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Accueil > Recherche > M3 : Matériaux Multi-échelles Multifonctionnels > Carbones nanostructurés > First-time synthesis of a new family of 2D carbon materials : diamane, diamanoids, and diamanoid/graphene hybrids

First-time synthesis of a new family of 2D carbon materials : diamane, diamanoids, and diamanoid/graphene hybrids

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Diamane was prepared from the exposure of bi-layer graphene to H radicals produced by the hot filament process. A sharp sp3-bonded carbon stretching mode was observed by UV Raman spectroscopy while no sp2-bonded carbon peak was simultaneously detected. This is the first time that Raman spectra of genuine diamane are reported, which, meanwhile, are the very first evidence for the successful synthesis of genuine diamane. First principle calculations support possible full hydrogenation and confirm the hydrogenated AB configuration to be the most stable one. We believe those results constitute a milestone in the path towards the synthesis of high-quality diamane and open the door to large-scale production.
See : Piazza et al, Carbon 145 (2019) 10 - Piazza et al., Carbon 156 (2020) 234 – Piazza et al., Carbon 169 (2020) 129 – Piazza et al., J. Carb. Res. 7 (2021) 9.

Synthesis and applications of graphenic carbon cones prepared from the deposition of pyrolytic carbon onto individual carbon nanotubes.
Graphene-based cones with nanosized apex are obtained by means of a high temperature pyrolytic carbon deposition process using methane and hydrogen as gaseous feedstock and single carbon nanotubes as deposition substrates.

Left : An all-carbon, cone-bearing morphology (blue) welded by W deposition (red) onto a doped-Si cantilever holder (yellow) to be used as a probe for near-field microscopy. Right : Half of an all-carbon, cone-bearing morphology welded onto a truncated W tip to be used as electron emitter in a cold-field emission gun electron source.

Aside the cones, micrometer-sized carbon beads or fibre segments are deposited meanwhile which are a key morphological component for allowing handling and mounting the carbon cones and then using them for various applications. Based on both the literature dealing with pyrolytic carbon deposition processes and experimental observations, a peculiar deposition mechanism is proposed, involving the transient formation of pitch-like liquid phase droplets which deposit onto the individual carbon nanotubes. In this picture, it is believed that a key parameter is the diameter ratio for the droplets and the nanotubes, respectively. The cone concentric texture and perfect nanotexture are shown by high resolution transmission electron microscopy, which allows interesting mechanical and conducting properties to be predicted. Correspondingly, applications of the carbon nanocones as electron emitters for cold-field electron sources on the one hand, and as probes for various modes of near-field microscopy on the other hand, have been tested.
See : Mamishin et al, Ultramicrosc. 182 (2107) 303 - Monthioux & Houdellier, Eur. Patent (2018) - Paredes et al, Ind. J. Eng. Mater. Sci. 27 (2020) 1091.

Development of carbon meta-nanotubes of various kinds following various routes, and subsequent applications
Carbon meta-nanotubes designate carbon nanotubes which have been modified by various means such as filling their cavity, substituting some of the carbon atoms by others in the lattice, grafting chemical functions and/or nanoparticules of foreign phases, etc. The Carbons Team at CEMES has pioneered the field, and published the only book dedicated to it so far.
Iodine atoms encapsulated in carbon nanotubes and aligned in the nanotube cavities (carbon walls are not seen).
Right : cover of the only book dedicated to this topic.

Electrodes for fuel cells, batteries and supercapacitors : Proton exchange membrane fuel cells (PEMFC) are promising green technology alternatives. The high cost resulting from the use of Pt-based electrocatalysts and stability issues are bottlenecks in the commercialization of PEMFC. Oxygen reduction reaction (ORR) kinetics is much slower than the hydrogen oxidation reaction (HOR) occurring at the anode, which implies high amount of catalyst loading at the cathode side. Efforts are being made to reduce Pt loading either by alloying or by appropriately tailoring and doping the support material. Using a support material with excellent graphene nanotexture like carbon nanotubes/graphene composite materials has the advantage to present a good thermal stability and electrochemical conductivity and to be electrochemically stable. Hybrid support consists of unzipped carbon nanotubes and nitrogen and sulfur co-doped multi walled carbon nanotubes as high performance electrocatalyst for the oxygen reduction reaction in proton exchange membrane fuel cells. Raman and TEM investigations showed that improved and stronger interaction between the Pt nanoparticles and the support material increases performance and durability at high power density of 642 mW/cm2. (in collaboration with IIT Madras, India)

Schematic of exfoliated carbon nanotubes doped with nitrogen and sulfur with and without reduced graphene oxide.

See : Zubaïr et al, Phys. Rev. Mater. 1 (2017) 064002 - Nie et al, IEEE Trans. Nanotechnol. 16 (2017) 759 - Lassègue et al., Surf. Coat. Technol. 331 (2017) 129 - Almadori et al., Carbon 149 (2019) 772 - Mittal et al., J. Nanosci. Nanotechnol. 19 (2019) 4129 - Nechiyil et al., J. Colloid Interf. Sci. 561 (2020) 439.

Behavior and properties of graphene
As opposed to graphenic materials which include all types of materials built from graphene layers whatever the number and orientation of the latter, hence including bulk graphenic carbons such as chars, cokes, and graphite, graphene is a 2D material made of a limited number of layers, typically in the range of 1 to 10. Graphene is tentatively used as a single film-like nano-object in electronic devices and other applications, hence understanding well the graphene structure and accurately characterizing the stacking sequences and the consequences on the behavior (mechanical, chemical…) is of an utmost importance. We investigated the graphene structure by means of Raman spectroscopy, transmission electron microscopy, and electron diffraction. We determined how the turbostratic versus Bernal stacking type influences the mechanical behavior. Typically, the former induces crumpling, whereas the latter induces folding. The work demonstrated that, reversely, it is enough to see whether a graphene flake is folded or crumpled in low magnification imaging mode, even by means of optical microscopy, to ascertain the related stacking structure.

The way graphene layers are stacked in graphene flakes determines the way they behave when subjected to mechanical constraints. In (a) the stacking type is the same as in graphite (Bernal). In (b), the stacking type is random (turbostratic).

Single-layer graphene exhibits specific mechanical and thermodynamical properties. Few-layer graphenes are remarkably similar to graphite, because of their 3D structure, but also display 2D features. We have reviewed the various approaches going from first-principle to classical mechanics considering core  bonds and surrounding π material bonds for this family. In the case of bulk materials, high pressure can reveal and separate the various contributions to understand the physics, in our case, the Raman spectrum of defective materials. In the case of Moiré materials, which is a rapidly growing field among 2D materials due to fantastic new effects corresponding to the modification of the electronic band structure, we have probed twisted bilayer graphenes where intralayer and interlayer electron-phonon interactions are visible through new features in the Raman spectra.

Graphene bubble and optical standing wave. The red spot indicates the focal spot when scanning the laser across the bubble.

When heating large graphene bubbles with a laser beam, Raman spectral bands provide information on the temperature distribution in the bubble which depends on the thermal conductivity.
Comparison with model calculations allows to determine the thermal conductivity of graphene and explore its mechanical properties above 1000°C in ambient atmosphere. Furthermore, the formation of optical standing waves gives the opportunity to map out the shape of the graphene bubble when heated by the laser. (collaboration with UNIST, South Korea).

See : Monthioux et al., Carbon 115 (2017) 128 - Eliel et al., Nature Comm. 9 (2018) 1221 – Huang et al., Phys. Rev. Lett. 120 (2018) 186104. Sun et al., Appl. Phys. Rev. (2021) in print.

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