ABSTRACT
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 (H2S, SO2, SOF2, SO2F2) produced by SF6 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 H2S and SO2 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 H2S and SO2 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.
ABSTRACT
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 BN2 (P-BN2) 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-BN2-based device. Our findings demonstrate that the CO, H2S, NH3, SO2, C2H5OH, C3H6OH, CH3OH, and CH4 undergo physisorption on the P-BN2 monolayer, while NO, NO2, C2H2, C2H4, and HCHO undergo chemisorption. Then, we analyzed the impact of gas molecules chemisorbed on the P-BN2 monolayer on the electronic transport properties of the P-BN2-based gas sensor. When these five gas molecules are adsorbed, the current of the P-BN2-based gas sensor is greatly reduced. In addition, the effect of defects on the quantum transport properties of the P-BN2-based device is investigated. The results indicate that defects of N, B, and BN atoms lead to a decrease in the current of P-BN2-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.
ABSTRACT
The electronic transport properties of the four carbon isomers: graphene+, T-graphene, net-graphene, and biphenylene, as well as the gas-sensing properties to the nitrogen-based gas molecules including NO2, NO, and NH3 molecules, are systematically studied and comparatively analyzed by combining the density functional theory with the nonequilibrium Green's function. The four carbon isomers are metallic, especially with graphene+ being a Dirac metal due to the two Dirac cones present at the Fermi energy level. The two-dimensional devices based on these four carbon isomers exhibit good conduction properties in the order of biphenylene > T-graphene > graphene+ > net-graphene. More interestingly, net-graphene-based and biphenylene-based devices demonstrate significant anisotropic transport properties. The gas sensors based on the above four structures all have good selectivity and sensitivity to the NO2 molecule, among which T-graphene-based gas sensors are the most prominent with a maximum ΔI value of 39.98 µA, being only three-fifths of the original. In addition, graphene+-based and biphenylene-based gas sensors are also sensitive to the NO molecule with maximum ΔI values of 29.42 and 25.63 µA, respectively. However, the four gas sensors are all physically adsorbed for the NH3 molecule. By the adsorption energy, charge transfer, electron localization functions, and molecular projection of self-consistent Hamiltonian states, the mechanisms behind all properties can be clearly explained. This work shows the potential of graphene+, T-graphene, net-graphene, and biphenylene for the detection of toxic molecules of NO and NO2.
Subject(s)
Graphite , Nitrogen Dioxide , Carbon , Adsorption , ElectronicsABSTRACT
As is well known, Kasieret alfirst synthesized a cyclic molecule C18, 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 Kaiseret al(2019Science3651299-301). Early studies have found that the C18molecule 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.
ABSTRACT
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-C4N3/MoS2 van der Waals (vdW) heterostructure have been investigated by using density functional theory with non-equilibrium Green's function method. First, the g-C4N3/MoS2 vdW heterostructure demonstrates ferromagnetic half-metallicity and superior adsorption capacity for gas molecules. The spin-dependent electronic transport of the g-C4N3/MoS2-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-C4N3/MoS2 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-C4N3/MoS2-based gas sensor is more sensitive to CO, NO, NO2, and NH3 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-C4N3/MoS2 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.
ABSTRACT
Recently, Dirac material BeN4has been synthesized by using laser-heated diamond anvil-groove technology (Bykovet al2021Phys. Rev. Lett.126175501). BeN4layer, 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 BeN4using the density functional theory combined with non-equilibrium Green's function method. The results manifest that the 2D BeN4shows a typical semi-metallic property. The electronic transport properties of the intrinsic BeN4devices 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 105. Then the adsorption characteristics indicate that H2S, CO, CO2and H2molecules are physisorption, while the NH3, NO, NO2, SO2molecules are chemisorption. Among these chemisorption cases, the 2D gas sensor devices show an extremely high response for SO2recognition, and the high anisotropy of the original 2D BeN4device still maintains after adsorbing gas molecules. Finally, high switching ratio and inorganic gas sensing performance of BeN4monolayer could be clearly understood with local density of states, bias-dependent spectra, scattered state distribution. In general, the results indicate that the designed BeN4devices have potential practical application in high-ratio switching devices and high gas-sensing molecular devices.
ABSTRACT
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.
