Metallic SWCNTs Research Articles

Direct Synthesis of Semiconducting Single‐Walled Carbon Nanotubes Toward High‐Performance Electronics

AbstractThe large‐scale synthesis of high‐purity semiconducting single‐walled carbon nanotubes (s‐SWCNTs) plays a crucial role in fabricating high‐performance and multiapplication‐scenario electronics. This work develops a straightforward, continuous, and scalable method to synthesize high‐purity and individual s‐SWCNTs with small‐diameters distribution (≈1 nm). It is believed that the water and carbon dioxide resulting from the decomposition of isopropanol act as oxidizing agents and selectively etch metallic SWCNTs, hence enhancing the production of s‐SWCNTs. The performance of individual‐SWCNTs field effect transistors confirms the high abundance of s‐SWCNTs, presenting a mean mobility of 376 cm2 V−1 s−1 and a high mobility of 2725 cm2 V−1 s−1 with an on‐current to off‐current (Ion/Ioff) ratio as high as 2.51 × 107. Moreover, thin‐film transistors based on the as‐synthesized SWCNTs exhibit excellent performance with a mean mobility of 9.3 cm2 V−1 s−1 and Ion/Ioff ratio of 1.3× 105, respectively, verifying the enrichment of s‐SWCNTs. This work presents a simple and feasible route for the sustainable synthesis of high‐quality s‐SWCNTs for electronic devices.

Fluorinated carbon nanotubes as nonvolatile additive to the active layer of polymer/fullerene solar cells

Highly dispersed fluorinated SWCNTs of submicron length were prepared, characterized and tested as nonvolatile additive to the active layer of polymer/fullerene organic solar cells. Two types of initial SWCNT materials – TUBALL® (OCSiAl) and Super purified plasma tubes (Nanointegris Inc.) – were used. The absence of big CNT aggregates was revealed by atomic force microscopy. The absence of metallic SWCNTs is confirmed by optical spectra of fluorinated SWCNT dispersions. Reproducible increase of the main performance parameters of solar cells (short circuit current, open circuit voltage, fill factor and power conversion efficiency) was obtained upon admixing a small amount of fluorinated SWCNTs (less than 1% weight) into the polymer/fullerene active layer, with either P3HT or PCDTBT donor and either PC60BM or PC70BM acceptor for both direct and inverted device architectures. Since effective charge mobility did not change upon fluorinated SWCNT admixture, the improvement of solar cell performance is not related to SWCNT-induced modification of the electronic structure of the active layer components or charge transfer via fluorinated SWCNTs. Presumably, the origin of this improvements is geometric optimization of the active layer morphology (improving connectivity of donor and acceptor domains) by fluorinated SWCNTs due to their high aspect ratio.

(Invited) Thermoelectric Performance of Fermi-Level Tuned and Aligned Single Walled Carbon Nanotubes

Thermoelectric power generation is one of important technologies for realization of highly efficient energy uses. Improvement of performance of thermoelectric materials is required, and theoretical studies suggest one-dimensional materials have potentials for the realization of the highest performance [1]. However, how 1D materials can really improve the thermoelectric performance has not been experimentally verified yet. In this context, thermoelectric properties of single walled carbon nanotubes attract a lot of attention because of their one-dimensional structure and electronic structures (See a review by Blackburn et al. [2]). Thermoelectric properties significantly depend on the electronic structures of SWCNTs, and relationships among Seebeck coefficient (S), electrical conductivity (σ), power factor, doping levels and their electronic structures have been revealed through various studies [3-5]. As a result, a very unique characteristics on thermoelectric properties of SWCNTs has been clarified [5]. In conventional materials, there is a trade-off between Seebeck coefficient and electrical conductivity, but in the metallic SWCNTs, the trade-off is broken because of the presence of 1D electronic structures, indicating the uniqueness of SWCNTs [5]. For the correct understanding of the thermoelectric performance, zT, in SWCNT thin films, clarification of the relationships among S, σ, and thermal conductivity κ is very important. Although the relationships between S and σ have been well understood, the relationships among those parameters and κ have not yet. Avery et al. clarified κ is almost constant by the change of σ, and they estimated the zT value is approximately 0.01-0,05 [3]. Recently we developed a technique to clarify the cross-plane thermal conductivity κ ⊥ in SWCNT thin films with tuned Fermi level by a combination of time-domain thermoreflectance method and electrolyte gating technique [6], and then clarified that the κ ⊥ is almost constant even when in-plane σ is changed three order of magnitude from ~10 Sm-1 to 104 Sm-1 [5]. Such constant behavior of κ by the change of σ in SWCNT thin films is interesting in both basic science and application perspectives. Now we can prepare Fermi-level tuned and microscopically aligned SWCNT thin films [7], and the relationships between S and σ in the aligned directions have been clarified [8]. In this talk, I would like to discuss the recent results in our group and the estimated zT values of Fermi-level tuned and aligned SWCNTs.

