Non-covalent interactions in carbon nanotubes

In this project we suggest to study noncovalent interactions between single wall carbon nanotubes, between concentric multiwall carbon nanotubes and between the inside of the tubes and carbon cages or other molecules which will be established inside the cage. Such interactions were claimed to be rather strong on the one side since nanotubes are observed to aggrgate, into bundles or very stable multiwall hoses. Transport experiments demonstrated on the other side a current flow only through the outermost walls of concentric tubes with hardly any intertube leaking. Experiments will be carried out by light scattering spectroscopy in combination with analyses by scanning probe microscopy. Very special modes observable by the light scattering process allow to draw information on the tube- tube interaction and on the tube-cage interaction. Such modes have been observed sofar only in single wall carbon nanotubes but are expected to be also observable in multiwall. tubes if the thickness of the tubes can be reduced to a small enough value. Tube-tube interactions in isomorphous double wall tubes of boron nitride are an other target of the proposed research work. The project will be carried out in cooperation with research institutes in USA and in Germany from where special sample material will be provided. The results of the research work will provide new insight into macroscopic quantum phenomena in carbon nanotubes, in the possibilities to prepare material of individual single wall nanotubes, and in the possibilities to use fullerene filled nanotubes for information storage.

In the research project the non-covalent interaction between carbon nanotubes and other new carbon nänophases such as e. g. fullerenes was investigated by light scattering, scanning probe microscopy, and theoretical calculations. The geometrical arrangement of the tubes was either in bundles or as concentric cylinders in double wall carbon nanotubes. The strong interaction between tubes and fullerene molecules was resulted in a condensation of the cage molecules into the carbon nanotubes after the latter were opened by chemical treatment. This filling process can be performed either at elevated temperature from the vapour phase or from solution at almost room temperature. Consequently, by the latter process temperature sensitive molecules can be inserted. As an example two special molecules which carry a spin were investigated. One of them is C6o into which atomic nitrogen was encapsulated. Sinee the nitrogen is shielded from its environment, it keeps its spin S = 3/2 even alter filling the tubes with the N-C60 system. After the filling process linear chains of nitrogen spins are obtained. This was demonstrated by electron spin resonance experiments. A similar filling experiment could be performed with a fullerene molecule where one carbon of the cage was substituted by nitrogen. This substitution resulted in the cage molecule C59N. Sinee C59N is a radical and as such very reactive, an organic side group had to be attached first. This group was thermally split off alter the C59N-sidegroup complex had entered the tube. In several additional experiments the fullerene molecules were heated to temperatures as high as 1550 C. This led to an as yet not fully understood fusion of the fullerene cages to a new inner shell tube with a high degree of perfection. The latter was concluded from a set of very narrow Raman lines observed from the inner tubes. The width of these lines was about a factor ten narrower than the lines known from carbon nanotubes so far. This result delnonstrates the clean room conditions that are established inside the tubes. By using isotepe substituted fullerenes a double-wall carbon nanotube could be grown where the guter tubes are almost exclusively 12C and the inner tubes are 13C. The linear spin chains inside the tubes are promising systems which might be used in quantum Information technology. Due to their higher stability the double wall carbon nanotubes are considered as improved candidates for field ernission and scanning probe tips.