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Studies on high pressure behavior of carbon nanotubes: X-ray diffraction measurements using synchrotron radiation
Nuclear Instruments and Methods in Physics Research B 238 (2005) 281–284 www.elsevier.com/locate/nimb
Studies on high pressure behavior of carbon nanotubes: X-ray diffraction measurements using synchrotron radiation S. Karmakar
a,*
, Surinder M. Sharma a, A.K. Sood
b,c
a
c
Synchrotron Radiation Section, Bhabha Atomic Research Centre, Mumbai 400085, India b Department of Physics, Indian Institute of Science, Bangalore 560012, India Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research Centre, Jakkur Campus, Jakkur, Bangalore 560064, India Available online 27 July 2005
Abstract High-pressure behavior of novel one-dimensional material – carbon nanotubes (single-walled and multi-walled, pristine and Fe-filled) have been investigated by in situ powder X-ray diffraction (XRD) studies. Single-walled nanotubes show remarkable mechanical resilience. The presence of non-hydrostatic stresses makes compression behavior much different from that under the hydrostatic stress. Our results also suggest pressure-induced elliptization of the tubes in a bundle. Iron-filled multi-walled nanotubes, unlike pristine, show a structural modification at a pressure of 9 GPa where the outer component (Fe3C) of the encapsulated nanowire undergoes an iso-structural transition. Also the high-pressure behavior of the a-Fe is quite different from the bulk. Ó 2005 Elsevier B.V. All rights reserved. PACS: 64.70.Nd; 61.10.Nz Keywords: Carbon nanotubes; High pressure; X-ray diffraction
1. Introduction The elastic properties of carbon nanotubes have been widely investigated since it was recognized * Corresponding author. Tel.: +91 22 2559 1312; fax: +91 22 2550 5151. E-mail addresses: [email protected], [email protected] (S. Karmakar).
that the low atomic weight of carbon combined with a strong covalent bond has a high potential usage as a large tensile-strength-material. Due to the novel one-dimensional nature as well as potential use in nanoscale electronic devices, single walled nanotubes (SWNTs), multiwalled nanotubes (MWNTs) and also metal filled carbon nanotubes have attracted a lot of research attention. A carbon nanotube can be viewed as a roll
0168-583X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.06.064
S. Karmakar et al. / Nucl. Instr. and Meth. in Phys. Res. B 238 (2005) 281–284 15.8 15.6 o
of graphene sheet. A SWNT is characterized by two indices (n, m) or simply by the chiral vector Ch = na1 + ma2, where a1 and a2 are two lattice vectors in the graphene plane [1]. SWNTs usually self-organize into bundle-like two-dimensional (2D) lattice with hexagonal symmetry containing tens to hundreds of parallel tubes. MWNTs consist of 10–100 concentric such tubes. Here we present the results of our recent high pressure studies on (11, 11) SWNTs under hydrostatic and nonhydrostatic conditions. Results of high pressure structural investigations on pristine and Fe-filled MWNTs are also presented.
d-spacing (A)
282
15.4 15.2 15.0 14.8 0
1
2
3
4
5
6
7
8
Pressure (GPa)
2. High pressure techniques Quasi-hydrostatic pressure upto 30 GPa is generated on the sample by filling it in a Mao-Bell kind of diamond anvil cell (DAC) with methanol:ethanol:water (16:3:1) mixture as pressure transmitting medium. For non-hydrostatic study, no pressure transmitter is used. Pressure is measured using ruby fluorescence technique or Au/Cu(1 1 1) diffraction line. Angle resolved powder XRD measurements have been carried out at BL10XU beamline of Spring8 (Undulator source) and at 5.2R beamline of ELETTRA (Wiggler ˚ , Si(1 1 1) monochromasource) (wavelength = 1 A tor) using Rigaku R-axis IV and MAR345 imaging plate area detectors respectively. In some cases, Raman measurements were also carried out for a detailed understanding of the structural evolution under high pressures.
