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📘 Publication 12
📘 Publication 12
Title: Resonance Raman spectroscopy of carbon nanotubes: pressure effects on G-mode
Title: Resonance Raman spectroscopy of carbon nanotubes: pressure effects on G-mode
Authors: Y.W. Sun, I. Hernández, A.J. Ghandour, C. Rice, I.F. Crowe, M.P. Halsall, A. Sapelkin, J. Gonzalez, F. Rodriguez & D.J. Dunstan
Authors: Y.W. Sun, I. Hernández, A.J. Ghandour, C. Rice, I.F. Crowe, M.P. Halsall, A. Sapelkin, J. Gonzalez, F. Rodriguez & D.J. Dunstan
Journal: HIGH PRESSURE RESEARCH, 2014, Vol 34, pp 191–197
Journal: HIGH PRESSURE RESEARCH, 2014, Vol 34, pp 191–197
Abstract: We use 488 and 568 nm laser Raman spectroscopy under high pressure to selectively follow evolution of Raman G-mode signals of single-walled carbon nanotubes (SWCNTs) of selected diameters and chiralities ((6, 5) and (6, 4)). The G-mode pressure coefficients of tubes from our previous work are consistent with the thick-wall tube model. Here we report the observation of well-resolved G-minus peaks in the Raman spectrum of SWCNTs in a diamond-anvil cell. The pressure coefficients of these identified tubes in water, however, are unexpected, having the high value of over 9 cm−1 GPa−1 for the G-plus and the G-minus, and surprisingly the shift rates of the same tubes in hexane have clearly lower values. We also report an abrupt increase of G-minus peak width at about 4GPa superposed on a continuous peak broadening with pressure.
Abstract: We use 488 and 568 nm laser Raman spectroscopy under high pressure to selectively follow evolution of Raman G-mode signals of single-walled carbon nanotubes (SWCNTs) of selected diameters and chiralities ((6, 5) and (6, 4)). The G-mode pressure coefficients of tubes from our previous work are consistent with the thick-wall tube model. Here we report the observation of well-resolved G-minus peaks in the Raman spectrum of SWCNTs in a diamond-anvil cell. The pressure coefficients of these identified tubes in water, however, are unexpected, having the high value of over 9 cm−1 GPa−1 for the G-plus and the G-minus, and surprisingly the shift rates of the same tubes in hexane have clearly lower values. We also report an abrupt increase of G-minus peak width at about 4GPa superposed on a continuous peak broadening with pressure.
2014_HPR_Resonance Raman spectroscopy of.pdf📘 Publication 11
📘 Publication 11
Title: Pressure coefficients of Raman modes of carbon nanotubes resolved by chirality: Environmental effect on graphene sheet
Title: Pressure coefficients of Raman modes of carbon nanotubes resolved by chirality: Environmental effect on graphene sheet
Authors: A. J. Ghandour, I. F. Crowe, J. E. Proctor, Y. W. Sun, M. P. Halsall, I. Hernandez, A. Sapelkin, and D. J. Dunstan
Authors: A. J. Ghandour, I. F. Crowe, J. E. Proctor, Y. W. Sun, M. P. Halsall, I. Hernandez, A. Sapelkin, and D. J. Dunstan
Journal: PHYSICAL REVIEW B, 2013, Vol 87, pp 085416
Journal: PHYSICAL REVIEW B, 2013, Vol 87, pp 085416
Abstract: Studies of the mechanical properties of single-walled carbon nanotubes are hindered by their availability only as ensembles of tubes with a range of diameters. However, tunable Raman spectroscopy is capable of identifying individual tubes from such ensembles. Interestingly, both the radial breathing mode and, surprisingly, the G-mode pressure coefficients exhibit strong environmental effects, which are largely independent of the nature of the environment. We show that the G-mode pressure coefficient varies with diameter, consistent with the thick-wall tube model. Reappraisal of literature data for graphene and graphite suggests revision of both the G-mode Gr¨uneisen parameter γ and the shear deformation parameter β toward the value of 1.34.
