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Recently, a novel two-dimensional (2D) BC3N2 monolayer has gained a lot of attention due to its graphene-like structure, and it was first reported by using the particle swarm optimization algorithm and ab initio calculations. Combining density functional theory with the non-equilibrium Green's function method, a 2D BC3N2-based nanodevice has been theoretically constructed and the gas sensing performance of the BC3N2 monolayer for inorganic and organic molecules has been extensively investigated. The results revealed that the BC3N2 monolayer remains metallic with thermodynamic stability. Meanwhile, the results of sensing performance analysis show that the inorganic molecules CO, NO, and NO2 and organic molecules C2H2 and HCHO have strong chemical interactions with BC3N2 and were chemically adsorbed onto BC3N2. In contrast, the interactions between NH3, SO2, CH4, C2H4 and CH3OH and BC3N2 are very weak and these molecules adopt physical adsorption. In the case of chemisorption, the electronic transport behaviors of the 2D BC3N2 devices are sensitive to molecules, and the gas sensitivity of BC3N2 is strongly anisotropic, especially for organic C2H2 with the gas sensing ratios from 7.30 to 10.43 (from 2.51 to 2.79) under different bias voltages along the zigzag (armchair) direction. For inorganic molecules, the gas sensing device is not particularly sensitive, and the maximum gas sensing ratio is only 1.36 for CO. Meanwhile, the large anisotropic gas sensitivity can reach up to 2.66/6.22 for electron transport along the armchair and zigzag directions for CO/C2H2 in the BC3N2-based sensing devices. Accordingly, the high gas sensitivity can be disclosed by displaying the scattering state around the Fermi level at different bias voltages during the transport process. As a result, BC3N2 could be used in 2D gas sensing devices, especially for sensing organic molecule C2H2. [ABSTRACT FROM AUTHOR]

The highly sensitive gas sensors used to monitor the decomposition of toxic gases in the dielectric materials of electrical equipment are vital in preventing safety problems arising from corrosion of the equipment. Recently, biphenylene (BPN) has been prepared through surface interpolymer hydrofluorination (HF zipper) reaction, whereas potential gas-sensitive devices based on the BPN monolayer have lacked in-depth investigation. The stable geometries, adsorption energies, interlayer distances, and charge transfers of small molecules of toxic gases (H 2 S, SO 2 , SOF 2 , SO 2 F 2 ) produced by SF 6 chalcogenide molecules of decomposition adsorbed on the original BPN monolayer are systematically researched by using nonequilibrium Green's function methods and density functional theory. The results indicated that all small molecules adsorbed on the BPN monolayer are physisorbed, while the type of adsorption turned from physisorption to chemisorption when BPN carried out adsorption with adsorbing a transition metal atom (TMA). In addition, the characteristics of current-voltage ( I - V ) curves of H 2 S and SO 2 based on the TMA-BPN gas sensors revealed that the currents in BPN-based gas sensors displayed an obvious anisotropy, and the currents in the zigzag direction are larger than that in the armchair orientation regardless of the molecular adsorption cases. Moreover, the difference of currents for TMA-decorated BPN sensors changed more remarkably before and after the adsorption of H 2 S and SO 2 in the zigzag direction. This work offers insights into the design of gas-sensitive devices through the adsorption of small molecules on the TMA-decorated BPN monolayer.

Two-dimensional atomic layer materials, as an important part of the post-Moore era, have recently become an ideal choice for the preparation of high-efficiency, low-power, and miniaturized gas sensors. In this work, our study utilized density functional theory and the nonequilibrium Green's function method to investigate the electronic properties of the pentagonal BN 2 (P-BN 2 ) monolayer, as well as its gas-sensing properties for organic and inorganic gases. We also investigated how defects affect the quantum transport properties of the P-BN 2 -based device. Our findings demonstrate that the CO, H 2 S, NH 3 , SO 2 , C 2 H 5 OH, C 3 H 6 OH, CH 3 OH, and CH 4 undergo physisorption on the P-BN 2 monolayer, while NO, NO 2 , C 2 H 2 , C 2 H 4 , and HCHO undergo chemisorption. Then, we analyzed the impact of gas molecules chemisorbed on the P-BN 2 monolayer on the electronic transport properties of the P-BN 2 -based gas sensor. When these five gas molecules are adsorbed, the current of the P-BN 2 -based gas sensor is greatly reduced. In addition, the effect of defects on the quantum transport properties of the P-BN 2 -based device is investigated. The results indicate that defects of N, B, and BN atoms lead to a decrease in the current of P-BN 2 -based nanodevices. Moreover, both the adsorption of gas molecules and the formation of vacancy defects leading to a decrease in device current can be revealed by the local device density of states near the zero-bias Fermi level, elucidating their microscopic mechanisms. Finally, gas molecules can also cause a decrease in the current of defect systems. These theoretical studies are of great significance for exploring two-dimensional atomic layer materials as high-efficiency gas sensors.

As is well known, Kasier et al first synthesized a cyclic molecule C 18 , as characterized by high-resolution atomic force microscopy, is a polyalkylene structure in which the 18 carbon atoms are linked by alternating single and triple bonds Kaiser et al (2019 Science 365 1299-301). Early studies have found that the C 18 molecule has semiconducting properties, suggesting that a similar straight-chain carbon structure could become a molecular device. Inspired by this, an analysis of spin-resolved electronic transport of nanodevices made by C18 sandwiched between zigzag graphyne nanoribbon leads or zigzag graphene nanoribbon leads presents here. The computational results demonstrate that a good spin-filtering effect, spin rectifying effect and an obvious negative differential resistance behavior in designed model devices can be obtained. Moreover, a stable dual-spin filtering effect or diode effect can be occurred in considered model devices with leads in an antiparallel state. The intrinsic mechanisms of molecular nanodevices are explained in detail by analyzing the transmission spectrum under different bias voltage, local density of states, molecular projection Hamiltonian, Current-Voltage ( I-V ) characteristics, transmission pathways, et al . These results are particularly significant for the development of multifunctional spintronic nanodevices., (© 2023 IOP Publishing Ltd.)

