This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.
Article Cite This: ACS Omega 2019, 4, 1941−1946
http://pubs.acs.org/journal/acsodf
Toward a Predominant Substitutional Bonding Environment in B‑Doped Single-Walled Carbon Nanotubes Carlos Reinoso,† Claudia Berkmann,† Lei Shi,†,‡ Alexis Debut,§ Kazuhiro Yanagi,∥ Thomas Pichler,† and Paola Ayala*,† †
Faculty of Physics. University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria School of Materials Science & Engineering, Sun Yat-sen University, 510275 Guangzhou, Guangdong, P. R. China § Centro de Nanociencia y Nanotecnología, Universidad de las Fuerzas Armadas--ESPE, P.O. Box 171102, Sangolqui, Ecuador ∥ Department of Physics, Tokyo Metropolitan University, Hachioji, 192-0397 Tokyo, Japan
Downloaded via 5.101.222.240 on January 28, 2019 at 19:59:09 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
‡
ABSTRACT: B-doped single-walled carbon nanotubes have been synthesized from sodium tetraphenyl borate and record incorporation percentages of B heteroatoms have been found in this material as-synthesized. However, carbonaceous impurities, besides other byproducts, can still contain boron and therefore exhibit various types of competing bonding environments. To circumvent this issue, which has constantly hindered a conclusive insight to the existing bonding environments in materials alike, we have employed a purification method, which leaves ∼7% at. of B atoms of the total sample composition almost exclusively in the sp2 configuration. This record B substitutional doping, together with the identification of the competing bonding environments are revealed here unambiguously from X-ray photoelectron spectroscopy. The doping level in the purified tubes is about an order of magnitude larger than in other B-doped single-walled tubes even without purification, and brings the state-of-the-art closer to the controlled applicability of this material.
■
INTRODUCTION The research seeking to control the physical properties of carbon nanotubes has led to propose creative functionalization pathways with different degrees of accuracy.1−3 Chemically stimulating the tube’s functionality by p- or n-type doping has been sought both theoretically and experimentally with substitutional dopants such as N, B, P, Si, and Ni so far.4−6 Heteroatoms at the carbon sites are expected to be a very promising candidate to have localized sites that induce changes in the physical properties of the tubes with very specific characteristics.7−9 To make this feasible, it is imperative to control the dopant’s concentration and bonding environment. However, this is still one of the major challenges in the field.10 A very large number of publications on the synthesis and some applications of single-walled and multiwalled N-doped nanotubes are available,1,3 whereas experimental research for the other mentioned dopants lags far behind. Nowadays, B-doped single-walled carbon nanotubes (CBx-SWNTs) can be produced in significant amounts with high temperature methods (arc discharge and laser ablation).11−13 Another effective way found in the literature corresponds to substitution reactions,14−16 but the highly desirable scalability at lower cost via chemical vapor deposition has constantly encountered drawbacks that limit the yield of CBxSWNTs.17−20 B-doping on nanotubes has not only been difficult from the sample production perspective. Identifying © 2019 American Chemical Society
the percentages of heteroatoms has constantly shown difficulties because of the low incorporation rates of substitutional atoms, which have imposed instrumental challenges for their detection.21−24 Most of the initial studies were done with Raman spectroscopy, given the extremely low incorporation of B, which hindered the effective use of analytical methods.11,13,25 In fact, the B-doping level in CBx-SWNTs has historically been investigated indirectly using as reference the amounts of B in the materials used for the synthesis. Also, the bulk solubility of B in C hinted a plausible limit of incorporation of heteroatoms in the structures,26 but it is important to bear in mind that the atomic arrangement in a structure like a nanotube could open a different perspective. On the other hand, the production of BC3 nanotubes and carbon SWNTs with BC3 nanodomains has also been reported.27,28 Taking this into consideration, B-doped samples could have nanodomains or islands of BC3, which are not necessarily in Raman resonance, and therefore their contribution to the quantification of doping levels must be carefully considered. Also, independent from the method used for synthesis, the presence of carbonaceous byproducts cannot be avoided and in samples as-synthesized, B atoms can also be Received: October 31, 2018 Accepted: January 11, 2019 Published: January 25, 2019 1941
DOI: 10.1021/acsomega.8b03031 ACS Omega 2019, 4, 1941−1946
ACS Omega
Article
detected from agglomerates and structures that are not necessarily nanotubes. In this context, the last decade’s research on carbon nanotubes has shown tremendous progress in the production of samples almost free of impurities through different purification and separation methods.29−31 However, substitutionally doped nanotubes have rarely been purified after synthesis, bearing in mind the potential reactivity of the active heteroatom sites.32 We have worked toward the production of CBx-SWNTs based on the use of sodium tetraphenyl borate, which is a solid C and B source, in highvacuum chemical vapor deposition as reported previously.33 This method reported the incorporation of up to 13 at. % of boron atoms in the sp2 configuration in the samples as-grown, but the exclusive localization of these atoms on the tubes’ wall could not be concluded. Here, we report the possibility to optimize the amount of nanotube material versus impurities. The B atoms are bonded to C in the sp2 configuration with record values around 7% at. in samples alike. The competing species in the byproducts that contain B and appear before and after purification are not related with C, and they can be removed with independent chemical processes.
