Strong, anisotropic, layer-independent second harmonic generation in multilayer SnS film

Abstract

Materials based on group IV chalcogenides exhibit extensive technologically important properties. Its unusual chemical bonding and off-centering of in-layer sublattices could cause chemical polarity and weakly broken symmetry, making optical field controlling feasible. Here, we fabricated large-area SnS multilayer films and observed unexpected strong SHG response at 1030 nm. The appreciable SHG intensities were obtained with an independence on layer, which is opposite to the generation principle of overall nonzero dipole moment only in odd-layer material. Taking GaAs for reference, the second-order susceptibility was estimated to be 7.25 pm/V enhanced by mixed-chemical bonding polarity. Further polarization-dependent SHG intensity confirmed the crystalline orientation of SnS films. The results imply surface inversion symmetry broken and nonzero polarization field modified by metavalent bonding should be the origin of SHG responses. Our observations establish multilayer SnS as a promising nonlinear material, and will guide in design of IV chalcogenides with improved optics and photonics properties for the potential applications.

Second Harmonic Generation Control in 2D Layered Materials: Status and Outlook

“…In the past decades, SHG has been discovered in a large amount of 2DLMs, including graphene, [107,109,[116][117][118] h-BN, [7,86,119,120] transition metal dichalcogenides, [24,29,61,73,[121][122][123][124] group IIIA-VIA compounds, [25,26,[125][126][127][128][129] group VIA monochalcogenides, [130][131][132][133][134][135][136][137][138] 2D vdW magnets and other materials. [70,111,[139][140][141][142][143][144][145][146][147] In addition, SHG spectrum of several hundred non-centrosymmetric 2DLMs have been systematically calculated and made available online in C2DB database.…”

“…Group IV monochalcogenides (MX, e.g. GeS, GeSe, SnS, and SnSe) are a class of orthorhombic 2DLMs [130][131][132][133][134][135][136][137][138] and share similar puckered or wavy lattice structures with phosphorene. [181] Group IV monochalcogenides exhibit fascinating properties such as large piezoelectricity, [182] multiferroics, [183] superior carrier mobility [184] and bandgap tunability.…”

“…[134] Notably, the 𝜒 (2) of multilayer SnS has been calculated to be 1.37 pm V −1 , indicating a high conversion efficiency compared to KDP crystal. [131,137] Moreover, the strength of SHG susceptibility of GeSe and SnSe has been predicted to be one order of magnitude higher than that of monolayer MoS 2 . [134]…”

Optical Second Harmonic Generation of Low-Dimensional Semiconductor Materials

“…Second harmonic generation (SHG) provides a non-invasive, straightforward, and efficient characterization method for determining the properties of low-dimensional materials. It can be employed to identify characteristics [ 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ], such as the layer number, crystal lattice symmetry and orientation, twist angle, strain direction, and intensity.…”

“…Subsequently, a polarizer selectively allows the light with specific polarization directions to pass through, employing a spectrometer for polarization analysis. Finally, the signals, having passed through the spectrometer, are transmitted to the detector for precise measurement of the SHG signals [ 49 , 50 , 56 , 57 ]. In addition, transmission measurements are a common approach in the study of SHG ( Figure 3 b) [ 8 , 45 , 58 , 59 ].…”