C. Journet | Université Claude Bernard Lyon 1 (original) (raw)
Papers by C. Journet
Physical Review Letters, 2002
Field emission (FE) electron spectroscopy from an individual multiwalled carbon nanotube (MWNT) i... more Field emission (FE) electron spectroscopy from an individual multiwalled carbon nanotube (MWNT) is used to measure quantitatively stable temperatures at the apex, T A , of up to 2000 K induced by FE currents ഠ1 mA. The high T A is due to Joule heating along the length of the MWNT. These measurements also give directly the resistance of the individual MWNT which is shown to decrease with temperature, and explain the phenomenon of FE-induced light emission which was observed simultaneously. The heating permits thermal desorption of the MWNT and, hence, excellent current stability.
AIP Conference Proceedings, 1998
ABSTRACT
AIP Conference Proceedings, 2000
The 13th international winterschool on electronic properties of novel materials- science and technology of molecular nanostructures, 1999
PCQHs^kQol is an ideal model system to study C 60 mono radical anion in a charged surrounding sin... more PCQHs^kQol is an ideal model system to study C 60 mono radical anion in a charged surrounding since the C 60 radical anions are well separated on a regular crystal lattice by the aid of large organic counter ions. They do not contribute to the ESR signal as they are all closed shell molecules. At low temperatures two Lorentzian ESR lines are observed which can be ascribed to two different orientations of the C 6 o molecules as detected by x-ray analysis of the crystal structure. The g-tensor of the two lines corresponds to the Jahn-Teller distortion of C 60 ". Tetragonal crystal symmetry, molecular symmetry together with the crystal field support the D y , distortion of C 60 " which is in agreement with the observed non axial g-tensor.-I-ions shown schematically in figure 4. The C2 axis of the COO" anion is parallel to the c axis of the crystal. Symmetry considerations for the Jahn-Teller distorted COO" and the crystal field of tetragonal symmetry lead to the conclusion that only the D-u, distortion fit together. This is in agreement with our ligand field calculations which stabilizes the D21, distortion symmetry [7] and the experimentally observed non axial g-tensor. At low temperatures the dynamics of the charge distortion is hindered i.e. jumps between different possible Ü2h orientations are not favored due to the charged surrounding (static Jahn-Teller effect). Increasing the temperature the distortion randomly jumps between symmetry equivalent Dih states (or D=,d and D3J) by phonon assisted tunneling. This corresponds to a pseudo rotation of the Jahn-Teller distortion [8] which results in averaging the gtensor to an isotropic value (dynamic Jahn-Teller effect). This study has shown that two effects have to be distinguished: a charged environment prevents COO anions from a free rotation due to a coordination with the counter ions. However, the electronic distortion still can jump independently until an intrinsic counter ion interaction prevails. This is seen in the frequency independent splitting temperature for the two lines with an anisotropic g-tensor which corresponds to the Jahn-Teller distortion of C6o~'. FIGURE 4. Schematic sketch of the charge environment of C 60~. The arrow corresponds to the c-axis of the tetragonal unit cell which is the direction of the most favorable D 2 h Jahn-Teller distortion of C 6 o~ (shaded area).
Synthetic Metals, 1997
We have previously shown that the high intensity of solar radiation, obtained with the Gdeillo (F... more We have previously shown that the high intensity of solar radiation, obtained with the Gdeillo (France) solar furnace facilities, can be used to vaporize graphite in inert gas atmosphere to produce fullerenes. After a short survey of the possible mechanisms of formation of these molecules, we report some results in agreement with the proposed model and discuss the possibilities of increasing the fullerene yield which currently reaches 20%
Physical Review B, 2000
Low-coverage adsorption isotherms for CH 4 on single-walled carbon nanotube bundles have been mea... more Low-coverage adsorption isotherms for CH 4 on single-walled carbon nanotube bundles have been measured at eight temperatures between 155 and 195 K. The nanotubes used in this study were untreated, so that the tubes have closed ends. The isosteric heat of adsorption was determined from the isotherms and, from this quantity, the binding energy of the methane on the nanotube substrate was obtained. The binding energy was found to be 76% larger on the nanotube bundles than it is on planar graphite.
