nedjma bendiab | Centre National de la Recherche Scientifique / French National Centre for Scientific Research (original) (raw)

Papers by nedjma bendiab

Advanced materials (Deerfield Beach, Fla.), Jan 17, 2017

Carbon nanotube-chromophore hybrids are promising building blocks in order to obtain a controlled... more Carbon nanotube-chromophore hybrids are promising building blocks in order to obtain a controlled electro-optical transduction effect at the single nano-object level. In this work, a strong spectral selectivity of the electronic and the phononic response of a chromophore-coated single nanotube transistor is observed for which standard photogating cannot account. This paper investigates how light irradiation strongly modifies the coupling between molecules and nanotube within the hybrid by means of combined Raman diffusion and electron transport measurements. Moreover, a nonconventional Raman enhancement effect is observed when light irradiation is on the absorption range of the grafted molecule. Finally, this paper shows how the dynamics of single electron tunneling in the device at low temperature is strongly modified by molecular photoexcitation. Both effects will be discussed in terms of photoinduced excitons coupled to electronic levels.

Nano Letters, 2014

We investigate the organized formation of strain, ripples, and suspended features in macroscopic ... more We investigate the organized formation of strain, ripples, and suspended features in macroscopic graphene sheets transferred onto corrugated substrates made of an ordered array of silica pillars with variable geometries. Depending on the pitch and sharpness of the corrugated array, graphene can conformally coat the surface, partially collapse, or lie fully suspended between pillars in a fakir-like fashion over tens of micrometers. With increasing pillar density, ripples in collapsed films display a transition from random oriented pleats emerging from pillars to organized domains of parallel ripples linking pillars, eventually leading to suspended tent-like features. Spatially resolved Raman spectroscopy, atomic force microscopy, and electronic microscopy reveal uniaxial strain domains in the transferred graphene, which are induced and controlled by the geometry. We propose a simple theoretical model to explain the structural transition between fully suspended and collapsed graphene. For the arrays of high density pillars, graphene membranes stay suspended over macroscopic distances with minimal interaction with the pillars' apexes. It offers a platform to tailor stress in graphene layers and opens perspectives for electron transport and nanomechanical applications.

Journal of Optics, 2013

We present fabrication and optical characterization of micro-cavities made of multilayer graphene... more We present fabrication and optical characterization of micro-cavities made of multilayer graphene (MLG) cantilevers clamped by metallic electrodes and suspended over Si/SiO2 substrate. Graphene cantilevers act as a semi-transparent mirrors closing an air-wedge optical cavity. This simple geometry implements a standing-wave optical resonator along with a mechanical one. Equal thickness interference fringes are observed in both Raman and Rayleigh backscattered signals with interfringe given by their specific wavelength. Chromatic dispersion within the cavity makes possible spatial modulation of graphene Raman lines and selective rejection of the silicon background signals. Electrostatic actuation of the multilayer graphene cantilever by gate voltage tunes the cavity length and induces space and time modulation of backscattered light including Raman lines. We demonstrate the potential of those systems for high sensitivity Raman measurements of generic molecular species grafted on multilayer graphene surface. The Raman signal of the molecular layer can be modulated both in time and in space in a similar fashion and show enhancement with respect to a collapsed membrane.

Physical Review B, 2020

We report the observation of an intense anomalous peak at 1608 cm −1 in the Raman spectrum of gra... more We report the observation of an intense anomalous peak at 1608 cm −1 in the Raman spectrum of graphene associated to the presence of chromium nanoparticles in contact with graphene. Bombardment with an electron beam demonstrates that this peak is distinct from the well studied D peak appearing as defects are created in graphene; the new peak is found non dispersive. We argue that the bonding of chromium atoms with carbon atoms softens the out-of-plane optical (ZO) phonon mode, in such a way that the frequency of its overtone decreases to 2ωZO ∼ ωG, where ωG=1585 cm −1 is the frequency of the Raman-active E2g mode. Thus, the observed new peak is attributed to the 2ZO mode which becomes Raman-active following a mechanism known as Fermi resonance. First-principles calculations on vibrational and anharmonic properties of the graphene/Cr interface support this scenario.