Preparation, characterization, and nonlinear optical properties of graphene oxide thin film doped with low chirality metallic SWCNTs

We present non-linear optical properties of graphene oxide (GO) doped with low chirality metallic single walled carbon nanotubes (m-SWCNTs) thin films. The weight percentage of the m-SWCNTs was 5, 10, and 20 wt%. High-resolution transmission electron microscope (HRTEM), high resolution scanning electron microscope (HRSEM), Raman, and UV–vis spectroscopy were used to characterize the prepared samples. We have investigated their nonlinear optical properties using open and closed Z-scan technique at Nd:YAG laser at 1064 nm laser pulses (7 ns, 10 Hz). The nonlinear absorption coefficient β, nonlinear refractive index n2, and third order nonlinear susceptibility χ3 were calculated. The results show that all samples exhibit reverse saturable absorption (RSA) because of increasing metallicity and/or partial reduction of GO during laser illumination. The nonlinearity response of the GO/m-SWCNT films increase as the m-SWCNTs percentage increases. The high non-linear optical parameters of the GO/m-SWCNTs films make them as superior candidates for near-infrared (NIR) laser protection applications.

Selective Chemistry-Based Separation of Semiconducting Single-Walled Carbon Nanotubes and Alignment of the Nanotube Array Network under Electric Field for Field-Effect Transistor Applications.

Semiconducting single-walled carbon nanotubes (s-SWCNTs) are considered as a replacement for silicon in field-effect transistors (FETs), solar cells, logic circuits, and so forth, because of their outstanding electronic, optical, and mechanical properties. Herein, we have studied the reaction of pristine SWCNTs dispersed in a pluronic F-68 (PF-68) polymer solution with para-amino diphenylamine diazonium sulfate (PADDS) to separate nanotubes based on their metallicity. The preferential selectivity of the reactions was monitored by changes in the semiconducting (S22 and S33) and metallic (M11) bands by ultraviolet–visible–near infrared spectroscopy. Metallic selectivity depended on the concentrations of PADDS, reaction time, and the solution pH. Furthermore, separation of pure s-SWCNTs was confirmed by Raman spectroscopy and Fourier-transform infrared spectroscopy. After the removal of metallic SWCNTs, direct current electric field was applied to the pure s-SWCNT solution, which effectively directed the nanotubes to align in one direction as nanotube arrays with a longer length and high density. After that, electrically aligned s-SWCNT solution was cast on a silicon substrate, and the length of the nanotube arrays was measured as ∼2 to ∼14 μm with an areal density of ∼2 to ∼20 tubes/μm of s-SWCNTs. Next, electrically aligned s-SWCNT arrays were deposited on the channel of the FET device by drop-casting. Field-emission scanning electron microscopy and electrical measurements have been carried out to test the performance of the aligned s-SWCNTs/FETs. The fabricated FETs with a channel length of 10 μm showed stable electrical properties with a field-effect mobility of 30.4 cm2/Vs and a log10 (Ion/Ioff) current ratio of 3.96. We envisage that this new chemical-based separation method and electric field-assisted alignment could be useful to obtain a high-purity and aligned s-SWCNT array network for the fabrication of high-performance FETs to use in digital and analog electronics.

