The application of novel core-shell nanowires composed of ZnGa₂O₄/ZnO to improve the sensitivity of NO₂ gas sensors is demonstrated in this study. The growth of ZnGa₂O₄/ZnO core-shell nanowires is performed by reactive evaporation on patterned ZnO:Ga/SiO₂/Si templates at 600 °C. This is to form the homogeneous structure of the sensors investigated in this report to assess their sensitivity in terms of NO₂ detection. These novel NO₂ gas sensors were evaluated at working temperatures of 25 °C and at 250 °C, respectively. The result reveals the ZnGa₂O₄/ZnO core-shell nanowires present a good linear relationship (R² > 0.99) between sensitivity and NO₂ concentration at both working temperatures. These core-shell nanowire sensors also possess the highest response (<90 s) and recovery (<120 s) values with greater repeatability seen for NO₂ sensors at room temperature, unlike traditional sensors that only work effectively at much higher temperatures. The data in this study indicates the newly-developed ZnGa₂O₄/ZnO core-shell nanowire based sensors are highly promising for industrial applications.

Vertically well aligned P-doped ZnO nanowires were prepared on ZnO–Ga/glass templates at 550 °C by reactive evaporation without metal catalysts and the nanowires were found to be single crystalline with the würtzite structure, oriented in the c-axis direction; the P-doping shortened the physical lengths of the ZnO nanowires without changing their diameter, and furthermore, the introduction of P atoms resulted in a much weaker and broader ZnO band edge emission.

High-density, single-crystal, vertically aligned, Al-doped ZnO nanowires with an Al content of 1.05 atom % were synthesized on <mml:math display="inline"><mml:mrow><mml:mi>ZnO</mml:mi><mml:mo>:</mml:mo><mml:mi>Ga</mml:mi><mml:mo>∕</mml:mo><mml:mtext>glass</mml:mtext></mml:mrow></mml:math>ZnO:Ga∕glass templates at 550°C. Although introducing Al did not change the physical dimensions of the ZnO nanowires, the lattice constant increased by 0.25% and the optical properties of the ZnO nanowires were degraded. However, the experimental results also showed that the threshold emission field can be significantly decreased from 16 to <mml:math display="inline"><mml:mrow><mml:mn>10</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">V</mml:mi><mml:mo>∕</mml:mo><mml:mi>μ</mml:mi><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:math>10V∕μm , and the work function, ϕ, can also be reduced from 5.3 to 3.39 eV by introducing Al atoms into the ZnO nanowires.

A novel fiber-optic probe based on reflection-based localized surface plasmon resonance (LSPR) was developed to quantify the concentration of hydrofluoric acid (HF) in aqueous solutions. The LSPR sensor was constructed with a gold nanoparticle-modified PMMA fiber, integrated with a SiO₂ sol-gel coating. This fiber-sensor was utilized to assess the relationship between HF concentration and SiO₂ sol-gel layer etching reduction. The results demonstrated the LSPR sensor was capable of detecting HF-related erosion of hydrofluoric acid solutions of concentrations ranging from 1% to 5% using Relative RI Change Rates. The development of the LSPR sensor constitutes the basis of a detector with significant sensitivity for practical use in monitoring HF solution concentrations.