Sorting carbon nanotubes by electronic structure using density differentiation

Wang, Jialiang; Green, Alexander A.; Hulvat, James F.; Stupp, Samuel I.; Hersam, Mark C.

doi:10.1038/nnano.2006.52

Cited by 2,143 publications

(2,616 citation statements)

References 26 publications

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“…Recent work has also demonstrated that it is possible to achieve limited separation of exfoliated SWNTs according to (n,m) structure, 58,121,136 left-or right-handed chirality, 95 length, 137,138 and electronic character (i.e., metallic or semiconducting). [139][140][141][142][143][144][145] SWNT surfactants are classified in terms of their ionic character (i.e., anionic, cationic, or nonionic). Ionic surfactants have a positively or negatively charged head group that interacts with the solvent and a nonpolar tail that associates with the nanotube sidewall; SWNT aggregation is hindered by charge repulsion between the polar head groups that extend into the solvent.…”

Section: Motivationmentioning

confidence: 99%

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%

Photophysics of Individual Single-Walled Carbon Nanotubes

2008

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“…[14,15] This has a big impact on many opto-electronic applications, and especially in microelectronics, where the presence of metallic SWNTs, even at concentrations of few parts per thousand, could dramatically degrade device performances. [2,15] To overcome this issue, various post-synthetics sorting methods have been recently developed, such as gel chromatography, [16] density gradient ultracentrifugation [17] and polymer wrapping [18][19][20][21] . Among these methods, polymer wrapping with conjugated polymers, such as polyfluorene-based derivatives, [18][19][20][21] is the simplest and most effective way of dispersing and sorting semiconducting SWNTs with specific diameters.…”

Section: Introductionmentioning

confidence: 99%

Nanoscale Charge Percolation Analysis in Polymer‐Sorted (7,5) Single‐Walled Carbon Nanotube Networks

Bottacchi

Späth

et al. 2016

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The current percolation in polymer-sorted semiconducting (7,5) single-walled carbon nanotube (SWNT) networks, processed from solution, is investigated using a combination of electrical field-effect measurements, atomic force microcopy (AFM) and conductive AFM (C-AFM) techniques. From AFM measurements, the nanotube length in the as-processed (7,5) SWNTs network is found to range from ~100 nm to ~1500 nm, with a SWNT surface density well above the percolation threshold and a maximum surface coverage ≈ 58%. Analysis of the field-effect charge transport measurements in the SWNT network using a two-dimensional -2 -plane and reveal the isotropic nature of the as-spun (7,5) SWNT networks. This work demonstrates the tremendous potential of combining advanced scanning probe techniques with field-effect charge transport measurements for quantification of key network parameters including current percolation, surface coverage and degree of SWNT alignment. Most importantly, the proposed approach is general and applicable to other nanoscale networks, including metallic nanowires as well as hybrid nano-composites.

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“…Density gradient ultracentrifugation isolates the narrow distributed, chirality enriched nanotubes. 17,[30][31][32] The mica layer was positively charged with Mg 2+ ions by exposure to 1 M MgCl 2 to make the negatively charged DNA site of the hybrid adhere to the surface. 20 Figure 1 displays the histogram of PL emission energies from 203 HiPCO nanotubes (a), 235 DNA-wrapped HiPCO nanotubes spin-coated on glass (b), and 232 DNA-wrapped CoMoCAT nanotubes spin-coated on mica (c) obtained using confocal spectroscopy.…”

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Visualizing the Local Optical Response of Semiconducting Carbon Nanotubes to DNA-Wrapping

et al. 2008

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We studied the local optical response of semiconducting single-walled carbon nanotubes to wrapping by DNA segments using high resolution tip-enhanced near-field microscopy. Photoluminescence (PL) near-field images of single nanotubes reveal large DNA-wrapping-induced red shifts of the exciton energy that are two times higher than indicated by spatially averaging confocal microscopy. Near-field PL spectra taken along nanotubes feature two distinct PL bands resulting from DNA-wrapped and unwrapped nanotube segments. The transition between the two energy levels occurs on a length scale smaller than our spatial resolution of about 15 nm.Semiconducting single-walled carbon nanotubes (SWNTs) as photoluminescent quasi-one-dimensional systems have attracted enormous scientific interest and have large potential for various applications in photonics and opto-and nanoelectronics. 1-3 Photoluminescence (PL) of nanotubes results from exciton recombination and occurs in the near-infrared spectral range with emission energies controlled mainly by the nanotube structure (n,m). [4][5][6][7][8] Since nanotubes consist of surface atoms only, the detected emission energy is very sensitive to the nanotube environment, making them promising candidates for sensing applications. 9 At present, the influence of the environment is described by its relative dielectric constant ε influencing exciton binding energies but also renormalizing the band gap through charge carrier screening. 10-14 As a result, the emission energy of nanotubes is modulated by the dielectric constant, which can be expected to be nonuniform along nanotubes, leading to nonuniform emission energies in single nanotube measurements. 8,15,16 The use of DNA for hybridization of carbon nanotube sidewalls has facilitated sorting nanotubes and building chemical sensors. 9,[17][18][19] Single-strand DNA-wrapping introduces DNA segments with finite length, while the details of the secondary DNA structure will be determined by a complex interplay between π-π stacking interactions between DNA bases and nanotube surface as well as electrostatic interactions of the phosphate backbone. [20][21][22] The effect of helical wrapping by the charged DNA backbone was modeled by applying a helical potential causing symmetry breaking of the nanotube electronic structure and small energetic shifts for semiconducting nanotubes (0.01 meV in water). 23,24 It is well-known that DNA-wrapping red-shifts the PL energy depending on the nanotube chirality by several tens of meV compared to the values reported for micelleencapsulated nanotubes in aqueous solution, 7,25,26 which can be attributed to an increasing ε. 14 The surface coverage with DNA segments of finite length is expected to result in a nonuniform dielectric environment along the nanotubes. 25 Limited by diffraction, the PL information collected in confocal microscopy contains the optical response from a nanotube length of about 300 nm, which is far too large to clarify details of individual DNA-nanotube interactions. Tipenhanced n...

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Sorting carbon nanotubes by electronic structure using density differentiation

Cited by 2,143 publications

References 26 publications

Photophysics of Individual Single-Walled Carbon Nanotubes

Photophysics of Individual Single-Walled Carbon Nanotubes

Nanoscale Charge Percolation Analysis in Polymer‐Sorted (7,5) Single‐Walled Carbon Nanotube Networks

Visualizing the Local Optical Response of Semiconducting Carbon Nanotubes to DNA-Wrapping

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