| Carbon nanotubes (CNTs) are molecular wires that exhibit a number of exceptional chemical, electronic, and mechanical properties. Investigating on these properties and exploring conceptual usages of these properties in devices are conducted by using simulation tools ranging from molecular dynamics, tight-binding, to ab-initio simulations. Four major aspects of carbon nanotube devices are studied.; First, we investigate the mechanism of using CNTs to detect the presence of chemical gases such as NO2, NH3, and O2. We discover that the process of NO2 gas sensing is not simply the process of adsorption and desorption of NO2 gas on the CNT surface, but rather it involves the complex process of NO2 gas molecule's reaction on the CNTs surface, which produce NO and NO3 molecules. These findings show that NO3 is the real agent behind the slow recovery of SWCNTs as sensing devices. We also conduct analysis on molecular adsorption on charged SWCNT by electric field manipulation.; Secondly, to detect the presence of CO and water molecules that have long evaded the detection of intrinsic carbon nanotubes as sensing devices, we propose the design of a new breed of nanotube based sensor devices. These devices are developed by substitutional doping of the so-called impurity atoms (such as Boron, Nitrogen atoms) into intrinsic single wall carbon nanotubes, or by using composite BxCyNz nanotubes.; Thirdly, the effects of flattening and bending on the size of the band gap in CNT are examined. Increasing cross-sectional flattening is found to initially close the band gap in semiconducting tubes, while ultimately re-opening the gap at high degrees of flattening. Using the properties of deformed nanotubes, a simple design for a CNT based quantum well device is proposed.; Finally, interactions of metal atoms (Al, Ti) with semiconducting single walled carbon nanotube (SWCNT) are investigated. Comparison of the energetics of these metal atoms on (8,0) CNT surface shows significant differences in binding energy and diffusion barriers. These differences provide us with an explanation of why most of metal atoms (such as Al) form discrete particles on nanotube, while titanium atoms form continuous nanowires. |
