Annealing, design and long-term operation of graphite crucibles for the growth of epitaxial graphene on SiC

We describe the annealing, geometry, storage, and lifespan of graphite crucibles for the growth of epitaxial graphene on SiC. We monitor residual gas content during the annealing of the as-manufactured graphite crucible before the growth of the first graphene samples. The high-temperature evolution of carbon monoxide points towards the reaction of solid carbon and residual water. Therefore, we propose a procedure consisting of four annealing cycles to eliminate this reaction. The residual gas evolution after long-term storage of well-baked crucibles in the air shows a similar increase in water and carbon monoxide as that in unbaked crucibles. Hence, we propose the crucible storage in argon ambient. Further, we discuss the role of the crucible shape on graphene quality. Namely, we compare the cylindrical semi-closed crucible to the flat opened crucibles. The flow-aided gas exchange in the opened crucible is more beneficial for graphene growth than the diffusion-driven gas exchange in the semi-closed cylindrical crucibles. The flow-aided gas exchange leads to more efficient removal of outgassed residual contaminants, thus outperforming the advantage of increased silicon vapor pressure in the semi-closed cylindrical crucible. We also study the graphite crucible lifespan, showing that the aged crucible leads to the enhanced inhomogeneous strain in graphene.