Charge Photogeneration in Composites of Fluorinated Carbon Nanotubes and Semiconducting Polymer P3HT

Spectroscopic and photovoltaic properties of composites of purified and subsequently fluorinated single‐walled carbon nanotubes (F‐SWCNTs) with conjugated polymer poly(3‐hexylthiophene) (P3HT) are tested. Adding cyclohexanone into o‐dichlorobenzene solution of P3HT and F‐SWCNTs significantly affects the composite morphology and promotes P3HT/F‐SWCNT nanofilament formation, as evidenced from atomic force microscopy (AFM) images of spin‐coated composite films. Also, nanofilament formation enhances quenching of P3HT photoluminescence by F‐SWCNTs. The performance of P3HT‐based organic photovoltaics (OPV) devices with separated semiconducting SWCNTs and F‐SWCNTs as the acceptor component of the active layer is comparable. Light‐induced electron paramagnetic resonance (EPR) signal intensity in P3HT/F‐SWCNT composite films and frozen solutions grows with increase in F‐SWCNT content, which is a signature of photoinduced electron transfer. Dramatic change in SWCNT electronic structure upon fluorination is also evidenced by UV–vis– near infra red optical absorption spectra, from which the bandgap of about 1.0 eV is derived for F‐SWCNTs. Overall, the experimental results confirm that fluorination efficiently converts metallic SWCNTs into semiconducting ones, and F‐SWCNTs can be used for as an electron acceptor component in OPV devices, in combination with polymer donors. Presently, the performance of P3HT/F‐SWCNT devices is limited by F‐SWCNT aggregation into bundles, which decreases P3HT/F‐SWCNT interface area.

Aqueous two-phase extraction of semiconducting single-wall carbon nanotubes with isomaltodextrin and thin-film transistor applications

Semiconducting single-wall carbon nanotubes (s-SWCNTs) are promising materials with potential applications in thin-film transistors (TFTs). However, separation techniques are required to obtain highly enriched s-SWCNTs since conventional as-grown SWCNTs are a mixture of 70% semiconducting and 30% metallic SWCNTs. Here, we developed a rapid single-step aqueous two-phase extraction of high-purity s-SWCNTs using isomaltodextrin, which is a cost-effective polysaccharide that contains a large amount of α-1,6-glucosidic linkages. We also succeeded in fabricating high-density uniform films directly from the high-purity s-SWCNT extract. Fabricated TFTs exhibited an excellent on/off ratio, carrier mobility, and on-current density.

Thermoelectric properties of low-cost transparent single wall carbon nanotube thin films obtained by vacuum filtration

Abstract The dispersions of semiconducting (sc-) and metallic (m-) SWCNTs with purity more than 98 and 86%, correspondingly, were obtained by using the aqueous two-phase extraction method. The unseparated (un-) SWCNTs contained ~3/4 of semiconducting and ~1/4 of metallic nanotubes. Thin films based on unseparated, semiconducting and metallic SWCNTs were prepared by vacuum filtration method. An Atomic Force Microscopy (AFM) and a Transmission Electronic Microscopy (TEM) were used to investigate the thin film microstructure. The thin SWCNT film transmittance was measured in the wavelength range of 300–1500 nm. Thermoelectric properties were carried out in the temperature range up to 200 °C. The largest Seebeck coefficient was observed for thin films based on semiconducting SWCNTs. The maximum value was 98 μV/K under the temperature of 170 °C. The lowest resistivity was 7.5·10−4·Ohm·cm at room temperature for thin un-SWCNT films. The power factor for m-SWCNT and un-SWCNT films was 47 and 213 μW m−1 K−2, correspondingly, at room temperature and 74 and 54 μW m−1 K−2 at 200 °C, respectively. For a thin sc-SWCNT film the maximum power factor was 2.8 μW m−1 K−2 at 160 °C. The un-SWCNT film thermal conductivity coefficient was 5.63 and 3.64 W m−1 K−1 and a thermoelectric figure of merit was 0.011 and 0.016 at temperatures of 23 and 50 °C, respectively.

(Invited) Probing Optical and Magneto-Optical Properties of Carbon Nanotubes Using Enriched Carbon Nanotube Materials