Figure 1. (a) Multifrequency Raman spectra recorded with 633, 532, 514, and 488 nm excitation wavelengths in the RBM region corresponding to the sample synthesized at the optimal synthesis temperature and the same purified with methods S1 and S2. (b) Raman spectra recorded on the same three samples with the 488 nm laser line on the G and D band region.
■
RESULTS AND DISCUSSION Our CBx-SWNT synthesis process involves the chemical vapor deposition of a vapor of sodium tetraphenyl-borate obtained from the sublimation of the solid precursor.33 Assuming the temperature window for the synthesis of the CBx-SWNTs is given by the eutectic limit of the catalysts and the sodium tetraphenyl borate pyrolysis temperature, the optimal nanotube growth could be defined,34 but the temperature window for optimal B incorporation is narrow. Taking both into account, we applied various purification processes and two of them were optimized toward obtaining clean and crystalline material, as reported here. The purification procedures were performed using mild chemical oxidation to achieve a better understanding of the B incorporation. The two protocols discussed from this point were (S1) HCl and (S2) HCl + H2O2 (both in aqueous solution). Analyzing both purification pathways toward keeping the crystallinity of the material, the first part of our studies was focused on the overall morphology via Raman spectroscopy and electron microscopy. Figure 1a shows a multifrequency study on the two purification methods employed against the spectra recorded for pristine material. The top spectra (in color) correspond to the samples as-synthesized. For these purposes, the 633, 532, 514, and 488 nm excitation wavelengths were used to record spectra on the radial breathing mode (RBM) resonance region. The samples contain predominantly SWCNTs, revealing the strongest RBM response between 140 and 270 cm−1 corresponding to diameters between 0.89 and 1.9 nm determined by RBM = 223/dt + 10.35 This is a representative sample of the highest abundance region for tubes produced with sodium tetraphenyl borate.33 The vertical dashed lines are a guide to the eye to identify this size region. Compared to the previously reported material synthesized with high vacuum chemical vapor deposition, these nanotubes have a slightly larger diameter distribution36 but still small compared to the most pure carbon nanotubes made with the same technique.37−39 However, the yield in this case is clearly larger, which has actually allowed us to purify the CBx-SWNTs and in turn is the reason why previously reported materials were not purified. Focusing on the spectra recorded after purification, we can observe that
both processes destroy the smaller diameter tubes, and although some thin tubes are observed in the RBM region, it is not possible to state unambiguously that one or the other process is better to preserve a certain diameter population. On the other hand, both processes have damaged the tubes above 1.5 nm. This end product is analogous in diameter distribution to the pristine purified samples made from DIPs, arc discharge, and laser ablation. To complement this study, we measured optical absorption, and the spectra recorded from the S2-purified and the nonpurified material (not shown here) were weighed against each other. Clearly, the purified material has a more defined fine structure and the diameter distribution of the samples remains after purification but with different abundances. Still, the effect of the dopants given by observable shifts on the optical absorption of these materials is a part of ongoing studies. Additionally, buckypapers of the material right after S1 and S2 were observed using scanning electron microscopy (SEM), whereas dispersed samples were seen using transmission electron microscopy (TEM). After purification with S1, agglomerates (presumably carbonaceous) and rests with the typical morphology of catalyst supports were still present in the sample. However, the material purified with S2 exhibited much more homogeneous nanotube morphology. Figure 2b is a low magnification image of the S2-purified material, where a clean and homogeneous film can be seen. Figure 2c shows a TEM micrograph with long strands of very straight CBx-SWNTs. From the point of view of preserving the shape and low defect concentration, combined with a good purity, the purification method S2 showed better performance. Furthermore, it is well understood that purification methods of pristine tubes can induce specific types of defects in the end material.30 Here, it is therefore crucial to understand how the applied purification procedures change the starting CBx-SWNTs. The first clues in this respect can be provided by Raman spectroscopy, although it does not represent a pathway to quantify absolute values of dopants in SWNTs. However, it may allow understanding pand n-type doping because of the modifications in the Kohn 1942
