Surface electrical contacts to two-dimensional materials suffer from the poor coupling between the 2D surface and the 3D metal. The situation is further degraded by
contamination in the lithographic processing and/or layer transfer. The best innovation is the recent realization of one-dimensional edge-contacts to graphene possibly
combined with large doping. However, the improvement of contact resistance is made at the expense of technological simplicity since the contact fabrication necessitates
Edge bonding and large electron transfer are known to occur during the growth of graphene on SiC and could be exploited for electrical contacts if SiC was
replaced by a similar yet conducting material. Conducting carbides appear as good candidates since they have similar chemical properties and since they could allow new
functionalities owing to additional material properties such as magnetism or superconductivity.
The growth of graphene on carbides other than SiC was first demonstrated by Foster, Long and Strumpf. In 1958, they showed that “aluminum carbide dissociates in the vicinity of 2200-2500 ◦ C, at atmospheric pressures, to aluminum vapor
and pure single crystals of graphite” establishing that other carbides could potentially be used for graphene technology. Nevertheless, this subject has remained unexplored
owing to the lack of commercial substrates. In this work, we have demonstrated that few graphene layer can be grown on a metallic carbide by thermal annealing of a carbide forming
metal film (niobium or tantalum) on SiC in high vacuum circumventing the problem of metallic carbide substrate availability. Based on this discovery we have described a resist-free
and scalable method to fabricate few graphene layers (FGL) with electrical contacts in a single growth step. The combined effect of edge-contact and partially-covalent surface
epitaxy between graphene and the metallic carbide allowed us to fabricate devices in which low contact-resistance and Josephson effect were observed.
CEA is a French government-funded technological research organisation in four main areas: low-carbon energies, defense and security, information technologies and health technologies. A prominent player in the European Research Area, it is involved in setting up collaborative projects with many partners around the world.