Theoretical Studies Of Boron-doped Carbon Nanotube Structure And Gas-sensing Properties

The viability of single-walled carbon nanotube (SWCNT) as sensors has been demonstrated for detecting gas molecules by determining the sensitive conductance changes of nanotubes before and after the absorption of those molecules. Carbon nanotubes are perfect materials as gas sensors due to their short response times, high sensitivities to gaseous molecules, and low reaction temperature. However, these devices can not detect molecules which do not bind to or adsorb weakly on the surface of intrinsic SWCNTs, such as toxic molecules (e.g., CO, NO, and HCN), water molecules and biomolecules. To overcome this problem, recent interesting propositions have been presented based on functionalized SWCNTs using physical or chemical method. So gas molecules can be detected by these functionalized carbon nanotubes. In this thesis, boron doped (B-doped) single-walled carbon nanotubes are investigated using theoretical calculations as sensor models to detect the presence of cyanides and ammonia. The present results provide guidance to experimental scientists in developing CNT-based chemical sensors.We perform density function theory (DFT) calculations on nanotube systems, using Perdew and Wang's local density approximation (LDA) with a double numerical basis set including d-polarization function (DND). All the calculations carry on DMol~3 program. We first calculate the binding energy (E_b), energy gap (E_g) between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), and charge-transfer (Q_T) between a gas molecule and a SWCNT. To evaluate the electronic properties of intrinsic and doped SWCNT systems, we also determine their electronic densities of state (DOSs).Taking (8, 0) and (5, 5) carbon nanotubes as a example, we investigate the effection of boron doping on carbon nanotubes. The conclusions indicate that the properties of carbon nanotubes change dramatically after doping with boron atoms, which enhance the activity of nanotubes. Therefor we deduce that doping with boron can enhance the sensitivity of carbon nanotubes.We perform density function theory (DFT) calculations on cyanide-nanotube...