2D materials

The Nobel Prize in Physics awarded to Geim and Novoselov in 2010 came to reward their work on graphene. If today the industrial revolution announced for graphene is delayed, it is clear that this first 2D materials is at the origin of a scientific revolution in which we discover new properties on materials which we thought to know everything. The list of 2D materials grows from year to year: graphene, boron nitride, transition metal dichalcogenides, black phosphorus, to which are added new crystalline forms of known materials: silicene, two-dimensional AlN, etc ... The However, the main weakness of these 2D materials remains their manufacture, most often using exfoliation, an artisanal method that certainly makes it easy to combine various 2D materials of excellent quality, but only on surfaces of less than 1 mm2. It is precisely in the field of 2D materials manufacturing on large surfaces that CRHEA has focused.

Images d'échantillons de graphène épitaxiés sur SiC
Figure 1. Graphene samples epitaxially grown on SiC with different hydrogen / argon mixtures with CRHEA. Left, with a small proportion hydrogen, the graphene film is monocrystalline. With a proportion increasing hydrogen in the atmosphere (center then right), we see creases that indicate that graphene takes more and more varied orientations in the growth plan, which betrays the presence of hydrogen at the graphene / SiC interface. In depending on the growing conditions, there may also be hydrogen at the graphene / SiC interface of monocrystalline samples, such as the one on the right. The control of this hydrogenation allows to obtain a graphene with n-type or p-type doping.

Based on its expertise in the field of SiC and high temperature growth reactors, in 2010 CRHEA developed a new method for graphene growth by CVD on SiC. This method differs from the sublimation of SiC on the one hand by the use of an external source of carbon (propane), and on the other hand by the presence of hydrogen which strongly modifies the growth. This method makes it possible to control the properties of graphene (doping, number of layers), but also to epitax graphene on materials other than SiC, in particular AlN. On SiC, it is possible to obtain a graphene of high quality, usable for the metrology of the ohm resting on the quantum Hall effect. In particular, a collaboration with the LNE (Graphmet project) has set new records in this area.

Grpahique présentant l'ffet Hall quantique dans un étalon de graphène épitaxié au CRHEA
Figure 2. Quantum Hall effect in a graphene standard epitaxially grown at CRHEA (technology: C2N, measurements: LNE). Hall resistance (in red) reaches a plateau at the value of h/2e2 from 2.5 T, while the longitudinal resistance (in green) drops to zero. The blue curve presents, for comparison, the resistance Hall in a GaAs standard. Similarly, the horizontal bars red and blue present the ranges of magnetic field for which a precision of 10-9 is obtained in the graphene and GaAs standards.

Work on graphene has recently been extended towards the integration of graphene and nitrides, focusing both on the growth of graphene on AlN and the growth of nitrides on graphene, particularly in the framework of the GraNitE project (FLAG -ERA) and collaborations with the CEA. CRHEA is also developing a new reactor dedicated to the growth of nitrides at high temperature, and more particularly of boron nitride (BN) in its hexagonal phase, allowing the direct growth of graphene / BN heterostructures to be considered.

Collaborations

L2C (Montpellier), LNE (Trappes), CEMES (Toulouse), C2N (Palaiseau), CEA (Grenoble), IM2NP, CINaM (Marseille), CNR (Italie), Sherbrooke University (Canada).

Selected publications:

A. Michon et al., "Direct growth of few-layer graphene on 6H-SiC and 3C-SiC/Si via propane chemical vapor deposition",
Applied Physics Letters 97, 171909 (2010).

R. Ribeiro-Palau et al., "Quantum Hall resistance standard in graphene devices under relaxed experimental conditions",
Nature Nanotechnology 10, 965 (2015).

R. Dagher et al., "A comparative study of graphene growth on SiC by hydrogen-CVD or Si sublimation through thermodynamic simulations",
Cryst. Eng. Comm. 20, 3702 (2018).

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