Two-dimensional (2D) magnetic materials are the key to the development of the new generation in spintronics technology and engineering multifunctional devices. Herein, the electronic, spin-resolved transmission, and gas sensing properties of the 2D g-C 4 N 3 /MoS 2 van der Waals (vdW) heterostructure have been investigated by using density functional theory with non-equilibrium Green's function method. First, the g-C 4 N 3 /MoS 2 vdW heterostructure demonstrates ferromagnetic half-metallicity and superior adsorption capacity for gas molecules. The spin-dependent electronic transport of the g-C 4 N 3 /MoS 2 -based nanodevice is obviously regulated by parallel or anti-parallel spin configuration in electrodes, leading to perfect single-spin conduction behavior with a nearly 100% spin filtering efficiency, a negative differential resistance effect, and other interesting electrical transport phenomena. Moreover, g-C 4 N 3 /MoS 2 exhibits directional dependency and strong transport anisotropic behavior under bias windows, indicating that the electric current propagates more easily through the vertical direction than the horizontal direction. The physical mechanisms are revealed and analyzed by presenting the bias-dependent transmission spectra in combination with the projected local device density of states. Finally, the g-C 4 N 3 /MoS 2 -based gas sensor is more sensitive to CO, NO, NO 2 , and NH 3 molecules with the chemisorption type. The strong chemical adsorption leads to the formation of electrons on the local scattering center and ultimately affects the transport properties, resulting in the maximum gas sensitivity reaching 6.45 for NO at the bias of 0.8 V. This work not only reveals that the g-C 4 N 3 /MoS 2 vdW heterostructure with high anisotropy, perfect spin filtering, and outstanding gas sensitivity is a promising 2D material but also provides an insight into the further application in futuristic electronic nanodevices.

Recently, a novel two-dimensional (2D) BC 3 N 2 monolayer has gained a lot of attention due to its graphene-like structure, and it was first reported by using the particle swarm optimization algorithm and ab initio calculations. Combining density functional theory with the non-equilibrium Green's function method, a 2D BC 3 N 2 -based nanodevice has been theoretically constructed and the gas sensing performance of the BC 3 N 2 monolayer for inorganic and organic molecules has been extensively investigated. The results revealed that the BC 3 N 2 monolayer remains metallic with thermodynamic stability. Meanwhile, the results of sensing performance analysis show that the inorganic molecules CO, NO, and NO 2 and organic molecules C 2 H 2 and HCHO have strong chemical interactions with BC 3 N 2 and were chemically adsorbed onto BC 3 N 2 . In contrast, the interactions between NH 3 , SO 2 , CH 4 , C 2 H 4 and CH 3 OH and BC 3 N 2 are very weak and these molecules adopt physical adsorption. In the case of chemisorption, the electronic transport behaviors of the 2D BC 3 N 2 devices are sensitive to molecules, and the gas sensitivity of BC 3 N 2 is strongly anisotropic, especially for organic C 2 H 2 with the gas sensing ratios from 7.30 to 10.43 (from 2.51 to 2.79) under different bias voltages along the zigzag (armchair) direction. For inorganic molecules, the gas sensing device is not particularly sensitive, and the maximum gas sensing ratio is only 1.36 for CO. Meanwhile, the large anisotropic gas sensitivity can reach up to 2.66/6.22 for electron transport along the armchair and zigzag directions for CO/C 2 H 2 in the BC 3 N 2 -based sensing devices. Accordingly, the high gas sensitivity can be disclosed by displaying the scattering state around the Fermi level at different bias voltages during the transport process. As a result, BC 3 N 2 could be used in 2D gas sensing devices, especially for sensing organic molecule C 2 H 2 .

Recently, Dirac material BeN 4 has been synthesized by using laser-heated diamond anvil-groove technology (Bykov et al 2021 Phys. Rev. Lett. 126 175501). BeN 4 layer, i.e. beryllonitrene, represents a qualitatively class of two-dimensional (2D) materials that can be built of a metal atom and polymeric nitrogen chains, and hosts anisotropic Dirac fermions. Enlighten by this discovered material, we study the electronic structure, anisotropic transport properties and gas sensitivity of 2D BeN 4 using the density functional theory combined with non-equilibrium Green's function method. The results manifest that the 2D BeN 4 shows a typical semi-metallic property. The electronic transport properties of the intrinsic BeN 4 devices show a strong anisotropic behavior since electrons transmitting along the armchair direction is much easier than that along the zigzag direction. It directly results in an obvious switching characteristic with the switching ratio up to 10 5 . Then the adsorption characteristics indicate that H 2 S, CO, CO 2 and H 2 molecules are physisorption, while the NH 3 , NO, NO 2 , SO 2 molecules are chemisorption. Among these chemisorption cases, the 2D gas sensor devices show an extremely high response for SO 2 recognition, and the high anisotropy of the original 2D BeN 4 device still maintains after adsorbing gas molecules. Finally, high switching ratio and inorganic gas sensing performance of BeN 4 monolayer could be clearly understood with local density of states, bias-dependent spectra, scattered state distribution. In general, the results indicate that the designed BeN 4 devices have potential practical application in high-ratio switching devices and high gas-sensing molecular devices., (© 2022 IOP Publishing Ltd.)