Nanoparticle-directed bimodal crystallization of the quasi-1D van der Waals phase, Bi₄I₄

Abstract

Anisotropy often yields unexpected structures and properties in the solid state. In van der Waals (vdW) solids comprised of 1D or quasi-1D (q-1D) building blocks, anisotropy in both intra- and...

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 .…”