Molecular Spectroscopy of Carbon Nanotubes

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The objective of this project is to advance the spectroscopy of single wall carbon nanotubes (SWNTs) in a major way by studying new phenomena in their discovery phase, by examining controversial and unresolved issues concerning spectroscopic phenomena associated with the one-dimensionality of carbon nanotubes, and by developing new capabilities for studying the spectroscopy of carbon nanotubes. The approach is to focus on four topics: 1) experimentally elucidate the newly discovered unusual phenomena associated with combination modes in the resonance Raman spectra in the intermediate frequency range of 600-1100 cm-1 where new turn-on/turn-off phenomena are observed, as the laser excitation energy is varied, and then explaining the physics behind the newly observed phenomena; 2) develop a strategy for resolving through experimental investigation of the two seemingly different interpretations for the fundamental mechanism responsible for the dominant G-band spectral features in single wall carbon nanotubes, namely, whether these features are due to first-order scattering processes or to double resonance processes. According to this strategy, conditions favorable for the study of the two processes will be created so that their interrelation can be studied quantitatively; 3) improvement of the signal-to-noise in Raman spectroscopy measurements at the single nanotube level by developing techniques for measuring spectra on freely suspended individual single wall nanotubes. This research is expected to experimentally resolve phenomena that were previously buried in the noise and thus to open up new research directions; 4) develop a strategy for gaining an understanding of the relationship between the singularities in the electronic density of states as observed in single molecule Raman scattering and in photoluminescence, by systematically carrying out the two types of studies on the same individual nanotubes. Measurements on both bundles of SWNTs and on individual SWNTs will be carried out. At present, the two techniques give results that appear to differ regarding both the values of the resonant energies that have been reported and the spread of the ensemble of resonant energies observed at constant diameter.%%% The project addresses basic research issues in a topical area of materials science with high technological relevance. An important feature of the program is the integration of research and education through the training of students and postdoctoral researchers in a fundamentally and technologically significant area. The project assists development of technical, communication, and organizational/management skills in students through unique educational experiences made possible by a highly collaborative forefront research environment. The research is expected to have broad impacts through the training of young men and women leaders in the field, by the wide dissemination of the findings of this research through invited talks and publications, and through the preparation of tutorial review articles to interrelate the work of various researchers in the field, and to identify future research areas of importance and promise. The principal investigator and her students will continue to disseminate advances in nanoscience and nanotechnology to the public through invited talks to general audiences, and through advisory work for the government, industrial laboratories, universities and professional societies.***