Local Electronic Properties in Carbon Nanotube Hybrids

Hybrid nanostructures are an emerging class of systems that aim to exploit the interactions between different components at the nanoscale. Their raison d'etre is to address problems by combining the best characteristics of their individual parts: such combinations greatly expand the range of functionalities available. Ultimately, we can imagine how the combination of these functionalities in single such nanostructures can be used to create all in one devices, and thus push the miniaturization level to the nanoscale. A single-walled carbon nanotube (SWCNT), where a single graphene sheet is rolled into a hollow tube with a diameter of about 1-2 nm, is a particularly good vehicle to create hybrids: its external surface, ends and inner hollow space can all be made to couple with other systems. Such SWCNT-based hybrids also have the great advantage that the nanotube component of the system is already well characterized both experimentally and theoretically. Using the hollow space inside the nanotube to encapsulate another system is a particularly powerful approach to create functional hybrids, as the following examples illustrate: (1) controlled, environmentally stable, p- and n-doping of nanotubes was recently achieved by encapsulation of organic molecules. This was a very important achievement, as it lifted previous barriers to creating complementary transistors made out of carbon nanotubes. (2). Encapsulation of metallofullerene molecules has been shown to modulate the bandgap (i.e. to locally change the electronic structure) along a nanotube's length. This project aims to synthesize and characterize novel hybrids of SWCNTs with encapsulated inorganic nanowires or tailor-made organometallic complexes (spin- or redox-active) in order to create and identify new functionalities. On one hand this will entail local investigation, with atomic resolution, of fundamental phenomena arising from the interaction of the nanotube with the encapsulate using scanning probe microscopy. On the other hand, it will allow us to explore new devices that integrate an individual such hybrid, one whose morphological structure we will already have determined through prior measurements. Furthermore, we aim to explore for the first time the capability of a new magneto-optical technique to study spin-based interactions of a magnetic encapsulate with the nanotube. This programme will provide a playground for fundamental science. As such, these hybrids will give access to a wealth of physical phenomena, e.g. arising from the interaction of spins located on the encapsulated species and the nanotube's electrons, or from electronic transport where the electron population is spin polarized, or from the synthesis of nanowires so thin that their physical properties become different to those in their bulk counterparts. At the same time, the programme targets the demonstration of device concepts based on such phenomena. Finally, as some of the encapsulation procedures used here are relevant to nanotubes grown directly on a substrate, such hybrids may in the future go beyond being merely demonstrators and reach the stage of broad technological application.