Abstract:

Tin sulfide (SnS) is an important binary IV–VI semiconductor compound. High-pressure study on the bulk-SnS exist controversy and the nano-SnS still hasn't been reported because it is difficult to obtain the high-purity sample. The high-purity two-dimensional single-crystalline SnS nanoflakes with an average thickness of ∼18 nm and a lateral dimension of ∼500 nm have been synthesized by the plasma-assisted direct current arc method, which high-pressure behaviors have been investigated by in situ synchrotron ADXRD and Raman scattering studies up to ∼30 GPa at room temperature.

A second-order isostructural continuous phase transition from orthorhombic structure Pnma symmetry to Cmcm symmetry and a first-order phase transition from orthorhombic phase to monoclinic phase have been observed at ∼3 and 13 GPa, respectively, which is considerably lower than the transition pressure of bulk SnS and different from our previous studies on SnSe nanoflakes [1]. The decreased transition pressure can be attributed to the volumetric expansion with the softening of the Poisson ratio and shear modulus. In addition, the bulk modulus of the Pnma phase is consistent with that of bulk SnS, which is different from most nanomaterials. This abnormal compressibility arises from the unique intrinsic geometry in the nanoflakes. Moreover, a significantly enhanced bulk modulus of the Cmcm phase compared with the theoretical results has been observed, which is considered to be caused by the pressure-induced morphology change. Furthermore, the bulk modulus of the monoclinic phase coincided with bulk SnS. This is attributed to the primitive structure have been destroyed under high pressure, and the small pieces were unable to preserve property of SnS nanoflakes. This study not only provides valuable experimental information about SnS nanoflakes, but might also shed some light onto the pressure-induced phase transition behaviors of other IV–VI layered structural compounds at the nanoscale.

Reference:

[1]  J. Zhang, HY Zhu, QL Cui, et al., Nanoscale 7, 10807-10816 (2015)