Natural van der Waals heterostructure cylindrite with highly anisotropic optical responses

Abstract

The mechanical exfoliation of naturally occurring layered materials has emerged as an easy and effective method for achieving ultrathin van der Waals (vdW) heterostructures with well-defined lattice orientations of the constituent two-dimensional (2D) material layers. Cylindrite is one such naturally occurring vdW heterostructure, where the superlattice is composed of alternating stacks of SnS2-like and PbS-like layers. Although the constituent 2D lattices are isotropic, inhomogeneous strain occurring from local atomic alignment for forcing the commensuration makes the cylindrite superlattice structurally anisotropic. Here, we demonstrate the highly anisotropic optical responses of cylindrite thin flakes induced by the anisotropic crystal structure, including angle-resolved polarized Raman scattering, linear dichroism, and polarization-dependent anisotropic third-harmonic generation. Our results provide a promising approach for identifying various natural vdW heterostructure-based 2D materials with tailored optical properties and can be harnessed for realizing anisotropic optical devices for on-chip photonic circuits and optical information processing.

Natural 2D layered mineral cannizzarite with anisotropic optical responses

“…The out-of-plane rippling also induces strong in-plane structural anisotropy. Similar interlayer moiré patterns have been observed in other natural vdW heterostructures of cylindrite 31 , 32 , franckeite 33 , 34 , 37 , and lengenbachite 35 . The zoomed-in high-resolution (HR) TEM image in Fig.…”

“…However, these methods are technically challenging, time consuming, and susceptible to induce unwanted defects and interlayer adsorbates in the fabricated vdW heterostructures. Recently, mechanical exfoliation of natural vdW superlattices such as cylindrite 31 , 32 , franckeite 33 , 34 , and lengenbachite 35 has come into foray as an alternative way to fabricate defect and adsorbate free vdW heterostructures. Cylindrite and franckeite belong to the material class where the superlattice is made of the alternative PbS-type and SnS 2 -type layers, while the superlattice of lengenbachite consists of the alternative PbS-type and As 2 S 3 -type layers.…”

“…In these cases, the formed vdW heterostructures exhibit in-plane structural and optical anisotropy, even though the individual layers of PbS, SnS 2 or As 2 S 3 are structurally isotropic in nature. Recently, several reports on these materials have demonstrated their anisotropic optical behavior in the linear and nonlinear optical regime 32 , 35 – 37 . Therefore, it is an imperative to search for other materials which can be mechanically exfoliated to obtain ultrathin vdW heterostructures composed of other kinds of 2D material layers.…”

Polarization-sensitive optical responses from natural layered hydrated sodium sulfosalt gerstleyite

“…From literature, the real part of the refractive index of gerstleyite crystal is around 2.01 58 . Thus, considering all the experimental parameters into account, the third-order nonlinear susceptibility magnitude of for gerstleyite crystal is estimated as 1.81 × 10 –20 m 2 /V 2 , which has the same order of magnitude as the recently explored multi-element anisotropic nonlinear vdW layered materials for example franckeite (1.87 × 10 –19 m 2 /V 2 ) 26 , cylindrite (3.06 × 10 –19 m 2 /V 2 ) 27 , teallite (3.49 × 10 –19 m 2 /V 2 ) 29 , gillulyite (2.05 × 10 –20 m 2 /V 2 ) 30 , getchellite (2.89 × 10 –20 m 2 /V 2 ) 18 , and nagyágite (1.49 × 10 –20 m 2 /V 2 ) 59 .…”

Polarization-dependent optical responses in natural 2D layered mineral teallite

“…In addition, the high contribution of carbon (C) and oxygen (O) can be ascribed to the sample processing for TEM analysis and the underlying carbon support film of TEM grid. We used polymethyl methacrylate (PMMA)-assisted wet transfer method for transferring the mechanically exfoliated teallite flakes from glass substrate to TEM grid, which further leads to the accumulation of carbon-based adsorbates during the flake transfer 39 . Additionally, the recorded Raman modes of the teallite mineral sample are also compared with the Raman modes of the previously reported chemically synthesized pure teallite crystal to further elucidate any significant influence of these doped elements on the intrinsic and optical properties of teallite mineral.…”