3. Results and discussion 3.1. SWNTs The triangular 2D lattice of (11, 11) SWNTs bundle gives the strongest feature at the d-spacing ˚ (Fig. 1). Our high pressure studies d100 15.65 A upto 13 GPa [2] show that SWNTs loose translational coherence reversibly at 10 GPa, superceding a previous observation which showed irreversibility beyond 4 GPa [3]. This compression behavior has also been verified by a first-prin-
Fig. 1. Pressure variation of the d-spacing of the 2D lattice of SWNTs, hydrostatic (open circle) versus non-hydrostatic pressures (closed circle).
ciples calculation [4]. Just prior to this loss of translational order the lattice displays a sudden basal plane strain relaxation, which may be attributed to the heterogeneous distortion in the tubes. Our Raman scattering studies [5] also agree with this remarkable mechanical resilience of the nanotubes. To interpret the occurrence of transformation at lower pressures (1.5 GPa), as observed by others and to understand the effect of pressure medium, we re-investigated SWNTs under the non-hydrostatic stresses up to 30 GPa [6]. The observed loss of the 2D lattice order at 2 GPa is in agreement with some earlier results [7]. This transformation is irreversible for pressure beyond 6 GPa, in sharp contrast to our studies under hydrostatic conditions. However, in our Raman measurements on the pressure cycled samples from 21 to 30 GPa, radial breathing (RBM) and tangential modes (TM) reappear. These results clearly indicate that the ordering of tubes in the pressure quenched SWNT bundles is only marginally regained, with very short coherence length – not enough for re-emergence of X-ray diffraction peaks. Fig. 1 compares the pressure variation of d-spacings of the triangular lattice under non-hydrostatic conditions with that under hydrostatic conditions. SWNTs are found to be much more compressible
S. Karmakar et al. / Nucl. Instr. and Meth. in Phys. Res. B 238 (2005) 281–284
way by which triangular lattice deforms into an oblique shape. This causes systematic loss of the diffracted intensity. Our XRD results, therefore, suggest the pressure induced elliptization for the SWNTs. 3.2. MWNTs (pristine and Fe-filled) MWNTs are composed of several concentric cylindrical graphene tubules, with an intertube ˚ . We find that pure separation d0 of 3.4 A MWNT become partly amorphous when compressed above 8 GPa. To understand the effect of Fe filling on the mechanical properties of MWNTs, we have carried out high pressure structural investigations on Fe-filled MWNTs upto 20 GPa with X-ray diffraction measurements carried out at ELETTRA [8]. Unlike pristine MWNTs, a sharp change is seen in the intertubular distance d0 for Fe-filled MWNTs at 9 GPa, possibly due to polygonization of the tubes (Fig. 3). Encapsulated iron in the nanotubes remains in the form of a-Fe and Fe3C. The high pressure behavior of a-Fe and
(7.46 , 7.46)
(9.5 , 4.5)
5
10
15
20
25
3.4
3.5
3.3
3.4
3.2
3.3
3.1
3.2
3.0
3.1
2.9
3.0
2.8
2.9
2.7
2.8
2.6
2.7
(10.1 , 2.9) 0
3.6
o
o
dfe-mwnt , d002 (A)
Intensity (arb. unit)
λ = 1 Aº
dmwnt (A)
(B 10 GPa) under non-hydrostatic condition compared to that under hydrostatic pressures (B 34 GPa). A similar behavior is also observed from the pressure behavior of its TM vibrations [6]. The effect of pressure on the structural deformations (polygonization or elliptization) of the tubes has not been understood unambiguously. For that we have computed the diffraction pattern of the crystalline bundles under various structural deformations. We find that faceting or polygonization of the (11, 11) SWNTs does not reduce (10) diffracted intensity of the 2D lattice, whereas elliptization systematically reduces intensity of this peak, as shown in Fig. 2. For this, starting with the triangular array of (11, 11) circular tubes, the diffraction patterns are generated (by PowderCell ˚ ) for various software, X-ray wavelength = 1 A elliptic deformations of the tubes. Perimeters of the tubes are retained fixed due to strong C–C bond and therefore the deformation in the close packed structure takes place only in a particular
283
2.5 0
5
10 P (GPa)
15
20
30
2θ (deg) Fig. 2. Computed diffraction pattern of (11, 11) SWNT bundles having various elliptical distortions. Elliptic deformation of the tubes in a bundle is specified on each diffraction pattern by its dimensions (a,b) along the major and minor axes. X-ray ˚ was used for all the computations. wavelength k = 1 A
Fig. 3. Variation of the average intershell distance d0 with pressure for Fe-filled MWNTs (solid triangles for increasing pressure and open triangles for decreasing pressure) and for pristine MWNTs (solid circle). Variation of d002 line of graphite (dash line) is also plotted for comparison. For the sake of clarity, the left side Y-axis is for the filled tubes and graphite, whereas the right side is for pristine tubes.