Journal of the Chemical Society, Faraday Transactions, 1998
Carbon nanotubes were produced in large amounts by catalytic decomposition of acetylene over a Co... more Carbon nanotubes were produced in large amounts by catalytic decomposition of acetylene over a Co incorporated zeolite NaY support. PuriÐcation of multi-wall nanotubes was required in order to eliminate catalyst and amorphous carbon produced by thermal decomposition of hydrocarbon. First, separation of nanotubes and catalyst particles was carried out by hydroÑuoric acid treatment. Then, two ways of removing amorphous carbon were studied : permanganate oxidation and air oxidation. The quality of nanotubes was characterized by means of transmission electron microscopy and the yield of pure nanotubes was quantitatively determined. Changes caused by treatment of the nanotubes were investigated by high resolution electron microscopy and a comparison was made between the nanotubes produced by this method and those synthesized by an arc discharge process after oxidation treatment.
Fullerenes and Photonics IV, 1997
ABSTRACT Carbon single walled nanotubes produced in high yields by the electric arc technique hav... more ABSTRACT Carbon single walled nanotubes produced in high yields by the electric arc technique have been studied by several techniques including HRTEM. It is shown in particular that they have a narrow diameter distribution around an average value of 1.3 nm. In this paper, we mainly report characterization results obtained by high resolution Raman spectroscopy. Raman spectra exhibit a very rich structure especially in the low frequency range where several components are observed. Using previous calculations, we attribute the main features to armchair tubes with (6,6) to (12,12) geometry, in agreement with the narrow diameter distribution observed by HRTEM measurements.
Physical Review B, 2002
In this paper we simulate the resistive heating of carbon nanotubes ͑CNT's͒ during field emission... more In this paper we simulate the resistive heating of carbon nanotubes ͑CNT's͒ during field emission ͑FE͒ using the one-dimensional heat equation including radiation and conductive losses. The simulations are in relatively good agreement with our recent experiments in which we measured the heating of individual CNT's to as high as 2000 K during FE for currents I FE of Ϸ2 A. For low temperatures where radiation is negligible the simulations reduce to an analytic solution that provides a universal guide to estimating current-induced heating in CNT's. The effects of this heating are included in the calculations of I FE as a function of voltage.
Synthetic Metals, 1999
We report results on purification and characterization of single wall carbon nanotubes prepared b... more We report results on purification and characterization of single wall carbon nanotubes prepared by the electric arc method. The process consists of a chemical treatment based on a reflux with nitric acid followed by successive filtration steps (tangential flow and frontal filtration) of a suspension of the raw material. The effects of each step are analysed by SEM and TEM.
Synthetic Metals, 1999
In this paper, we present Surface Enhanced Raman Scattering SERS experiments performed successful... more In this paper, we present Surface Enhanced Raman Scattering SERS experiments performed successfully on some conducting polymers and carbon nanotubes deposited in thin films on rough metallic surfaces. The enhancement mechanism in SERS has a twofold origin: electromagnetic and chemical. The electromagnetic enhancement is, however, the dominant mechanism and consists in the Ž. excitation of localized and delocalized surface plasmons SP. The second enhancing mechanism for SERS, not yet convincingly supported by experimental data, is of chemical origin. This mechanism is due to the increase of the polarizability of the molecules on the metal surface under the action of the incident radiation, leading to the formation of new chemical bonds between the molecules and the metal surface. Unfortunately, the experimental data available to argue the presence of a chemical process are scarce and scattered. In this Ž. paper, we try to present some details regarding this aspect. In order to do so, we studied poly 3-hexylthiophene 3-PHT and polyaniline Ž. Ž. PAN as a function of the type of the rough metallic support Ag, Au or Cu , the oxidization state and thickness of the polymer layer. We studied also carbon single walled nanotubes. Our experiments reveal the existence of a chemical surface effect. The results obtained for 3-PHT show that SERS spectra depend on the oxidizing properties of the metal surface and on the nature of the solvent. This dependence is explained by the existence of some interfacial reactions that lead to the formation of interface compounds. The SERS measurements reported here reveal an increase of the intensities of the Raman lines, accompanied by a modification of the corresponding intensity ratios, when the degree of doping is increased. We observe for the first time by SERS spectroscopy that doping of 3-PHT with FeCl leads to the appearance of a state of disorder in the structure of the macromolecular chain, as a result of steric hindrance effects. 3 The type of the rough metallic support can modify SERS spectra and such an effect is clearly shown for the polyaniline case. No such dependence on metallic support type is observed on the SERS spectra of carbon nanotubes.
