Photoluminescence Mapping of “As-Grown” Single-Walled Carbon Nanotubes:  A Comparison with Micelle-Encapsulated Nanotube Solutions

Okazaki, Toshiya; Saito, Tetsuya; Matsuura, Koji; Ohshima, Satoshi; Yumura, Motoo; Iijima, Sumio

doi:10.1021/nl051888y

Cited by 65 publications

(123 citation statements)

References 21 publications

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“…129,130 To isolate SWNTs from aggregated bundles, an ultrasonic dispersion process is used to induce gaps at the bundle ends, allowing surfactant adsorption to propagate along the length of the bundle. 131 Since the seminal work of O'Connell et al…”

Section: Motivationmentioning

confidence: 99%

“…For example, transition energies for surfactant-coated nanotubes are red shifted by an average of ~28 meV compared with unprocessed SWNTs suspended across pillars 154 or ~50 meV compared with as-grown SWNTs. 129 These shifts may result from screening of electronhole interactions by the surrounding dielectric medium. 155 The peak position can depend upon defects in the nanotube sidewalls introduced during their suspension 156 and upon the choice of surfactant used for solubilization.…”

Section: Recommended Swnt Dispersing Agentsmentioning

confidence: 99%

“…155 The peak position can depend upon defects in the nanotube sidewalls introduced during their suspension 156 and upon the choice of surfactant used for solubilization. 119,129 SWNT fluorescence is also affected by other environmental factors such as temperature, 157,158 mechanical strain, 159 surrounding dielectric constant, 155 or the presence of a magnetic field. 160 In particular, the large variation in Stokes shifts highlights the importance of the local environment surrounding the SWNT.…”

Section: Recommended Swnt Dispersing Agentsmentioning

confidence: 99%

“…In addition, the natural curvature of the CAS molecule leads to enhanced suspension of (6,5) and (7,5) SWNTs. 129 Tween 80 did not suspend or isolate SWNTs as efficiently as the other surfactants or DNA, and its use is not generally recommended. On the other hand, DNAwrapped samples displayed high dispersing concentrations and long-term stability, and are more amenable to biological applications than Tween 80.…”

Section: Recommended Swnt Dispersing Agentsmentioning

confidence: 99%

“…For example, fluorescence from an SWNT varies with surfactant system, 119,129,155,227 solvent, 218 atmosphere, 155 temperature, 157 and pressure, 158 and quenches when in direct contact with some substrates like silicon. 189 Indeed, the fluorescence spectra of SWNTs changed dramatically upon rinsing, displaying greatly reduced intensities and broader line widths ( Figure 6-4).…”

Section: Influence Of Local Environment On Swnt Fluorescencementioning

confidence: 99%

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Photophysics of Individual Single-Walled Carbon Nanotubes

2008

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Single-walled carbon nanotubes (SWNTs) are cylindrical graphitic molecules that have remained at the forefront of nanomaterials research since 1991, largely due to their exceptional and unusual mechanical, electrical, and optical properties. The motivation for understanding how nanotubes interact with light (i.e., SWNT photophysics) is both fundamental and applied. Individual nanotubes may someday be used as superior near-infrared fluorophores, biological tags and sensors, and components for ultrahigh-speed optical communications systems. Establishing an understanding of basic nanotube photophysics is intrinsically significant and should enable the rapid development of such innovations. Unlike conventional molecules, carbon nanotubes are synthesized as heterogeneous samples, composed of molecules with different diameters, chiralities, and lengths. Because a nanotube can be either metallic or semiconducting depending on its particular molecular structure, SWNT samples are also mixtures of conductors and semiconductors. Early progress in understanding the optical characteristics of SWNTs was limited because nanotubes aggregate when synthesized, causing a mixing of the energy states of different nanotube structures. Recently, significant improvements in sample preparation have made it possible to isolate individual nanotubes, enabling many advances in characterizing their optical properties. In this Account, single-molecule confocal microscopy and spectroscopy were implemented to study the fluorescence from individual nanotubes. Single-molecule measurements naturally circumvent the difficulties associated with SWNT sample inhomogeneities. Intrinsic SWNT photoluminescence has a simple narrow Lorentzian line shape and a polarization dependence, as expected for a one-dimensional system. Although the local environment heavily influences the optical transition wavelength and intensity, single nanotubes are exceptionally photostable. In fact, they have the unique characteristic that their single molecule fluorescence intensity remains constant over time; SWNTs do not “blink” or photobleach under ambient conditions. In addition, transient absorption spectroscopy was used to examine the relaxation dynamics of photoexcited nanotubes and to elucidate the nature of the SWNT excited state. For metallic SWNTs, very fast initial recovery times (300–500 fs) corresponded to excited-state relaxation. For semiconducting SWNTs, an additional slower decay component was observed (50–100 ps) that corresponded to electron–hole recombination. As the excitation intensity was increased, multiple electron–hole pairs were generated in the SWNT; however, these e−h pairs annihilated each other completely in under 3 ps. Studying the dynamics of this annihilation process revealed the lifetimes for one, two, and three e−h pairs, which further confirmed that the photoexcitation of SWNTs produces not free electrons but rather one-dimensional bound electron–hole pairs (i.e., excitons). In summary, nanotube photophysics is a rapidly developing area o...

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Section: Motivationmentioning

confidence: 99%