Gas sensors based on tin oxide (SnO2) and palladium doped SnO2 (Pd:SnO2) active materials are fabricated by a laser printing method, i.e. reactive laser-induced forward transfer (rLIFT). Thin films from tin based metal-complex precursors are prepared by spin coating and then laser transferred with high resolution onto sensor structures. The devices fabricated by rLIFT exhibit low ppm sensitivity towards ethanol and methane as well as good stability with respect to air, moisture, and time. Promising results are obtained by applying rLIFT to transfer metal-complex precursors onto uncoated commercial gas sensors. We could show that rLIFT onto commercial sensors is possible if the sensor structures are reinforced prior to printing. The rLIFT fabricated sensors show up to 4 times higher sensitivities then the commercial sensors (with inkjet printed SnO2). In addition, the selectivity towards CH4 of the Pd:SnO2 sensors is significantly enhanced compared to the pure SnO2 sensors. Our results indicate that the reactive laser transfer technique applied here represents an important technical step for the realization of improved gas detection systems with wide-ranging applications in environmental and health monitoring control.
Amorphous Nb2O5 thin films of three different thicknesses (10, 100, 400 nm) were deposited onto SiO2/Si substrates by reactive sputtering in an Ar–O2 plasma. Thermal treatments were performed at different temperatures between 500 and 1100 °C. The structural and morphological evolution with temperature is shown to be dependent on the film thickness. At 600 °C, the films essentially crystallize in the TT phase. On the thickest films, the T phase also appears. Annealing at higher temperature progressively increases the concentration of the T phase. The films show large flat grains extending over the whole film thickness. In addition, a large number of polyhedral bubbles is present in the 100 and 400 nm films due to Ar atoms trapped during sputtering. After annealing at 1100 °C the Ar bubbles are no longer present and partial diffusion of the films into the substrate is observed. The modification at high temperature, explained either by the M or the H phase, is favored on the thickest films and leads to plate shaped grains.
Raman scattering and infrared reflectivity results are reported for the 2H and 4H polytypes of PbI,. The two polytypes can be clearly distinguished by their vibrational properties. The infrared reflectivity shows a broad reststrahlen band, pointing to the significantly ionic character of this compound.Cet article presente des mesures de diffusion Raman et de reflectivitb infrarouge pour les polytypes 2H et 4H de PbI,. Les deux polytypes se distinguent clairement par leurs proprietes vibratoires. En reflexion infrarouge, une large bande de rayons restants montre le caractere ionique de ce compose.
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