We report the fabrication of gas sensor elements by pulsed laser deposition in air at atmospheric pressure. We focused our attention on metal-oxide semiconductors, namely, SnO2, TiO2 and MoO3 and studied the samples’ structure and morphology. The deposition technology applied leads to the formation of nanostructures composed of nanoparticles and nano-aggregates. We report preliminary results on the gas-sensing properties of the metal-oxide nanostructures. The sensors were exposed to CO, acetone and ethanol, with the TiO2 nanostructure demonstrating the highest response to CO exposure.
In this work, we present fabrication of ZnO nanostructures by pulsed laser deposition in air at atmospheric pressure. The use of this technology leads to formation of nanostructures composed by nanoparticles and nanoaggregates. These nanostructures possess a large surface-to-volume ratio, which makes them suitable for gas-sensor application. The samples were exposed to NH3 and the effect was investigated of light irradiation on the gas response and recovery time of the sensor element. It was found that the response of the sensor element increases even by irradiation by sunlight. The gas sensing properties of the ZnO nanostructures were compared when irradiated by light of different wavelengths.
Different types of ZnO nanostructures were fabricated on metal (Au or Ag) coated silicon substrates by applying the pulsed laser deposition (PLD) method. The samples were prepared at substrate temperatures in the range of 300 – 650 °C, oxygen pressure of 5 Pa, and laser fluence ≤ 1 J.cm-2– process parameters usually used for thin-film deposition. The metal layer is essential for the preparation of nanostructures. The nanostructures grown at different substrate temperatures showed obvious morphological differences. The substrate temperature increase led to changes in the morphology of the nanostructures from nanowhiskers to nanowalls when a thin Au layer was used. It was also observed that the type and thickness of the metal layer affect the morphology of the nanostructure.
The composite nanostructures of double layer, multilayer and mosaic Ag/ZnO containing nano-sized particles have been produced by laser deposition and annealing procedures. The samples are investigated and the results indicated that laser annealing of Ag or Ag/ZnO layer is a feasible method to tune the optical properties of the nanostructures. Their morphology and optical absorption were investigated as a function of annealing regime and preparation procedure, leading to different silver arrangement. All annealed samples showed surface plasmon resonance (SPR) properties. The red shifted SPR was observed with the increase of the number of layers and is associated with the reduction of the interparticle distance. The absorption minimum of a mosaic samples broadens towards the longer wavelengths with reducing the thickness, due to the broader NPs size distribution. A ZnO excitonic feature visible in the spectra of double layer and multilayer structures disappear in the spectrum of a mosaic sample. The X-ray photoelectron spectroscopy was used to study the composition and chemical state of the double layer Ag/ZnO nanocomposites on the surface and in depth. The binding energy of Ag3d5/2 shifts to the lower values compared to the pure metallic Ag due to the interaction between Ag and ZnO.
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