Nanotechnology, 2008

We present a fabrication method producing large and flat graphene flakes that have a few layers d... more We present a fabrication method producing large and flat graphene flakes that have a few layers down to a single layer based on substrate bonding of a thick sample of highly oriented pyrolytic graphite (HOPG), followed by its controlled exfoliation down to the few to single graphene atomic layers. As the graphite underlayer is intimately bonded to the substrate during the exfoliation process, the obtained graphene flakes are remarkably large and flat and present very few folds and pleats. The high occurrence of single-layered graphene sheets being tens of microns wide in lateral dimensions is assessed by complementary probes including spatially resolved micro-Raman spectroscopy, atomic force microscopy and electrostatic force microscopy. This versatile method opens the way for deposition of graphene on any substrates, including flexible ones.

Nanotechnology, 2008

We present a fabrication method producing large and flat graphene flakes that have a few layers d... more We present a fabrication method producing large and flat graphene flakes that have a few layers down to a single layer based on substrate bonding of a thick sample of highly oriented pyrolytic graphite (HOPG), followed by its controlled exfoliation down to the few to single graphene atomic layers. As the graphite underlayer is intimately bonded to the substrate during the exfoliation process, the obtained graphene flakes are remarkably large and flat and present very few folds and pleats. The high occurrence of single layered graphene sheets having tens of micron wide in lateral dimensions is assessed by complementary probes including spatially resolved Micro-Raman Spectroscopy, Atomic Force Microscopy and Electrostatic Force Microscopy. This versatile method opens the way of deposition of graphene on any substrates including flexible ones. PACS: 42.82.Cr , 81.15.-z , 81.05.Uw.

Nature Nanotechnology, 2012

1 Nanoelectromechanical systems 1 can be operated as ultrasensi-2 tive mass sensors 2,3 and ultra... more 1 Nanoelectromechanical systems 1 can be operated as ultrasensi-2 tive mass sensors 2,3 and ultrahigh-frequency resonators 4 , and 3 can also be used to explore fundamental physical phenomena 4 such as nonlinear damping 5 and quantum effects in macro-5 scopic objects 6 . Various dissipation mechanisms are known to 6 limit the mechanical quality factors of nanoelectromechanical 7 systems and to induce aging due to material degradation, so 8 there is a need for methods that can probe the motion of 9 these systems, and the stresses within them, at the nanoscale. 10 Here, we report a non-invasive local optical probe for the quan-11 titative measurement of motion and stress within a nanoelec-12 tromechanical system, based on Fizeau interferometry and 13 Raman spectroscopy. The system consists of a multilayer gra-14 phene resonator that is clamped to a gold film on an oxidized 15 silicon surface. The resonator and the surface both act as 16 mirrors and therefore define an optical cavity. Fizeau interfero-17 metry provides a calibrated measurement of the motion of the 18 resonator, while Raman spectroscopy can probe the strain 19 within the system and allows a purely spectral detection of 20 mechanical resonance at the nanoscale.

Applied Physics Letters, 2011

Uniform single layer graphene was grown on single-crystal Ir films a few nanometers thick which w... more Uniform single layer graphene was grown on single-crystal Ir films a few nanometers thick which were prepared by pulsed laser deposition on sapphire wafers. These graphene layers have a single crystallographic orientation and a very low density of defects, as shown by diffraction, scanning tunnelling microscopy, and Raman spectroscopy. Their structural quality is as high as that of graphene produced on Ir bulk single crystals, i.e., much higher than on metal thin films used so far.