DOI: 10.1021/acsomega.8b03031 ACS Omega 2019, 4, 1941−1946
ACS Omega
Article
measured with photoemission spectroscopy at synchrotron facilities with optimal resolution.42,43 However, the prerequisite for such type of study is the use of samples with narrow diameter distribution (narrower at least in half of the value we have in the samples of this study). On the other hand, the best values reported for CBx-SWNTs measured with the laboratorybased equipment are around ∼1 eV, but it is important to remark that those nanotubes were produced via hightemperature methods and are less defective than chemical vapor deposition (CVD) tubes. Furthermore, the doping levels in those previous studies were one order of magnitude smaller than the values reported here, as explained later. In this context, given that the introduction of defects in the hexagonal wall of a nanotube induces disorder, broadening and shifts on the C 1s line are naturally expected. Figure 3a shows the C 1s signal recorded from the nanotubes as-grown and purified with S1 and S2 with
Figure 2. (a) SEM micrograph of a buckypaper made of a material after the purification method S2. (b) SEM micrograph of a buckypaper made of a material after purification method S1. (c) TEM micrograph of bundles of single-walled nanotubes at high magnification on the dispersed samples of a material after purification method S2.
anomaly.40 Figure 1b shows the G and D band region recorded with a 488 nm excitation wavelength. The G line in the top spectrum corresponds to the sample as-synthesized. One can observe a clear separation and characteristic frequency of the G− and G+ split of the G band. This is a clear evidence for a good crystallinity of the as-grown material. Although the top spectrum shows this more structured and outspread response compared to the spectra recorded after purification, the shift of the G-line main component depends on which tubes are mainly in resonance with the excitation wavelength. Combining the information gained from Raman spectroscopy, optical absorption, and TEM imaging and comparing the results shown here with the CBx-SWNTs produced in our and other groups, this material represents a significant step forward toward the controllable production of tubes with a defined morphology, which is necessary for explaining questions remaining from the point of view of fundamental research on physical properties of B-doped nanotubes. The next step is corroborating the incorporation of the dopants on the nanotube walls rather than as part of the synthesis byproducts. To understand the elemental composition of the samples asproduced and after purification, we made use of X-ray photoelectron spectroscopy (XPS) to determine the nature of different elements and to understand their bonding environments. The spectrometer’s Al Kα source was used with pass energies of 200 eV for survey scans and 100 and 50 eV for high-resolution scans. The measurements on samples purified with both S1 and S2 revealed the presence of C, B, and O, followed by small amounts of Fe, Na, and Cl. Comparing the spectra recorded on samples with and without purification, the intensity of the C 1s signal turns at least three times stronger, confirming the presence of carbonaceous species in the predominant amount. On the other hand, the survey studies of the sample made using the purification procedure S2 show a sharper B 1s line and amounts below 0.5 at. % of other elements. It is therefore necessary to focus on the carbon core signal to start this analysis. Previous studies done with high resolution photoemission on pristine SWNTs have shown that the fine structure in the C 1s line can be used to discern the presence of the single-walled tubes with a specific binding energy.41−43 The full width at half maximum (fwhm) of the C 1s is around ∼0.4 eV for purified samples of pristine SWNTs
Figure 3. (a) C 1s core level spectra recorded with a photon excitation energy of 1486.7 eV from an Al Kα source. From top to bottom, the spectra correspond to a sample grown at 770 °C and after the two purification procedures. (b) Deconvolution of the B 1s core level spectrum recorded from the sample purified with procedure S2.