Synthetic Metals, 1999
A mid-infrared reflection study on single-walled carbon nanotubes revealed weak absorption struct... more A mid-infrared reflection study on single-walled carbon nanotubes revealed weak absorption structures which we assign to the vibrational modes of the tubes. The results are in good agreement with theoretical predictions for nanotubes. In comparison to graphite phonons a small shift to higher frequencies was found. First measurements at different temperatures indicate no temperature dependence of the phonon frequencies.
Synthetic Metals, 1999
The electric arc discharge and the solar energy are two methods among a large number to produce s... more The electric arc discharge and the solar energy are two methods among a large number to produce single wall carbon nanotubes. They are based on the same process: sublimation of mixture of graphite and catalyst under an inert gas atmosphere. While the solar furnace is a small scale experiment, the electric arc discharge presents a better yield of production. Samples synthesized by both methods in the same conditions of gas pressure and catalysts are characterized by SEM, TEM and RAMAN spectroscopy.
Synthetic Metals, 1999
After being dispersed in liquid solvents (Ethanol, CHCl,), conducting polymers and singlewalled n... more After being dispersed in liquid solvents (Ethanol, CHCl,), conducting polymers and singlewalled nanotubes have been deposited on ruguous substrats (Au, Ag, Cu). With FT Raman technique (laser excitation : 1064 nm), we have obtained SERS signal of both conductiong polymers and singlewalled nanotubes. The Raman signals change with substrat and/or solvent, which could be correlated with the size of clusters formed at the surface and then to the deposition mechanism. The main advantage of the >SERS technique will be emphasized in terms of enhancement as a powerful technique to study nanoparticles.
Synthetic Metals, 1999
The adsorption of carbon SWNTs from purified aqueous dispersions on electrode patterns is describ... more The adsorption of carbon SWNTs from purified aqueous dispersions on electrode patterns is described, As an alternative approach to electrically contacted SWNTs, mixed Langmuir films consisting of surfactant molecules and SWNTs were traflsferred onto electrode arrays. Room temperature conductivity measurements on both types of samples revealed a (two point) resistance in the MSZ range. From these values, the presence of a closed surfactant layer between the tubes and electrode surface is excluded. As astep towards increasing the functionality of SWNTs, gold particles were attached to SWNT ropes after chemical tube modification by a two-step oxidation process. Using this technique, lateral electrode lines (100 nm distance) can be connected by a chain of closely arranged nanoparticles.
Physical Review Letters, 2002
Field emission (FE) electron spectroscopy from an individual multiwalled carbon nanotube (MWNT) i... more Field emission (FE) electron spectroscopy from an individual multiwalled carbon nanotube (MWNT) is used to measure quantitatively stable temperatures at the apex, T A , of up to 2000 K induced by FE currents ഠ1 mA. The high T A is due to Joule heating along the length of the MWNT. These measurements also give directly the resistance of the individual MWNT which is shown to decrease with temperature, and explain the phenomenon of FE-induced light emission which was observed simultaneously. The heating permits thermal desorption of the MWNT and, hence, excellent current stability.
AIP Conference Proceedings, 1998
ABSTRACT
AIP Conference Proceedings, 2000
The 13th international winterschool on electronic properties of novel materials- science and technology of molecular nanostructures, 1999
PCQHs^kQol is an ideal model system to study C 60 mono radical anion in a charged surrounding sin... more PCQHs^kQol is an ideal model system to study C 60 mono radical anion in a charged surrounding since the C 60 radical anions are well separated on a regular crystal lattice by the aid of large organic counter ions. They do not contribute to the ESR signal as they are all closed shell molecules. At low temperatures two Lorentzian ESR lines are observed which can be ascribed to two different orientations of the C 6 o molecules as detected by x-ray analysis of the crystal structure. The g-tensor of the two lines corresponds to the Jahn-Teller distortion of C 60 ". Tetragonal crystal symmetry, molecular symmetry together with the crystal field support the D y , distortion of C 60 " which is in agreement with the observed non axial g-tensor.-I-ions shown schematically in figure 4. The C2 axis of the COO" anion is parallel to the c axis of the crystal. Symmetry considerations for the Jahn-Teller distorted COO" and the crystal field of tetragonal symmetry lead to the conclusion that only the D-u, distortion fit together. This is in agreement with our ligand field calculations which stabilizes the D21, distortion symmetry [7] and the experimentally observed non axial g-tensor. At low temperatures the dynamics of the charge distortion is hindered i.e. jumps between different possible Ü2h orientations are not favored due to the charged surrounding (static Jahn-Teller effect). Increasing the temperature the distortion randomly jumps between symmetry equivalent Dih states (or D=,d and D3J) by phonon assisted tunneling. This corresponds to a pseudo rotation of the Jahn-Teller distortion [8] which results in averaging the gtensor to an isotropic value (dynamic Jahn-Teller effect). This study has shown that two effects have to be distinguished: a charged environment prevents COO anions from a free rotation due to a coordination with the counter ions. However, the electronic distortion still can jump independently until an intrinsic counter ion interaction prevails. This is seen in the frequency independent splitting temperature for the two lines with an anisotropic g-tensor which corresponds to the Jahn-Teller distortion of C6o~'. FIGURE 4. Schematic sketch of the charge environment of C 60~. The arrow corresponds to the c-axis of the tetragonal unit cell which is the direction of the most favorable D 2 h Jahn-Teller distortion of C 6 o~ (shaded area).