Europhysics Letters (epl), 2011

Motivated by recent experimental studies on single molecular magnets grafted on graphene and sing... more Motivated by recent experimental studies on single molecular magnets grafted on graphene and single walled carbon nanotubes, we investigate the structural, electronic, and magnetic properties of an iron based magnetic molecule grafted on a graphene sheet using ab initio calculations. In particular, the induced charge transfer and magnetization are described in terms of the coupling between the molecule and the graphene orbitals. This interaction and its effects on graphene electronic properties are determined and discussed in view of the potential utilization of graphene in spintronics.

Carbon, 2010

In aerosol-assisted catalytic chemical vapor deposition (CCVD), the catalyst and carbon precursor... more In aerosol-assisted catalytic chemical vapor deposition (CCVD), the catalyst and carbon precursors are introduced simultaneously in the reactor. Catalyst particles are formed in situ and aligned multi-walled CNTs grow at a high rate. To scale-up the process, it is crucial to ...

European Physical Journal B, 2009

We present in situ high pressure X-ray diffraction experiments on multi-walled carbon nanotubes (... more We present in situ high pressure X-ray diffraction experiments on multi-walled carbon nanotubes (MWNTs) filled with iron-based nanowires. In addition to our diffraction results, we provide a detailed characterization of our samples in terms of nanotube length, iron contents, nanotube number of walls and radial dimension. Both carbon nanotubes and encapsulated iron-based nanowires were found to be stable under high pressure conditions, in contrast with previous experiments performed on Fe-filled MWNTs where structural transitions of nanotubes and Fe3C nanowires were recorded around 9 GPa. We point out the importance of providing a complete structural characterization of the studied material and we propose an explanation for the contradictory results found in the literature based on different structural characteristics of the samples and on recent results on the non-hydrostaticity of some pressure transmitting media.

The aim of this work is to understand the structural organization of inserted alkali atoms inside... more The aim of this work is to understand the structural organization of inserted alkali atoms inside single walled carbon nanotube bundles. First of all, we present X-rays and neutrons diffraction results obtained on rubidium inserted carbon nanotubes (n-doping). The results of X-rays and neutrons diffraction experiments are surprising and in apparent contradiction, and will be discussed in connection with the debated question of the lattice expansion of the hexagonal tubes framework under insertion. The possible insertion sites of the rubidium atoms in the nanotube bundle will be discussed in terms of their effects on the diffraction spectra. The experimental results will be compared to diffraction simulations and ab initio DFT calculations. The main outcome of our combined experimental and theoretical study is that: i) up to saturation, the spectra show no lattice expansion; ii) the extinction of the (10) peak is only compatible with Rb insertion inside the tubes; iii) DFT calculations show that at constant lattice parameter the insertion within the tubes is energetically favored with respect to insertion between the tubes.

Physica B-condensed Matter, 2002

We study the Raman spectra of Li-doped SWNT films. A monotonic upshift of the tangential modes, a... more We study the Raman spectra of Li-doped SWNT films. A monotonic upshift of the tangential modes, and a concomitant progressive loss of the resonant behavior of the Raman signal, are evidenced when the Li rate increases. No significant change is observed all over the temperature range 10-300 K. r (E. Anglaret). 0921-4526/02/$ -see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 -4 5 2 6 ( 0 2 ) 0 0 9 8 3 -3

Physica Status Solidi B-basic Solid State Physics, 2006

We performed high pressure Raman experiments on purified open-ended single wall carbon nanotubes ... more We performed high pressure Raman experiments on purified open-ended single wall carbon nanotubes using different pressure transmitting media (paraffin oil, argon and 4:1 methanol ethanol mixture) and two excitating wavelength (514.5 nm and 632.8 nm). We state that the behavior of the Raman spectrum under pressure is significantly dependent on the pressure transmitting medium. This result points out the relevance of the interactions between the medium and the nanotubes, at the origin of the disagreement between the phase transition sequences reported in literature. The comparaison of tangential modes profiles clearly shows that 4:1 methanol ethanol induces few strain on nanotubes in the opposite of what is observed for argon and paraffin oil pressure transmitting media. These observations are discussed in terms of intercalation and stress due to non hydrostatic conditions. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Physical Review B, 2005

... PHYSICAL REVIEW B 72, 035409 2005 Resonant Raman spectroscopy of single-wall carbon nanotubes... more ... PHYSICAL REVIEW B 72, 035409 2005 Resonant Raman spectroscopy of single-wall carbon nanotubes under pressure A. Merlen, N. Bendiab, P. Toulemonde, A. Aouizerat, and A. San Miguel* Laboratoire de Physique de la Mati? ...

