Silicon Driven Facet Regulation Enables Tunable Micro-Diamond Architectures in Liquid Ga In

We report an ambient pressure liquid metal assisted CVD strategy that enables shape programmable growth of micro scale diamond by coupling liquid metl Ga In with ferrocene (Fe(C5H5)2) as an carbon precursor, nanodiamond seeds, and nanosilicon. Building on liquid metal diamond synthesis, this approach pushes liquid metal growth toward a low temperature (900 {\deg}C, 1 atm) while enabling single crystal diamonds to be scaled from ~10 {\mu}m to several tens of micrometers with well developed faceting. Ferrocene decomposition supplies a sustained interfacial carbon flux that is captured and redistributed by the Ga In melt toward seed rich liquid solid interfaces. Defect rich nanodiamond provides the crystallographic template required for reliable sp3 nucleation despite the intrinsically low carbon solubility of Ga In. Nanosilicon plays a distinct, complementary role by tuning interfacial kinetics and facet competition, enabling deliberate control of crystal habit: cubic (~10 {\mu}m), truncated tetrahedral, and fully faceted octahedral diamonds are reproducibly obtained by adjusting the nanosilicon:nanodiamond ratio, with octahedral crystals reaching ~50 {\mu}m. Importantly, crystal size is further scaled by regulating hydrogen flow: lowering the H2 rate increases net carbon retention at the liquid metal interface, raises effective supersaturation, and accelerates diamond deposition. Together, habit control (via nanosilicon: nanodiamond) and size scaling (via H2 flow) establish a practical route silicon driven facet regulation and size under ambient pressure, offering a pathway to tunable micro sized single crystal diamonds under mild conditions.