Tin selenide (SnSe) is an important binary IV–VI semiconductor compound with a wide range of potential applications such as infrared optoelectronic devices, anode materials for rechargeable lithium batteries, solar cell and photoelectric property. Most recently, ultralow thermal conductivity and a high thermoelectric figure of merit have been found in SnSe bulk crystals, which have also extended their prospects with regard to applications in thermoelectric energy conversion. However, the high-pressure study on SnSe bulk crystals exist a lot of controversy. Meanwhile, the high-pressure study on nanoscale SnSe still hasn't been reported because it is difficult to obtain the high-purity sample through the traditional preparation methods. A research team of Jilin university State Key Laboratory of Superhard Materials successfully synthesized the high-purity two-dimension single-crystalline SnSe nanosheets, which high-pressure behaviors have been investigated. Their research has been published on May 18^th, 2015 in Nanoscale.

The high-pressure behaviors of as-synthesized sample have been investigated by in situ synchrotron angle-dispersive X-ray diffraction in the 4W2 beamline of Beijing Synchrotron Radiation Facility. A second-order isostructural continuous phase transition from orthorhombic structure Pnma symmetry to Cmcm symmetry has been observed at 6.8 GPa, which is considerably lower than the transition pressure of bulk SnSe (10.5 GPa). 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 SnSe, which is different from most nanomaterials. We suggest that this abnormal compressibility arises from the unique intrinsic geometry in the nanosheets. Moreover, we observed a significantly enhanced bulk modulus of the Cmcm phase compared with the theoretical results, which is considered to be caused by the pressure-induced morphology change.

We believe that this study not only provides valuable experimental information about SnSe nanosheets, but might also shed some light onto the pressure-induced phase transition behaviors of other IV–VI layered structural compounds at the nanoscale.