284
S. Karmakar et al. / Nucl. Instr. and Meth. in Phys. Res. B 238 (2005) 281–284
Fe3C are found to be very different (more compressible) from their bulk counterpart. The structural transition in MWNTs is coincident with an iso-structural phase transition in Fe3C at 9 GPa, in sharp contrast to the absence of a transition in the bulk Fe3C upto 70 GPa. In summary, SWNTs in a bundle act as elastically coupled tubes and possess remarkable mechanical resilience. These undergo elliptic deformation under pressure and their compression behavior under hydrostatic and non-hydrostatic stress conditions is quite different. Fe-filled MWNTs undergo pressure-induced transitions at 9 GPa and the encapsulated Fe3C also changes its compression behavior at this pressure.
Acknowledgements X-ray diffraction experiments were performed at BL10XU (Spring8) and 5.2 R (ELETTRA) beamlines. We thank DST, India for financial assistance. We thank Dr. S.K. Sikka, Prof. C.N.R. Rao, Dr. A. Govindarajan, Dr. P.V.
Teredesai and Dr. D.V.S. Muthu for their supports for carrying out the experiments and fruitful discussions.
References [1] R. Saito, G. Dresselhaus, M.S. Dresselhaus, Physical Properties of Carbon Nanotubes, Imperial College Press, London, 1998. [2] S.M. Sharma, S. Karmakar, S.K. Sikka, P.V. Teredesai, A.K. Sood, A. Govindaraj, C.N.R. Rao, Phys. Rev. B 63 (2001) 205417. [3] J. Tang, L.C. Qin, T. Sasaki, M. Yudasaka, A. Matsushita, S. Iijima, Phys. Rev. Lett. 85 (2000) 1887. [4] S. Reich, C. Thomsen, P. Ordejo´n, Phys. Rev. B 65 (2002) 153407. [5] P.V. Teredesai, A.K. Sood, Surinder M. Sharma, S. Karmakar, S.K. Sikka, A. Govindraj, C.N.R. Rao, Phys. Stat. Sol. (b) 223 (2001) 479. [6] S. Karmakar, S.M. Sharma, P.V. Teredesai, D.V.S. Muthu, A. Govindaraj, S.K. Sikka, A.K. Sood, New J. Phys. 5 (2003) 143. [7] S. Rols, I.N. Gontcharenko, R. Almirac, J.L. Sauvajol, I. Mirebeau, Phys. Rev. B 65 (2001) 153401. [8] S. Karmakar, S.M. Sharma, P.V. Teredesai, A.K. Sood, Phys. Rev. B 69 (2004) 165414.
Studies on high pressure behavior of carbon nanotubes: X-ray diffraction measurements using synchrotron radiation S. Karmakar
a,*
, Surinder M. Sharma a, A.K. Sood
b,c
a
c
Synchrotron Radiation Section, Bhabha Atomic Research Centre, Mumbai 400085, India b Department of Physics, Indian Institute of Science, Bangalore 560012, India Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research Centre, Jakkur Campus, Jakkur, Bangalore 560064, India Available online 27 July 2005
Abstract High-pressure behavior of novel one-dimensional material – carbon nanotubes (single-walled and multi-walled, pristine and Fe-filled) have been investigated by in situ powder X-ray diffraction (XRD) studies. Single-walled nanotubes show remarkable mechanical resilience. The presence of non-hydrostatic stresses makes compression behavior much different from that under the hydrostatic stress. Our results also suggest pressure-induced elliptization of the tubes in a bundle. Iron-filled multi-walled nanotubes, unlike pristine, show a structural modification at a pressure of 9 GPa where the outer component (Fe3C) of the encapsulated nanowire undergoes an iso-structural transition. Also the high-pressure behavior of the a-Fe is quite different from the bulk. Ó 2005 Elsevier B.V. All rights reserved. PACS: 64.70.Nd; 61.10.Nz Keywords: Carbon nanotubes; High pressure; X-ray diffraction
1. Introduction The elastic properties of carbon nanotubes have been widely investigated since it was recognized * Corresponding author. Tel.: +91 22 2559 1312; fax: +91 22 2550 5151. E-mail addresses: [email protected], [email protected] (S. Karmakar).
