Growth

- Graphene preparation

Over the last few years we developed the preparation of high quality graphene onto a variety of substrates, mostly by chemical vapor deposition (CVD). By controlling different growth mechanisms (surface confined ones, temperature-controlled segregation) we are able to prepare single layer graphene under a variety of environments, from ultra-high vacuum to close-to-ambient-pressure atmospheres inside a CVD reactor, and by using different kinds of substrates, from ultra-high quality bulk single-crystal metals like Ir(111) and Re(0001) ones, to high quality thin metal films (e.g. Ir, Re), and low-cost commercial metal foils (Cu, Co).

Recently, we developed a pulsed CVD-process yielding purely single-layer graphene from copper foils, while standard CVD usually comes together with the formation of multilayer patches. The transfer of these graphene samples to a non-conductive support (oxidized silicon wafers) established their very good electrical properties, including a mobility of several 1000 cm2V-1s-1.

 

(Left) Scanning tunneling microscopy image of graphene on Re(0001) thin films.
(Right) Optical image of a logo of the CNRS, made of graphene obtained by pulsed and standard CVD.

 

Contact : vincent.bouchiat@neel.cnrs.fr ; johann.coraux@neel.cnrs.fr


 
- Carbon nanotubes synthesis

In order to decouple sp2 materials from the substrate, we have developed SOI-based silicon membranes at Nanofab and PTA facilities. These are used to perform optical measurements in a transmitted mode, and to prevent thermal/vibrational/non radiative coupling to the underlying substrate. Self-assembly during the synthesis allows for suspending carbon nanotubes over micron-wide trenches. We have access to the hot filament assisted chemical vapour deposition system from SC2G group, in close interaction with the Epitaxy and Layer Deposition technical group.

 

Suspended nanotube over a trench in a 10 µm thick silicon membrane

 

Contact : laetitia.marty@neel.cnrs.fr


 
- Epitaxial growth of TMDCs

The unique optoelectronic properties of 2D transition metal dichalcogenides generates intense interest, one motivation being the development of innovative optoelectronic devices. This calls for the demonstration of synthesis method yielding large-area materials with very high quality, and epitaxial growth is a possible such route. We investigate the growth of transition metal disulphides and diselenides, and use, as a powerful tool to finely characterise the structure, surface synchrotron X-ray scattering to perform this characterisation with high resolution in situ during growth. This analysis, which is implemented at the INS2 instrument installed at the BM32 CRG beamline located at the ESRF, allows us to explore the rich, multi-parameter space that is involved during growth, and to select the optimum region in this parameter space that leads to highest quality materials. This work is a joint work with Gilles Renaud, Matthieu Jamet and Alain Marty at CEA-INAC and SPINTEC.

 

Contact : johann.coraux@neel.cnrs.fr


 
- Confined growth under a 2D deformable surfactant

In crystal growth, surfactants are additive molecules used in dilute amount or as dense, permeable layers to control surface morphologies. We investigate the properties of a strikingly different surfactant : graphene, which contrary to known surfactants is 2D and covalent layer with close atomic packing. We have explained why metallic atomic layers can actually be intercalated and grow below an impermeable graphene membrane, contrary to what could have been initially expected. Upon confined growth of the metal intercalant, graphene dynamically opens nanochannels called wrinkles, facilitating mass transport, while at the same time storing and releasing elastic energy via lattice distortions. Graphene thus behaves as a mechanically active, deformable surfactant. This opens new routes to use graphene as a two-dimensional surfactant forcing the growth of flat films, nanostructures and unconventional crystalline phases. This work is the outcome of a collaboration with colleagues from the MNM and TMC groups, from ESPCI Paris, CEA-INAC and ELETTRA. [1]

 

[1] S. Vlaic et al., J. Phys. Chem. Lett., 9, 2523−2531 (2018) -> doi.org/10.1021/acs.jpclett.8b00586

 

Graphene forming a wrinkle as intercalated metal atoms take part to the confined growth
of a 2D metallic film

 

Contact : johann.coraux@neel.cnrs.fr

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