Sorting of Single-Walled Carbon Nanotubes Based on Metallicity by

ARTICLE pubs.acs.org/JPCC

Sorting of Single-Walled Carbon Nanotubes Based on Metallicity by Selective Precipitation with Polyvinylpyrrolidone Junluo Feng,† Sk. Mahasin Alam,† Liang Yu Yan,† Chang Ming Li,† Zaher Judeh,† Yuan Chen,† Lain-Jong Li,§ Kok Hwa Lim,‡ and Mary B. Chan-Park*,† †

School of Chemical and Biomedical Engineering, ‡School of Electrical and Electronics Engineering, and School of Materials Science and Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore

§

bS Supporting Information ABSTRACT: Noncovalent polymer sorting of single-walled carbon nanotubes (SWNTs) was carried out using polyvinylpyrrolidone (PVP) in dimethylformamide (DMF) solvent. With long-term (i.e., 14-day) standing of SWNTs/PVP/DMF in ambient condition, the semiconducting SWNTs remain suspended in solvent while metallic SWNTs precipitated out. The preferential semiconducting nanotube suspension was confirmed by optical absorption spectroscopy, Raman spectroscopy, and field effect transistor measurements. Field-effect transistors made from the enriched semiconducting SWNTs show enhanced switching performance with typical on/off ratios of at least 1000. We propose that noncovalent charge transfer occurs between PVP and SWNTs, and metallic nanotubes with mobile electrons at/near the Fermi level are more susceptible to environmental temperature fluctuations than semiconducting nanotubes, so that with the small temperature increase experienced during 14 days of standing under normal laboratory condition, polymer unwrapping from metallic nanotubes occurs, leading to their selective precipitation.

’ INTRODUCTION Single-wall carbon nanotubes (SWNTs) produced by present synthesis methods are mixtures of metallic and semiconducting tubes that have different characteristics, depending on their chiralities. The presence of both metallic and semiconducting nanotubes in any sample of SWNTs has impeded the application of SWNTs in electronic devices as well as detailed study of the physical properties of specific nanotube species. The separation of metallic nanotubes from semiconducting ones has been a subject of great interest, and a number of separation techniques including dielectrophoretic deposition,1,2 electrophoresis,3 density differentiation,4 chemical selectivity to metallic tubes,5,6 and selective absorption using polymer in solvents7,8 have been reported. Chemical selectivity of specific nanotube species,5-7,9-11 either based on noncovalent or covalent interaction, appears attractive because of the simplicity of these methods. Noncovalent separation of SWNTs (e.g., by adsorbed amines, DNA, or aromatic polymer) can preserve their intrinsic structures and electronic properties,9,12-15 while covalent modification tends to interrupt the continuous SWNT π-system.16 The noncovalent approach is preferable and is employed in this study. Poly(9,9dioctylfluorenyl-2,7-diyl) (commonly referred to as PFO), a conjugated polymer that has strong noncovalent π-π interaction with SWNT surface, has been shown to have selective solubilization of SWNTs with specific diameters or chiral structures.7,11 Porphyrin and pyrene derivatives have been reported to preferentially suspend semiconducting and metallic SWNTs in the supernatant respectively.17,18 Despite these advancements, r 2011 American Chemical Society

the efficiency of the chemical-based selection may not be high or the polymer/organic molecule may not be easily washed away, so that field-effect transistors (FETs) made from them are not so commonly reported.17 Further, as-synthesized SWNTs are typically in the form of bundles due to the strong van der Waals interaction on the order of 500-1000 eV/μm.19 The dispersion of SWNTs into individuals in solution is a prerequisite for good separation. With the aid of dispersants, surfactants, and/or solvents, carbon nanotubes have been well-dispersed in water and solvents. Surfactants, such as sodium dodecyl sulfate (SDS)20 and sodium dodecylbenzene sulfonate (SDBS),21 significantly increase the dispersion stability of SWNTs. N,N-Dimethylformamide (DMF) and N-methylpyrrolidone (NMP) are some of the best solvents for dispersion of SWNTs.22 Polyvinylpyrrolidone (PVP), a polymeric dispersant, has been shown to improve the dispersion of SWNTs in NMP and increases the proportion of individually suspended SWNTs.23 Further, PVP suspends nanotubes by helical wrapping and not by strong π-π interaction.23 Further, PVP is water-soluble, making its removal by water afterward greener. In this paper, we use PVP to debundle CoMoCat SWNT aggregates in DMF solvent and further show that with extended (i.e., 14 day) standing of PVP/DMF/SWNT solution, the PVP selectively suspends semiconducting tubes. The SWNTs were analyzed with UV-visible-near infrared (UV-vis-NIR) Received: August 19, 2010 Revised: January 26, 2011 Published: March 04, 2011 5199