that the low atomic weight of carbon combined with a strong covalent bond has a high potential usage as a large tensile-strength-material. Due to the novel one-dimensional nature as well as potential use in nanoscale electronic devices, single walled nanotubes (SWNTs), multiwalled nanotubes (MWNTs) and also metal filled carbon nanotubes have attracted a lot of research attention. A carbon nanotube can be viewed as a roll
0168-583X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.06.064
S. Karmakar et al. / Nucl. Instr. and Meth. in Phys. Res. B 238 (2005) 281–284 15.8 15.6 o
of graphene sheet. A SWNT is characterized by two indices (n, m) or simply by the chiral vector Ch = na1 + ma2, where a1 and a2 are two lattice vectors in the graphene plane [1]. SWNTs usually self-organize into bundle-like two-dimensional (2D) lattice with hexagonal symmetry containing tens to hundreds of parallel tubes. MWNTs consist of 10–100 concentric such tubes. Here we present the results of our recent high pressure studies on (11, 11) SWNTs under hydrostatic and nonhydrostatic conditions. Results of high pressure structural investigations on pristine and Fe-filled MWNTs are also presented.
d-spacing (A)
282
15.4 15.2 15.0 14.8 0
1
2
3
4
5
6
7
8
Pressure (GPa)
2. High pressure techniques Quasi-hydrostatic pressure upto 30 GPa is generated on the sample by filling it in a Mao-Bell kind of diamond anvil cell (DAC) with methanol:ethanol:water (16:3:1) mixture as pressure transmitting medium. For non-hydrostatic study, no pressure transmitter is used. Pressure is measured using ruby fluorescence technique or Au/Cu(1 1 1) diffraction line. Angle resolved powder XRD measurements have been carried out at BL10XU beamline of Spring8 (Undulator source) and at 5.2R beamline of ELETTRA (Wiggler ˚ , Si(1 1 1) monochromasource) (wavelength = 1 A tor) using Rigaku R-axis IV and MAR345 imaging plate area detectors respectively. In some cases, Raman measurements were also carried out for a detailed understanding of the structural evolution under high pressures.
3. Results and discussion 3.1. SWNTs The triangular 2D lattice of (11, 11) SWNTs bundle gives the strongest feature at the d-spacing ˚ (Fig. 1). Our high pressure studies d100 15.65 A upto 13 GPa [2] show that SWNTs loose translational coherence reversibly at 10 GPa, superceding a previous observation which showed irreversibility beyond 4 GPa [3]. This compression behavior has also been verified by a first-prin-
Fig. 1. Pressure variation of the d-spacing of the 2D lattice of SWNTs, hydrostatic (open circle) versus non-hydrostatic pressures (closed circle).
ciples calculation [4]. Just prior to this loss of translational order the lattice displays a sudden basal plane strain relaxation, which may be attributed to the heterogeneous distortion in the tubes. Our Raman scattering studies [5] also agree with this remarkable mechanical resilience of the nanotubes. To interpret the occurrence of transformation at lower pressures (1.5 GPa), as observed by others and to understand the effect of pressure medium, we re-investigated SWNTs under the non-hydrostatic stresses up to 30 GPa [6]. The observed loss of the 2D lattice order at 2 GPa is in agreement with some earlier results [7]. This transformation is irreversible for pressure beyond 6 GPa, in sharp contrast to our studies under hydrostatic conditions. However, in our Raman measurements on the pressure cycled samples from 21 to 30 GPa, radial breathing (RBM) and tangential modes (TM) reappear. These results clearly indicate that the ordering of tubes in the pressure quenched SWNT bundles is only marginally regained, with very short coherence length – not enough for re-emergence of X-ray diffraction peaks. Fig. 1 compares the pressure variation of d-spacings of the triangular lattice under non-hydrostatic conditions with that under hydrostatic conditions. SWNTs are found to be much more compressible
S. Karmakar et al. / Nucl. Instr. and Meth. in Phys. Res. B 238 (2005) 281–284