Comptes Rendus Physique, 2003

We review Raman spectroscopy of alkali-doped single-wall carbon nanotube bundles. These results a... more We review Raman spectroscopy of alkali-doped single-wall carbon nanotube bundles. These results are correlated to resistivity and optical absorption measurements performed on the same samples. In this review we focus on the behavior of the high-frequency tangential modes upon doping. A doping-induced upshift of the tangential modes, concomitant to a loss of absorption bands in the optical spectra and to a monotonic decrease of the resistivity, is stated. The Raman response measured on the first plateau of the resistivity curve is featured by a symmetric single component upshifted with respect to pristine sample. This response is assigned to the Raman signature of a specific doped phase, labelled phase I. By contrast the Raman response of the saturated phase, associated to a second plateau in the resistance curve, is featured by a Breit-Wigner-Fano component downshifted with respect to the pristine sample.

Physical Review B, 2008

X-ray and neutron-diffraction investigations of rubidium-intercalated single-walled carbon nanotu... more X-ray and neutron-diffraction investigations of rubidium-intercalated single-walled carbon nanotubes are reported. Ab initio calculations conducted in combination with our experiments show that for a single Rb ion the most energetically favorable intercalation site is the interstitial channel between three tubes in a bundle. At higher doping levels, as the Rb content increases, this site becomes however unfavored with respect to the interior of the tubes or the external surface of the bundle. Model simulations of the diffraction patterns, capable of well reproducing both the x-ray and neutron-diffraction patterns, indicate that only the latter insertion sites are compatible with the experimental data. Finally we show that the bundle surface site is the most probable one in the case of saturation at an estimated stoichiometry close to RbC 8 .

Carbon, 1998

A Raman scattering characterization is reported that confirms the preparation of single wall carb... more A Raman scattering characterization is reported that confirms the preparation of single wall carbon nanotubes (SWNT ) by the solar energy route. The results are presented for samples synthesized with various catalysts-mixtures of Ni and Co ( Y, La)-and compared to those obtained from electric arc discharge or laser ablation. In the light of the calculations of the vibrational spectra of SWNT by Eklund et al. (Carbon, 1995, 33, 959) it is shown that both the diameter and structure of the nanotubes depend strongly on the synthesis conditions. For the first time the presence of nanotubes with ''zigzag'' or ''chiral'' helical pitches for some of the samples are shown as well as a large distribution of tube diameters.

Physical Review B, 2005

The structure of ternary compounds involving alkali, tetrahydrofuran (THF) and single-walled carb... more The structure of ternary compounds involving alkali, tetrahydrofuran (THF) and single-walled carbon nanotubes have been investigated using neutron diffraction (ND). Hydrogen-deuterium substitution in THF, as well as the study of different alkali-based compounds, allow a layered structure around the nanotubes to be determined. ND results indicate that the alkali cations form a monolayer surrounding each tube of the bundle, while

Physical Review B, 2001

ABSTRACT Phase transitions and staging in doped single-wall carbon nanotubes (SWNT’s) are controv... more ABSTRACT Phase transitions and staging in doped single-wall carbon nanotubes (SWNT’s) are controversial issues. Here, we report on combined in situ conductivity and Raman measurements of Rb-doped SWNT’s. Striking correlations between resistance, changes of resistance under laser irradiation, and frequency of the main Raman peak are observed. In the last steps of doping, two different Raman signatures, with peaks at 1596 and 1555 cm-1, respectively, are observed and assigned to two different stable doped phases. The two phases coexist in a specific range of doping with the latter growing progressively at the expense of the former.