dx.doi.org/10.1021/jp107865m | J. Phys. Chem. C 2011, 115, 5199–5206

The Journal of Physical Chemistry C absorption spectroscopy, photoluminescence emission (PLE) spectroscopy, and Raman spectroscopy, and FETs were fabricated to demonstrate the enrichment of semiconducting tubes. We applied density functional calculations to calculate the charge distribution of PVP to understand the nature of its interactions with semiconducting and metallic nanotube species present. This novel method to separate metallic and semiconducting SWNTs with high yield and high purities (the ratio of metallic SWTNs is 0% after PVP separation) using PVP.

’ EXPERIMENTAL SECTION Materials. CoMoCAT SG65 single-wall carbon nanotubes were purchased from South West Nanotechnologies. PVP with the chemical structure shown in Scheme 1 was purchased from Sigma-Aldrich. They were used as received without purification. Methods. A 0.5 mg portion of the nanotubes was dispersed in 10 mL of DMF containing 5-25 mg of PVP solution. The solutions were sonicated in a sonic bath for 10 min, followed by probe sonication (500 W, 35%) for 10 min. The solution was allowed to stand at 30 °C for 14 days. This was followed by centrifugation at 10 000g for 10 min. Some of the supernatant in DMF was extracted for UV-vis-NIR spectroscopy. The rest of the supernatant was heated at 100 °C until the PVP had desorbed from the nanotubes, causing them to precipitate, and the precipitate was collected, washed with DMF and distilled water several times, and dried by vacuum oven at 50 °C for 48 h. The obtained PVP-separated SWNTs were dispersed in aqueous SDS, sonicated by probe sonication (500 W, 35%) for 10 min, and centrifuged at 10 000g for 10 min. The PVP suspended in

Scheme 1. Chemical Structure of Polyvinylpyrrolidone (PVP)

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SDS/H2O was used for UV-vis-NIR, Raman, and PLE spectroscopies and FET measurements. To form a FET, a drop of 50 μL of supernatant solution was cast on a SiO2/Si substrate (300 nm SiO2) with Au electrodes. The channel length was 20 μm and the channel width was 60 μm. After drying, the substrate was rinsed with deionized water and acetone. UV-vis-NIR absorption spectra, Raman spectra, and photoluminescence excitation (PLE) measurements were performed using a Varian Cary 5000 UV-vis-NIR spectrophotometer, a Renishaw inVia Raman microscope with 514.5 nm (2.41 eV) and 633 nm (1.96 eV) laser wavelengths, and a Jobin-Yvon Nanolog spectrofluorometer, respectively. The separation yield is calculated as yield = mass of semiSWNT obtained/mass of starting SWNT. The purity ratio of metallic nanotube species (RMet) in the sample was calculated as24 RMet ¼ 1=ð1 þ IS11 =IM11 Þ where the integrated intensity IM11 (IS11) for the M11 (S11) band could be calculated on the basis of the areas of the metallic and semiconducting UV-vis-NIR peaks peaks. The topography of the SWNTs on a flat surface was characterized with atomic force microscopy using an Asylum Research molecular force probe 3D microscope. Electrical measurements on the FETs were conducted at room temperature using a Keithley Instruments source meter analyzer (model 2636A). Computer Simulation. Density functional calculations25 were performed using the Becke’s three-parameter hybrid function26 with the nonlocal correlation of Lee, Yang, and Parr (B3LYP)27 theoretical calculations with the 6-311þG(d,p) basis set28 as implemented in the Gaussian 03 suite of programs.29 NPA analysis as implemented in the NBO 5.0 program30 was used to estimated the atomic charges in PVP. Previous reports have showed that the accuracy of the methods are sufficient for our current purposes.31,32

