  Direct growth of large-area vertically stacked two-dimensional (2D) van der
Waal (vdW) materials is a prerequisite for their high-end applications in
integrated electronics, optoelectronics and photovoltaics. Currently,
centimetre- to even metre-scale monolayers of single-crystal graphene (MLG) and
hexagonal boron nitride (h-BN) have been achieved by epitaxial growth on
various single-crystalline substrates. However, in principle, this success in
monolayer epitaxy seems extremely difficult to be replicated to bi- or
few-layer growth, as the full coverage of the first layer was believed to
terminate the reactivity of those adopting catalytic metal surfaces. Here, we
report an exceptional layer-by-layer chemical vapour deposition (CVD) growth of
large size bi-layer graphene single-crystals, enabled by self-transmitting
catalytic activity from platinum (Pt) surfaces to the outermost graphene
layers. In-situ growth and real-time surveillance experiments, under
well-controlled environments, unambiguously verify that the growth does follow
the layer-by-layer mode on open surfaces of MLG/Pt(111). First-principles
calculations indicate that the transmittal of catalytic activity is allowed by
an appreciable electronic hybridisation between graphene overlayers and Pt
surfaces, enabling catalytic dissociation of hydrocarbons and subsequently
direct graphitisation of their radicals on the outermost sp2 carbon surface.
This self-transmitting catalytic activity is also proven to be robust for
tube-furnace CVD in fabricating single-crystalline graphene bi-, tri- and
tetra-layers, as well as h-BN few-layers. Our findings offer an exceptional
strategy for potential controllable, layer-by-layer and wafer-scale growth of
vertically stacked few-layered 2D single crystals.