Advanced materials (Deerfield Beach, Fla.), Jan 17, 2017

Carbon nanotube-chromophore hybrids are promising building blocks in order to obtain a controlled... more Carbon nanotube-chromophore hybrids are promising building blocks in order to obtain a controlled electro-optical transduction effect at the single nano-object level. In this work, a strong spectral selectivity of the electronic and the phononic response of a chromophore-coated single nanotube transistor is observed for which standard photogating cannot account. This paper investigates how light irradiation strongly modifies the coupling between molecules and nanotube within the hybrid by means of combined Raman diffusion and electron transport measurements. Moreover, a nonconventional Raman enhancement effect is observed when light irradiation is on the absorption range of the grafted molecule. Finally, this paper shows how the dynamics of single electron tunneling in the device at low temperature is strongly modified by molecular photoexcitation. Both effects will be discussed in terms of photoinduced excitons coupled to electronic levels.

Nano Letters, 2014

We investigate the organized formation of strain, ripples, and suspended features in macroscopic ... more We investigate the organized formation of strain, ripples, and suspended features in macroscopic graphene sheets transferred onto corrugated substrates made of an ordered array of silica pillars with variable geometries. Depending on the pitch and sharpness of the corrugated array, graphene can conformally coat the surface, partially collapse, or lie fully suspended between pillars in a fakir-like fashion over tens of micrometers. With increasing pillar density, ripples in collapsed films display a transition from random oriented pleats emerging from pillars to organized domains of parallel ripples linking pillars, eventually leading to suspended tent-like features. Spatially resolved Raman spectroscopy, atomic force microscopy, and electronic microscopy reveal uniaxial strain domains in the transferred graphene, which are induced and controlled by the geometry. We propose a simple theoretical model to explain the structural transition between fully suspended and collapsed graphene. For the arrays of high density pillars, graphene membranes stay suspended over macroscopic distances with minimal interaction with the pillars' apexes. It offers a platform to tailor stress in graphene layers and opens perspectives for electron transport and nanomechanical applications.

Journal of Optics, 2013

We present fabrication and optical characterization of micro-cavities made of multilayer graphene... more We present fabrication and optical characterization of micro-cavities made of multilayer graphene (MLG) cantilevers clamped by metallic electrodes and suspended over Si/SiO2 substrate. Graphene cantilevers act as a semi-transparent mirrors closing an air-wedge optical cavity. This simple geometry implements a standing-wave optical resonator along with a mechanical one. Equal thickness interference fringes are observed in both Raman and Rayleigh backscattered signals with interfringe given by their specific wavelength. Chromatic dispersion within the cavity makes possible spatial modulation of graphene Raman lines and selective rejection of the silicon background signals. Electrostatic actuation of the multilayer graphene cantilever by gate voltage tunes the cavity length and induces space and time modulation of backscattered light including Raman lines. We demonstrate the potential of those systems for high sensitivity Raman measurements of generic molecular species grafted on multilayer graphene surface. The Raman signal of the molecular layer can be modulated both in time and in space in a similar fashion and show enhancement with respect to a collapsed membrane.

Physical Review B, 2020

We report the observation of an intense anomalous peak at 1608 cm −1 in the Raman spectrum of gra... more We report the observation of an intense anomalous peak at 1608 cm −1 in the Raman spectrum of graphene associated to the presence of chromium nanoparticles in contact with graphene. Bombardment with an electron beam demonstrates that this peak is distinct from the well studied D peak appearing as defects are created in graphene; the new peak is found non dispersive. We argue that the bonding of chromium atoms with carbon atoms softens the out-of-plane optical (ZO) phonon mode, in such a way that the frequency of its overtone decreases to 2ωZO ∼ ωG, where ωG=1585 cm −1 is the frequency of the Raman-active E2g mode. Thus, the observed new peak is attributed to the 2ZO mode which becomes Raman-active following a mechanism known as Fermi resonance. First-principles calculations on vibrational and anharmonic properties of the graphene/Cr interface support this scenario.