’ RESULTS AND DISCUSSION Figure 1a shows the UV-vis-NIR absorption spectra of CoMoCAT SWNTs suspended using PVP in DMF with and without the 14-day standing of the nanotube suspension in

Figure 1. UV-vis-NIR spectra of CoMoCAT nanotube solution: (a) In DMF solvent (1) in DMF immediately after nanotube suspension, (2) in DMF/PVP immediately after nanotube suspension, and (3) in DMF/PVP after 14 days standing and (b) in SDS/water solution (1) after separation with PVP and resuspended with SDS/water (twice) and (2) pristine SWNTs in SDS/water. 5200

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The Journal of Physical Chemistry C

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Figure 2. Photoluminescence excitation maps of (a) pristine SWNTs in SDS/H2O and (b) SWNTs after separation with PVP and resuspension in SDS/H2O. (c) Graphene sheet map of the normalized PLE intensity; the thickness of each circle is proportional to the concentration of the (n,m) species.

ambient conditions. Another portion of the SWNTs after standing in PVP/DMF solution for 14 days was heat-precipitated, washed, dried, and then resuspended in SDS/water, and the spectrum of resuspended SWNTs is shown in Figure 1b (the pristine SWNTs suspended using SDS/water was included as the control). (The PVP-separated SWNTs that were resuspended in SDS/H2O were used for most of the tests below, except for the AFM in Figure 5.) For CoMoCAT SWNTs, the absorption peaks in the 800-1400, 550-800, and 400-600 nm regions are due to the first and second van Hove transitions of semiconducting nanotubes (S11 and S22) and first van Hove transition of metallic nanotubes (M11), respectively.33 The peak at around 466 nm is due to metallic species [specifically (6,6) and (7,4)].34 The major semiconducting species is (6,5), as seen by the pronounced S22 and S11 absorption bands at 576 and 1000 nm respectively. After the PVP/DMF suspended SWNTs were left standing for 14 days, the peak due to metallic (6,6) and (7,4) species was diminished to the point of undetectibility (Figure 1a), but the strong absorbance due to semiconducting (6,5) species in the

supernatant persists. It appears that PVP preferentially suspends the semiconducting (6,5) species, resulting in a SWNT solution enriched in semiconducting SWNTs and depleted in metallic SWNTs. Figure 1b shows that the absorbance peak due to (6,6) and (7,4) species is entirely or almost entirely suppressed. Using the PVP dispersant without the 14-day standing period, the metallic peak can, however, be observed (Figure 1a, line 2). Only after 14 days of standing at 30 °C does the (6, 6) and (7, 4) metallic peak become depressed (Figure 1a, line 3). After standing at 50 °C for 15 h, the metallic peak was also depressed (data not shown), indicating that the metallic nanotubes precipitation is temperature/time sensitive. The separation yield to obtain semiconducting tubes is 77%. From Figure 1b, the metallic nanotube content in the pristine CoMoCAT sample is 7.5% but decreases to about 0% after PVP separation. This simple method is competitive with other reported methods, which also results in a high separation efficiency of 86%100%, depending also on the type of nanotube used (see Supporting Information).8,35-38 5201



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Table 1. Relative PLE Intensities of CoMoCAT Species before and after Separation in SDS Solutions41,43,44 relative peak intensity (%)b (n,m)

diameter (nm)

chiral angle θ

calculated intensitya

pristine

after PVP treatment

(6,5)

0.757

27.0

0.67

55.1

43.3

(7,5)

0.829

24.5

0.71

18.3

3.9

(7,6)

0.895

27.5

0.47

2.1

5.5

(8,3)

0.782

15.3

2.13

5.4

5.0

(8,4)

0.84

19.1

0.46

19.2

42.4

74.3

85.7

(6,5) þ (8,4) a

The calculated PL intensity is from Oyama et al.41 b The corrected intensity = experimental PL peak intensity/calculated PL intensity.

