Nonlinear Optical Imaging of In‐Plane Anisotropy in Two‐Dimensional SnS

Abstract

Two‐dimensional (2D) tin(II) sulfide (SnS) crystals belong to a class of orthorhombic semiconducting materials with remarkable properties, such as in‐plane anisotropic optical and electronic response, and multiferroic nature. The 2D SnS crystals exhibit anisotropic response along the in‐plane armchair (AC) and zigzag (ZZ) crystallographic directions, offering an additional degree of freedom in manipulating their behavior. Here, advantage of the lack of inversion symmetry of the 2D SnS crystal, that produces second harmonic generation (SHG), is taken to perform polarization‐resolved SHG (P‐SHG) nonlinear imaging of the in‐plane anisotropy. The P‐SHG experimental data are fitted with a nonlinear optics model, allowing to calculate the AC/ZZ orientation from every point of the 2D crystal and to map with high resolution the AC/ZZ direction of several 2D SnS flakes belonging in the same field of view. It is found that the P‐SHG intensity polar patterns are associated with the crystallographic axes of the flakes and with the relative strength of the second‐order nonlinear susceptibility tensor in different directions. Therefore, the method provides quantitative information of the optical in‐plane anisotropy of orthorhombic 2D crystals, offering great promise for performance characterization during device operation in the emerging optoelectronic applications of such crystals.

Liquid Phase Isolation of SnS Monolayers with Enhanced Optoelectronic Properties

“…It is observed that the shape of the polar-diagrams changes for different nanosheets, which is the signature of differences in their in-plane anisotropy. [67] X-ray photoelectron spectroscopy (XPS) measurements were carried out to investigate the chemical states and stoichiometry of the isolated SnS nanosheets. Figure S6, Supporting Information presents the Sn3d and S2p core level spectra of the isolated FL-SnS sheets, confirming the high purity of isolated SnS crystals.…”

“…As an alternative, here the in‐plane structural anisotropy of the exfoliated crystals is explored by polarized second harmonic generation (P‐SHG). [ 67 ] In Figure 2h, we present the sum of the P‐SHG intensity images, obtained from different SnS crystals belonging to the same field of view, for all orientations of the excitation linear polarization φ . It is observed that the shape of the polar‐diagrams changes for different nanosheets, which is the signature of differences in their in‐plane anisotropy.…”

“…It is observed that the shape of the polar‐diagrams changes for different nanosheets, which is the signature of differences in their in‐plane anisotropy. [ 67 ]…”

High-Pressure Synthesis of Single-Crystalline SnS Nanoribbons

“…Two-dimensional (2D) materials consisting of atomically thin sheets with covalent intralayer bonding and van der Waals interlayer bonding have attracted significant attention due to their fascinating physicochemical properties. , Shaping 2D materials into one-dimensional (1D) nanoribbons is one of the effective strategies for tuning or enhancing their electronic, magnetic, and optical properties as a result of the large aspect ratio, quantum confinement, and edge effect, enabling their applications in multidisciplinary areas such as photodetectors, sensing, field emission, energy storage, and catalysis. − As one important class of 2D materials, layered group IV–VIA monochalcogenides (e.g., SnS, SnSe, GeSe, and GeS) are recognized as analogues of phosphorene with buckled structures, which give rise to their structural anisotropy manifested in the Raman response, nonlinear optical property, electrical mobility, and photoactivity. − Of particular interest, SnS is a p-type semiconductor with a sizable bandgap, and few-layer SnS exhibits desirable electronic and optoelectronic properties such as a large absorption coefficient, tunable electrical conductivity, and high carrier mobility. − Moreover, SnS is chemically stable, abundant on Earth, and nontoxic. , These advantageous features render SnS a promising candidate to be employed in various applications such as photodetectors, photovoltaic cells, and field-effect transistors …”

Dynamical Response of Nonlinear Optical Anisotropy in a Tin Sulfide Crystal under Ultrafast Photoexcitation

“…Recently, Luan et al reported the real-time observation of an anisotropic exciton–polariton in an SnS waveguide . Maragkakis et al demonstrated polarization-resolved second harmonic generation imaging of in-plane anisotropy in a layered SnS crystal . Alberding et al investigated the ultrafast optical response of a nano- to micrometer-sized SnS film with transient terahertz spectroscopy, in which the carrier mobility and carrier dynamics of the thin films exhibit the strong particle size dependence .…”