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Polypyrrole (PPy)–Zn₂SnO₄ nanocomposites with different weight percentages (0–20%) of Zn₂SnO₄ were successfully prepared by chemical oxidative polymerization. The prepared nanocomposites were deposited on epoxy glass substrate using a spin coating technique and have been characterized using various techniques such as X-ray diffractometer, field emission scanning electron microscopy (FESEM) and Fourier transform infrared (FTIR) spectrometer. The physicochemical characterization confirmed well-formed dodecylbenzene (DBSA)-doped PPy–Zn₂SnO₄ nanocomposites with granular morphology and high porosity. Among various nanocompositions, DBSA-doped PPy–Zn₂SnO₄ (10 wt.%) nanocomposite was found to be highly sensitive towards NH₃ vapor at room temperature i.e. with a chemiresistive response of 5.44% at 27 ppm with a reasonably fast recovery time of 76 s. Additionally, it shows a linear response and appropriate recovery time at all concentrations of NH₃ vapor. The DBSA-doped PPy–Zn₂SnO₄ nanocomposite response is four times better than pure PPy toward NH₃ vapor at room temperature. Therefore, it is expected that such material with excellent gas sensing properties at room temperature can be used for high-performance NH₃ sensors.

Excellent properties of gallium nitride (GaN) make it an ideal material for realizing gas sensors, especially for ammonia (NH${}_3)$ detection. Although many researchers have pursued to describe the characteristics of GaN-based NH₃ gas sensors by different approaches, few models have been reported. In this paper, with the consideration of the exponential distribution of interfacial states, a model for ammonia concentration detection of GaN gas sensors has been presented. The Poisson equation is applied to model the effect of defect states on the potential. By taking advantage of the current-voltage characteristics, the value of Schottky barrier height can be obtained. The concentration of the adsorbed NH₃ gas is derived by exploiting the surface potential. It indicates that densities of acceptor interfacial trap states are in the order of 10${}^{11}\sim 10^{12}$cm${}^{-2}$eV${}^{-1}$. The current increases with the NH₃ concentration at the same applied voltage. In addition, detailed investigations of physical mechanisms and the analysis of the sensitivity have been depicted. It shows that the sensitivity followed an approximately exponential dependence on NH₃ density. Results compared well with experimental data that verify the proposed model and simulation method.

A novel and uncomplicated method for preparing nanocrystalline zinc oxide by precipitation in a basic aqueous solution with the addition of an oxidation agent and in the presence of flowing gas is presented. Firstly, the value of pH of the starting solution containing the zinc salts is adjusted to a value of 5–5.5. Then, zinc oxide is precipitated by adding NH₄OH and bubbling flowing air. Finally, the precipitated materials are washed with a basic solution (0.01 M NaOH). The X-ray diffraction patterns show nanocrystalline single-phase ZnO with a grain size of 12–14 nm (Scherrer method). No further thermal treatment of the prepared material is required. The surface of the prepared material can be successfully modified. This new route is reproducible and can be used on industrial level.