Figure 3. Resonant Raman scattering spectra of pristine SWNTs and PVP-treated supernatant SWNTs (resuspended in SDS/H2O) using (a) 514 nm laser, (b) 633 nm laser, (i) RBM modes, and (ii) D and G bands.

Also, the SWNTs after treatment with PVP show a spectral red shift of (6,5) S11 and S22 peaks by about 26 and 6 nm, respectively (Figure 1b). Red shifts in the nanotube absorption peaks may be attributed to an increase of the tube diameter39 or charge transfer onto the nanotubes. We postulate the spectral red shifts here to result from noncovalent charge-transfer interaction between PVP and SWNTs40 (to be further discussed below). Photoluminescence emission (PLE) spectroscopy can provide quantitative information about the abundance of semiconducting

nanotube species.41 Metallic nanotubes are not detectable by PLE because excitons are quenched nonradiatively near/at the Fermi level. Figures 2a and b show the semiconducting nanotube species present, and these are identified on the basis of the paper by Bachilo and Weisman.42 In the PLE map of pristine CoMoCAT nanotubes (Figure 2a), (6,5), (7,5), (8,4), (8,3), and (7,6) species are apparent, with (6,5) being the dominant species, corroborating the UV-vis-NIR spectra. After 14-day standing with PVP/DMF (Figure 2b), the (6,5) tubes remains the dominant species but somewhat decrease, while the (8,4) 5202



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Figure 4. (a) Id-Vg characteristics measured with Vd = 2 V at room temperature. (b) AFM image of a FET device made with PVP-treated SWNTs (and resuspended in SDS/H2O and washed). (c) Comparison of on/off ratio with and without separation. (d) On-current of nanotube FET devices.

intensity seems to be strongly enhanced, and the other minor species (7,5), (8,3) and (7,6) persist (Table 1).41,43,44 It also seems possible that the (8,4) intensity increase may be partially due to energy transfer happening within the bundles containing (8,4) and (6,5). The broadness of the (8,4) peak corroborates the existence of bundled SWNTs. Also, with the PVP-treated samples, the excitation wavelength of (8,4) peak is shifted downward toward (6,5). Energy transfer can occur between semiconducting SWNTs in small bundles, and it appears likely that there could be energy transfer from (6,5) to (8,4), since the new (8,4) peak has excitation wavelength that quite closely coincides with the excitation of (6,5) but the emission of (8,4). The peak at excitation of 566 nm and emission of 1025 nm is possibly caused by energy transfer from (6, 5) to (7,5).45 It appears that PVP likely wraps a few nanotubes so that energy transfer seems more pronounced.

To gain further understanding of the interaction between PVP and SWNTs, the supernatant solution of PVP-treated SWNTs was examined by resonant Raman scattering (RRS) using excitation lasers of 514 and 633 nm, which will probe both semiconducting and metallic CoMoCAT species, since they have diameters in the 0.7-0.9 nm range. The RRS spectra are normalized at the Gþ band (around 1590 cm-1 in Figure 3). The diameters of tubes are inversely proportional to radial breathing modes (RBM) peaks in the 100-400 cm-1 range. According to the Kataura plot, excitation with 514 nm laser probes semiconducting and metallic nanotubes with RBM peaks below and above 220 cm-1 respectively46,47 (Figure 3). It can be distinctly seen that, in the supernatant, the metallic species (8,5) and (7,4) peaks decreased after PVP treatment. The corresponding increase of the metallic SWNTs in the sediment portion was also observed with the 514 nm excitation laser (Supporting 5203



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Figure 5. AFM images of the SWNTs after standing as SWNTs/PVP/DMF for 14 days, heat precipitation, washing the precipitated SWNTs, and resuspending in DMF.