Nanotechnology, 2008

We present a fabrication method producing large and flat graphene flakes that have a few layers d... more We present a fabrication method producing large and flat graphene flakes that have a few layers down to a single layer based on substrate bonding of a thick sample of highly oriented pyrolytic graphite (HOPG), followed by its controlled exfoliation down to the few to single graphene atomic layers. As the graphite underlayer is intimately bonded to the substrate during the exfoliation process, the obtained graphene flakes are remarkably large and flat and present very few folds and pleats. The high occurrence of single-layered graphene sheets being tens of microns wide in lateral dimensions is assessed by complementary probes including spatially resolved micro-Raman spectroscopy, atomic force microscopy and electrostatic force microscopy. This versatile method opens the way for deposition of graphene on any substrates, including flexible ones.

Nanotechnology, 2008

We present a fabrication method producing large and flat graphene flakes that have a few layers d... more We present a fabrication method producing large and flat graphene flakes that have a few layers down to a single layer based on substrate bonding of a thick sample of highly oriented pyrolytic graphite (HOPG), followed by its controlled exfoliation down to the few to single graphene atomic layers. As the graphite underlayer is intimately bonded to the substrate during the exfoliation process, the obtained graphene flakes are remarkably large and flat and present very few folds and pleats. The high occurrence of single layered graphene sheets having tens of micron wide in lateral dimensions is assessed by complementary probes including spatially resolved Micro-Raman Spectroscopy, Atomic Force Microscopy and Electrostatic Force Microscopy. This versatile method opens the way of deposition of graphene on any substrates including flexible ones. PACS: 42.82.Cr , 81.15.-z , 81.05.Uw.

Nature Nanotechnology, 2012

1 Nanoelectromechanical systems 1 can be operated as ultrasensi-2 tive mass sensors 2,3 and ultra... more 1 Nanoelectromechanical systems 1 can be operated as ultrasensi-2 tive mass sensors 2,3 and ultrahigh-frequency resonators 4 , and 3 can also be used to explore fundamental physical phenomena 4 such as nonlinear damping 5 and quantum effects in macro-5 scopic objects 6 . Various dissipation mechanisms are known to 6 limit the mechanical quality factors of nanoelectromechanical 7 systems and to induce aging due to material degradation, so 8 there is a need for methods that can probe the motion of 9 these systems, and the stresses within them, at the nanoscale. 10 Here, we report a non-invasive local optical probe for the quan-11 titative measurement of motion and stress within a nanoelec-12 tromechanical system, based on Fizeau interferometry and 13 Raman spectroscopy. The system consists of a multilayer gra-14 phene resonator that is clamped to a gold film on an oxidized 15 silicon surface. The resonator and the surface both act as 16 mirrors and therefore define an optical cavity. Fizeau interfero-17 metry provides a calibrated measurement of the motion of the 18 resonator, while Raman spectroscopy can probe the strain 19 within the system and allows a purely spectral detection of 20 mechanical resonance at the nanoscale.

Applied Physics Letters, 2011

Uniform single layer graphene was grown on single-crystal Ir films a few nanometers thick which w... more Uniform single layer graphene was grown on single-crystal Ir films a few nanometers thick which were prepared by pulsed laser deposition on sapphire wafers. These graphene layers have a single crystallographic orientation and a very low density of defects, as shown by diffraction, scanning tunnelling microscopy, and Raman spectroscopy. Their structural quality is as high as that of graphene produced on Ir bulk single crystals, i.e., much higher than on metal thin films used so far.

Europhysics Letters (epl), 2011

Motivated by recent experimental studies on single molecular magnets grafted on graphene and sing... more Motivated by recent experimental studies on single molecular magnets grafted on graphene and single walled carbon nanotubes, we investigate the structural, electronic, and magnetic properties of an iron based magnetic molecule grafted on a graphene sheet using ab initio calculations. In particular, the induced charge transfer and magnetization are described in terms of the coupling between the molecule and the graphene orbitals. This interaction and its effects on graphene electronic properties are determined and discussed in view of the potential utilization of graphene in spintronics.

