1. Molecular Spectroscopy of Carbon Nanotubes M.S. Dresselhaus MIT; DMR 0405538 Research Summary: In this project, a novel resonant Raman mode related to linear carbon chains in double walled carbon nanotubes(DWNTs) has been identified, and its behavior is correlated with the coalescence of the DWNTs, as observed by high resolution TEM. This mode, termed “the coalescence inducing mode” (CIM) is located at 1855 cm-1 and arises from the generation of 1D carbon chains (3-5 atoms long) established covalently between adjacent DWNTs. The CIM is induced by thermal annealing, and its effect on coalescence is enhanced by boron doping. Carbon chains trigger nanotube coalescence via a zipper mechanism. Before the tubes actually coalesce, the CIM vibration disappears. The CIM mode is now under detailed study and the results can be used to identify sp hybridized carbon in various systems, such as irradiated graphite, polymerized and functionalized fullerenes and carbines. a)HRTEM images showing DWNT coalescence and the appearance of larger diameter nanotubes as the heat treatment temperature (htt) is increased. b) Raman spectra taken at 2.33 eV on boron doped DWNT samples with various heat treatment temperatures showing the CIM mode appear at 1200˚C and disappear at 1500˚C. Linear Carbon Chain Triggering Coalescence of Double Walled Carbon Nanotubes

2. Molecular Spectroscopy of Carbon Nanotubes M. S. Dresselhaus MIT; DMR 0405538 Research Summary: A non-degenerate pump-probe fast optics study was carried out on DNA-wrapped singled walled carbon nanotubes (SWNTs) to further understand the phonon- assisted processes observed from previous static photoluminescence measurements, using a sample that is strongly enriched in (6,5) SWNTs. With a carefully chosen E pump that corresponds to E 11 (6,5)+2E ph and probing at E 11 (6,5), an intermediate decay time component that is associated with the hot D- band phonon-absorption relaxation process could be studied in detail. Here 2E ph denotes the energy of 2 D- band phonons. By systematically varying the pump fluence and the values of E probe to be in and out of resonance with the (7,5) and (8,3) SWNTs, the different mechanisms of band edge exciton population decay for the minority SWNT species in the sample were also studied in detail. This study clarifies the role of hot phonon absorption and emission processes, as well as the Auger process, in the filling and depletion of band edge exciton populations for individual SWNTs. A transient spectrum monitoring the differential transmission intensity vs. delay time for E pump ~E 11 (6,5) + 2E ph and E probe ~E 11 (6,5). The inset shows a magnified portion of the plot indicating more clearly the range of the delay time, pertinent to  int. Time Resolved Spectroscopy of DNA-wrapped Single Walled Carbon Nanotubes

3. Molecular Spectroscopy of Carbon Nanotubes M. S. Dresselhaus MIT; DMR 0405538 Education: 5 graduate students (Georgii Samsonidze, S. Grace Chou, Hyongbin Son, Daniel Nezich, and Federico Villalpando Paez) and 2 visiting graduate students (Mario Hofmann from the Technical University of Ilmenau, Germany and Eduardo Barros from the Federal University of Ceara, Brazil) worked collaboratively on the synthesis, characterization, and the molecular spectroscopy of carbon nanotubes, making scientific advances documented in scientific publications and presentations at national and international conferences. In 2005, Georgii Samsonidze spent 1 month in Tohoku University (Japan) to work with foreign collaborators. S. Grace Chou, Eduardo Barros and Federico Villalpando also spent one week attending an international conference in Mexico while working with their Mexican counterparts on a joint MIT-Mexico research program. During the summer, our research group hosted a high school student (Jeffrey Iqbal from Germany) who worked on isolated nanotube depositions on different substrates. Outreach: When giving colloquia at other universities, the principal investigator typically holds a mentoring session with graduate, post-doc, and undergraduate students where mentoring and career issues are informally and openly discussed. Mentoring sessions with women faculty also take place on some of these visits. The particular universities where such mentoring sessions occurred during the 2004-05 academic year were the University of Illinois at Urbana- Champaign, Penn State University, U. C. Berkeley, University of Utah, Arizona State University, Stanford University, McGill University, and the University of Montreal.