Enriched carbon nanotubes materials, whether purified in electronic type, diameter, filling or even specific chirality, have deepened researchers' understanding of the fundamental optical properties of single-wall carbon nanotubes (SWCNTS). In particular, density gradient ultracentrifugation and aqueous two-phase extraction techniques have enabled the production of sizable aqueous suspensions and aligned films, allowing the interrogation of chiral-specific absorption, emission and scattering properties. In this talk, I will discuss two particular aspects: the chiral-specific nature of the Raman M-mode in small-diameter semiconducting SWNCTs and the large orbital magnetic susceptibility anisotropy of large-diameter metallic SWCNTs. In the first part of the talk, I examine the unusual frequency dependence and excitation profile shape of the M-mode (~1620-1800 cm-1) in small-diameter semiconducting species such as the (5,4), (6,4), (8,3), (9,1), (6,5), (7,6), (11,0), (9,4) & (8,6). In particular, semiconducting species exhibit a mod- and diameter-dependent "fanning-out" behavior for E22 excitation, reminescent of that observed for optical transition energies. Even more interesting is the strongly asymmetrical excitation profile of the M-mode for a specific (n,m) species, deviating from the standard symmetrical profile observed for the radial breathing mode and the non-Condon-violating profile observed for the G-band. At certain energies in the excitation profile, the M-mode exceeded the G-band in intensity and unlike the G-band, the most intense peaks in the M-mode profile do not correspond to either the incoming or outgoing resonances. The M-mode seems to exhibit a new type of excitation profile shape. In the second part of the talk, I discuss the magneto-optical properties of metallic SWCNTs. Using the strongly anisotropic optical and magnetic properties arising from the one-dimensional nature of carbon nanotubes, we aligned SWCNTs in aqueous suspension in magnetic fields up to 22T. Specifically, the orbital magnetic susceptibility anisotropy (Δχ) was measured, via magnetic linear dichroism spectroscopy enabled by the unique Florida Split-Helix magnet system, of multiple large-diameter metallic and semiconducting SWCNT species. In particular for the metallic species, Δχ’s on the order of 10-4 emu/mol, an order of magnitude larger than any Δχ measured previously for SWCNTs, were observed. Additionally, broadening and the beginnings of peak splitting of metallic optical absorption features, due to the Aharanov-Bohm effect, were also seen. The emergence of such magneto-optical behavior at such relatively “low” magnetic fields, combined with new developments in carbon nanotube sample preparation science, opens the door to observing new many-body effects through magneto-optics. Lastly, I will share a few memories of my time with my friend and mentor, Robert Hauge.

Different mechanism of capacitance change for gas detection using semiconducting and metallic single-walled carbon nanotubes

Semiconducting single-walled carbon nanotubes (s-SWCNTs) with lower absorption energy of NO2 gas exhibited higher sensitivity than metallic SWCNTs. The result originated from quantum capacitance of s-SWCNTs, which was readily affected by charge transfer, whereas that of m-SWCNTs showed no change with even more transferred charges. However, m-SWCNT that were aligned polarize adsorbed gases on the surface by a local field that contributed the capacitance changes of m-SWCNT networks. This is a newly introduced detection mechanism of gas sensing using m-SWCNTs.

Functionalization and defunctionalization of single walled carbon nanotubes: Electrochemical and morphologic consequences

Electrochemical oxidation and subsequent electrochemical reduction of single walled carbon nanotubes was carried out by cyclic voltammetry. Using methods of Raman and absorption spectra it was revealed that oxidation of SWCNT electrodes leads to significant disruption of electronic structure of nanotubes; the structure can be substantially restored in the course of subsequent cathodic polarization. The quantitative relationship between the concentration of various oxygen-containing functional groups present on the pristine surface, electrochemically oxidized and subsequently reduced single walled carbon nanotubes was demonstrated with the use of XPS. It was shown that upon application of anodic potentials, functionalization of metallic SWCNTs proceeds deeper than in the case of semiconductor ones. The correlation between the degree of functionalization of SWCNT electrodes and kinetic parameters of electron transfer were studied using redox couples: [Ru(NH3)6]2+/3+, [Fe(CN)6]4−/3−, and Fe2+/3+. The essential growth of the electron transfer rate constant observed for couple Fe+2/+3 was suggested to results from the coordination of iron ion to oxygen from functional groups, formed at water electrolysis. It was demonstrated that the maximum rate constant for the system is reached at the medium functionalization degree.

A Continuous Flow Device for the Purification of Semiconducting Nanoparticles by AC Dielectrophoresis

ABSTRACTSingle-walled carbon nanotubes (SWCNTs) have attracted significant attention as building blocks for future nanoscale electronics due to their small size and unique electronic properties. However, current SWCNT production techniques generate a mixture of two types of nanotubes with divergent electrical behaviors due to structural variations. Some of the nanotubes act as metallic materials while others display semiconducting properties. This random mixture has prevented the realization of functional carbon nanotube-based nanoelectronics. Here, a method of purifying a continuous flow of semiconducting nanotubes from an initially random mixture of both metallic and semiconducting SWCNTs in suspension is presented. This purification uses A/C dielectrophoresis (DEP), and takes advantage of the large difference of the relative dielectric constants between metallic and semiconducting SWCNTs. Because of a difference in magnitude and opposite directions of a dielectrophoretic force imposed on the random SWCNT solution, metallic SWCNTs deposit onto an electrode while semiconducting SWCNTs remain in suspension [3]. A discussion of these techniques is presented, along with a dielectrophoretic force-utilized microfluidic lab-on-a-chip device that can accomplish purification of semiconducting nanoparticles at high processing rates. The effectiveness of the device is characterized using Raman spectroscopy analysis on separated samples.