Abstract: Studies of the mechanical properties of single-walled carbon nanotubes are hindered by their availability only as ensembles of tubes with a range of diameters. However, tunable Raman spectroscopy is capable of identifying individual tubes from such ensembles. Interestingly, both the radial breathing mode and, surprisingly, the G-mode pressure coefficients exhibit strong environmental effects, which are largely independent of the nature of the environment. We show that the G-mode pressure coefficient varies with diameter, consistent with the thick-wall tube model. Reappraisal of literature data for graphene and graphite suggests revision of both the G-mode Gr¨uneisen parameter γ and the shear deformation parameter β toward the value of 1.34.
2013_PRB_87_085416.pdf📘 Publication 10
📘 Publication 10
Title: Raman excitation spectroscopy of carbon nanotubes: effects of pressure medium and pressure
Title: Raman excitation spectroscopy of carbon nanotubes: effects of pressure medium and pressure
Authors: A.J. Ghandour, A. Sapelkin, I. Hernandez, D.J. Dunstan, I.F. Crowe and M.P. Halsall
Authors: A.J. Ghandour, A. Sapelkin, I. Hernandez, D.J. Dunstan, I.F. Crowe and M.P. Halsall
Journal: HIGH PRESSURE RESEARCH, 2012, Vol 32, pp 67–71
Journal: HIGH PRESSURE RESEARCH, 2012, Vol 32, pp 67–71
Abstract: Raman excitation and emission spectra for the radial breathing mode (RBM) are reported, together with a preliminary analysis. From the position of the peaks on the two-dimensional plot of excitation resonance energy against Raman shift, the chiral indices (m, n) for each peak are identified. Peaks shift from their positions in air when different pressure media are added – water, hexane, sulphuric acid – and when the nanotubes are unbundled in water with surfactant and sonication. The shift is about 2–3 cm−1 in RBM frequency, but unexpectedly large in resonance energy, being spread over up to 100 meV for a given peak. This contrasts with the effect of pressure. The shift of the peaks of semiconducting nanotubes in water under pressure is orthogonal to the shift from air to water. This permits the separation of the effects of the pressure medium and the pressure, and will enable the true pressure coefficients of the RBM and the other Raman peaks for each (m, n) to be established unambiguously.
Abstract: Raman excitation and emission spectra for the radial breathing mode (RBM) are reported, together with a preliminary analysis. From the position of the peaks on the two-dimensional plot of excitation resonance energy against Raman shift, the chiral indices (m, n) for each peak are identified. Peaks shift from their positions in air when different pressure media are added – water, hexane, sulphuric acid – and when the nanotubes are unbundled in water with surfactant and sonication. The shift is about 2–3 cm−1 in RBM frequency, but unexpectedly large in resonance energy, being spread over up to 100 meV for a given peak. This contrasts with the effect of pressure. The shift of the peaks of semiconducting nanotubes in water under pressure is orthogonal to the shift from air to water. This permits the separation of the effects of the pressure medium and the pressure, and will enable the true pressure coefficients of the RBM and the other Raman peaks for each (m, n) to be established unambiguously.
2012_HPR_Raman excitation spectroscopy of carbon nanotubes.pdf📘 Publication 9
📘 Publication 9
Title: Effect of water on resonant Raman spectroscopy of closed single-walled carbon nanotubes
Title: Effect of water on resonant Raman spectroscopy of closed single-walled carbon nanotubes
Authors: Ahmad J. Ghandour, David J. Dunstan, Andrei Sapelkin, Ignacio Hernandez, Matthew P. Halsall, and Iain F. Crowe
Authors: Ahmad J. Ghandour, David J. Dunstan, Andrei Sapelkin, Ignacio Hernandez, Matthew P. Halsall, and Iain F. Crowe
Journal: Phys. Stat. Sol. (b), 2011, Vol 248, pp 2548–2551
Journal: Phys. Stat. Sol. (b), 2011, Vol 248, pp 2548–2551
Abstract:  Tunable Raman excitation spectroscopy with 1.55–1.77 eV laser energies was used to map the second van Hove singularities of semiconducting single-walled carbon nanotubes ropes in air and immersed in water. The optical transitions are assigned to different (n,m) tubes using a correlation of the diameter and radial breathing mode (RBM) in the Raman spectrum. The resonance energies are blue-shifted when the tubes are immersed in water and the shift depends on the chiral angle. In addition, the RBM frequencies are also blue-shifted upon immersion in water.