Synthetic Metals, 1997
We have previously shown that the high intensity of solar radiation, obtained with the Gdeillo (F... more We have previously shown that the high intensity of solar radiation, obtained with the Gdeillo (France) solar furnace facilities, can be used to vaporize graphite in inert gas atmosphere to produce fullerenes. After a short survey of the possible mechanisms of formation of these molecules, we report some results in agreement with the proposed model and discuss the possibilities of increasing the fullerene yield which currently reaches 20%
Physical Review B, 2000
Low-coverage adsorption isotherms for CH 4 on single-walled carbon nanotube bundles have been mea... more Low-coverage adsorption isotherms for CH 4 on single-walled carbon nanotube bundles have been measured at eight temperatures between 155 and 195 K. The nanotubes used in this study were untreated, so that the tubes have closed ends. The isosteric heat of adsorption was determined from the isotherms and, from this quantity, the binding energy of the methane on the nanotube substrate was obtained. The binding energy was found to be 76% larger on the nanotube bundles than it is on planar graphite.
Journal of the Chemical Society, Faraday Transactions, 1998
Carbon nanotubes were produced in large amounts by catalytic decomposition of acetylene over a Co... more Carbon nanotubes were produced in large amounts by catalytic decomposition of acetylene over a Co incorporated zeolite NaY support. PuriÐcation of multi-wall nanotubes was required in order to eliminate catalyst and amorphous carbon produced by thermal decomposition of hydrocarbon. First, separation of nanotubes and catalyst particles was carried out by hydroÑuoric acid treatment. Then, two ways of removing amorphous carbon were studied : permanganate oxidation and air oxidation. The quality of nanotubes was characterized by means of transmission electron microscopy and the yield of pure nanotubes was quantitatively determined. Changes caused by treatment of the nanotubes were investigated by high resolution electron microscopy and a comparison was made between the nanotubes produced by this method and those synthesized by an arc discharge process after oxidation treatment.
Fullerenes and Photonics IV, 1997
ABSTRACT Carbon single walled nanotubes produced in high yields by the electric arc technique hav... more ABSTRACT Carbon single walled nanotubes produced in high yields by the electric arc technique have been studied by several techniques including HRTEM. It is shown in particular that they have a narrow diameter distribution around an average value of 1.3 nm. In this paper, we mainly report characterization results obtained by high resolution Raman spectroscopy. Raman spectra exhibit a very rich structure especially in the low frequency range where several components are observed. Using previous calculations, we attribute the main features to armchair tubes with (6,6) to (12,12) geometry, in agreement with the narrow diameter distribution observed by HRTEM measurements.
Physical Review B, 2002
In this paper we simulate the resistive heating of carbon nanotubes ͑CNT's͒ during field emission... more In this paper we simulate the resistive heating of carbon nanotubes ͑CNT's͒ during field emission ͑FE͒ using the one-dimensional heat equation including radiation and conductive losses. The simulations are in relatively good agreement with our recent experiments in which we measured the heating of individual CNT's to as high as 2000 K during FE for currents I FE of Ϸ2 A. For low temperatures where radiation is negligible the simulations reduce to an analytic solution that provides a universal guide to estimating current-induced heating in CNT's. The effects of this heating are included in the calculations of I FE as a function of voltage.
Synthetic Metals, 1999
We report results on purification and characterization of single wall carbon nanotubes prepared b... more We report results on purification and characterization of single wall carbon nanotubes prepared by the electric arc method. The process consists of a chemical treatment based on a reflux with nitric acid followed by successive filtration steps (tangential flow and frontal filtration) of a suspension of the raw material. The effects of each step are analysed by SEM and TEM.