Carbon, 2010

In aerosol-assisted catalytic chemical vapor deposition (CCVD), the catalyst and carbon precursor... more In aerosol-assisted catalytic chemical vapor deposition (CCVD), the catalyst and carbon precursors are introduced simultaneously in the reactor. Catalyst particles are formed in situ and aligned multi-walled CNTs grow at a high rate. To scale-up the process, it is crucial to ...

European Physical Journal B, 2009

We present in situ high pressure X-ray diffraction experiments on multi-walled carbon nanotubes (... more We present in situ high pressure X-ray diffraction experiments on multi-walled carbon nanotubes (MWNTs) filled with iron-based nanowires. In addition to our diffraction results, we provide a detailed characterization of our samples in terms of nanotube length, iron contents, nanotube number of walls and radial dimension. Both carbon nanotubes and encapsulated iron-based nanowires were found to be stable under high pressure conditions, in contrast with previous experiments performed on Fe-filled MWNTs where structural transitions of nanotubes and Fe3C nanowires were recorded around 9 GPa. We point out the importance of providing a complete structural characterization of the studied material and we propose an explanation for the contradictory results found in the literature based on different structural characteristics of the samples and on recent results on the non-hydrostaticity of some pressure transmitting media.

The aim of this work is to understand the structural organization of inserted alkali atoms inside... more The aim of this work is to understand the structural organization of inserted alkali atoms inside single walled carbon nanotube bundles. First of all, we present X-rays and neutrons diffraction results obtained on rubidium inserted carbon nanotubes (n-doping). The results of X-rays and neutrons diffraction experiments are surprising and in apparent contradiction, and will be discussed in connection with the debated question of the lattice expansion of the hexagonal tubes framework under insertion. The possible insertion sites of the rubidium atoms in the nanotube bundle will be discussed in terms of their effects on the diffraction spectra. The experimental results will be compared to diffraction simulations and ab initio DFT calculations. The main outcome of our combined experimental and theoretical study is that: i) up to saturation, the spectra show no lattice expansion; ii) the extinction of the (10) peak is only compatible with Rb insertion inside the tubes; iii) DFT calculations show that at constant lattice parameter the insertion within the tubes is energetically favored with respect to insertion between the tubes.

Physica B-condensed Matter, 2002

We study the Raman spectra of Li-doped SWNT films. A monotonic upshift of the tangential modes, a... more We study the Raman spectra of Li-doped SWNT films. A monotonic upshift of the tangential modes, and a concomitant progressive loss of the resonant behavior of the Raman signal, are evidenced when the Li rate increases. No significant change is observed all over the temperature range 10-300 K. r (E. Anglaret). 0921-4526/02/$ -see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 -4 5 2 6 ( 0 2 ) 0 0 9 8 3 -3

Physica Status Solidi B-basic Solid State Physics, 2006

We performed high pressure Raman experiments on purified open-ended single wall carbon nanotubes ... more We performed high pressure Raman experiments on purified open-ended single wall carbon nanotubes using different pressure transmitting media (paraffin oil, argon and 4:1 methanol ethanol mixture) and two excitating wavelength (514.5 nm and 632.8 nm). We state that the behavior of the Raman spectrum under pressure is significantly dependent on the pressure transmitting medium. This result points out the relevance of the interactions between the medium and the nanotubes, at the origin of the disagreement between the phase transition sequences reported in literature. The comparaison of tangential modes profiles clearly shows that 4:1 methanol ethanol induces few strain on nanotubes in the opposite of what is observed for argon and paraffin oil pressure transmitting media. These observations are discussed in terms of intercalation and stress due to non hydrostatic conditions. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Physical Review B, 2005

... PHYSICAL REVIEW B 72, 035409 2005 Resonant Raman spectroscopy of single-wall carbon nanotubes... more ... PHYSICAL REVIEW B 72, 035409 2005 Resonant Raman spectroscopy of single-wall carbon nanotubes under pressure A. Merlen, N. Bendiab, P. Toulemonde, A. Aouizerat, and A. San Miguel* Laboratoire de Physique de la Mati? ...