corresponding fwhm of ∼1.86, ∼1.7, and ∼1.5 eV. The spectra corresponding to the samples after purification exhibit a Doniac−Sunjic line shape. The reduction of the spectral contribution at higher binding energies is consistent with the elimination of amorphous carbonaceous impurities.41 As stated above, these values are higher than those corresponding to purified SWCNT films. However, this broadening in the purified CBx-SWNTs cannot be attributed exclusively to impurities beyond 1% as in the case of the arc discharge material in ref 41 because the introduction of B dopants in the lattice is much larger, and also the C 1s has two broadening contributions. First, a down shift has been observed for doped samples, substantiated by previous reports,18,36,41 suggesting that the first B neighboring atoms in carbon systems are responsible for this shift. On the other hand, with the introduction of B, asymmetries arise around the band gap because of the mixing of the π orbitals, which should add to other morphological effects such as defects and vacancies extending the linewidth to higher binding energies. Before turning to the B 1s analysis, it is worth keeping in mind that survey scans revealed the presence of O in the samples, therefore the samples were heated at 600 °C, which is sufficient to remove adsorbed O. This leads to the conclusion 1943
DOI: 10.1021/acsomega.8b03031 ACS Omega 2019, 4, 1941−1946
ACS Omega
Article
account that this material was made in a two-stage highvacuum CVD system and this is unavoidable. However, the component of boric acid is significantly reduced with S1 but it is eliminated with S2, suggesting that the use of H2O2 is additionally useful in the removal of the rests of boric acid efficiently.46 This is consequent with the proportions of boron oxide and substitutional boron observed in the profile resulting for the procedure S2. Here, it is remarkable that most of the B contained in a sample purified with this last sequence is predominantly in substitutional configuration. Because the stability of boron oxide clusters is still not understood and studies have suggested that their chemistry and stability could depend on their size,47 the efforts toward the complete purification of CBx-SWNTs need to overcome this challenge. Also, the homogeneity of the heteroatom distribution along the tube should be the focus of future research with more local probes.
that the O content in the samples arises from a compound that must contain B because the residual presence of the supporting catalyst (MgO) can be disregarded after the purification. The B 1s measurements of the samples can interestingly be deconvoluted into different line profiles. Although in both cases, a line width narrowing above 0.25 eV is observed compared to the unpurified material as reported in ref 33, for both purification methods a downshift is seen, which is slightly more pronounced in the case of S2. We have applied Voigt symmetric spectral deconvolution adjusting a Gaussian resolution component in order to unravel the bonding environments contributing to the B 1s line. Figure 3b shows a spectrum corresponding to S2 in the optimal synthesis temperature. As observed, besides the substitutional configuration, in this case, two components corresponding to boron oxide and substitutional boron (shaded) are found. Signals between 191.5 and 192.1 eV have been consistently reported for B in the substitutional configuration for CBx-SWNTs and also in double-walled and multiwalled nanotubes.18,36,41,44 None of those materials were purified, but in our case, after employing both purification methods , we are able to confirm that this component first observed from the onset of the B 1s edge in EELS experiments45 and later observed for nanotubes directly with XPS (as mentioned above) indeed corresponds to the B bonding environment in the sp2 configuration. Our best fits suggest that the position of the substitutional B component is around 191.65 eV once the material is purified. The other two components that can be seen in our purified samples correspond to boron oxide (192.8 eV) and boric acid (193.6 eV). To better understand the B incorporation profile in these samples, Figure 4 shows a histogram summarizing the B
■
CONCLUSIONS
■
METHODS
We have applied purification techniques to CBx-SWNTs with very high B contents and found distinctive and remarkable aspects as compared to other nanotubes synthesized with methods alike. First, these type of nanotubes produced from a solid precursor are able to incorporate B atoms in an order of magnitude above any other method used to produce these materials. We have been able to unravel the bonding environments that make part of the B 1s core level signal recorded in XPS before and after purifying the nanotubes with two different methods. We have observed that using water peroxide can be very effective toward the removal of boric acid. However, the highest competing bonding environment for substitutional boron is boron oxide, and its removal should be the matter of further intensive studies. These results pave the way toward the purification of substitutionally doped nanotubes not only for B as heteroatoms but with a broader perspective.
