Atomic-Step-Induced Screw-Dislocation-Driven Spiral Growth of SnS

Abstract

The in-plane piezoelectricity or ferroelectricity of two-dimensional (2D) materials can vanish due to the appearance of inversion symmetry with increasing flake thickness, which drastically limits the development of their energy-harvesting application. Although the inversion symmetry breaking in spiral structure of 2D material may solve this problem, the control of spiral growth remains immature. Here, a novel technique to achieve high percentage of spiral SnS flakes with superior control of nucleation position is demonstrated. By introducing atomic steps on substrates, the screw dislocation can be easily formed when SnS partially grows across these steps and leads to over 90% of spiral SnS flakes grown by physical vapor deposition (PVD). Furthermore, the preference for SnS to nucleate at steps can introduce remarkable nucleation site control of spiral growth even on substrates with artificially transferred graphene atomic steps. Interestingly, it turns out that the spiral SnS structure exhibits centrosymmetric characteristic, indicating that single-spiral 2D materials with monolayer step height do not guarantee an inversion symmetry breaking structure. The high spiral flake percentage and precise control of nucleation sites in this study will facilitate future development of spiral 2D materials.

Chemical Etching of Screw Dislocated Transition Metal Dichalcogenides

“…In addition to the conventional monolayer or layer-by-layer structures, 2D materials often contain screw dislocations. ,− A screw dislocation is a line defect that shears part of the crystal lattice. In layered materials, it typically shears along the out-of-plane direction, connects layers into one continuous helicoid, and results in a spiral morphology. , Screw dislocation growth has been observed in CVD grown 2D materials, such as graphene, h-BN, MoS 2 , , WS 2 , ,− WSe 2 , , SnS 2 , SnSe 2 , SnS, and GeS, , as well as Bi 2 Se 3 and Sb 2 Te 3 grown via solution synthesis and molecular beam epitaxy. − Screw dislocations drive the growth of layered materials in a different way from the typical layer-by-layer growth and can influence the vertical stacking configurations and overall crystal symmetry to yield complex morphologies as well as varied physical properties. − , Screw dislocations combined with non-Euclidean surfaces also provide a pathway to introduce interlayer twists rationally . Although dislocations are commonly observed in layered materials, the studies on the structures of screw dislocations and their formation process have been limited.…”

“…In addition to the monolayer or layer-by-layer structures, screw dislocation growth has been observed frequently in 2D materials growth, ,− and they influence the vertical stacking configurations of MX 2 materials. , Screw dislocated MX 2 nanoplates can be categorized by the number of layers and the orientation of each layer in the repeating stacking sequence, which correlate with the distinct shape of the nanoplates caused by the assembled Wulff construction of each individual layer. MX 2 spiral nanoplates exhibit three classes of shapes caused by three stacking configurations: triangular spirals have a [+] (3R-like) stacking, hexagonal spirals have a [+ – ] (2H) stacking, and truncated triangular shapes consist of mixed repeating stacking sequence such as [+ – + ]. , Here, in the square brackets, the orientation of a layer is represented by “+” (0° or ±120°) or “–” (±60° or 180°) signs.…”

“…In layered materials, it typically shears along the out-of-plane direction, connects layers into one continuous helicoid, and results in a spiral morphology. 24,43 Screw dislocation growth has been observed in CVD grown 2D materials, such as graphene, 25 h-BN, 26 MoS 2 , 27,28 WS 2 , 12,28−31 WSe 2 , 32,33 SnS 2 , 34 SnSe 2 , 35 SnS, 36 and GeS, 37,38 as well as Bi 2 Se 3 and Sb 2 Te 3 grown via solution synthesis and molecular beam epitaxy. 39−42 Screw dislocations drive the growth of layered materials in a different way from the typical layer-bylayer growth and can influence the vertical stacking configurations and overall crystal symmetry to yield complex morphologies as well as varied physical properties.…”

Epitaxial Integration and Defect Structure of Layered SnSe Films on PbSe/III–V Substrates

“…Both single (0.32 nm) and double (0.67 nm) layer steps of graphene resulted in effectively "a/2" screw dislocations (i.e., one bilayer, 0.62 nm, spiral step height). 18 The tendency to form bilayers was again strong enough that vdW bilayers again folded up and over surface features, creating line defects rather than breaking their own internal structure. Surprisingly, the "a/2" screw dislocation in SnS did not yield A−A or related stacking in the spiral, instead reverting to centrosymmetric A−B stacking when these spirals were characterized using TEM.…”

Tunability of the bandgap of SnS by variation of the cell volume by alloying with A.E. elements

“…For applications, SnS ( Pnma ) may be useful in next-generation solar cells and thermoelectric materials 1 – 3 since it is composed of non-toxic and earth-abundant elements, similar to Cu 2 ZnSn(S x ,Se 1− x ) 4 4 – 7 . Mono-sulphide SnS films have been fabricated by methods including sputtering 8 – 12 , atomic layer deposition 13 – 16 , chemical vapour deposition 17 – 20 , pulsed laser deposition 21 , chemical bath deposition 22 – 25 , spray pyrolysis 26 , 27 , spin coating 28 , physical vapour deposition 29 – 32 , and molecular beam epitaxy 33 . Noguchi et al proved that SnS ( Pnma ) can function as a photovoltaic absorber 34 , and SnS ( Pnma ) solar cells have recently been developed owing to the establishment of n -type doping.…”