A systematic study on the use of 9,9-dialkylfluorene homopolymers (PFs) for large-diameter semiconducting (sc-) single-walled carbon nanotube (SWCNT) enrichment is the focus of this report. The enrichment is based on a simple three-step extraction process: (1) dispersion of as-produced SWCNTs in a PF solution; (2) centrifugation at a low speed to separate the enriched sc-tubes; (3) filtration to collect the enriched sc-SWCNTs and remove excess polymer. The effect of the extraction conditions on the purity and yield including molecular weight and alkyl side-chain length of the polymers, SWCNT concentration, and polymer/SWCNT ratio have been examined. It was observed that PFs with alkyl chain lengths of C10, C12, C14, and C18, all have an excellent capability to enrich laser-ablation sc-SWCNTs when their molecular weight is larger than ∼10 000 Da. More detailed studies were therefore carried out with the C12 polymer, poly(9,9-di-n-dodecylfluorene), PFDD. It was found that a high polymer/SWCNT ratio leads to an enhanced yield but a reduced sc-purity. A ratio of 0.5-1.0 gives an excellent sc-purity and a yield of 5-10% in a single extraction as assessed by UV-vis-NIR absorption spectra. The yield can also be promoted by multiple extractions while maintaining high sc-purity. Mechanistic experiments involving time-lapse dispersion studies reveal that m-SWCNTs have a lower propensity to be dispersed, yielding a sc-SWCNT enriched material in the supernatant. Dispersion stability studies with partially enriched sc-SWCNT material further reveal that m-SWCNTs : PFDD complexes will re-aggregate faster than sc-SWCNTs : PFDD complexes, providing further sc-SWCNT enrichment. This result confirms that the enrichment was due to the much tighter bundles in raw materials and the more rapid bundling in dispersion of the m-SWCNTs. The sc-purity is also confirmed by Raman spectroscopy and photoluminescence excitation (PLE) mapping. The latter shows that the enriched sc-SWCNT sample has a narrow chirality and diameter distribution dominated by the (10,9) species with d = 1.29 nm. The enriched sc-SWCNTs allow a simple drop-casting method to form a dense nanotube network on SiO2/Si substrates, leading to thin film transistors (TFTs) with an average mobility of 27 cm(2) V(-1) s(-1) and an average on/off current ratio of 1.8 × 10(6) when considering all 25 devices having 25 μm channel length prepared on a single chip. The results presented herein demonstrate how an easily scalable technique provides large-diameter sc-SWCNTs with high purity, further enabling the best TFT performance reported to date for conjugated polymer enriched sc-SWCNTs.

Boron nitride nanotubes (BNNTs) exhibit a range of properties that are as compelling as those of carbon nanotubes (CNTs); however, very low production volumes have prevented the science and technology of BNNTs from evolving at even a fraction of the pace of CNTs. Here we report the high-yield production of small-diameter BNNTs from pure hexagonal boron nitride powder in an induction thermal plasma process. Few-walled, highly crystalline small-diameter BNNTs (∼5 nm) are produced exclusively and at an unprecedentedly high rate approaching 20 g/h, without the need for metal catalysts. An exceptionally high cooling rate (∼10(5) K/s) in the induction plasma provides a strong driving force for the abundant nucleation of small-sized B droplets, which are known as effective precursors for small-diameter BNNTs. It is also found that the addition of hydrogen to the reactant gases is crucial for achieving such high-quality, high-yield growth of BNNTs. In the plasma process, hydrogen inhibits the formation of N2 from N radicals and promotes the creation of B-N-H intermediate species, which provide faster chemical pathways to the re-formation of a h-BN-like phase in comparison to nitridation from N2. We also demonstrate the fabrication of macroscopic BNNT assemblies such as yarns, sheets, buckypapers, and transparent thin films at large scales. These findings represent a seminal milestone toward the exploitation of BNNTs in real-world applications.

Gold nanoparticles were produced by femtosecond laser ablation of a gold metal plate in an aqueous solution of α-cyclodextrin (CD), β-CD, or γ-CD. The gold nanoparticles exhibited the UV−vis absorption spectrum with a maximum absorption band at 520 nm, similar to that of gold nanoparticles chemically prepared in a solution. The size distribution of the nanoparticles measured by transmission electron microscopy (TEM) shifted to a drastically smaller size of ∼2−2.4 nm and narrower size distribution of less than 1−1.5 nm fwhm with an increase in the concentration of cyclodextrins. Both the particle size and size distribution were also dependent on the type of cyclodextrins used in aqueous solution. In particular, the gold colloids resulting from ablation in 10 mM β-CD were conspicuously stable under aerobic conditions without any protective agent present. CDs formed an inclusion complex with ablated atoms to reduce the total concentration of embryonic nanoparticles formed in the plume CDs, as evident by Raman spectroscopy. The consecutive particle growth due to the mutual coalescence between nanoclusters and their neighboring free gold atoms was severely limited in the presence of CDs.