A high-vacuum two-stage heating CVD procedure was used for synthesis as reported elsewhere.48 These CBx-SWNTs have observable diameters from ∼0.89 to ∼1.9 nm and a B incorporation of up to 13% at. These results hold the record in B content among materials alike produced with both high and low temperature synthesis methods. Subsequent purification procedures were performed using mild chemical oxidation. Two aqueous acid solutions were prepared: (S1) HCl and (S2) HCl + H2O2. The raw nanotube material was first purified immersing the black powder in deionized water and subsequently dispersing this suspension with the diluted HCl solution S1; given the chemistry of the compounds present in this step, we could not rule out the formation of NaCl because of residual Na contained in the sodium tetraphenyl borate molecule. Therefore, a small amount of NaOH (0.5 M) was used for its removal. The nanotubes were filtered and dispersed in water at 90 °C in order to eliminate NaCl and H3BO3 simultaneously. Finally, the aqueous solution was filtered and heated at 380 °C for 2 h to remove any remaining amorphous carbon. The same sequence was followed with the S2 mix. As the last step, an 800 °C heating treatment for 1 h was applied to stabilize the structures. Raman spectra were recorded with a Horiba Jobin LabRAM HR800 spectrometer equipped with a liquid nitrogen-cooleddetector. All spectra were recorded in
Figure 4. Boron-incorporation profile on samples as-grown and after the use of the purification procedures S1 and S2.
bonding environments identified in CBx-SWNT samples assynthesized versus the material obtained after both purification methods. The three different patterns in the bars correspond to three different bonding environments from left to right: boric acid, boron oxide, and B in the sp2 configuration. The sample purification procedures have both advantages and disadvantages if we examine the type of remaining bonding environments after they have been applied. In the raw sample, substitutional B corresponds to the largest component of the spectrum; meanwhile; boric acid and boron oxide are present. The same three components remain after the procedure S1 but in different proportions. The formation of boric acid in the raw material is most likely due to the adsorption of water in the porous catalyst previous to the synthesis process, taking into 1944
DOI: 10.1021/acsomega.8b03031 ACS Omega 2019, 4, 1941−1946
ACS Omega
Article
(13) McGuire, K.; Gothard, N.; Gai, P. L.; Dresselhaus, M. S.; Sumanasekera, G.; Rao, A. M. Synthesis and Raman characterization of boron-doped single-walled carbon nanotubes. Carbon 2005, 43, 219−227. (14) Golberg, D.; Bando, Y.; Han, W.; Kurashima, K.; Sato, T. Single-walled B-doped carbon, B/N-doped carbon and BN nanotubes synthesized from single-walled carbon nanotubes through a substitution eaction. Chem. Phys. Lett. 1999, 308, 337−342. (15) Borowiak-Palen, E.; Pichler, T.; Fuentes, G. G.; Graff, A.; Kalenczuk, R. J.; Knupfer, M.; Fink, J. Efficient production of Bsubstituted single-wall carbon nanotubes. Chem. Phys. Lett. 2003, 378, 516−520. (16) Pichler, T.; Borowiak-Palen, E.; Fuentes, G.; Knupfer, M.; Graff, A.; Fink, J.; Wirtz, L.; Rubio, A. Electronic structure and optical properties of boron doped single-wall carbon nanotubes. AIP Conference Proceedings 2003, 685, 361−365. (17) Panchakarla, L. S.; Govindaraj, A.; Rao, C. N. R. Nitrogen- and boron-doped double-walled carbon nanotubes. ACS Nano 2007, 1, 494−500. (18) Monteiro, F. H.; Larrude, D. G.; Maia da Costa, M. E. H.; Terrazos, L. A.; Capaz, R. B.; Freire, F. L., Jr. Production and