Plasma-Driven Solid–Liquid Dynamics in Cu–Sn Catalysts and Nucleation of Silicon Nanowires Revealed by Environmental TEM

We employ environmental TEM to observe phase transitions driven by plasma radicals, in Cu–Sn catalysts for silicon nanowire (SiNW) growth. Previously unrecognized solid–liquid dynamics enables the stable growth of ultrathin (∼7 nm) SiNWs with alternating cubic and hexagonal segments. At 250 °C, H radicals induce a solid–liquid Cu₆Sn₅–Sn nanostructure, defining small nucleation sites. At 400 °C, SiH₃radicals drive SiNW nucleation simultaneously with catalyst phase separation. A Sn-rich liquid supplies atomic steps that propagate into the solid catalyst. A solid Cu₃Si phase remains epitaxially aligned with the SiNW, anchoring the liquid phase. The solid–liquid catalyst actively reorients, causing the Si step propagation direction to reverse periodically. These dynamic behaviors are reproduced using a Cu–In system, underscoring the versatility of combining high- and low-melting-point catalysts. Our findings demonstrate that plasma-radical-driven nonequilibrium chemistry can be harnessed to control nanowire growth at the atomic scale.