way by which triangular lattice deforms into an oblique shape. This causes systematic loss of the diffracted intensity. Our XRD results, therefore, suggest the pressure induced elliptization for the SWNTs. 3.2. MWNTs (pristine and Fe-filled) MWNTs are composed of several concentric cylindrical graphene tubules, with an intertube ˚ . We find that pure separation d0 of 3.4 A MWNT become partly amorphous when compressed above 8 GPa. To understand the effect of Fe filling on the mechanical properties of MWNTs, we have carried out high pressure structural investigations on Fe-filled MWNTs upto 20 GPa with X-ray diffraction measurements carried out at ELETTRA [8]. Unlike pristine MWNTs, a sharp change is seen in the intertubular distance d0 for Fe-filled MWNTs at 9 GPa, possibly due to polygonization of the tubes (Fig. 3). Encapsulated iron in the nanotubes remains in the form of a-Fe and Fe3C. The high pressure behavior of a-Fe and
(7.46 , 7.46)
(9.5 , 4.5)
5
10
15
20
25
3.4
3.5
3.3
3.4
3.2
3.3
3.1
3.2
3.0
3.1
2.9
3.0
2.8
2.9
2.7
2.8
2.6
2.7
(10.1 , 2.9) 0
3.6
o
o
dfe-mwnt , d002 (A)
Intensity (arb. unit)
λ = 1 Aº
dmwnt (A)
(B 10 GPa) under non-hydrostatic condition compared to that under hydrostatic pressures (B 34 GPa). A similar behavior is also observed from the pressure behavior of its TM vibrations [6]. The effect of pressure on the structural deformations (polygonization or elliptization) of the tubes has not been understood unambiguously. For that we have computed the diffraction pattern of the crystalline bundles under various structural deformations. We find that faceting or polygonization of the (11, 11) SWNTs does not reduce (10) diffracted intensity of the 2D lattice, whereas elliptization systematically reduces intensity of this peak, as shown in Fig. 2. For this, starting with the triangular array of (11, 11) circular tubes, the diffraction patterns are generated (by PowderCell ˚ ) for various software, X-ray wavelength = 1 A elliptic deformations of the tubes. Perimeters of the tubes are retained fixed due to strong C–C bond and therefore the deformation in the close packed structure takes place only in a particular
283
2.5 0
5
10 P (GPa)
15
20
30
2θ (deg) Fig. 2. Computed diffraction pattern of (11, 11) SWNT bundles having various elliptical distortions. Elliptic deformation of the tubes in a bundle is specified on each diffraction pattern by its dimensions (a,b) along the major and minor axes. X-ray ˚ was used for all the computations. wavelength k = 1 A
Fig. 3. Variation of the average intershell distance d0 with pressure for Fe-filled MWNTs (solid triangles for increasing pressure and open triangles for decreasing pressure) and for pristine MWNTs (solid circle). Variation of d002 line of graphite (dash line) is also plotted for comparison. For the sake of clarity, the left side Y-axis is for the filled tubes and graphite, whereas the right side is for pristine tubes.
284
S. Karmakar et al. / Nucl. Instr. and Meth. in Phys. Res. B 238 (2005) 281–284
Fe3C are found to be very different (more compressible) from their bulk counterpart. The structural transition in MWNTs is coincident with an iso-structural phase transition in Fe3C at 9 GPa, in sharp contrast to the absence of a transition in the bulk Fe3C upto 70 GPa. In summary, SWNTs in a bundle act as elastically coupled tubes and possess remarkable mechanical resilience. These undergo elliptic deformation under pressure and their compression behavior under hydrostatic and non-hydrostatic stress conditions is quite different. Fe-filled MWNTs undergo pressure-induced transitions at 9 GPa and the encapsulated Fe3C also changes its compression behavior at this pressure.
Acknowledgements X-ray diffraction experiments were performed at BL10XU (Spring8) and 5.2 R (ELETTRA) beamlines. We thank DST, India for financial assistance. We thank Dr. S.K. Sikka, Prof. C.N.R. Rao, Dr. A. Govindarajan, Dr. P.V.
Teredesai and Dr. D.V.S. Muthu for their supports for carrying out the experiments and fruitful discussions.
References [1] R. Saito, G. Dresselhaus, M.S. Dresselhaus, Physical Properties of Carbon Nanotubes, Imperial College Press, London, 1998. [2] S.M. Sharma, S. Karmakar, S.K. Sikka, P.V. Teredesai, A.K. Sood, A. Govindaraj, C.N.R. Rao, Phys. Rev. B 63 (2001) 205417. [3] J. Tang, L.C. Qin, T. Sasaki, M. Yudasaka, A. Matsushita, S. Iijima, Phys. Rev. Lett. 85 (2000) 1887. [4] S. Reich, C. Thomsen, P. Ordejo´n, Phys. Rev. B 65 (2002) 153407. [5] P.V. Teredesai, A.K. Sood, Surinder M. Sharma, S. Karmakar, S.K. Sikka, A. Govindraj, C.N.R. Rao, Phys. Stat. Sol. (b) 223 (2001) 479. [6] S. Karmakar, S.M. Sharma, P.V. Teredesai, D.V.S. Muthu, A. Govindaraj, S.K. Sikka, A.K. Sood, New J. Phys. 5 (2003) 143. [7] S. Rols, I.N. Gontcharenko, R. Almirac, J.L. Sauvajol, I. Mirebeau, Phys. Rev. B 65 (2001) 153401. [8] S. Karmakar, S.M. Sharma, P.V. Teredesai, A.K. Sood, Phys. Rev. B 69 (2004) 165414.