Abstract:  Tunable Raman excitation spectroscopy with 1.55–1.77 eV laser energies was used to map the second van Hove singularities of semiconducting single-walled carbon nanotubes ropes in air and immersed in water. The optical transitions are assigned to different (n,m) tubes using a correlation of the diameter and radial breathing mode (RBM) in the Raman spectrum. The resonance energies are blue-shifted when the tubes are immersed in water and the shift depends on the chiral angle. In addition, the RBM frequencies are also blue-shifted upon immersion in water.
2011_PSS_248_2548.pdf📘 Publication 8
📘 Publication 8
Title: Raman G-mode of single-wall carbon nanotube bundles under pressure
Title: Raman G-mode of single-wall carbon nanotube bundles under pressure
Authors: Ahmad J. Ghandour, David J. Dunstan and Andrei Sapelkin
Authors: Ahmad J. Ghandour, David J. Dunstan and Andrei Sapelkin
Journal: JOURNAL OF RAMAN SPECTOSCOPY, 2011, Vol 42, pp 1611–1613
Journal: JOURNAL OF RAMAN SPECTOSCOPY, 2011, Vol 42, pp 1611–1613
Abstract: Raman studies of nanotubes under pressure have been a lively area of research.However, the results are not always as expected and at times have not been adequately explained. One example of the diversity of the results is the higher energy Raman mode (the graphitic mode, GM) shift to higher wavenumber under pressure. Here we report a new high-pressure Raman study showing that the effects of the variation in the tube diameters and the pressure transmitting medium are both crucial for understanding the outcomes of such high-pressure experiments.
Abstract: Raman studies of nanotubes under pressure have been a lively area of research.However, the results are not always as expected and at times have not been adequately explained. One example of the diversity of the results is the higher energy Raman mode (the graphitic mode, GM) shift to higher wavenumber under pressure. Here we report a new high-pressure Raman study showing that the effects of the variation in the tube diameters and the pressure transmitting medium are both crucial for understanding the outcomes of such high-pressure experiments.
2011_JRS_42_1611.pdf📘 Publication 7
📘 Publication 7
Title: High-pressure studies of carbon nanotubes
Title: High-pressure studies of carbon nanotubes
Authors: David J. Dunstan and Ahmad J. Ghandour
Authors: David J. Dunstan and Ahmad J. Ghandour
Journal: HIGH PRESSURE RESEARCH, 2009, Vol 29, pp 548–553
Journal: HIGH PRESSURE RESEARCH, 2009, Vol 29, pp 548–553
Abstract: Considering carbon nanotubes as a rolled-up graphene sheet, the basic properties of the Raman scattering of nanotubes can be predicted from the Raman of graphite. We expect increased pressure coefficients if the nanotubes are impermeable to the pressure medium and the same as graphite if they are filled; also if they collapse at high pressures. The literature is reviewed to see how well these predictions are borne out in practice. New experiments are reported, which confirm the crucial effects of the nature of the pressuretransmitting medium (solvent), which is unexpected, and the resonances with the Raman excitation energy (expected). Key open questions include the mechanism of the solvent effect and the influence of bundling.
Abstract: Considering carbon nanotubes as a rolled-up graphene sheet, the basic properties of the Raman scattering of nanotubes can be predicted from the Raman of graphite. We expect increased pressure coefficients if the nanotubes are impermeable to the pressure medium and the same as graphite if they are filled; also if they collapse at high pressures. The literature is reviewed to see how well these predictions are borne out in practice. New experiments are reported, which confirm the crucial effects of the nature of the pressuretransmitting medium (solvent), which is unexpected, and the resonances with the Raman excitation energy (expected). Key open questions include the mechanism of the solvent effect and the influence of bundling.
