Salt‐Assisted Vapor–Liquid–Solid Growth of 1D van der Waals Materials

Abstract

We introduce the method of salt‐assisted vapor‐liquid‐solid (VLS) growth to synthesize one‐dimensional (1D) nanostructures of trichalcogenide van der Waals (vdW) materials, exemplified by niobium trisulfide (NbS3). The method uses a unique catalyst consisting of an alloy of Au and an alkali metal halide (NaCl) to enable rapid and directional growth. We demonstrate high yields of two types of NbS3 1D nanostructures, nanowires and nanoribbons, each with sub‐ten nanometer diameter, tens of micrometers length, and distinct 1D morphology and growth orientation. We present strategies to control the location, size, and morphology of growth, and extend the growth method to synthesize other transition metal trichalcogenides, NbSe3 and TiS3, as nanowires. Finally, we describe the role of the Au‐NaCl alloy catalyst in guiding VLS synthesis and discuss the growth mechanism based on the relationships we measure between structure (growth orientation, morphology and dimensions) and growth conditions (catalyst volume and growth time). These results introduce opportunities to expand the library of emerging 1D vdW materials to make use of their unique properties through controlled growth at nanoscale dimensions.This article is protected by copyright. All rights reserved

GaSI: A Wide-Gap Non-centrosymmetric Helical Crystal

“…The case of the Sn(Br/I)P crystals suggests that the propagation of crystallographic screw axes along the long-axis of weakly bound chains leads to helical structures. ,,, Encouragingly, the immense interest in exfoliable 1D crystals has sparked the search for classes of inorganic crystals with sub-nanometer-thick chains held by vdW interactions. − Thus, the identification of screw axis symmetry within emergent 1D vdW crystal classes led to our discovery of helical motifs in III–VI–VII 1D vdW crystals (III = Al, Ga, In; VI = S, Se, Te; VII = Cl, Br, I). ,,,,− We found that crystals in this class manifest tetrahelical motifs along chains held by vdW interactions. ,,,− For example, InSeI is a semiconductor consisting of periodic helical chains defined by a 4 1 screw axis and shows highly temperature-sensitive bandgaps in the visible range (Figure S1). ,,,− Substitution of Ga atoms to the In site led to GaSeI, which is the first freestanding inorganic tetrahelix that is an approximate Boerdjik–Coxeter (B–C) helix .…”