Our researches in this field are mainly focused on the growth mechanism, atomic structure and configuration, as well as physical (electronic, optical, vibrational, mechanical) properties of nanostructured carbon-based and related materials. Those nanomaterials involve: (a) pure and functionalized carbon nanomaterials (nanotubes (NT), nanoparticles, flakes, graphene-like…), (b) nanostructures based on carbon, boron and nitrogen including pure boron nitride nanomaterials (hexagonal, nanotubes…), (c) nanodiamond, (d) amorphous carbons (as diamond-like carbon (DLC)) and (e) dichalcogenides (WS2, MoS2,…).
For accomplishing these studies we utilize different transmission electron microscopy (TEM) techniques: high resolution imaging (HRTEM), electron diffraction, electron energy loss spectroscopy (EELS) and energy dispersive x-ray spectroscopy (X-EDS). It is worth mentioning that TEM studies on these beam-sensitive materials require working under particular conditions, low acceleration voltages (in our case, 60 or 80 kV) and minimizing the electron dose.
The atomic structure of a Carbon nanotube determines their transport/electronic/optoelectronic properties and then, also their applications. Thus, the study of the atomic structure of a NT is very important. We have deeply investigated this aspect for different kind of carbon nanotubes (and also other kind of nanotubes) by the combination of electron diffraction and HRTEM. As an example, we will show our works on ultra-long (UL) carbon nanotubes (Coll. V. Jourdain (U. Montpellier, Fr.)). We have shown that there is a marked tendency (> 2/3) of these NT to Double-Walled (DW). Furthermore, these DW-NT display a chiral angle and diameter correlation between the inner and outer NT which is important for the mechanical and vibrational properties of the DW-NT [D. Levshov, T.X. Than, R. Arenal, et al., Nano Letters, 11, 4800 (2011)]. Among all the UL-NT we investigated also triple-walled NTs, see Fig. 1. The combination of HRTEM and ED allows fully identifying the NT, which is a (21, 21) @ (28, 26) @ (36, 29) nanotube.
Another very important aspect that we have observed in these UL-CNT is that there is no chiral angle modification, nor diameter change along the whole nanotube´s length. In addition, we observed selectivity toward high chiral angles manifesting by the facts that the chiral angle of most of NT ranges between 20 and 30 deg., that 12.5 % of the NT are pure armchair and that no zig-zag NT were observed.
A particular interest is devoted to the study of the atomic configuration and physical properties of heteroatomic nanotubes (based on B, C and/or N). Indeed the incorporation of foreign atoms into the hexagonal network of the carbon nanotube (C-NT) walls strongly modifies the chemical and physical properties of the pure C-NT [R. Arenal, X. Blase, A. Loiseau, Advances in Physics 59, 101 (2010); P. Ayala, R. Arenal, A. Rubio, A. Loiseau, T. Pichler, Rev. Mod. Phys. 82, 1843 (2010); P. Ayala, R. Arenal, M. Rummeli, A. Rubio, T. Pichler, Carbon 48, 575 (2010)]. TEM is the most powerful technique for undertaking such kind of studies. Thus, we have carried out several studies for better understanding the atomic configuration of these heteroatomic NT and the distribution of these foreign atoms. A recent work on this topic is this one concerning nitrogen doped C-NT (Coll. with O. Stephan et al. (LPS, Orsay U.-CNRS, Fr.) and C.P. Ewels & R. Rocquefelte (IMN, Nantes U.-CNRS, Fr.)), see Fig. 2. In this work we have developed atomically-resolved EELS studies, identifying, for the first time, individual atomic dopants in these single-walled CNx-NTs. Moreover, from a close analysis of the fine structures near absorption edges (ELNES), we have shown that nitrogen local environment correspond to the so-called pyridine-like configuration. A second nitrogen configuration is also observed, which could be assigned to the graphitic-like arrangement.
In parallel with all these studies, we also investigate pure and functionalized carbon nanostructures (NT, graphene, flakes, nanoparticles…). Concerning the study of the C-NTs’ functionalization via TEM, one recent example of these works is shown in Fig. 3. Here we have studied, by spatially-resolved EELS and HRTEM measurements, hybrid systems composed by perylene units and C-NTs (Coll. S. Reich, Berlin Frei U. (Germany)). Thus, we have demonstrated the robustness and the stability of this system, which is very interesting as it satisfies the biocompatibility requirements.
Spatial-resolved EELS and HRTEM studies have been also developed on other kind of hybrid carbon nanomaterials as Pt nanoparticles supported on graphene (coll. W. Maser & A.M. Benito, ICB-CSIC, Zaragoza) [M. Cano, et al., Nanoscale (2013)] or iron oxide nanoparticles also deposited on graphene [G. Melinte et al., Nature Comm. (2014)].
In addition, we have also studied the mechanical, electrical properties of these NTs as well as their behavior under irradiation (electronic, ionic) via in-situ TEM [R. Arenal, et al., Nanotechnology (2012); T. Susi, J. Kotakoski, R. Arenal, et al., ACS Nano, (2012); A.C.Y. Liu, R. Arenal, G. Montagnac, Carbon (2013), R. Arenal and A. Bezanilla-Lopez, submitted].
R. Arenal, P. Loehtman, M. Picher, T. Than, V. Jourdain, Direct Evidence of Atomic Structure Conservation Along Ultra-Long Carbon Nanotubes, J. Phys. Chem. C (2012).
I. Florea, O. Ersen, R. Arenal, D. Ihiawakrim, C. Messaoudi, K. Chizar, I. Janowska, C. Pham-Huu, 3D Analysis of the Morphology and Spatial Distribution of Nitrogen in Nitrogen-doped Carbon Nanotubes by EFTEM Tomography, J. Amer. Chem. Soc., 134, 9672 (2012).
T. Susi, J. Kotakoski, R. Arenal, et al., Atomistic Description of Electron Beam Damage in Nitrogen-Doped Graphene and Single-Walled C- Nanotubes, ACS Nano, 6, 8837 (2012).
L. Alvarez, Y. Almadori, R. Arenal, R. Babaa, T. Michel, R. Leparc, J-L. Bantignies, P. Hermet, J-L. Sauvajol, Transfer evidence between carbon nanotubes and encapsulated conjugated oligomers, J. Phys. Chem. C 115, 11898 (2011).
G. Melinte, I. Florea, S. Moldovan, I. Janowska, W. Baaziz, R. Arenal, A. Wisnet, C. Scheu, S. Begin-Colin, D. Begin, C. Pham-Huu, O. Ersen, A 3D insight on the catalytic nanostructuration of few-layer graphene, Nature Comm. (2014).