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a) Schematic of the VHS in semiconducting (left) and metallic (right) SWCNTs with respective optical transitions ii. Semiconducting species exhibit in contrast to metallic SWCNTs a band gap. b) UV/vis spectrum observed from a typical HiPCO SWCNT sample dispersed in an SDBS aqueous solution with marked regions of the metallic and semiconducting optical transitions. c) 3D photoluminescence excitation map observed from semiconducting enriched HiPCO SWCNTs dispersed in an SDBS aqueous solution and d) the respective contour plot. The assignment of present SWCNT chiralities from the contour plot as depicted for some species is possible by the correlation of the Sii/S11 transition pairs which are unique for each species.
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Within this thesis it was possible to uncover fundamental metallicity, diameter, and chirality related aspects in the electron doping mechanism and the recovery processes of alkali metal intercalated HiPCO single-walled carbon nanotube (SWCNT) bulk materials. The choice of metallicity enriched samples enabled to emphasize the importance of the mate...
Contexts in source publication
Context 1
... If an excitation wavelength matches a VHS an absorption peak is obtained. The principal is schematically depicted in Figure 13a and an exemplary absorbance spectrum for a typical HiPCO sample dispersed in SDBS is given in Figure 13b. Since HiPCO samples comprise SWCNTs with smaller diameters of about 0.7 -1.2 nm a better energy separation of their transition energies is observed compared to the larger-diameter arc-discharge SWCNTs, for example, what shows up in a more defined peak separation. ...
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... If an excitation wavelength matches a VHS an absorption peak is obtained. The principal is schematically depicted in Figure 13a and an exemplary absorbance spectrum for a typical HiPCO sample dispersed in SDBS is given in Figure 13b. Since HiPCO samples comprise SWCNTs with smaller diameters of about 0.7 -1.2 nm a better energy separation of their transition energies is observed compared to the larger-diameter arc-discharge SWCNTs, for example, what shows up in a more defined peak separation. ...
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... absorption in SWCNTs creates a so-called exciton (bounded state of an electron-hole-pair) due to the excitation of an electron to an excited state by the absorbed photon. While in metallic nanotubes the excited electron decays via an electron-phonon-coupling to its ground state, [161] in semiconducting species an additional photon emission at their S 11 transition is involved (blue arrow in Figure 13a). This energy distance in the VHS defines the bandgap width of semiconducting SWCNTs which is determined by their diameter and chiral angle [212] and is specific for each chirality. ...
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... the excitation energy is in resonance with an S ii transition of a specific SWCNT a sharp increase in the PL intensity is observed. This is resulting in a threedimensional map with the PL intensity plotted versus excitation and emission wavelength as depicted in Figure 13c. Pairs of S ii /S 11 transitions observed from this map can then be used for the (n,m) assignment of SWCNTs present in a sample. ...
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... the S 22 /S 11 pairs are used as a fingerprint for the assignment but also pairs which include S 33 and S 44 transitions can be applied. [120] For a better overview and an easier assignment the 3D map can be transformed into a contour plot by illustrating the signal intensity as color gradient (Figure 13d). Bachilo et al. introduced an empirical Kataura plot based on the results from their PL excitation mapping of individualized SWCNTs in an aqueous surfactant suspension and they have assigned the experimentally measured S 11 and S 22 transition energies for a large number of SWCNT chiralities. ...
