title: Spontaneous, Defect-Free Kinking via Capillary Instability during Vapor-Liquid-Solid Nanowire Growth.
abstract: Kinking, a common anomaly in nanowire (NW) vapor-liquid-solid (VLS) growth, represents a sudden change of the wire's axial growth orientation. This study focuses on defect-free kinking during germanium NW VLS growth, after nucleation on a Ge (111) single crystal substrate, using Au-Ge catalyst liquid droplets of defined size. Statistical analysis of the fraction of kinked NWs reveals the dependence of kinking probability on the wire diameter and the growth temperature. The morphologies of kinked Ge NWs studied by electron microscopy show two distinct, defect-free, kinking modes, whose underlying mechanisms are explained with the help of 3D multiphase field simulations. Type I kinking, in which the growth axis changes from vertical [111] to ⟨110⟩, was observed in Ge NWs with a nominal diameter of ∼ 20 nm. This size coincides with a critical diameter at which a spontaneous transition from ⟨111⟩ to ⟨110⟩ growth occurs in the phase field simulations. Larger diameter NWs only exhibit Type II kinking, in which the growth axis changes from vertical [111] directly to an inclined ⟨111⟩ axis during the initial stages of wire growth. This is caused by an error in sidewall facet development, which produces a shrinkage in the area of the (111) growth facet with increasing NW length, causing an instability of the Au-Ge liquid droplet at the tip of the NW.
authors.affiliation: Department of Applied Physics, Stanford University , Stanford, California 94305, United States.
authors.forename: Yanying
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Materials Science and Engineering, Stanford University , Stanford, California 94305, United States.
authors.forename: Yanming
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology , 291 Daehak-ro, Yuseong-gu, Daejeon, South Korea.
authors.forename: Seunghwa
authors.initials: S
authors.lastname: Ryu
authors.affiliation: Stanford Nano Shared Facilities, Stanford University , Stanford, California 94305, United States.
authors.forename: Ann F
authors.initials: AF
authors.lastname: Marshall
authors.affiliation: Department of Mechanical Engineering, Stanford University , Stanford, California 94305, United States.
authors.forename: Wei
authors.initials: W
authors.lastname: Cai
authors.affiliation: Department of Materials Science and Engineering, Stanford University , Stanford, California 94305, United States.
authors.forename: Paul C
authors.initials: PC
authors.lastname: McIntyre
keywords: Germanium nanowire; nanowire kinking; phase field modeling; vapor−liquid−solid growth