Information). Using 633 nm excitation laser, the peaks at around 280, 298, and 331 cm-1 are attributed to (7,5), (8,3), and (6,4) tubes, respectively, while the peak at 305 cm-1 is due to (6,5) tubes.48,49 After treatment with PVP, the intensity of the (6,5) peak in the supernatant becomes lower compared to the corresponding peak of pristine nanotubes, indicating the relative decrease of (6,5) tubes. This is consistent with an increase of the (6,5) peak in the sediment portion (Supporting Information, Figure S1b) and the PLE maps of PVP-treated SWNTs. (The 633 nm excitation laser does not cause resonance with major metallic nanotube species present in the CoMoCAT sample.) The 633 nm G band of pristine SWNTs comprises a broad Gband (1520-1560 cm-1) and a sharper Gþ band (around 1590 cm-1), indicative of the presence of metallic and semiconducting tubes, respectively.15 After treatment with PVP, the G- band narrows and becomes of lower intensity, indicating decreased metallic tubes. Also, the G- and Gþ bands red-shifted by about 4 and 3 cm-1, respectively, after separation with PVP, possibly due to charge transfer interactions.15,50 The disorder band (D) at 1325 cm-1 is generally reasoned to be due to defects in the lattice structure of tubes.15,51 The D band before and after PVP treatment seems to be similar, indicating that PVP does not interact with the nanotube sp3 structure covalently. The electronic properties of the separated semiconducting SWNTs were confirmed by the performance of FET devices employing them as the active material. Figure 4a shows the characteristics of a bottom-gated FET made with pristine and PVP-separated SWNTs. Figure 4b shows the AFM image of the

SWNT network in the channel region of the FET. Devices fabricated from pristine tubes have low on/off ratio (of less than 1000, Figure 4c), which indicates the presence of abundant metallic tubes. FETs made with PVP-separated SWNTs have high on/off ratios (between 103 and 105), indicating depletion of the metallic tubes, consistent with the UV-vis-NIR and Raman data. However, the on-current of around 0.1-0.01 μA for these devices is low (Figure 4d). This is possibly caused by poor nanotube contacts due to the insulating PVP layer wrapping around and lower carrier mobility of smaller diameter SWNTs.51 The high current on/off ratio up to 105 validates the prospect of improving electronic performance of FET device using SWNTs separated with PVP. For high-performance field effect transistor device applications, it is necessary that the PVP separation agent be desorbed from the nanotubes. The dipole-π interaction between PVP and SWNT surfaces makes it difficult to desorb this dispersant from a well-dispersed SWNT solution. We found that heating promotes the PVP desorption and decreases the precipitation time. The microstructure of desorbed SWNTs (after washing with DMF and resuspending in DMF) was examined by AFM (Figure 5). The image shows that the SWNTs are about 2-3 nm in diameter. We propose that there is noncovalent charge transfer between PVP and SWNTs. Removing electron density from a SWNT has been found to result in an upshift in the Gþ band peak at 1590 cm-1 (to e.g. 1593 cm-1), while adding electron density to a SWNT resulted in a downshift.50 From Figure 3b ii, we can see 5204



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Table 2. Computed Charge Distribution on the VP Monomer

a

atomb

NPA chargea

N1

-0.53

C2

-0.16

C3

-0.39

C4

-0.46

C5

þ0.70

O6

-0.64

C7

-0.02

C8 C9

-0.39 -0.58

C10

-0.58

Gaussian DFT-B3LYP using 6-311þG(d,p) basis set. b see Scheme 1.

Fermi level aggregated with higher rates than semiconducting ones, which remain mainly suspended in the supernatant. Separately, when citric acid solution was added to SWNTs/ PVP/DMF solution, flocculates appeared gradually. The mixture of DMF/citric acid solution provided intense heat (10 °C increase from 20 to 30 °C) just in a few seconds. Due to this heat, the SWNTs start to form flocculates. Too much heating (e.g., at 100 °C) causes PVP to desorb from all tube species but the little, gradual heating caused by standing for 14 days at ambient conditions causes PVP to selectively desorb only from metallic tube species.

