new hybrid heterojunction gas-sensitive device by combining a molecular material with a metal oxide. WO₃ was synthesised via an aerosol-assisted chemical vapour deposition technique from a tungsten hexacarbonyl precursor. Onto an inorganic film, LuPc₂ was vacuum evaporated. The morphology of the WO₃–LuPc₂ hybrid films is dominated by the morphological features of the tungsten oxide film, as shown by scanning electron microscopy and atomic force microscopy. Raman spectroscopy of the device confirms the presence of both materials. The non-linear I–V characteristics demonstrate the existence of an energy barrier at the interface between the inorganic and molecular materials. The interfacial phenomenon was confirmed by means of impedance spectroscopy. Finally, the positive response to ammonia confirms the n-type nature of the charge carriers responsible for the transport properties through the device, in accordance with the n-type conductivity of WO₃. This response is fully reversible whatever the relative humidity value in the range 10–70% r_h. Even though the current is shifted when the relative humidity decreases, ammonia sensitivity remains almost unchanged (2.5 nA ppm⁻¹) for r_h ranging from 30 to 50%. It is worth noting that the present device operates at room temperature with excellent reversibility and stability, showing the lowest limit of detection for ammonia ever reported for this device architecture (250 ppb).