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Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Covalent functionalization of boron nitride nanotubes via reduction chemistry Shin, Homin; Guan, Jingwen; Zgierski, Marek Z.; Kim, Keun S.; Kingston, Christopher T.; Simard, Benoit http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=fr L'accès à ce site Web et l'utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D'UTILISER CE SITE WEB. NRC Publications Record / Notice d'Archives des publications de CNRC:http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=21277400&lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=21277400&lang=fr READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions?Contact the NRC Publications Archive team at PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous.http://doi.org/10.1021/acsnano.5b06523 ACS Nano, 9, 12, pp. 12573-12582, 2015-11-18 B oron nitride nanotubes (BNNTs) consist of seamless cylinders of alternating boron and nitrogen atoms in a hexagonal BN bonding network. 1,2 Since their first synthesis in 1995, 1 BNNTs have been considered as revolutionary materials due to their unique properties, which are as compelling as those of carbon nanotubes (CNTs). Despite their structural similarity to CNTs, BNNTs also exhibit a range of physical and chemical properties distinct from CNTs, which are mainly attributed to the partial ionic bonding character of BN. For example, the mixed ionic and covalent bonding nature of BNNTs results in their wide band gaps, around 6.0 eV independent of diameter and chirality. Figure 1 illustrates the calculated valence electron density distribution of a (6,6) CNT and BNNT. The valence charges of a CNT are equally distributed around C atoms, indicating a strong covalent CÀC bond network as well as the delocalized electrons, while the bonding electrons of BNNT are more concentrated around N atoms with an asymmetric charge distribu...

We recently demonstrated scalable manufacturing of boron nitride nanotubes (BNNTs) directly from hexagonal BN (hBN) powder by using induction thermal plasma, with a high-yield rate approaching 20 g/h. The main finding was that the presence of hydrogen is crucial for the high-yield growth of BNNTs. Here we investigate the detailed role of hydrogen by numerical modeling and in situ optical emission spectroscopy (OES) and reveal that both the thermofluidic fields and chemical pathways are significantly altered by hydrogen in favor of rapid growth of BNNTs. The numerical simulation indicated improved particle heating and quenching rates (∼10 K/s) due to the high thermal conductivity of hydrogen over the temperature range of 3500-4000 K. These are crucial for the complete vaporization of the hBN feedstock and rapid formation of nanosized B droplets for the subsequent BNNT growth. Hydrogen is also found to extend the active BNNT growth zone toward the reactor downstream, maintaining the gas temperature above the B solidification limit (∼2300 K) by releasing the recombination heat of H atoms, which starts at 3800 K. The OES study revealed that H radicals also stabilize B or N radicals from dissociation of the feedstock as BH and NH radicals while suppressing the formation of N or N species. Our density functional theory calculations showed that such radicals can provide faster chemical pathways for the formation of BN compared with relatively inert N.

With recent improvements in carbon nanotube separation methods, the accurate determination of residual metallic carbon nanotubes in a purified nanotube sample is important, particularly for those interested in using semiconducting single-walled carbon nanotubes (SWCNTs) in electronic device applications such as thin-film transistors (TFTs). This work demonstrates that Raman microscopy mapping is a powerful characterization tool for quantifying residual metallic carbon nanotubes present in highly enriched semiconducting nanotube networks. Raman mapping correlates well with absorption spectroscopy, yet it provides greater differentiation in purity. Electrical data from TFTs with channel lengths of 2.5 and 5 μm demonstrate the utility of the method. By comparing samples with nominal purities of 99.0% and 99.8%, a clear differentiation can be made when evaluating the current on/off ratio as a function of channel length, and thus the Raman mapping method provides a means to guide device fabrication by correlating SWCNT network density and purity with TFT channel scaling.As-prepared single-walled corbon nanotube (SWCNT) raw materials contain bundles of nanotubes with a 2:1 semiconducting (sc-) to metallic (m-) ratio and other impurities such as catalysts and amorphous carbon [1][2][3]. For electrical devices, these raw materials must be debundled, purified, and enriched [4][5][6][7][8][9][10][11]. It has been demonstrated that for network thin-film transistors (TFTs), the m-tube content should be less than 2% [3]. For more demanding applications, such as high-frequency logic circuits and display backplanes, the m-tube content should be less than a few ppm given the need for high mobility and high current on/off ratios [12]. In recent years, multiple efforts have led to significant progress in solution-based enrichment techniques, with sc-SWCNT purities in excess of 99% routinely achieved. This leap, however, has now started to reveal the limits of common characterization methods, and other tools are required to provide accurate purity assessment [13,14].Typically, the purity of enriched sc-SWCNTs is Nano Research 2 Nano Res. estimated from the UV absorption spectrum by comparing the peak areas associated with the m-or sc-species [12,[15][16][17]. This method works well for samples whose peaks are well defined and for which background absorption is not dominant. However, as the sc-species purity increases, the features associated with m-tube absorption will gradually disappear and the precise subtraction of the background absorption will dramatically influence the calculated results and introduce uncertainty [18]. As an alternative, we have previously used a different purity metric, denoted as φ, which is based on the ratio of the sc-peak area over the total absorption background from the metallic (M 11 ) and semiconducting (S 22 ) absorption bands [16].Although we presume that φ correlates well with purity for highly pure samples, it does not provide a quantitative assessment. Furthermore, a solution sample is not nece...