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SWCN characterization by neutron diffraction
ARTICLE IN PRESS
Physica B 350 (2004) e1027–e1029
SWCN characterization by neutron diffraction A. Giannasia,b,*, M. Cellia, J.L. Sauvajolc, M. Zoppia, D.T. Bowrond b
a IFAC-CNR, Via Madonna del Piano, 50019 Florence, Italy Department of Physics, University of Florence, Via Sansone, Sesto Fiorentino, 50019 Florence, Italy c University of Montpellier II, 34095 Cedex 5 Montpellier, France d RAL, Chilton, Didcot OX11 0QX, UK
Abstract Single-wall carbon nanotube structure has been investigated by neutron diffraction using the SANDALS time of flight diffractometer (at R.A.L.). The Q range of the detector allows for the determination of single the tube diameter, diameter distribution, and mean number of tubes in the bundle. Results are compared to theoretical predictions. r 2004 Elsevier B.V. All rights reserved. PACS: 61.46.+w; 61.12.Id; 81.07.De Keywords: SWCN; Neutron diffraction; Characterization
A single-wall carbon nanotube (SWCN) can be described as a honeycomb lattice rolled into a long cylinder, the ratio of the diameter to the length being of the order of 104. Carbon nanotubes are assembled into bundles consisting of about 10 to several hundreds of single tubes and forming a 2D limited-size crystal. Since their discovery they showed some peculiar behaviour which is strongly dependent on their molecular structure, chirality and bundle packing. For this reason the characterization of newly produced SWCN results are of primary importance in the study of their physical properties as well as in the development of refined production methods. Here we present *Corresponding author. IFAC-CNR, Via Madonna del Piano, Florence 50019, Italy. Tel.: +39-055-5225336. E-mail address: [email protected] (A. Giannasi).
neutron diffraction data collected at the SANDALS time of flight diffractometer which covers a ( 1. Data are Q range between 0.2 and 50 A compared to theoretical results which take into account the finite size of the bundles, the number of tubes in the bundles, and diameter polydispersivity [1]. The calculated spectrum shows the most ( 1, and intense peak, which is located around 0.4 A is due to the (1 0) Bragg reflection of the 2D hexagonal lattice of uniform cylinders. The nanotube sample was prepared by an electric arc method in a He atmosphere using a Ni/Y mixture in the atomic ratio 4.2 at%/1% by the Montpellier group [2]. The sample was purified and then sealed into a glass cylinder under vacuum. Neutron diffraction data were collected using a vanadium flat plate cell at 14 K to minimize the Debye–Waller contribution. The
0921-4526/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.03.282
ARTICLE IN PRESS e1028
A. Giannasi et al. / Physica B 350 (2004) e1027–e1029
data were then treated to subtract the empty cell contribution and to correct for the multiple scattering and adsorption. It has been demonstrated that the diffraction spectra from carbon nanotubes is sensitive to the diameter of the tubes and to nanotubes diameter polydispersivity [1]. Moreover, the diffraction spectra profiles are sensitive to the number of tubes in the bundle, as is shown in the right part of Fig. 1. A correct interpretation of neutron diffraction spectra has to take into account that all these parameters contribute to modify both the width and the position of the main (1 0) Bragg peak. Diffraction data can be divided into two main Q regions: that ( 1 which describes the bundle packing, for Qo2 A ( 1 which deals with the single and that for Q > 2 A tube characteristics. This first analysis looks for the determination of the bundle 2D lattice parameters. Starting from the general formula for diffraction and using a uniform density of scatterers on the surface of the tubes, the diffraction intensity is obtained as a function of the tube’s radius and the tube–tube distance in the bundle: Nt X r2 IðQÞpexpð2W ðQÞÞ 0 PðQÞ J0 ðRi;j QÞ; Q i;j
where W ðQÞ is the Debye–Waller factor, PðQÞ is proportional to the carbon scattering length and to J0 ðr0 QÞ; r0 is the tube radius and the Rij stands for the tube–tube centre distance. The diffraction spectra is modulated by the cylindrical Bessel function which is the nanotube form factor. The diameter of the tubes is assumed to be Gaussian distributed with /2r0 S ¼ ( and s ¼ 1:6 A. ( The calculated /d0 S ¼ 13:6 A spectrum is the result of an averaged sum of the spectra corresponding to 1000 different diameter values in the distribution; the bundle for the reconstructed profile was made up of 126/137 tubes. ( 1 and The actual approximation is valid for Qo2 A is not sensitive to the presence of peaks which are located around the boundary Q value. Fig. 2 shows experimental data relative to the 2y ¼ 7 detectors group in the low-Q region: on the left part data are shown before and after background subtraction while on the right, the diffraction spectrum is compared to the calculated diffraction profile. The mean diameter of the tubes result is ( according to previous Raman (13.671.6) A, investigation of the radial breathing mode ( (12.772) A.
