Probing the Phonon-Assisted Relaxation Processes in DNA-wrapped Carbon Nanotubes Using Photoluminescence Spectroscopy
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Probing the Phonon-Assisted Relaxation Processes in DNA-wrapped Carbon Nanotubes Using Photoluminescence Spectroscopy S. G. Chou,1 F. Plentz,2 J. Jiang,3 R. Saito,3 D. Nezich,4 H. B. Ribeiro,2 A. Jorio,2 M. A. Pimenta,2 Ge. G. Samsonidze,5 A. P. Santos,6 M. Zheng,7 G. B. Onoa,7 E. D. Semke,7 G. Dresselhaus,8 M. S. Dresselhaus,4,5 Department of Chemistry, 4Department of Physics, 5Department of Electrical Engineering and Computer Science, 8Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139-4307 2 Depto. Fisica, Universidade Federal Minas Gerais, Belo Horizonte-MG, 30123-970 Brazil 3 Department of Physics, Tohoku University and CREST JST, Aoba, Sendai, 980-8578, Japan 6 Centro de Desenvolvimento da Tecnologia Nuclear, CDTN/CNEN, Belo Horizonte-MG, Brazil 7 DuPont, Central Research and Development, Experimental Station, Wilmington,DE19880-0328 1
Abstract: We present a detailed photoluminescence study of a (6,5) enriched DNA-wrapped single wall carbon nanotube (DNA-CNT) solid sample and an as-produced DNA-CNT solution. Multiple strong PL peaks were observed at excitation energies that do not correspond to the interband electronic transitions that are strongly enhanced by electronic van Hove singularities. These strong PL peaks are assigned to different mechanisms of excitation and relaxation, including one phonon, two phonon, hot luminescence processes, as well as radiative and nonradiative energy transferring mechanisms between neighboring nanotubes. These processes are assigned to different channels of phonon-assisted electron relaxation. The study shows that the electronic relaxation processes observed in PL can be used as a means to probe different physical interactions between photons, electrons, and phonons that are not separately identified in bulk semiconducting materials. Introduction: The mechanisms of carrier relaxation in low dimensional system has been a subject of interest both for physicists and engineers for the past decade because such observations are difficult to identify separately in bulk solid state systems. Even though carrier relaxation processes have been studied extensively in quantum dot [1-4] and quantum well [4-6] systems by photoluminescence (PL) spectroscopy, very little is known about the carrier relaxation mechanisms in carbon nanotube systems because of the short lifetime associated with the interactions between semiconducting and metallic nanotubes. These interactions have for a long times been preventing detailed PL studies to be carried out on the relaxation processes for photoexcited states in carbon nanotubes. Also, the optical signals from the different (n, m) species in a given sample often interfere with the accurate identifications of the different relaxation processes. However, as the technology of nanotube isolation and separation become further developed [7-10], many important advances in nanotube photo-physics, that could not be probed previously, has now become accessible using PL measurements [7-8, 11-17]. PL studies ha
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