Growth of metal-catalyst-free nitrogen-doped metallic single-wall carbon nanotubes.

Nitrogen-doped (N-doped) single-wall carbon nanotubes (SWCNTs) were synthesized by chemical vapor deposition using SiOx nanoparticles as a catalyst and ethylenediamine as the source of both carbon and nitrogen. The N-doped SWCNTs have a mean diameter of 1.1 nm and a narrow diameter range, with 92% of them having diameters from 0.7 to 1.4 nm. Multi-wavelength laser Raman spectra and temperature-dependent electrical resistance indicate that the SWCNT sample is enriched with metallic nanotubes. These N-doped SWCNTs showed excellent electrocatalytic activity for the oxygen reduction reaction and highly selective and sensitive sensing ability for dopamine detection.

A betavoltaic microcell based on Au/s-SWCNTs/Ti Schottky junction

This paper reports a new type betavoltaic (BV) microcell based on intrinsic p-type semiconductive single-walled carbon nanotubes (s-SWCNTs). Our device composes of Au and Ti asymmetrical electrode pairs with s-SWCNTs laid over them forming Schottky junction with Ti and ohmic contact with Au. SWCNT bundles were self-assembled between Au and Ti electrodes by Dieletrophoretic (DEP) technique, and metallic SWCNTs (m-SWCNTs) were selectively eliminated by current-induced electrical breakdown method. 3.3mCi/cm2 thin-film radioisotope 63Ni serves as beta particles source, with 100-year half-time and low toxicity. Test results show that SWCNTs BV microcell has the open circuit voltage (VOC) of 26mV, short circuit current density (JSC) of 2.19μA/cm2 and energy conversion efficiency (η) of 5.20%.

Structural Control of Carbon Nanotubes due to Magnetic Fields Applied in Preparation

Abstract Multi- and single-walled carbon nanotubes (MWCNTs and SWCNTs) were prepared by the chemical vapor deposition from ethanol-saturated Ar gas onto catalytic substrates at 1073 K under magnetic fields of up to 10 T. MWCNTs were aligned in parallel to magnetic fields more than 4 T in the growth process even at 1073 K. Also, the formation of metallic SWCNTs of around 1.0-nm diameter was promoted over 4 T. These results demonstrate that magnetic fields may control the growth of CNTs.

Highly enhanced gas sensing in single-walled carbon nanotube-based thin-film transistor sensors by ultraviolet light irradiation

Single-walled carbon nanotube (SWCNT) random networks are easily fabricated on a wafer scale, which provides an attractive path to large-scale SWCNT-based thin-film transistor (TFT) manufacturing. However, the mixture of semiconducting SWCNTs and metallic SWCNTs (m-SWCNTs) in the networks significantly limits the TFT performance due to the m-SWCNTs dominating the charge transport. In this paper, we have achieved a uniform and high-density SWCNT network throughout a complete 3-in. Si/SiO2 wafer using a solution-based assembly method. We further utilized UV radiation to etch m-SWCNTs from the networks, and a remarkable increase in the channel current on/off ratio (Ion/Ioff) from 11 to 5.6 × 103 was observed. Furthermore, we used the SWCNT-TFTs as gas sensors to detect methyl methylphosphonate, a stimulant of benchmark threats. It was found that the SWCNT-TFT sensors treated with UV radiation show a much higher sensitivity and faster response to the analytes than those without treatment with UV radiation.