Fig. 1. On the left there is shown the diffraction spectra profile which changes with the increase of the tubes diameter dispersion. The ( On the right there is shown the peaks slightly shift in their position while they get more smoothed with the s increase from 0.2 to 2.0 A. effect on the diffraction profile due to the number of tubes Nt per bundle: the peaks become more intense for the bundle consisting of 7–130 tubes.
ARTICLE IN PRESS A. Giannasi et al. / Physica B 350 (2004) e1027–e1029
e1029
Fig. 2. On the left there are shown the diffraction data before and after background subtraction. The intense rise on the left part of the spectrum is produced both by the nanotubes form factor and the nanoparticles impurities. After subtraction the main (1 0) Bragg peak is clearly isolated. On the right part figure the same data are compared to the calculus results: here a 126–137 bundle is considered, ( where the mean nanotube diameter value is assumed to be equal to 13.6 A.
( 1 peaks are due to the bundle The 0.7 and 1.5 A array, the first one is the sum of 2 narrower peaks ( 1 (0.73, 0.86 A ( 1), while located between 0.7/0.9 A 1 ( the 1.5 A one is due to the sum of two peaks ( 1; their intensity and posilocated at 1.45/1.55 A tion are very sensitive to the tube diameter because ( 1 is a of the modulating Bessel function; the 1.1 A single peak.
References [1] S. Rols, R. Almairac, L. Henrard, E. Anglaret, S.L. Sauvajol, Eur. Phys. J. B 10 (1999) 263. [2] C. Journet, W.K. Maser, P. Bernier, A. Loiseau, M. Lamydela Chapelle, S. Lefrant, P. Deniard, R. Lee, J.E. Fisher, Nature 388 (1997) 756.
Physica B 350 (2004) e1027–e1029
SWCN characterization by neutron diffraction A. Giannasia,b,*, M. Cellia, J.L. Sauvajolc, M. Zoppia, D.T. Bowrond b
a IFAC-CNR, Via Madonna del Piano, 50019 Florence, Italy Department of Physics, University of Florence, Via Sansone, Sesto Fiorentino, 50019 Florence, Italy c University of Montpellier II, 34095 Cedex 5 Montpellier, France d RAL, Chilton, Didcot OX11 0QX, UK
Abstract Single-wall carbon nanotube structure has been investigated by neutron diffraction using the SANDALS time of flight diffractometer (at R.A.L.). The Q range of the detector allows for the determination of single the tube diameter, diameter distribution, and mean number of tubes in the bundle. Results are compared to theoretical predictions. r 2004 Elsevier B.V. All rights reserved. PACS: 61.46.+w; 61.12.Id; 81.07.De Keywords: SWCN; Neutron diffraction; Characterization
A single-wall carbon nanotube (SWCN) can be described as a honeycomb lattice rolled into a long cylinder, the ratio of the diameter to the length being of the order of 104. Carbon nanotubes are assembled into bundles consisting of about 10 to several hundreds of single tubes and forming a 2D limited-size crystal. Since their discovery they showed some peculiar behaviour which is strongly dependent on their molecular structure, chirality and bundle packing. For this reason the characterization of newly produced SWCN results are of primary importance in the study of their physical properties as well as in the development of refined production methods. Here we present *Corresponding author. IFAC-CNR, Via Madonna del Piano, Florence 50019, Italy. Tel.: +39-055-5225336. E-mail address: [email protected] (A. Giannasi).