Characterization of Boron-Doped Single Wall Carbon Nanotubes. J. Phys. Chem. C 2012, 116, 3281−3285. (19) Ayala, P.; Rümmeli, M. H.; Gemming, T.; Kauppinen, E.; Kuzmany, H.; Pichler, T. CVD growth of single-walled B-doped carbon nanotubes. Phys. Status Solidi B 2008, 245, 1935−1938. (20) Daothong, S.; Parjanne, J.; Kauppinen, E. I.; Valkeapäa,̈ M.; Pichler, T.; Singjai, P.; Ayala, P. Study of the role of Fe based catalysts on the growth of B-doped SWCNTs synthesized by CVD. Phys. Status Solidi B 2009, 246, 2518−2522. (21) Kim, Y. A.; Fujisawa, K.; Muramatsu, H.; Hayashi, T.; Endo, M.; Fujimori, T.; Kaneko, K.; Terrones, M.; Behrends, J.; Eckmann, A.; Casiraghi, C.; Novoselov, K. S.; Saito, R.; Dresselhaus, M. S. Raman Spectroscopy of Boron-Doped Single-Layer Graphene. ACS Nano 2012, 6, 6293−6300. (22) Susi, T.; Pichler, T.; Ayala, P. X-ray photoelectron spectroscopy of graphitic carbon nanomaterials doped with heteroatoms. Beilstein J. Nanotechnol. 2015, 6, 177−192. (23) Stephan, O.; Ajayan, P. M.; Colliex, C.; Redlich, P.; Lambert, J. M.; Bernier, P.; Lefin, P. Doping graphitic and carbon nanotube structures with boron and nitrogen. Science 1994, 266, 1683. (24) Susi, T.; Mowbray, D. J.; Ljungberg, M. P.; Ayala, P. Calculation of the graphene C 1s core level binding energy. Phys. Rev. B: Condens. Matter Mater. Phys. 2015, 91, 081401. (25) Rao, A. M.; Eklund, P. C.; Bandow, S.; Thess, A.; Smalley, R. E. Evidence for charge transfer in doped carbon nanotube bundles from Raman scattering. Nature 1997, 388, 257−259. (26) Gai, P. L.; Stephan, O.; McGuire, K.; Rao, A. M.; Dresselhaus, M. S.; Dresselhaus, G.; Colliex, C. Structural systematics in borondoped single wall carbon nanotubes. J. Mater. Chem. 2004, 14, 669− 675. (27) Carroll, D. L.; Redlich, P.; Blase, X.; Charlier, J.-C.; Curran, S.; Ajayan, P. M.; Roth, S.; Rühle, M. Effects of nanodomain formation on the electronic structure of doped carbon nanotubes. Phys. Rev. Lett. 1998, 81, 2332. (28) Borowiak-Palen, E.; Pichler, T.; Graff, A.; Kalenczuk, R. J.; Knupfer, M.; Fink, J. Synthesis and electronic properties of B-doped single wall carbon nanotubes. Carbon 2004, 42, 1123. (29) Krupke, R.; Hennrich, F.; Löhneysen, H. v.; Kappes, M. M. Separation of metallic from semiconducting single-walled carbon nanotubes. Science 2003, 301, 344−347. (30) Hou, P.-X.; Liu, C.; Cheng, H.-M. Purification of carbon nanotubes. Carbon 2008, 46, 2003−2025. (31) Heras, A.; Colina, A.; López-Palacios, J.; Ayala, P.; Sainio, J.; Ruiz, V.; Kauppinen, E. I. Electrochemical purification of carbon nanotube electrodes. Electrochem. Commun. 2009, 11, 1535−1538. (32) Ruiz-Soria, G.; Ayala, P.; Puchegger, S.; Kataura, H.; Yanagi, K.; Pichler, T. On the purification of CVD grown boron doped singlewalled carbon nanotubes. Phys. Status Solidi B 2011, 248, 2504−2507.
ambient conditions with a 180° backscattered light. XPS was done with a Scienta Spectrometer equipped with a monochromatic Al Kα source (1486.6 eV) and a hemispherical RS4000 photoelectron analyzer, operating at a base pressure of 6 × 10−10 mBar.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Carlos Reinoso: 0000-0002-6003-219X Lei Shi: 0000-0003-4175-7803 Kazuhiro Yanagi: 0000-0002-7609-1493 Thomas Pichler: 0000-0001-5377-9896 Paola Ayala: 0000-0002-5851-6638 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS C.R. was supported by the National Secretary of Higher Education Science and Technology of Ecuador (SENESCYT). P.A. would like to acknowledge the contribution of the COST Action CA15107 (MultiComp). K.Y. acknowledges support by JST CREST through grant number JPMJCR17I5, Japan.