TEMPERATURE DEPENDENCE OF ELECTRICAL RESISTANCE OF INDIVIDUAL CARBON NANOTUBES AND CARBON NANOTUBES NETWORK

We present a model to understand the effect of temperature on the electrical resistance of individual semiconducting single wall carbon nanotubes (s-SWCNTs) of various diameters under various electric fields. The temperature dependence of the resistance of s-SWCNTs and metallic SWCNTs (m-SWCNTs) are compared. These results help us to understand the temperature dependence of the resistance of SWCNTs network. We experimentally examine the temperature dependence of the resistance of random networks of SWCNTs, prepared by dispersing CNTs in ethanol and drop-casting the solution on prefabricated metallic electrodes. Examining various samples with different electrode materials and spacings, we find that the dominant resistance in determination of the temperature dependence of resistance of the network is the resistance of individual tubes, rather than the tube–tube resistance or tube–metal contact resistance. It is also found that the tube–tube resistance depends on the electrode spacing and it is more important for larger electrode spacings. By applying high electric field to burn the all-metallic paths of the SWCNTs network, the temperature dependence of the resistance of s-SWCNTs is also examined. We also investigate the effect of acid treatment of CNTs on the temperature dependence of the resistance of SWCNTs and also multi-wall CNTs (MWCNTs) networks.

Hydrogen adsorption on Na–SWCNT systems

We investigate the hydrogen adsorption capacity of Na-coated carbon nanotubes (Na-SWCNTs) using first-principles electronic structure calculations at absolute temperature and pressure. A single Na atom is always found to occupy the hollow site of a hexagonal carbon ring in all the six different SWCNTs considered, with a nearly uniform Na–C bond length of 2.5 A. Semiconducting zigzag nanotubes, (8,0) and (5,0), show stronger binding energies for the Na atom (−2.1 eV and −2.6 eV respectively), as compared to metallic SWCNTs with armchair and chiral geometries. The single Na atom can further adsorb up to six hydrogen molecules with a relatively constant binding energy of −0.26 eV per H2. Mulliken population analysis shows that positively charged Na atoms with 0.82e charge transfer to nearest carbon atoms which polarizes the SWCNT leading to local dipole moments. This charge-induced dipole interaction is responsible for the higher hydrogen uptake of Na-coated SWCNTs. The transition state search shows that the diffusion barrier of Na atom on the SWCNT between two adjoining C–C rings is 0.35 eV. We also investigate the clustering of Na atoms to find out the maximum weight percentage adsorption of H2 molecules. At high Na coverage, we show that Na-coated SWCNTs can adsorb 9.2–11.28 wt% hydrogen. Our analysis shows that, although indeed Na-coated SWCNTs present potential materials for the hydrogen storage, care should be taken to avoid Na atoms clustering on the support material at elevated temperature and pressure, to achieve higher hydrogen capacity.

Bulk Synthesis of Large Diameter Semiconducting Single-Walled Carbon Nanotubes by Oxygen-Assisted Floating Catalyst Chemical Vapor Deposition

Semiconducting single-walled carbon nanotubes (s-SWCNTs) with a mean diameter of 1.6 nm were synthesized on a large scale by using oxygen-assisted floating catalyst chemical vapor deposition. The oxygen introduced can selectively etch metallic SWCNTs in situ, while the sulfur growth promoter functions in promoting the growth of SWCNTs with a large diameter. The electronic properties of the SWCNTs were characterized by laser Raman spectroscopy, absorption spectroscopy, and field effect transistor measurements. It was found that the content of s-SWCNTs in the samples was highly sensitive to the amount of oxygen introduced. Under optimum synthesis conditions, enriched s-SWCNTs can be obtained in milligram quantities per batch.

Physico-Chemical Properties of Iodine-Adsorbed Single-Walled Carbon Nanotubes

I2 was adsorbed on single-walled carbon nanotube from ethanol solution at 303 K. The I2 adsorption isotherm was Langmuirian, giving 35 (+/-10) mg g(-1) of the saturated adsorption amount (coverage 0.06-0.09). The I2-adsorption treatment of SWCNT bundles reduced the N2 adsorption amount at 77 K by only 3%; the adsorption amount of supercritical H2 at 77 K was decreased by 30% because of the I2-adsorption treatment, indicating the blocking of interstitial pores by adsorbed I2. These adsorption results indicated the adsorption of I2 molecules in the narrow interstitial pores. The I2-adsorption treatment increases the Raman intensity coming from metallic SWCNTs, and the dc electrical conductivity increased by 15% because of the I2-adsorption treatment, strongly suggesting the presence of charge-transfer interaction between I2 and SWCNTs irrespective of small coverage by I2.