Steady state thermokinetic of ultra-thin Mo2C/G heterostructures grown on the prior-graphitized cu/graphene biasing

Abstract

In this work, the chemical vapor deposition synthesis of the Mo2C/graphene heterostructure above the melting temperature of Cu bias (1356 K) is studied. Two sets of Mo2C growth experiments at high CH4 flow rates (5 SCCM ≥ 3 SCCM) are performed, either using prior-graphene synthesis or having in situ graphitization, for three different Cu bias thicknesses. Raman mappings taken from all six-test samples show graphene covers not only over the Mo2C pillars but also over their untransformed Cu bias substrate regions. The only difference is that the Mo2C pillar grows over the prior graphene bias; on the other hand, the in situ graphene grown Mo2C pillar nucleates and grows over the fresh Cu bias surfaces. A steady-state laminate model for flows of Mo and C species with phase transformations is developed for the radial and vertical growth kinetics of synthesized Mo2C/graphene heterostructure. The computer simulation reproduces those experimental observations performed recently in our laboratories on the prior or no-prior graphitized (G) test modules with Cu/G bias, having three different thicknesses at 1363 K. AFM-topography and SEM photos for a prior graphitized test module of 25 µm thick Cu and 4.72 Å graphene bias show a three layered Mo2C/graphene heterostructure; the first layer is almost perfect hexagonal flat, and the other two circular shaped layers constitute the whole pillar of 140 nm height. This may be compared to a 250 µm thick Cu/4.7 Å graphene bias sample, which furnishes an ultra-thin single flat layer of 10–13 nm thick Mo2C crystallites having a perfect planar hexagonal structure.