Free-radical gases on two-dimensional transition-metal disulfides (XS2, X = Mo/W): robust half-metallicity for efficient nitrogen oxide sensors

Modeling a multiple-chain emeraldine gas sensor for NH3 and NO2 detection

This paper describes atomistic device models of a multiple-chain polyaniline (PANI) gas sensing component, utilizing the non-equilibrium Green's functions formalism. The numerical results are compared with experimental data of ammonia and nitrogen dioxide detection. Multiple molecules of PANI in the form of emeraldine salt were studied with more than one absorbed molecule of ammonia or nitrogen dioxide. From the I-V characteristics of the system with and without adsorbed gas molecules for gas concentrations of 3, 6, 9, and 12 ppm, the effective resistance changes, (R - R ₀)/R ₀, were obtained and compared with experimental results. A good agreement with the measured values was obtained. In summary, PANI as emeraldine salt was numerically modeled for several adsorbed gas concentrations, several gas configurations, and different PANI molecule positions, including carrier hopping between them. The results are comparable to the experiment and show good properties for the application as gas sensor device for NH₃ detection and rather good properties for NO₂ detection.

Prediction of Co and Ru nanocluster morphology on 2D MoS2 from interaction energies

Layered materials, such as MoS₂, have a wide range of potential applications due to the properties of a single layer, which often differ from the bulk material. They are of particular interest as ultrathin diffusion barriers in semiconductor device interconnects and as supports for low-dimensional metal catalysts. Understanding the interaction between metals and the MoS₂ monolayer is of great importance when selecting systems for specific applications. In previous studies the focus has been largely on the strength of the interaction between a single atom or a nanoparticle of a range of metals, which has created a significant knowledge gap in understanding thin film nucleation on 2D materials. In this paper, we present a density functional theory (DFT) study of the adsorption of small Co and Ru structures, with up to four atoms, on a monolayer of MoS₂. We explore how the metal-substrate and metal-metal interactions contribute to the stability of metal clusters on MoS₂, and how these interactions change in the presence of a sulfur vacancy, to develop insight to allow for a prediction of thin film morphology. The strength of interaction between the metals and MoS₂ is in the order Co > Ru. The competition between metal-substrate and metal-metal interaction allows us to conclude that 2D structures should be preferred for Co on MoS₂, while Ru prefers 3D structures on MoS₂. However, the presence of a sulfur vacancy decreases the metal-metal interaction, indicating that with controlled surface modification 2D Ru structures could be achieved. Based on this understanding, we propose Co on MoS₂ as a suitable candidate for advanced interconnects, while Ru on MoS₂ is more suited to catalysis applications.

Two-dimensional graphitic carbon nitride (g-C4N3) for superior selectivity of multiple toxic gases (CO, NO2, and NH3)

Using first principles calculations, we investigated the possibility of selecting multiple toxic gases using one substrate material. Here, we explored the transport property of H₂, N₂, O₂, CO, CO₂, NO_2, and NH₃ gas molecules on two-dimensional graphitic carbon nitride (2D g-C₄N₃). The homonuclear molecule such as H₂, N₂, and O₂ has very weak adsorption energy (equal to or less than 0.1 eV) and also CO₂ has an adsorption energy of 0.23 eV. In the typical toxic gas molecule adsorption systems, we found an appreciable charge transfer. In CO and NH₃ adsorption systems, the charge transfer of 0.397 and 0.418 electrons from the molecule to the substrate was found, while the NO₂ molecule gained 0.124 electrons from the substrate. Due to this large amount of charge transfer, we obtained large adsorption energies of 4.57, 1.29, and 1.93 eV in CO, NO_2, and NH₃ systems. Moreover, through the I-V curve calculations, we found large difference in the current. The calculated current was 21, 13.11, and 16.16 μA for CO, NO_2, and NH₃ systems at the bias voltage of 0.5 V. Our results imply that the 2D g-C₄N₃ can be a superior substrate material for sensing of multiple toxic gases.