’ CONCLUSION We show that PVP preferentially suspends semiconducting nanotubes after 14-day standing in ambient conditions. The preferential suspension of semiconducting nanotubes is confirmed by Raman spectroscopy, UV-visible absorption spectroscopy, and the high current on/off ratios of up to 105 of FET devices fabricated using PVP-separated SWNTs. From the band shifts in RRS G band and UV-vis-NIR curve, we postulate the semiconducting nanotubes selection is due to the noncovalent charge-transfer, which is more sensitive to environmental temperature fluctuations for metallic nanotubes than semiconducting nanotubes. The bundling takes place when PVP is removed, and that occurs when heat is added, and metallic nanotubes are more sensitive to this fluctuation and will have a greater tendency to precipitate out on standing. ’ ASSOCIATED CONTENT

bS

Supporting Information. Species of CoMoCat, purity of separation, and Raman spectra of PVP-treated sediment. This material is available free of charge via the Internet at http://pubs. acs.org.

’ AUTHOR INFORMATION

Figure 6. Photoluminescence excitation maps of PVP.

that the Gþ band has upshifted by about 3 cm-1, indicating that electrons have been removed from SWNTs. Density functional simulation shows that the PVP is highly polar with electronwithdrawing positive centers at C5 (þ0.7 e, see Table 2). So charge transfer between PVP and SWNTs possibly occurs at C5 and SWNTs. We propose that the wrapping of PVP around the nanotubes is exothermic, and the backward desorption reaction is endothermic as follows:19 ½PVP þ ½SWNTbundled T ½PVP - SWNTsuspended

ðexothermicÞ

The precipitation, indicating aggregation of SWNT, i.e. the backward reaction, is triggered by heat or near-IR. No precipitant was observed immediately after the SWNTs were sonicated and centrifuged in the presence of PVP in DMF. Heat is likely to cause desorption of the polymer from SWNTs. We found that PVP can fluorescence and emit in the near-IR region (Figure 6). Others have reported that SWNTs can act as “molecular heaters” triggered by the NIR irradiation.52 The PVP appears to fluoresce and emit in the near-IR region, possibly heating up the nanotubes. The generated heat causes the backward reaction, i.e., bundling, and metallic tubes have a greater tendency to bundle. It seems that in our case, metallic tubes with mobile electrons at the

Corresponding Author

*E-mail: [email protected]. Tel: (65) 6790 6064. Fax: (65) 6792 4062.

’ ACKNOWLEDGMENT The work was supported by a Competitive Research Program grant from the Singapore National Research Foundation (NRFCRP2-2007-02). ’ REFERENCES (1) Krupke, R.; Hennrich, F.; von Lohneysen, H.; Kappes, M. M. Science 2003, 301, 344–347. (2) Krupke, R.; Linden, S.; Rapp, M.; Hennrich, F. Adv. Mater. 2006, 18, 1468–1470. (3) Kim, W. J.; Usrey, M. L.; Strano, M. S. Chem. Mater. 2007, 19, 1571–1576. (4) Arnold, M. S.; Green, A. A.; Hulvat, J. F.; Stupp, S. I.; Hersam, M. C. Nat. Nano. 2006, 1, 60–65. (5) Kanungo, M.; Lu, H.; Malliaras, G. G.; Blanchet, G. B. Science 2009, 323, 234–237. (6) Wang, C.; Cao, Q.; Ozel, T.; Gaur, A.; Rogers, J. A.; Shim, M. J. Am. Chem. Soc. 2005, 127, 11460–11468. (7) Chen, F. M.; Wang, B.; Chen, Y.; Li, L. J. Nano Lett. 2007, 7, 3013–3017. 5205


