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

ABSTRACT 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(C ₅ H ₅ ) 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 sp ³ 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 H ₂ 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.