2009_HPR_29_548.pdf📘 Publication 6
📘 Publication 6
Title: G-mode behaviour of closed ended single wall carbon nanotubes under pressure
Title: G-mode behaviour of closed ended single wall carbon nanotubes under pressure
Authors: Ahmad J. Ghandour, David J. Dunstan, and Andrei Sapelkin
Authors: Ahmad J. Ghandour, David J. Dunstan, and Andrei Sapelkin
Journal:Phys. Stat. Sol. (b), 2009, Vol 246, pp 491–495
Journal:Phys. Stat. Sol. (b), 2009, Vol 246, pp 491–495
Abstract: We have performed high pressure Raman experiments on closed-ended single wall carbon nanotubes using two different excitation wavelengths: 632.8 nm and 514 nm. We found that the shape of the G-mode spectrum changes while changing the excitation wavelength at lower pressures, while it becomes similar at 3.5 GPa. In addition we record that the value of the transition pressure, associated with the structural transitions in the tubes, has also changed with changing the excitation wavelength even though we are examining tubes from the same produced sample. We attribute these results to the tubes having different electronic nature (metallic; semiconducting) and different diameters in resonance with each excitation wavelength.
Abstract: We have performed high pressure Raman experiments on closed-ended single wall carbon nanotubes using two different excitation wavelengths: 632.8 nm and 514 nm. We found that the shape of the G-mode spectrum changes while changing the excitation wavelength at lower pressures, while it becomes similar at 3.5 GPa. In addition we record that the value of the transition pressure, associated with the structural transitions in the tubes, has also changed with changing the excitation wavelength even though we are examining tubes from the same produced sample. We attribute these results to the tubes having different electronic nature (metallic; semiconducting) and different diameters in resonance with each excitation wavelength.
2009_PSS_246_491.pdf📘 Publication 5
📘 Publication 5
Title: High-pressure Raman response of single-walled carbon nanotubes: Effect of the excitation laser energy
Title: High-pressure Raman response of single-walled carbon nanotubes: Effect of the excitation laser energy
Authors: Ahmad J. Ghandour, David J. Dunstan, Andrei Sapelkin, John E. Proctor, Matthew P. Halsall
Authors: Ahmad J. Ghandour, David J. Dunstan, Andrei Sapelkin, John E. Proctor, Matthew P. Halsall
Journal: PHYSICAL REVIEW B, 2008, Vol 78, pp 12542072
Journal: PHYSICAL REVIEW B, 2008, Vol 78, pp 12542072
Abstract: We report high-pressure Raman experiments on the tangential vibrational modes of CarboLex bundled single-walled carbon nanotubes up to 6.5 GPa using two different excitation energies: 1.96 and 2.41 eV. We show through the curve-fitting technique, together with the modified interband transition energies versus diameter plot, how the nature of the resonant tubes is modified under the excitation energy, in particular under the 1.96 eV excitation. Having metallic and semiconducting tubes in resonance at ambient pressure, we find that only semiconducting tubes are in resonance at 3.5 GPa. We associate this loss of resonance from the metallic tubes to a redshift pressure response of the first E11 transition energies from these tubes. Added to that, the change in the excitation energies leads to a change in the value of the transition pressure. This is simply associated with the fact of having different diameters in resonance under each excitation from the same sample.
Abstract: We report high-pressure Raman experiments on the tangential vibrational modes of CarboLex bundled single-walled carbon nanotubes up to 6.5 GPa using two different excitation energies: 1.96 and 2.41 eV. We show through the curve-fitting technique, together with the modified interband transition energies versus diameter plot, how the nature of the resonant tubes is modified under the excitation energy, in particular under the 1.96 eV excitation. Having metallic and semiconducting tubes in resonance at ambient pressure, we find that only semiconducting tubes are in resonance at 3.5 GPa. We associate this loss of resonance from the metallic tubes to a redshift pressure response of the first E11 transition energies from these tubes. Added to that, the change in the excitation energies leads to a change in the value of the transition pressure. This is simply associated with the fact of having different diameters in resonance under each excitation from the same sample.
