中央研究院 原子與分子科學研究所

The growth of two-dimensional materials into three-dimensional geometries holds the promise for high performance hybrid materials and novel architectures. The synthesis of such structures, however, proceeds in fundamentally different flow regimes than conventional CVD where pressure differences and wall collisions are neglected. We here demonstrate the remarkable stability of graphene growth under varying fluid dynamical flow regimes. We investigate the growth process across different flow conditions using confined growth in refractory pores. Analysis of the growth rate reveals a transport-limited process which allows experimental determination of the gas diffusion coefficient. The diffusion coefficient was found to be constant for large pore dimension but scales with pore dimension as the pore size decreases below the mean free path providing clear evidence for previously predicted Knudsen molecular-flow conditions for atomic confinement. Surprisingly, changes to the flow conditions by two orders of magnitude do not cause qualitative changes of the graphene growth process. This unique behavior was attributed to rarefied flow conditions by scaling analysis and an analytical relation between growth rate and constriction could be extracted that proves accurate throughout the investigated conditions. Our results demonstrate a fundamentally different growth process compared to traditional CVD processes that is akin to atomic layer deposition and highlight the feasibility of high-quality 2D-material growth on 3D morphologies with ultra-high aspect ratios.

The scalable production of high quality graphene could enable many applications ranging from high-speed electronics to transparent solar cells. While chemical vapor deposition has demonstrated the ability to produce graphene with suitable properties the scaling to application-relevant graphene quantities remains a challenge. We here demonstrate the high throughput synthesis of graphene in a batch process by growth on gapless substrate stacks. Refractory layers in direct contact with the growth substrate enable growth in close-packing and were shown to allow the simultaneous production of 280 cm2 graphene in a conventional 1-inch furnace. The presented gapless stacking method gives rise to a confinement effect and a molecular-flow controlled transport regime. This growth condition was found to result in a self-limiting nucleation density that is independent of growth conditions and causes the large scale uniformity of graphene properties within the stack, as elucidated by carrier transport and spectroscopy. Finally, the presented nucleation control yields a significant enhancement of graphene quality compared to conventional growth. The presented novel growth process is compatible with other 2D materials and opens up a new route towards their scalable production for research and commercial applications.