Comptes Rendus Physique, 2003

We review Raman spectroscopy of alkali-doped single-wall carbon nanotube bundles. These results a... more We review Raman spectroscopy of alkali-doped single-wall carbon nanotube bundles. These results are correlated to resistivity and optical absorption measurements performed on the same samples. In this review we focus on the behavior of the high-frequency tangential modes upon doping. A doping-induced upshift of the tangential modes, concomitant to a loss of absorption bands in the optical spectra and to a monotonic decrease of the resistivity, is stated. The Raman response measured on the first plateau of the resistivity curve is featured by a symmetric single component upshifted with respect to pristine sample. This response is assigned to the Raman signature of a specific doped phase, labelled phase I. By contrast the Raman response of the saturated phase, associated to a second plateau in the resistance curve, is featured by a Breit-Wigner-Fano component downshifted with respect to the pristine sample.

Physical Review B, 2008

X-ray and neutron-diffraction investigations of rubidium-intercalated single-walled carbon nanotu... more X-ray and neutron-diffraction investigations of rubidium-intercalated single-walled carbon nanotubes are reported. Ab initio calculations conducted in combination with our experiments show that for a single Rb ion the most energetically favorable intercalation site is the interstitial channel between three tubes in a bundle. At higher doping levels, as the Rb content increases, this site becomes however unfavored with respect to the interior of the tubes or the external surface of the bundle. Model simulations of the diffraction patterns, capable of well reproducing both the x-ray and neutron-diffraction patterns, indicate that only the latter insertion sites are compatible with the experimental data. Finally we show that the bundle surface site is the most probable one in the case of saturation at an estimated stoichiometry close to RbC 8 .

Carbon, 1998

A Raman scattering characterization is reported that confirms the preparation of single wall carb... more A Raman scattering characterization is reported that confirms the preparation of single wall carbon nanotubes (SWNT ) by the solar energy route. The results are presented for samples synthesized with various catalysts-mixtures of Ni and Co ( Y, La)-and compared to those obtained from electric arc discharge or laser ablation. In the light of the calculations of the vibrational spectra of SWNT by Eklund et al. (Carbon, 1995, 33, 959) it is shown that both the diameter and structure of the nanotubes depend strongly on the synthesis conditions. For the first time the presence of nanotubes with ''zigzag'' or ''chiral'' helical pitches for some of the samples are shown as well as a large distribution of tube diameters.

Physical Review B, 2005

The structure of ternary compounds involving alkali, tetrahydrofuran (THF) and single-walled carb... more The structure of ternary compounds involving alkali, tetrahydrofuran (THF) and single-walled carbon nanotubes have been investigated using neutron diffraction (ND). Hydrogen-deuterium substitution in THF, as well as the study of different alkali-based compounds, allow a layered structure around the nanotubes to be determined. ND results indicate that the alkali cations form a monolayer surrounding each tube of the bundle, while

Physical Review B, 2001

ABSTRACT Phase transitions and staging in doped single-wall carbon nanotubes (SWNT’s) are controv... more ABSTRACT Phase transitions and staging in doped single-wall carbon nanotubes (SWNT’s) are controversial issues. Here, we report on combined in situ conductivity and Raman measurements of Rb-doped SWNT’s. Striking correlations between resistance, changes of resistance under laser irradiation, and frequency of the main Raman peak are observed. In the last steps of doping, two different Raman signatures, with peaks at 1596 and 1555 cm-1, respectively, are observed and assigned to two different stable doped phases. The two phases coexist in a specific range of doping with the latter growing progressively at the expense of the former.