2008_PRB_78_125420.pdf📘 Publication 4
📘 Publication 4
Title: Raman G band in double-wall carbon nanotubes combining p doping and high pressure
Title: Raman G band in double-wall carbon nanotubes combining p doping and high pressure
Authors: Pascal Puech, Ahmad Ghandour, Andrei Sapelkin, Cyril Tinguely, Emmanuel Flahaut, David J. Dunstan, and Wolfgang Bacsa
Authors: Pascal Puech, Ahmad Ghandour, Andrei Sapelkin, Cyril Tinguely, Emmanuel Flahaut, David J. Dunstan, and Wolfgang Bacsa
Journal: PHYSICAL REVIEW B, 2008, Vol 78, pp 045413
Journal: PHYSICAL REVIEW B, 2008, Vol 78, pp 045413
Abstract: We report high-pressure Raman experiments on the tangential vibrational modes of CarboLex bundled single-walled carbon nanotubes up to 6.5 GPa using two different excitation energies: 1.96 and 2.41 eV. We show through the curve-fitting technique, together with the modified interband transition energies versus diameter plot, how the nature of the resonant tubes is modified under the excitation energy, in particular under the 1.96 eV excitation. Having metallic and semiconducting tubes in resonance at ambient pressure, we find that only semiconducting tubes are in resonance at 3.5 GPa. We associate this loss of resonance from the metallic tubes to a redshift pressure response of the first E11 transition energies from these tubes. Added to that, the change in the excitation energies leads to a change in the value of the transition pressure. This is simply associated with the fact of having different diameters in resonance under each excitation from the same sample.
Abstract: We report high-pressure Raman experiments on the tangential vibrational modes of CarboLex bundled single-walled carbon nanotubes up to 6.5 GPa using two different excitation energies: 1.96 and 2.41 eV. We show through the curve-fitting technique, together with the modified interband transition energies versus diameter plot, how the nature of the resonant tubes is modified under the excitation energy, in particular under the 1.96 eV excitation. Having metallic and semiconducting tubes in resonance at ambient pressure, we find that only semiconducting tubes are in resonance at 3.5 GPa. We associate this loss of resonance from the metallic tubes to a redshift pressure response of the first E11 transition energies from these tubes. Added to that, the change in the excitation energies leads to a change in the value of the transition pressure. This is simply associated with the fact of having different diameters in resonance under each excitation from the same sample.
2008_PRB_78_045413.pdf📘 Publication 3
📘 Publication 3
Title: Raman spectroscopy of single-walled carbon nanotubes at high pressure: Effect of interactions between the nanotubes and pressure transmitting media
Title: Raman spectroscopy of single-walled carbon nanotubes at high pressure: Effect of interactions between the nanotubes and pressure transmitting media
Authors: J. E. Proctor, M. P. Halsall, A. Ghandour and D. J. Dunstan
Authors: J. E. Proctor, M. P. Halsall, A. Ghandour and D. J. Dunstan
Journal: Phys. Stat. Sol. (b), 2007, Vol 244, pp 147–150
Journal: Phys. Stat. Sol. (b), 2007, Vol 244, pp 147–150
Abstract: We have studied single-walled carbon nanotubes (SWNT) at high pressure using Raman spectroscopy, in a variety of common solvents as hydrostatic pressure-transmitting media. We find that the response of the Raman G-band to high pressure varies significantly with choice of solvent. In particular, with hexane we observe a new irreversible effect – a flat Raman response to 0.7 GPa. We draw tentative conclusions from this work – that the solvents used can penetrate the interstitial spaces between nanotubes in a bundle and, following the approach of Amer et al. [1], that absorption of the pressure-transmitting media plays a role in the response of the SWNTs to high pressure.
Abstract: We have studied single-walled carbon nanotubes (SWNT) at high pressure using Raman spectroscopy, in a variety of common solvents as hydrostatic pressure-transmitting media. We find that the response of the Raman G-band to high pressure varies significantly with choice of solvent. In particular, with hexane we observe a new irreversible effect – a flat Raman response to 0.7 GPa. We draw tentative conclusions from this work – that the solvents used can penetrate the interstitial spaces between nanotubes in a bundle and, following the approach of Amer et al. [1], that absorption of the pressure-transmitting media plays a role in the response of the SWNTs to high pressure.