The Journal of Physical Chemistry C (8) Tu, X. M.; Manohar, S.; Jagota, A.; Zheng, M. Nature 2009, 460, 250–253. (9) Marquis, R.; Greco, C.; Sadokierska, I.; Lebedkin, S.; Kappes, M. M.; Michel, T.; Alvarez, L.; Sauvajol, J. L.; Meunier, S.; Mioskowski, C. Nano Lett. 2008, 8, 1830–1835. (10) Satake, A.; Miyajima, Y.; Kobuke, Y. Chem. Mater. 2005, 17, 716–724. (11) Nish, A.; Hwang, J. Y.; Doig, J.; Nicholas, R. J. Nat. Nano. 2007, 2, 640–646. (12) Chattopadhyay, D.; Galeska, I.; Papadimitrakopoulos, F. J. Am. Chem. Soc. 2003, 125, 3370–3375. (13) Maeda, Y.; Kimura, S.-i.; Kanda, M.; Hirashima, Y.; Hasegawa, T.; Wakahara, T.; Lian, Y.; Nakahodo, T.; Tsuchiya, T.; Akasaka, T.; Lu, J.; Zhang, X.; Yu, Y.; Nagase, S.; Kazaoui, S.; Minami, N.; Shimizu, T.; Tokumoto, H.; Saito, R. J. Am. Chem. Soc. 2005, 127, 10287–10290. (14) Zheng, M.; Diner, B. A. J. Am. Chem. Soc. 2004, 126, 15490– 15494. (15) Yi, W. H.; Malkovskiy, A.; Chu, Q. H.; Sokolov, A. P.; Colon, M. L.; Meador, M.; Pang, Y. J. Phys. Chem. B 2008, 112, 12263–12269. (16) Fujigaya, T.; Nakashima, N. Polym. J. 2008, 40, 577–589. (17) Hersam, M. C. Nat. Nano. 2008, 3, 387–394. (18) Li, H. P.; Zhou, B.; Lin, Y.; Gu, L. R.; Wang, W.; Fernando, K. A. S.; Kumar, S.; Allard, L. F.; Sun, Y. P. J. Am. Chem. Soc. 2004, 126, 1014–1015. (19) O’Connell, M. J.; Boul, P.; Ericson, L. M.; Huffman, C.; Wang, Y. H.; Haroz, E.; Kuper, C.; Tour, J.; Ausman, K. D.; Smalley, R. E. Chem. Phys. Lett. 2001, 342, 265–271. (20) Richard, C.; Balavoine, F.; Schultz, P.; Ebbesen, T. W.; Mioskowski, C. Science 2003, 300, 775–778. (21) Islam, M. F.; Rojas, E.; Bergey, D. M.; Johnson, A. T.; Yodh, A. G. Nano Lett. 2003, 3, 269–273. (22) Ausman, K. D.; Piner, R.; Lourie, O.; Ruoff, R. S.; Korobov, M. J. Phys. Chem. B 2000, 104, 8911–8915. (23) Hasan, T.; Scardaci, V.; Tan, P. H.; Rozhin, A. G.; Milne, W. I.; Ferrari, A. C. J. Phys. Chem. C 2007, 111, 12594–12602. (24) Miyata, Y.; Yanagi, K.; Maniwa, Y.; Kataura, H. J. Phys. Chem. C 2008, 112, 13187–13191. (25) Hohenberg, P.; Kohn, W. Phys. Rev. B 1964, 136, B864. (26) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652. (27) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B 1988, 37, 785–789. (28) Hehre, W. J. R., L.; Schleyer, P. V. R.; Pople, J. A. Ab Initio Molecular Orbital Theory; Wiley: New York, 1996. (29) Frisch, M. J. T., G., W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; P. Y. Ayala, K. M.; G. A. Voth, P. S.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Q. C.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; G. Liu, A. L.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03; Gaussian Inc.: Wallingford CT, 2004. (30) Glendening, E. D. B., J., K.; Reed, A. E.; Carpenter, J. E.; Bohmann, J. A.; Morales, C. M.; Weinhold, F. NBO 5.G; Theoretical Chemistry Institute: Madison, 2001. (31) Sk, M. A.; Xi, H. W.; Lim, K. H. Organometallics 2009, 28, 3678–3685. (32) Jiayi Guo, H.-w. X.; Lim, K. H.; So, C.-W. Chem. Commun. 2010, 46, 1929–1931. (33) O’Connell, M. J.; Bachilo, S. H.; Huffman, C. B.; Moore, V. C.; Strano, M. S.; Haroz, E. H.; Rialon, K. L.; Boul, P. J.; Noon, W. H.;

