Atomic Imaging and Thermally Induced Dynamic Structural Evolution of Two-Dimensional Cr₂S₃

Abstract

In this study, facile salt-assisted chemical vapor deposition (CVD) was used to synthesize ultrathin non-van der Waals chromium sulfide (Cr 2 S 3 ) with a thickness of ∼1.9 nm. The structural transformation of as-grown Cr 2 S 3 was studied using advanced in situ heating techniques combined with transmission electron microscopy (TEM). Two-dimensional (2D) and quasi-one-dimensional (1D) samples were fabricated to investigate the connection between specific planes and the dynamic behavior of the structural variation. The rearrangement of atoms during the phase transition was driven by the loss of sulfur atoms at elevated temperatures, resulting in increased free energy. A decrease in the ratio of the (001) plane led to an overall increase in surface energy, thus lowering the critical phase transition temperature. Our study provides detailed insight into the mechanism of structural transformation and the critical factors governing transition temperature, thus paving the way for future studies on intriguing Cr−S compounds.

Modeling Chemical Exfoliation of Non-van der Waals Chromium Sulfides by Machine Learning Interatomic Potentials and Monte Carlo Simulations

“…90 The same thing applies for Cr 3 S 4 , being characterized as a CrS 2 -disordered Cr 1/2 −CrS 2 . 90 3.3. Strain-Induced vdW Gaps in Non-vdW CrS 2 Slabs.…”

“…8,9,90 However, structural characterization of CVD-grown Cr 2 S 3 slabs reveal a pronounced degree of disorder in the Cr-deficient layers, leading to the crystal being characterized as a CrS 2 -disordered Cr 1/3 −CrS 2 . 90 The same thing applies for Cr 3 S 4 , being characterized as a CrS 2 -disordered Cr 1/2 −CrS 2 . 90 3.3.…”

“…For instance, the ground-state ordered phase of Cr 2 S 3 displays a structural configuration akin to CrS 2 −Cr 1/3 −CrS 2 , wherein Cr 1/3 forms Cr lines extended along the armchair direction, separated by two vacant lines in either ABC or AB stacking. 8,9,90 However, structural characterization of CVD-grown Cr 2 S 3 slabs reveal a pronounced degree of disorder in the Cr-deficient layers, leading to the crystal being characterized as a CrS 2 -disordered Cr 1/3 −CrS 2 . 90 The same thing applies for Cr 3 S 4 , being characterized as a CrS 2 -disordered Cr 1/2 −CrS 2 .…”

Coexistence of Ferroelectricity and Ferromagnetism in Atomically Thin Two-Dimensional Cr2S3/WS2 Vertical Heterostructures

“…Besides, the cross-section STEM characterizations were also conducted on Cr 2 S 3 /WS 2 stacks and the atomically sharp interfaces were obviously observed (Figure j,k and Figures S10 and S11), reconfirming the high crystalline quality without any defects or cross-contaminations. Notably, the darker contrast of self-intercalated Cr atoms in comparison to the counterparts in the CrS 2 layer is attributed to the lower amount of atoms . In short, all of the aforementioned results indicate that the intrinsic Cr 2 S 3 /WS 2 vertical heterostructures have been successfully synthesized using a two-step CVD method, which lays a solid foundation for uncovering exotic physical properties, such as ferroelectricity and ferromagnetism.…”

“…Notably, the darker contrast of selfintercalated Cr atoms in comparison to the counterparts in the CrS 2 layer is attributed to the lower amount of atoms. 43 In short, all of the aforementioned results indicate that the intrinsic Cr 2 S 3 /WS 2 vertical heterostructures have been successfully synthesized using a two-step CVD method, which lays a solid foundation for uncovering exotic physical properties, such as ferroelectricity and ferromagnetism. 2D ferroelectric materials with switchable polarizations offer a new paradigm for constructing a low-power field-effect transistor, 1,2,44 nonvolatile memory, 4 in-memory sensor, 45 and neuromorphic computing.…”