2007_PSS_244_147.pdf📘 Publication 2
📘 Publication 2
Title: High pressure Raman spectroscopy of single-walled carbon nanotubes: Effect of chemical environment on individual nanotubes and the nanotube bundle
Title: High pressure Raman spectroscopy of single-walled carbon nanotubes: Effect of chemical environment on individual nanotubes and the nanotube bundle
Authors: John E. Proctor,, Matthew P. Halsall, Ahmad J. Ghandour, David J. Dunstan
Authors: John E. Proctor,, Matthew P. Halsall, Ahmad J. Ghandour, David J. Dunstan
Journal: Journal of Physics and Chemistry of Solids, 2006, Vol 67, pp 2468–2472
Journal: Journal of Physics and Chemistry of Solids, 2006, Vol 67, pp 2468–2472
Abstract: The pressure-induced tangential mode Raman peak shifts for single-walled carbon nanotubes (SWNTs) have been studied using a variety of different solvents as hydrostatic pressure-transmitting media. The variation in the nanotube response to hydrostatic pressure with different pressure transmitting media is evidence that the common solvents used are able to penetrate the interstitial spaces in the nanotube bundle. With hexane, we find the surprising result that the individual nanotubes appear unaffected by hydrostatic pressures (i.e. a flat Raman response) up to 0.7 GPa. Qualitatively similar results have been obtained with butanol. Following the approach of Amer et al. [J. Chem. Phys. 121 (2004) 2752], we speculate that this is due to the inability of SWNTs to adsorb some solvents onto their surface at lower pressures. We also find that the role of cohesive energy density in the solvent–nanotube interaction is more complex than previously thought. This study explores the geometric and mechanical transitions observed in twisted ribbons, highlighting the role of torque and boundary conditions.
Abstract: The pressure-induced tangential mode Raman peak shifts for single-walled carbon nanotubes (SWNTs) have been studied using a variety of different solvents as hydrostatic pressure-transmitting media. The variation in the nanotube response to hydrostatic pressure with different pressure transmitting media is evidence that the common solvents used are able to penetrate the interstitial spaces in the nanotube bundle. With hexane, we find the surprising result that the individual nanotubes appear unaffected by hydrostatic pressures (i.e. a flat Raman response) up to 0.7 GPa. Qualitatively similar results have been obtained with butanol. Following the approach of Amer et al. [J. Chem. Phys. 121 (2004) 2752], we speculate that this is due to the inability of SWNTs to adsorb some solvents onto their surface at lower pressures. We also find that the role of cohesive energy density in the solvent–nanotube interaction is more complex than previously thought. This study explores the geometric and mechanical transitions observed in twisted ribbons, highlighting the role of torque and boundary conditions.
2006_JPCS_67_2468.pdf📘 Publication 1
📘 Publication 1
Title: Effect of chemical environment on high-pressure Raman response of single-walled carbon nanotubes
Title: Effect of chemical environment on high-pressure Raman response of single-walled carbon nanotubes
Authors: John E. Proctor , Matthew P. Halsall , Ahmad Ghandour & David J. Dunstan
Authors: John E. Proctor , Matthew P. Halsall , Ahmad Ghandour & David J. Dunstan
Journal: HIGH PRESSURE RESEARCH, 2006, Vol 26, pp 335–339
Journal: HIGH PRESSURE RESEARCH, 2006, Vol 26, pp 335–339
Abstract: The pressure-induced Raman peak shifts for single-walled carbon nanotubes (SWNTs) have been studied using different solvents as hydrostatic pressure-transmitting fluids (PTF). We suggest that the variation in the nanotube response to hydrostatic pressure with different PTF is evidence that the common solvents used are able to penetrate the interstitial spaces in the nanotube bundle. With hexane, we find the surprising result that the individual nanotubes appear unaffected by hydrostatic pressures (i.e. a flat Raman response) up to 0.7 GPa. Qualitatively similar results have been obtained with butanol. Following the approach of Amer et al. [M. S. Amer, M. S. El-Ashry and J. F. Maguire, J. Chem. Phys. 121 2752 (2004)], we speculate that this is due to the inability of SWNTs to adsorb some solvents onto their surface at low pressure.
Abstract: The pressure-induced Raman peak shifts for single-walled carbon nanotubes (SWNTs) have been studied using different solvents as hydrostatic pressure-transmitting fluids (PTF). We suggest that the variation in the nanotube response to hydrostatic pressure with different PTF is evidence that the common solvents used are able to penetrate the interstitial spaces in the nanotube bundle. With hexane, we find the surprising result that the individual nanotubes appear unaffected by hydrostatic pressures (i.e. a flat Raman response) up to 0.7 GPa. Qualitatively similar results have been obtained with butanol. Following the approach of Amer et al. [M. S. Amer, M. S. El-Ashry and J. F. Maguire, J. Chem. Phys. 121 2752 (2004)], we speculate that this is due to the inability of SWNTs to adsorb some solvents onto their surface at low pressure.
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