A Surface Acoustic Wave (SAW) hydrogen sensor with a Pd/ZnO bilayer structure for room temperature sensing operation has been obtained by Pulsed Laser Deposition (PLD). The sensor structure combines a Pd layer with optimized porosity for maximizing mass effects, with the large acoustoelectric effect at the Pd/ZnO interface. The large acoustoelectric effect is due to the fact that ZnO has a surface conductivity which is highly sensitive to chemisorbed gases. The sensitivity of the sensor was determined for hydrogen concentrations between 0.2% and 2%. The limit of detection (LOD) of the bilayer sensor was about 4.5 times better than the single ZnO films and almost twice better than single Pd films.

The current-voltage characteristics of epitaxial ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{10+\mathrm{\delta }}$ films in zero applied magnetic field were investigated in a temperature interval of about 20 K below the mean-field critical temperature ${\mathit{T}}_{\mathit{c}0}$=110.4 K. Despite the large anisotropy (γ≊200), the data clearly indicate the occurrence of a finite critical-current density, resulting from the Josephson coupling between the (${\mathrm{CuO}}_2$ ${)}_3$ layers. By analyzing the shape of the current-voltage characteristics in terms of quasi-two-dimensional vortex unbinding, it was found that this ‘‘intrinsic’’ critical-current density vanishes well below ${\mathit{T}}_{\mathit{c}0}$, just above the hypothetical Kosterlitz-Thouless transition temperature (${\mathit{T}}_{\mathrm{KT}}$≊94.8 K). This is in agreement with Monte Carlo simulations, suggesting a vortex-fluctuation-induced layer decoupling in the case of quasi-two-dimensional superconductors. However, close to the layer decoupling temperature, an excess dissipation beyond the quasi-two-dimensional vortex unbinding model appears. This excess dissipation was attributed to the excitation of three-dimensional vortex structures close to the resistive transition.

Surface Acoustic Wave (SAW) sensors with several types of polymer sensing films, containing embedded Fe₃O₄ nanoparticles (NPs) with various dimensions and concentrations, were studied. A sensor with a sensing film consisting of the polymer alone was used for comparison. NPs with a mean diameter of 7 nm were produced by laser ablation with 5 ns pulse durations, and NPs with 13 nm diameters were obtained with a laser having 10 ps pulse durations. The properties of the Surface Acoustic Wave sensors with such sensing films were analyzed. Their response (frequency shift, sensitivity, noise and response time) to three different volatile organic components (VOCs) at various concentrations were compared with one another. The frequency shift and sensitivity increased with increasing NP concentration in the polymer for a given NP dimension and with decreasing NP diameter for a given concentration. The best results were obtained for the smallest NPs used. The SAW sensor containing 7 nm NPs had a limit of detection (LOD) of 65 ppm (almost five times better than the sensor with polymer alone), and a response time of about 9 s for ethanol.