Computational modeling of the electrical sensing properties of single wall carbon nanotubes

Abstract

Carbon nanotubes (CNTs) are an ever expanding field of research due to their unique physical and electrical properties since their discovery. Based on how they are cut and rolled from a graphene sheet, carbon nanotubes can exhibit semiconducting or metallic behavior. These electrical properties can change dramatically as molecules bond to their highly reactive surfaces. These property changes make CNTs very promising materials for bio-chemical sensing applications. In this work, the electrical properties of (8,0) single-wall carbon nanotubes in the presence of NO2 and NH3 have been studied and modeled using density functional tight binding theory and non-equilibrium Greens functions through the DFTB+ program. Explanation of how this initial modeling was performed, as well as literature review, results, and analysis are all contained within this work. The results obtained on the modeled CNTs exposed to NO2 and NH3 as dopant molecules under vacuum conditions appear to show conventional semiconductor behavior when varying an applied gate voltage. Here, NO2 is shown to function as a hole donating molecule, decreasing the conduction of the system, while NH3 is shown to function as an electron donating molecule, causing opposite effects on conductivity. The DFTB+ modeling program used demonstrates fast calculation times for reasonably sized systems and small bias voltages used. Using this program and the work performed herein, larger, more complicated systems with more and different dopant molecules could easily be modeled.