碳化硅纳米管二氧化氮气敏传感器的工作机理

The working mechanism of sensors plays an important role in their simulation and design, which is the foundation of their applications. A model of a nanotube NO2 gas sensor system is established based on an （8, 0） silicon carbide nanotube （SiCNT） with a NO2 molecule adsorbed. The transport properties of the system are studied with a method combining density functional theory （DFT） with the non-equilibrium Green＇s function （NEGF）. The adsorbed gas molecule plays an important role in the transport properties of the gas sensor, which results in the formation of a transmission peak near the Fermi energy. More importantly, the adsorption leads to different voltage current characteristics of the sensor to that with no adsorption; the difference is large enough to detect the presence of NO2 gas.     

Adsorption of oxygen molecular on pristine and defected SiC nanotubes

The structural and electronic properties of oxygen molecular adsorbed on the exterior surface of pristine and N_C or B_C defected (10,0) or (6,6) SiCNT have been investigated systematically using the first-principles projector-augmented wave potential within the density-functional theory under the generalized-gradient approximation. We find that for both pristine tubes the preferred adsorption sites of the O₂ molecule are above and nearly parallel to armchair Si-C bond whether physisorption or chemisorption. The strong chemical interaction between O₂ molecule and tube leads to not only a vanishing in magnetism of the O₂ molecule but also an outward relaxation of the underlying Si-C bond. The C atom substituted by N or B atom assists O₂ molecule adsorption above and nearly parallel to zigzag Si-N or Si-B bond as well as imparts a metallic character on the SiCNTs with higher concentration of the defects or a magnetism on the SiCNTs with lower concentration of the defects. Therefore, a combination of N or B doping followed by exposure to air may be an effective way to tune the electronic properties of the semiconducting SiCNTs. Furthermore, the lower binding energies for the pair of oxygen interstitials chemisorbed on N_C or B_C defected (10,0) or (6,6) SiCNT show that the oxygen molecule will dissociate to the pair of oxygen interstitials at the sidewall of N_C or B_C defected SiCNTs.     

Theoretical study on transport properties of a BN co-doped SiC nanotube

We investigate the electronic transport properties of silicon carbide nanotubes (SiCNT) in presence of both boron (B) and nitrogen (N) impurities. The results show that co-doping BN impurities suppresses the important negative differential resistance (NDR) property. NDR suppression is attributed to the introduction of new electronic states near the Fermi level followed by weak orbital localization. BN co-doping results in exponential current-voltage (I-V) characteristics which is in contrast to linear I-V characteristics for individual boron and nitrogen doped SiCNTs. HOMO has no contribution from B impurity, whereas, LUMO has contribution from N impurity at low and high bias.     

新型NO2化学传感器:碳化硅纳米管

气体吸附对碳化硅纳米管的电子结构的影响是理解碳化硅纳米管气敏传感器工作机理的基础.基于密度泛函理论,利用CASTEP软件包计算NO₂气体吸附前后的碳化硅纳米管的结构及其电子结构.结果表明,NO₂气体与碳化硅纳米管间形成了稳定的吸附,并明显的增强了碳化硅纳米管的导电特性.碳化硅纳米管是制备气体传感器的理想材料之一,为开发应用于NO₂气体检测的碳化硅纳米管提供必要的理论支持.     

Sensing and catalytic decomposition of hydrogen peroxide by silicon carbide nanotubes: A DFT study

In this study, by carrying out detailed density functional theory calculations, we investigate the adsorption and stepwise decomposition of hydrogen peroxide (H₂O₂) over (6,0) and (7,0) zigzag silicon carbide nanotubes (SiCNTs). The results indicate that the H₂O₂ can be adsorbed on the exterior surface of the SiCNTs with noticeable adsorption energies and charge transfers. To gain insight into the catalytic activity of the surface, the interaction between the H₂O₂ and SiCNT is analyzed by detailed electronic analysis such as adsorption energy, charge density difference and activation barrier. The decomposition of H₂O₂ into O₂ and H₂ species can be viewed as the kinetically preferred reaction pathway for dehydrogenation of hydrogen peroxide over SiCNTs. There is also a curvature effect on the dehydrogenation kinetics of hydrogen peroxide, that small diameter SiCNTs with large curvature would be beneficial for decomposition of H₂O₂. © 2015 Wiley Periodicals, Inc.     

Theoretical study on the effect of dopant positions and dopant density on transport properties of a BN co-doped SiC nanotube

We investigate the effect of dopant (boron ‘B’–nitrogen ‘N’) position and density on electronic transport properties of a BN co-doped silicon carbide nanotube (SiCNT). The results show an increase in conductance when both BN impurities are far in space from each other. Orbital delocalization and appearance of new electronic states around Fermi level contribute to the current when this spacing is increased. On the other hand, a reduction in SiCNT conductivity was observed when BN dopant density was increased. This is attributed to the electronic states moving away from the Fermi level and orbital localization at higher bias voltages.     

Working mechanism of a SiC nanotube NO_2 gas sensor

The working mechanism of sensors plays an important role in their simulation and design, which is the foundation of their applications. A model of a nanotube NO_2 gas sensor system is established based on an (8, 0) silicon carbide nanotube (SiCNT) with a NO_2 molecule adsorbed. The transport properties of the system are studied with a method combining density functional theory (DFT) with the non-equilibrium Green's function (NEGF). The adsorbed gas molecule plays an important role in the transport properties of the gas sensor, which results in the formation of a transmission peak near the Fermi energy. More importantly, the adsorption leads to different voltage current characteristics of the sensor to that with no adsorption; the difference is large enough to detect the presence of NO_2 gas.     

Silicon carbide nanotubes (SiCNTs) serving for catalytic decomposition of toxic diazomethane (DAZM) gas: a DFT study

In the present study, the adsorption and decomposition of diazomethane (DAZM) on the surface of (6,0) zigzag silicon carbide nanotube (SiCNT) are investigated using density functional theory calculations. The geometry structures of the three stable configurations, adsorption energies and electronic properties of DAZM adsorption on the surface of SiCNT are investigated. It was found that the DAZM molecule is decomposed over the surface of (6,0) SiCNT with activation energy (E_act) of 0.523 eV. The curvature effect on the adsorption energies of the DAZM molecule is also considered by studying (5,0) and (7,0) SiCNTs. The results display that DAZM adsorption over smaller diameter of SiCNT is thermodynamically more favourable than larger one.