The Synthesis And High-pressure Studies Of SnS、SnSe、SnS_xSe_1-x Low-dimensional Nanostructures

Tin sulfide(Sn S) and tin selenide(Sn Se) are IV-VI group P-type semiconductor compounds with layered orthorhombic structures. Their optical band gap between Si and Ga As, which is applied to the light absorption of solar cell, the near infrared detecting materials of ELD and the photoelectric voltage devices because of the unique photoelectric conversion characteristics perfect match the spectrum of solar radiation. In addition, Sn S and Sn Se are widely applied to the electrode of lithium battery. Recently, Sn Se was attracted widespread attention because it is considered as the simplest thermoelectric materials. With microelectronics and optoelectronics devices demand for integrated degree is higher and higher, the size of discrete component will develop to the nano-scaled, and the layered semiconductor materials have become the focus of the International nanomaterial research field. Many research groups at home and abroad have been study on the Sn S and Sn Se nanomaterials using the different methods, but most of the researches focused on the preparation of nanostructures and the physical nature under ambient pressure, and the major preparation strategies are chemical synthesis methods. Generally, these methods require complex reaction process, expensive, toxic and long chemical time.High-Pressure is an important approach for the atomic arrangement, electronic distribution, band gap regulation and physical properties optimization. A novel research field from combined high-pressure with nano materials is a new growing point in material science. High pressure researches show that nanomaterial is different from their corresponding bulk form on the size and shape, which will lead to diversified surface energy, different internal atoms and changed phase transition relaxation process. Base on the literature review and current research, theoretical and experimental studies on Sn S and Sn Se semiconductor materials under high pressure just begun. The study on the size and morphology-controlled synthesis of Sn S and Sn Se nanomaterials under high pressure has not been reported so far. In this work, we controlled synthesis of Sn S, Sn Se and Sn Sx Se1-x nanomaterials were controlled synthesize using a plasma-assisted direct current arc discharge method with tin powder, sulfur powder, selenium powder as reaction sources. The high pressure behaviors of the as-synthesized sample were investigated by in situ high-pressure synchrotron angle-dispersive X-ray diffraction and Raman scattering in diamond anvil cells at room temperature. The details are as follows:1. Using the plasma-assisted direct current arc discharge method, Sn and S powders(purity: 99.99%) were mixed with a molar ratio 1 : 1. the Ar pressure selected was 10 k Pa, the input current was maintained at 100 A and the voltage was 18 V, the discharging process was maintained for 3 min. Finally, the Sn S nanosheets and Sn S nanoparticles samples were collected at the head cover and the surface of water-cooling wall, respectively.2. Using the plasma-assisted direct current arc discharge method, Sn and Se powders(purity: 99.99%) were mixed with a molar ratio 1 : 1. the Ar and N2 pressure selected was 10 k Pa, the input current was maintained at 80 A and the voltage was 18 V, the discharging process was maintained for 2 min. Finally, the Sn Se nanosheets and Sn Se nanoparticles samples were collected at the head cover and the surface of water-cooling wall, respectively.3. Using the plasma-assisted direct current arc discharge method, Sn, S and Se powders(purity: 99.99%) were mixed with various molar ratio. the Ar pressure selected was 10 k Pa, the input current was maintained at 100 A and the voltage was 18 V, the discharging process was maintained for 3 min. Finally, the Sn Sx Se1-x nanosheets and Sn Sx Se1-x nanoparticles samples were collected at the head cover and the surface of water-cooling wall, respectively.4. The high pressure behaviors of the as-synthesized Sn S nanosheets were investigated by in situ high-pressure synchrotron angle-dispersive X-ray diffraction and Raman scattering in diamond anvil cells at room temperature. A second-order isostructural continuous phase transition(Pnma �' Cmcm) was observed at 3.0 GPa, and a first-order phase transition(orthorhombic �' monoclinic) was observed at 12.7 GPa. The transition pressures are considerably lower than that of bulk Sn S. The reduction of transition pressure is induced by the volumetric expansion with softening of the Poisson ratio and shear modulus. Moreover, the measured zero-pressure Pnma structure bulk modulus of the Sn S nanosheets coincides with bulk Sn S. This abnormal phenomenon is attributed to the unique intrinsic geometry in the nanosheets. The high-pressure Cmcm structure bulk modulus is considerably higher than the theoretical value. The pressure-induced morphology change should be responsible for the improved bulk modulus. The high-pressure monoclinic structure bulk modulus coincides with bulk Sn S. Because of the Sn S pieces lost the essential attribute of the single crystal nanosheets, and show the same structural stability with bulk Sn S.5. The high pressure behaviors of the as-synthesized Sn Se nanosheets were investigated by in situ high-pressure synchrotron angle-dispersive X-ray diffraction and Raman scattering in diamond anvil cells at room temperature. A second-order isostructural continuous phase transition(Pnma �' Cmcm) was observed at 6.8 GPa, which is considerably lower than the transition pressure of bulk Sn Se. The reduction of transition pressure is induced by the volumetric expansion with softening of the Poisson ratio and shear modulus. Moreover, the measured zero-pressure bulk modulus of the Sn Se nanosheets coincides with bulk Sn Se. This abnormal phenomenon is attributed to the unique intrinsic geometry in the nanosheets. The high-pressure bulk modulus is considerably higher than the theoretical value. The pressure-induced morphology change should be responsible for the improved bulk modulus. These new findings and the reasonable interpretations about the pressure-induced phenomenon of Sn S and Sn Se nanosheets will help to further understand the nature of metal sulfide layered nanostructures physical properties. The significance of this work is not only provides information about the high pressure behavior of metal sulfide nanomaterials for the first time, but also provides a new thought and new way for the pressure-induced phase transition behavior of whole IV-VI metal chalcogenide.