Berlin 2012 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 11: Carbon: Nanotubes, Diamond and Silicon Carbid
HL 11.6: Vortrag
Montag, 26. März 2012, 13:00–13:15, EW 203
Carbon nanotube Fermi energy shifts upon deposition on a substrate revealed by Raman spectroscopy — •Benjamin Hatting1, Sebastian Heeg1, Frank Hennrich2, Ralph Krupke2, and Stephanie Reich1 — 1Freie Universität Berlin, Berlin, Germany — 2Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
Raman spectroscopy of single-walled carbon nanotubes (SWNTs) reveals a variety of information about the samples under study, such as their composition in terms of chirality and the amount of defects. Additionally, the lower-frequency component of the high-energy modes (HEM) in metallic tubes is sensitive to the position of the Fermi level. This component arises from longitudinal optical (LO) vibrations. It appears at lowered frequencies of about 1550cm−1 when the Fermi energy is at its intrinsic value due to the presence of a Kohn anomaly at the Γ point in the LO phonon branch.[1] We report the observation of a downshift of the metallic LO peak along with a broadening of its width upon deposition of a chirality-enriched tube sample[2] on a Si substrate. We explain our observations in terms of two Fermi energy shifts. The results imply that simple inspection of the HEM lineshape is insufficient to judge the presence of metallic tubes in a sample with an unknown chirality distribution.