■
REFERENCES
(1) Terrones, M.; Jorio, A.; Endo, M.; Rao, A. M.; Kim, Y. A.; Hayashi, T.; Terrones, H.; Charlier, J.-C.; Dresselhaus, G.; Dresselhaus, M. S. New direction in nanotube science. Mater. Today 2004, 7, 30−45. (2) Hirsch, A. Functionalization of single-walled carbon nanotubes. Angew. Chem., Int. Ed. 2002, 41, 1853. (3) Ayala, P.; Arenal, R.; Rümmeli, M.; Rubio, A.; Pichler, T. The doping of carbon nanotubes with nitrogen and their potential applications. Carbon 2010, 48, 575−586. (4) Fagan, S. B.; Mota, R.; da Silva, A. J. R.; Fazzio, A. Substitutional Si doping in deformed carbon nanotubes. Nano Lett. 2004, 4, 975− 977. (5) Ruiz-Soria, G.; Susi, T.; Sauer, M.; Yanagi, K.; Pichler, T.; Ayala, P. On the bonding environment of phosphorus in purified doped single-walled carbon nanotubes. Carbon 2015, 81, 91−95. (6) Lu, J.; Zhang, X.; Wu, X.; Dai, Z.; Zhang, J. A Ni-Doped Carbon Nanotube Sensor for Detecting Oil-Dissolved Gases in Transformers. Sensors 2015, 15, 13522−13532. (7) Murata, N.; Haruyama, J.; Reppert, J.; Rao, A. M.; Koretsune, T.; Saito, S.; Matsudaira, M.; Yagi, Y. Superconductivity in thin films of boron-doped carbon nanotubes. Phys. Rev. Lett. 2008, 101, 027002. (8) Krstić, V.; Blumentritt, S.; Muster, J.; Roth, S.; Rubio, A. Role of disorder on transport in boron-doped multiwalled carbon nanotubes. Phys. Rev. B: Condens. Matter Mater. Phys. 2003, 67, 041401. (9) Hsu, W. K.; Firth, S.; Redlich, P.; Terrones, M.; Terrones, H.; Zhu, Y. Q.; Grobert, N.; Schilder, A.; Clark, R. J. H.; Kroto, H. W.; Walton, D. R. M. Boron-doping effects in carbon nanotubes. J. Mater. Chem. 2000, 10, 1425−1429. (10) Ayala, P.; Arenal, R.; Loiseau, A.; Rubio, A.; Pichler, T. The physical and chemical properties of heteronanotubes. Rev. Mod. Phys. 2010, 82, 1843. (11) Blackburn, J. L.; Yan, Y.; Engtrakul, C.; Parilla, P. A.; Jones, K.; Gennett, T.; Dillon, A. C.; Heben, M. J. Synthesis and characterization of boron-doped single-wall carbon nanotubes produced by the laser vaporization technique. Chem. Mater. 2006, 18, 2558−2566. (12) Anand, B.; Podila, R.; Ayala, P.; Oliveira, L.; Philip, R.; Sai, S. S. S.; Zakhidov, A. A.; Rao, A. M. Nonlinear optical properties of boron doped single-walled carbon nanotubes. Nanoscale 2013, 5, 7271− 7276. 1945
DOI: 10.1021/acsomega.8b03031 ACS Omega 2019, 4, 1941−1946
ACS Omega
Article
(33) Reinoso, C.; Shi, L.; Domanov, O.; Rohringer, P.; Pichler, T.; Ayala, P. Very high boron-doping on single-walled carbon nanotubes from a solid precursor. Carbon 2018, 140, 259−264. (34) Grüneis, A.; Kramberger, C.; Grimm, D.; Gemming, T.; Rümmeli, M. H.; Barreiro, A.; Ayala, P.; Pichler, T.; Schaman, C.; Kuzmany, H.; Schumann, J.; Büchner, B. Eutectic limit for the growth of carbon nanotubes from a thin iron film by chemical vapor deposition of cyclohexane. Chem. Phys. Lett. 2006, 425, 301−305. (35) Fantini, C.; Jorio, A.; Souza, M.; Strano, M. S.; Dresselhaus, M. S.; Pimenta, M. A. Optical transition energies for carbon nanotubes from resonant Raman spectroscopy: Environment and temperature effects. Phys. Rev. Lett. 2004, 93, 