SnS

Article pubs.acs.org/cm

Study of Tubular Structures of the Misfit Layered Compound SnS2/ SnS Gal Radovsky,† Ronit Popovitz-Biro,‡ and Reshef Tenne*,† †

Department of Materials and Interfaces and ‡Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel S Supporting Information *

ABSTRACT: Tubular structures of the SnS2/SnS misfit compound, which are currently prepared in large amounts, are reported. The lattice mismatch between the two alternating sublayers of SnS2 and SnS leads to a variety of chiral tubular structures. Such tubular structures are studied via high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). The diversity of the structures manifests itself through different stacking orders of SnS2 and SnS layers along their common c-axis and their relative in-plane orientation. Folding vectors and chiral angles of both subsystems can be determined.

KEYWORDS: tin sulfide, tin disulfide, inorganic nanotubes, electron diffraction, misfit compounds

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(known as Herzenbergite).9,10 The NbS2 adopts pseudo hexagonal structure with an ortho-hexagonal unit cell of a = 3.321, b = √3 × 3.321 = 5.752, c = 11.761 Å and Cm2m space group.7,8 Corresponding axes are parallel, and the lattice parameters of the two subsystems fit along the b axes, while along the a axes they are incommensurate. Almost similar behavior was observed in the (PbS)1.14NbS2 system.1,2 Misfit layered compounds are suitable candidates to form tubular structures. An example for such nanotubes in the “mistfit” pair PbS-NbS2 was shown in the past.1,2 The tendency for the folding of the layers is attributed to the difference in the lattice parameters, between the two lamellae, the bending axis being perpendicular to the direction along which the lattice parameters differ mostly. Upon bending the convex upper layer is subjected to a tensile stress while the lower (inner) concave layer is under compression strain. This situation leads to reduced differences between the lattice parameters of the two layers and hence the strain energy is reduced. The tubule axis is expected to coincide with the commensurate b direction. Surprisingly, most of PbS1.14(NbS2)2 tubes were found to be chiral.1,2 This fact was attributed to the small misfit between the b axes of the pristine compounds which accommodates elastically and causes the axis of curvature to deviate somewhat from the “commensurate” direction, that is, lead to chiral tubes.1 As will be discussed later, in the SnS2−SnS system incommensurate behavior is believed to be present along both directions of the basal planes of the two subsystems.

INTRODUCTION Misfit Layered Compounds. Tubular morphologies are known to exist in misfit layered compounds.1−3 Notwithstanding, large amounts of such tubular phases have not been reported, prior to this work. Therefore, no systematic studies of “misfit” nanotubes are known. Recently, copious amounts of tubular structures of the SnS2/SnS misfit compound were synthesized4 which led to systematic study of their internal structure. Misfit layered compounds (MX)1+x(TX2)m (with M = Sn, Pb, Sb, Bi, rare earths; T = Sn, Ti, V, Cr, Nb, Ta; X = S, Se; 0.08 < x