Synthetic Metals, 1999
In this paper, we present Surface Enhanced Raman Scattering SERS experiments performed successful... more In this paper, we present Surface Enhanced Raman Scattering SERS experiments performed successfully on some conducting polymers and carbon nanotubes deposited in thin films on rough metallic surfaces. The enhancement mechanism in SERS has a twofold origin: electromagnetic and chemical. The electromagnetic enhancement is, however, the dominant mechanism and consists in the Ž. excitation of localized and delocalized surface plasmons SP. The second enhancing mechanism for SERS, not yet convincingly supported by experimental data, is of chemical origin. This mechanism is due to the increase of the polarizability of the molecules on the metal surface under the action of the incident radiation, leading to the formation of new chemical bonds between the molecules and the metal surface. Unfortunately, the experimental data available to argue the presence of a chemical process are scarce and scattered. In this Ž. paper, we try to present some details regarding this aspect. In order to do so, we studied poly 3-hexylthiophene 3-PHT and polyaniline Ž. Ž. PAN as a function of the type of the rough metallic support Ag, Au or Cu , the oxidization state and thickness of the polymer layer. We studied also carbon single walled nanotubes. Our experiments reveal the existence of a chemical surface effect. The results obtained for 3-PHT show that SERS spectra depend on the oxidizing properties of the metal surface and on the nature of the solvent. This dependence is explained by the existence of some interfacial reactions that lead to the formation of interface compounds. The SERS measurements reported here reveal an increase of the intensities of the Raman lines, accompanied by a modification of the corresponding intensity ratios, when the degree of doping is increased. We observe for the first time by SERS spectroscopy that doping of 3-PHT with FeCl leads to the appearance of a state of disorder in the structure of the macromolecular chain, as a result of steric hindrance effects. 3 The type of the rough metallic support can modify SERS spectra and such an effect is clearly shown for the polyaniline case. No such dependence on metallic support type is observed on the SERS spectra of carbon nanotubes.
Synthetic Metals, 1999
A mid-infrared reflection study on single-walled carbon nanotubes revealed weak absorption struct... more A mid-infrared reflection study on single-walled carbon nanotubes revealed weak absorption structures which we assign to the vibrational modes of the tubes. The results are in good agreement with theoretical predictions for nanotubes. In comparison to graphite phonons a small shift to higher frequencies was found. First measurements at different temperatures indicate no temperature dependence of the phonon frequencies.
Synthetic Metals, 1999
The electric arc discharge and the solar energy are two methods among a large number to produce s... more The electric arc discharge and the solar energy are two methods among a large number to produce single wall carbon nanotubes. They are based on the same process: sublimation of mixture of graphite and catalyst under an inert gas atmosphere. While the solar furnace is a small scale experiment, the electric arc discharge presents a better yield of production. Samples synthesized by both methods in the same conditions of gas pressure and catalysts are characterized by SEM, TEM and RAMAN spectroscopy.
Synthetic Metals, 1999
After being dispersed in liquid solvents (Ethanol, CHCl,), conducting polymers and singlewalled n... more After being dispersed in liquid solvents (Ethanol, CHCl,), conducting polymers and singlewalled nanotubes have been deposited on ruguous substrats (Au, Ag, Cu). With FT Raman technique (laser excitation : 1064 nm), we have obtained SERS signal of both conductiong polymers and singlewalled nanotubes. The Raman signals change with substrat and/or solvent, which could be correlated with the size of clusters formed at the surface and then to the deposition mechanism. The main advantage of the >SERS technique will be emphasized in terms of enhancement as a powerful technique to study nanoparticles.
Synthetic Metals, 1999
The adsorption of carbon SWNTs from purified aqueous dispersions on electrode patterns is describ... more The adsorption of carbon SWNTs from purified aqueous dispersions on electrode patterns is described, As an alternative approach to electrically contacted SWNTs, mixed Langmuir films consisting of surfactant molecules and SWNTs were traflsferred onto electrode arrays. Room temperature conductivity measurements on both types of samples revealed a (two point) resistance in the MSZ range. From these values, the presence of a closed surfactant layer between the tubes and electrode surface is excluded. As astep towards increasing the functionality of SWNTs, gold particles were attached to SWNT ropes after chemical tube modification by a two-step oxidation process. Using this technique, lateral electrode lines (100 nm distance) can be connected by a chain of closely arranged nanoparticles.