147406. (36) Ayala, P.; Plank, W.; Grüneis, A.; Kauppinen, E. I.; Rümmeli, M. H.; Kuzmany, H.; Pichler, T. A one step approach to B-doped single-walled carbon nanotubes. J. Mater. Chem. 2008, 18, 5676− 5681. (37) Ayala, P.; Grüneis, A.; Kramberger, C.; Rümmeli, M. H.; Solórzano, I. G.; Freire, F. L., Jr.; Pichler, T. Effects of the reaction atmosphere composition on the synthesis of single and multiwalled nitrogen-doped nanotubes. J. Chem. Phys. 2007, 127, 184709. (38) Grüneis, A.; Kramberger, C.; Grimm, D.; Gemming, T.; Rümmeli, M. H.; Barreiro, A.; Ayala, P.; Pichler, T.; Schaman, C.; Kuzmany, H.; Schumann, J.; Büchner, B. Eutectic limit for the growth of carbon nanotubes from a thin iron film by chemical vapor deposition of cyclohexane. Chem. Phys. Lett. 2006, 425, 301−305. (39) Ayala, P.; Grüneis, A.; Grimm, D.; Kramberger, C.; Engelhard, R.; Rümmeli, M.; Schumann, J.; Kaltofen, R.; Büchner, B.; Schaman, C.; Kuzmany, H.; Gemming, T.; Barreiro, A.; Pichler, T. Cyclohexane triggers staged growth of pure and vertically aligned single wall carbon nanotubes. Chem. Phys. Lett. 2008, 454, 332−336. (40) Park, J. S.; Sasaki, K.; Saito, R.; Izumida, W.; Kalbac, M.; Farhat, H.; Dresselhaus, G.; Dresselhaus, M. S. Fermi energy dependence of the G-band resonance Raman spectra of single-wall carbon nanotubes. Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 80, 081402. (41) Ayala, P.; Reppert, J.; Grobosch, M.; Knupfer, M.; Pichler, T.; Rao, A. M. Evidence for substitutional boron in doped single-walled carbon nanotubes. Appl. Phys. Lett. 2010, 96, 183110. (42) De Blauwe, K.; Mowbray, D. J.; Miyata, Y.; Ayala, P.; Shiozawa, H.; Rubio, A.; Hoffmann, P.; Kataura, H.; Pichler, T. Combined experimental and ab initio study of the electronic structure of narrowdiameter single-wall carbon nanotubes with predominant (6,4),(6,5) chirality. Phys. Rev. B: Condens. Matter Mater. Phys. 2010, 82, 125444. (43) Ayala, P.; Miyata, Y.; De Blauwe, K.; Shiozawa, H.; Feng, Y.; Yanagi, K.; Kramberger, C.; Silva, S. R. P.; Follath, R.; Kataura, H.; Pichler, T. Disentanglement of the electronic properties of metallicityselected single-walled carbon nanotubes. Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 80, 205427. (44) Panchakarla, L. S.; Govindaraj, A.; Rao, C. N. R. Nitrogen- and Boron-Doped Double-Walled Carbon Nanotubes. ACS Nano 2007, 1, 494−500. (45) Borowiak-Palen, E.; Pichler, T.; Graff, A.; Kalenczuk, R. J.; Knupfer, M.; Fink, J. Synthesis and electronic properties of B-doped single wall carbon nanotubes. Carbon 2004, 42, 1123−1126. (46) Pizer, R.; Tihal, C. Peroxoborates. Interaction of boric acid and hydrogen peroxide in aqueous solution. Inorg. Chem. 1987, 26, 3639− 3642. (47) Drummond, M. L.; Meunier, V.; Sumpter, B. G. Structure and Stability of Small Boron and Boron Oxide Clusters. J. Phys. Chem. A 2007, 111, 6539−6551. (48) Ruiz-Soria, G.; Daothong, S.; Pichler, T.; Ayala, P. Spectroscopic study of the diameter distribution of B-doped singlewalled carbon nanotubes. Phys. Status Solidi B 2012, 249, 2469−2472.
1946
DOI: 10.1021/acsomega.8b03031 ACS Omega 2019, 4, 1941−1946