neutron diffraction data collected at the SANDALS time of flight diffractometer which covers a ( 1. Data are Q range between 0.2 and 50 A compared to theoretical results which take into account the finite size of the bundles, the number of tubes in the bundles, and diameter polydispersivity [1]. The calculated spectrum shows the most ( 1, and intense peak, which is located around 0.4 A is due to the (1 0) Bragg reflection of the 2D hexagonal lattice of uniform cylinders. The nanotube sample was prepared by an electric arc method in a He atmosphere using a Ni/Y mixture in the atomic ratio 4.2 at%/1% by the Montpellier group [2]. The sample was purified and then sealed into a glass cylinder under vacuum. Neutron diffraction data were collected using a vanadium flat plate cell at 14 K to minimize the Debye–Waller contribution. The
0921-4526/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.03.282
ARTICLE IN PRESS e1028
A. Giannasi et al. / Physica B 350 (2004) e1027–e1029
data were then treated to subtract the empty cell contribution and to correct for the multiple scattering and adsorption. It has been demonstrated that the diffraction spectra from carbon nanotubes is sensitive to the diameter of the tubes and to nanotubes diameter polydispersivity [1]. Moreover, the diffraction spectra profiles are sensitive to the number of tubes in the bundle, as is shown in the right part of Fig. 1. A correct interpretation of neutron diffraction spectra has to take into account that all these parameters contribute to modify both the width and the position of the main (1 0) Bragg peak. Diffraction data can be divided into two main Q regions: that ( 1 which describes the bundle packing, for Qo2 A ( 1 which deals with the single and that for Q > 2 A tube characteristics. This first analysis looks for the determination of the bundle 2D lattice parameters. Starting from the general formula for diffraction and using a uniform density of scatterers on the surface of the tubes, the diffraction intensity is obtained as a function of the tube’s radius and the tube–tube distance in the bundle: Nt X r2 IðQÞpexpð2W ðQÞÞ 0 PðQÞ J0 ðRi;j QÞ; Q i;j
where W ðQÞ is the Debye–Waller factor, PðQÞ is proportional to the carbon scattering length and to J0 ðr0 QÞ; r0 is the tube radius and the Rij stands for the tube–tube centre distance. The diffraction spectra is modulated by the cylindrical Bessel function which is the nanotube form factor. The diameter of the tubes is assumed to be Gaussian distributed with /2r0 S ¼ ( and s ¼ 1:6 A. ( The calculated /d0 S ¼ 13:6 A spectrum is the result of an averaged sum of the spectra corresponding to 1000 different diameter values in the distribution; the bundle for the reconstructed profile was made up of 126/137 tubes. ( 1 and The actual approximation is valid for Qo2 A is not sensitive to the presence of peaks which are located around the boundary Q value. Fig. 2 shows experimental data relative to the 2y ¼ 7 detectors group in the low-Q region: on the left part data are shown before and after background subtraction while on the right, the diffraction spectrum is compared to the calculated diffraction profile. The mean diameter of the tubes result is ( according to previous Raman (13.671.6) A, investigation of the radial breathing mode ( (12.772) A.
Fig. 1. On the left there is shown the diffraction spectra profile which changes with the increase of the tubes diameter dispersion. The ( On the right there is shown the peaks slightly shift in their position while they get more smoothed with the s increase from 0.2 to 2.0 A. effect on the diffraction profile due to the number of tubes Nt per bundle: the peaks become more intense for the bundle consisting of 7–130 tubes.
ARTICLE IN PRESS A. Giannasi et al. / Physica B 350 (2004) e1027–e1029
e1029
Fig. 2. On the left there are shown the diffraction data before and after background subtraction. The intense rise on the left part of the spectrum is produced both by the nanotubes form factor and the nanoparticles impurities. After subtraction the main (1 0) Bragg peak is clearly isolated. On the right part figure the same data are compared to the calculus results: here a 126–137 bundle is considered, ( where the mean nanotube diameter value is assumed to be equal to 13.6 A.
( 1 peaks are due to the bundle The 0.7 and 1.5 A array, the first one is the sum of 2 narrower peaks ( 1 (0.73, 0.86 A ( 1), while located between 0.7/0.9 A 1 ( the 1.5 A one is due to the sum of two peaks ( 1; their intensity and posilocated at 1.45/1.55 A tion are very sensitive to the tube diameter because ( 1 is a of the modulating Bessel function; the 1.1 A single peak.
References [1] S. Rols, R. Almairac, L. Henrard, E. Anglaret, S.L. Sauvajol, Eur. Phys. J. B 10 (1999) 263. [2] C. Journet, W.K. Maser, P. Bernier, A. Loiseau, M. Lamydela Chapelle, S. Lefrant, P. Deniard, R. Lee, J.E. Fisher, Nature 388 (1997) 756.