Superposition of semiconductor and semi-metal properties of self-assembled 2D SnTiS3 heterostructures

Srinivasa Reddy Tamalampudi,Shashikant P Patole,Harry Apostoleris,Boulos Alfakes,Chia-Yun Lai,Raman Sankar,Matteo Chiesa,Jin-You Lu,Ibraheem Almansouri,Nitul Rajput

doi:10.1038/s41699-020-0158-7

Abstract

Two-dimensional metal dichalcogenide/monochalcogenide thin flakes have attracted much attention owing to their remarkable electronic and electrochemical properties; however, chemical instability limits their applications. Chemical vapor transport (CVT)-synthesized SnTiS3 thin flakes exhibit misfit heterojunction structure and are highly stable in ambient conditions, offering a great opportunity to exploit the properties of two distinct constituent materials: semiconductor SnS and semi-metal TiS2. We demonstrated that in addition to a metal-like electrical conductivity of 921 S/cm, the SnTiS3 thin flakes exhibit a strong bandgap emission at 1.9 eV, owing to the weak van der Waals interaction within the misfit-layer stackings. Our work shows that the misfit heterojunction structure preserves the electronic properties and lattice vibrations of the individual constituent monolayers and thus holds the promise to bridge the bandgap and carrier mobility discrepancy between graphene and recently established 2D transition metal dichalcogenide materials. Moreover, we also present a way to identify the top layer of SnTiS3 misfit compound layers and their related work function, which is essential for deployment of van der Waals misfit layers in future optoelectronic devices.

Highlights

The library of atomically thin two-dimensional (2D) materials is continually expanding with the discovery of new naturally existing 2D materials beyond graphene
SnTiS3 grown by chemical vapor transport (CVT) naturally assumes a heterostructure of alternating SnS and TiS2 layers[22]
The measured powder X-ray diffraction (XRD) spectrum of SnTiS3 in Supplementary Fig. 1 indicates that a = b = 9.017, and c = 23.29 Å with α = 88.11° and γ = 37.75° in a triclinic crystal structure, which is in accordance with the trigonal phase of the TiS2 subsystem having a = 3.417, b = 3.417, and c = 5.823 Å and with an orthorhombic phase of SnS having a = 4.024, b = 4.443, and c = 11.68 Å, respectively

Summary

Introduction

The library of atomically thin two-dimensional (2D) materials is continually expanding with the discovery of new naturally existing 2D materials beyond graphene. Studies on SnS thin flakes have revealed many exotic effects, including a thicknesstunable optical bandgap of 1.0–1.6 eV8 and anisotropic electronic properties[4]. The fabrication of chemically stable monolayers of SnS or TiS2 has presented major challenges[9,10]. SnS exhibits high chemical reactivity due to the unshared electron pair in the group-IV atoms, which rapidly leads to surface oxidation[9]. A possible strategy to overcome this challenge is through encapsulation, which has yielded stable van der Waals heterostructures in ambient conditions[11]. These human-made van der Waals heterostructures exhibit some limitations due to interface residues and misalignment of crystal orientation[12]

Methods

Results

Conclusion