Identifying and counting point defects in carbon nanotubes

Fan, Yuwei; Goldsmith, Brett; Collins, Philip G.

doi:10.1038/nmat1516

Cited by 268 publications

(265 citation statements)

References 38 publications

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“…Naturally, SWNTs contain no edge-plane-like sites of the type held responsible for the EC response in MWNTs (41); also, for SWNTs grown by CVD, the ends are likely to be closed, which might be expected to lead to very slow HET kinetics (24,25). The only other type of defect site that one could reasonably consider is point defects in the sidewall, identified through electrodeposition (42). These have a spacing of 100 nm-4 μm (averaging approximately 400 nm) along the sidewall.…”

Section: Resultsmentioning

confidence: 99%

“…Given the defect density attributed from selective electrodeposition (42), vide supra, the SECCM pipet would be expected to encounter only one defect when passing over an SWNT. We thus consider this case, simulating a defect (at most) as a square of length 1 nm positioned in the plane of an inert substrate, for The SWNT height distribution from the AFM images.…”

Section: Resultsmentioning

confidence: 99%

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Quantitative nanoscale visualization of heterogeneous electron transfer rates in 2D carbon nanotube networks

Güell¹,

Ebejer²,

Snowden³

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

113

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Carbon nanotubes have attracted considerable interest for electrochemical, electrocatalytic, and sensing applications, yet there remains uncertainty concerning the intrinsic electrochemical (EC) activity. In this study, we use scanning electrochemical cell microscopy (SECCM) to determine local heterogeneous electron transfer (HET) kinetics in a random 2D network of single-walled carbon nanotubes (SWNTs) on an Si∕SiO 2 substrate. The high spatial resolution of SECCM, which employs a mobile nanoscale EC cell as a probe for imaging, enables us to sample the responses of individual portions of a wide range of SWNTs within this complex arrangement. Using two redox processes, the oxidation of ferrocenylmethyl trimethylammonium and the reduction of ruthenium (III) hexaamine, we have obtained conclusive evidence for the high intrinsic EC activity of the sidewalls of the large majority of SWNTs in networks. Moreover, we show that the ends of SWNTs and the points where two SWNTs cross do not show appreciably different HET kinetics relative to the sidewall. Using finite element method modeling, we deduce standard rate constants for the two redox couples and demonstrate that HET based solely on characteristic defects in the SWNT side wall is highly unlikely. This is further confirmed by the analysis of individual line profiles taken as the SECCM probe scans over an SWNT. More generally, the studies herein demonstrate SECCM to be a powerful and versatile method for activity mapping of complex electrode materials under conditions of high mass transport, where kinetic assignments can be made with confidence.W ithin the family of nanostructured materials, carbon nanotubes (CNTs) have attracted particular attention because they are readily synthesised at low cost, have exceptional electronic properties, exhibit chemical and mechanical stability, and are amenable to a wide range of simple chemical functionalization routes (1-3). These characteristics have led to CNTs being considered ideal substrates for electronics (4), sensing systems (5, 6), electrocatalytic supports (7), and batteries (8). Furthermore, the different configurations in which CNTs can be arranged broaden their versatility and allow custom design of devices for specific applications. Individual single-walled carbon nanotubes (SWNTs) (9), 2D networks (10-12), and 3D nanostructures (13) have all been employed successfully.Understanding heterogeneous electron transfer (HET) at CNTs is of considerable importance, due to the wide range of electroanalytical and electrocatalytic systems based on CNTs (14-17), and also because electrochemistry provides an attractive route to functionalize and tailor the properties of . Probing HET in 1D electrode materials is interesting fundamentally, given their inherent electronic structure and properties (21,22). However, as we highlight herein, despite many studies aimed at characterizing HET at CNTs, substantial questions remain unanswered, such as the location and rate of HET.A popular approach for studying electrochemistry at CNT...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Quantitative nanoscale visualization of heterogeneous electron transfer rates in 2D carbon nanotube networks

Güell¹,

Ebejer²,

Snowden³

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

113

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“…49 The role of defects is not well understood in terms of their impact on the mechanical, electronic, and optical behavior of SWNTs. For some applications, defect sites advantageously provide a reactive site for covalent attachment of particles to the SWNT sidewall.…”

Section: Purification Of Swntsmentioning

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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“…In particular, it was demonstrated that intrinsic defects in metallic SWNTs embodied in source-drain-gate devices can provide resonant backscattering characteristics 8,9 leading to low-temperature quantum dot devices, as well as a high gate sensitivity at the defect position. 10 Thus, the knowledge of how and to which extent different types of defects can change the electronic properties of SWNTs is important, as it may open a route toward controllable engineering of the properties of SWNT-based electronic devices or even result in the appearance of a different class of devices with the properties entirely designed by a controlled creation of particular defects.…”

Section: Introductionmentioning

confidence: 99%

Modifying the electronic structure of semiconducting single-walled carbon nanotubes byAr+ion irradiation

et al. 2009

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Local controllable modification of the electronic structure of carbon nanomaterials is important for the development of carbon-based nanoelectronics. By combining density-functional theory simulations with Arion-irradiation experiments and low-temperature scanning tunneling microscopy and spectroscopy ͑STM/STS͒ characterization of the irradiated samples, we study the changes in the electronic structure of single-walled carbon nanotubes due to the impacts of energetic ions. As nearly all irradiation-induced defects look as nondistinctive hillocklike features in the STM images, we compare the experimentally measured STS spectra to the computed local density of states of the most typical defects with an aim to identify the type of defects and assess their abundance and effects on the local electronic structure. We show that individual irradiationinduced defects can give rise to single and multiple peaks in the band gap of the semiconducting nanotubes and that a similar effect can be achieved when several defects are close to each other. We further study the stability of defects and their evolution during STM measurements. Our results not only shed light on the abundance of the irradiation-induced defects in carbon nanotubes and their signatures in STS spectra but also suggest a way the STM can be used for engineering the local electronic structure of defected carbon nanotubes.

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Identifying and counting point defects in carbon nanotubes

Cited by 268 publications

References 38 publications

Quantitative nanoscale visualization of heterogeneous electron transfer rates in 2D carbon nanotube networks

Quantitative nanoscale visualization of heterogeneous electron transfer rates in 2D carbon nanotube networks

Photophysics of Individual Single-Walled Carbon Nanotubes

Modifying the electronic structure of semiconducting single-walled carbon nanotubes byAr+ion irradiation

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