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Kittrell, C.; Ma, J.; Hauge, R. H.; Weisman, R. B.; Smalley, R. E. Science 2002, 297, 593–596. (34) Zhao, J. W.; Lee, C. W.; Han, X. D.; Chen, F. M.; Xu, Y. P.; Huang, Y. Z.; Chan-Park, M. B.; Chen, P.; Li, L. J. Chem. Commun. 2009, 46, 7182–7184. (35) An, K. H.; Yang, C.-M.; Seo, K.; Park; Lee, Y. H. Curr. Appl. Phys. 2006, e99–e109. (36) Qiu, H.; Maeda, Y.; Akasaka, T. J. Am. Chem. Soc. 2009, 131, 16529–16533. (37) Tanaka, T.; Jin, H.; Miyata, Y.; Kataura, H. Appl. Phys. Express 2008, 1, 114001. (38) An, K. H.; Lee, Y. H. NANO: Brief Rep. Rev. 2006, 1, 115–138. (39) Magadur, G.; Lauret, J. S.; Alain-Rizzo, V.; Voisin, C.; Roussignol, P.; Deleporte, E.; Delaire, J. A. Chemphyschem 2008, 9, 1250–1253. (40) Kauffman, D. R.; Kuzmych, O.; Star, A. J. Phys. Chem. C 2007, 111, 3539–3543. (41) Oyama, Y.; Saito, R.; Sato, K.; Jiang, J.; Samsonidze, G. G.; Gruneis, A.; Miyauchi, Y.; Maruyama, S.; Jorio, A.; Dresselhaus, G.; Dresselhaus, M. S. Carbon 2006, 44, 873–879. (42) Bachilo, S. M.; Strano, M. S.; Kittrell, C.; Hauge, R. H.; Smalley, R. E.; Weisman, R. B. Science 2002, 298, 2361–2366. (43) Wei, L.; Wang, B.; Goh, T. H.; Li, L. J.; Yang, Y. H.; Chan-Park, M. B.; Chen, Y. J. Phys. Chem. B 2008, 112, 2771–2774. (44) Hwang, J. Y.; Nish, A.; Doig, J.; Douven, S.; Chen, C. W.; Chen, L. C.; Nicholas, R. J. J. Am. Chem. Soc. 2008, 130, 3543–3553. (45) Tan, P. H.; Hasan, T.; Bonaccorso, F.; Scardaci, V.; Rozhin, A. G.; Milne, W. I.; Ferrari, A. C. Physica E 2008, 40, 2352–2359. (46) Maeda, Y.; Kanda, M.; Hashimoto, M.; Hasegawa, T.; Kimura, S.; Lian, Y. F.; Wakahara, T.; Akasaka, T.; Kazaoui, S.; Minami, N.; Okazaki, T.; Hayamizu, Y.; Hata, K.; Lu, J.; Nagase, S. J. Am. Chem. Soc. 2006, 128, 12239–12242. (47) Jorio, A.; Santos, A. P.; Ribeiro, H. B.; Fantini, C.; Souza, M.; Vieira, J. P. M.; Furtado, C. A.; Jiang, J.; Saito, R.; Balzano, L.; Resasco, D. E.; Pimenta, M. A. Phys. Rev. B 2005, 72 (7), 075207. (48) Strano, M. S. J. Am. Chem. Soc. 2003, 125, 16148–16153. (49) Yan, L. Y.; Li, W. F.; Fan, X. F.; Wei, L.; Chen, Y.; Kuo, J. L.; Li, L. J.; Kwak, S. K.; Mu, Y. G.; Chan-Park, M. B. Small 2010, 6, 110–118. (50) Wise, K. E.; Park, C.; Siochi, E. J.; Harrison, J. S. Chem. Phys. Lett. 2004, 391, 207–211. (51) Zhang, L.; Zaric, S.; Tu, X. M.; Wang, X. R.; Zhao, W.; Dai, H. J. J. Am. Chem. Soc. 2008, 130, 2686–2691. (52) Narimatsu, K.; Niidome, Y.; Nakashima, N. Chem. Phys. Lett. 2006, 429, 488–491.

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