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 microscale diamond by coupling a liquid-metal Ga-In with ferrocene (Fe(C₅H₅)₂) as a carbon precursor, nanodiamond seeds, and nanosilicon. Building on liquid-metal diamond synthesis, this approach pushes liquid-metal growth toward lower temperature (900°C, 1 atm) while enabling single-crystal diamonds to scale from ∼10 µm to several tens of micrometers with well-developed faceting. Ferrocene decomposition supplies a sustained interfacial carbon flux 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 low carbon solubility in Ga-In. Nanosilicon plays a complementary role by tuning interfacial kinetics and facet competition, enabling control of crystal habit: cubic (∼10 µm), truncated-tetrahedral, and fully faceted octahedral diamonds are obtained by adjusting the nanosilicon: nanodiamond ratio, with octahedral crystals reaching ∼50 µm. Crystal size is further scaled by regulating hydrogen flow: lowering the H₂ rate increases carbon retention at the liquid-metal interface, raises supersaturation, and accelerates diamond deposition. Together, habit control and size scaling establish a practical route for facet regulation and size control under ambient pressure, offering tunable microscale single-crystal diamonds under mild conditions.