Abstract
Present day semiconductor devices are rapidly approaching their physical limits, prompting an increasing number of researchers across multiple disciplines to attempt devising innovative ways for decreasing the size and increasing the performance of critical features in microelectronic circuits. One possible route is based on the idea of using molecules and molecular structures as functional electronic devices. Carbon nanotubes may provide one of the best materials for molecular electronic devices as they present a flexible and well structured architecture. However, practical realizations of new nanotube-based electronic devices hinge on a number of outstanding problems, such as the capability of achieving large-scale air-stable and controlled doping. Amphoteric doping by encapsulating suitable organic molecules inside of nanotubes may hold tremendous promise in this respect. In order to investigate and optimize the electronic transport properties in carbon nanotubes doped with organic molecules we have performed large-scale quantum electronic structure calculations coupled with a Green's function formulation for determining the conductance. By implementing this hybrid computational approach for examination of the electronic properties of molecular-based structures, an efficient and accurate procedure has been demonstrated for studying the effects of amphoteric doping of carbon nanotubes. With this method, a computational framework for the optimal design of nanotube based electronic devices is becoming routinely accessible. Results from our calculations suggest that the electronic structure of a carbon nanotube can be easily manipulated by encapsulating appropriate organic molecules leading to charge transfer processes that induce efficient n- and p-type doping of the carbon nanotube. Even though a molecule may cause n- or p-doping, we have found it to generally have minor effects on the transport properties of the nanotube as compared to a pristine tube.
