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, SiH₃ radicals 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.