Preparation And Properties Of SnSe And SnS Nanomaterials

Tin selenide(SnSe)and tin(?)sulfide(SnS)are group IV-VI narrow-bandgap layered semiconductor compounds with broad application prospects in near-infrared detections and photovoltaic products.Nanomaterials present novel physical properties and have received widespread attentions from the scientific communities.In this thesis,chemical vapor deposition technique was used to realize the controlled growth of SnSe single-crystalline nanowires(NWs)and SnS/SiO_X core/shell NWs by finely adjusting the growth parameters in the absence of catalysts.The two-dimensional growth habits caused by the intrinsic crystal structure of the materials was inhibited and the one-dimensional growth of SnSe SnS/SiO_x was achieved.The phases,microstructures and physical properties were studied,and the main results are as follows.(1)Using SnSe powder as raw material,ultra-long SnSe single-crystalline nanowires were synthesized by chemical vapor deposition technique.Scanning electron microscopy(SEM),X-ray powder diffraction(XRD),transmission electron microscopy(TEM),Raman spectroscopy(Raman)and X-ray photoelectron spectroscopy(XPS)were used to characterize the morphology,microstructure and chemical compositions of the as-prepared SnSe nanowires.The average diameter of the synthesized SnSe nanowires is about 270 nm and the length can reach about sub-millimeter.The aspect ratio of the SnSe NWs can be over 3000,showing a strong one-dimensional growth characteristic.The synthesized nanowires are single crystals with high crystallization.The growth direction is along the normal direction of the{011}planes.The electronic test on individual NWs indicated that the NWs have P-type conductivity.By analyzing the time-dependent evolution of the morphology of the NWs,the growth mechanism of NWs is proposed.It is thought that the growth of SnSe nanowires is due to dynamic growth factors of the CVD system to suppress spontaneous two-dimensional growth behavior and result in one-dimensional growth.The optical property of SnSe NWs were studied by UV-vis-NIR spectroscopy(UV-vis-NIR).It was found that SnSe NWs have a strong absorption in the near-infrared band,with a direct bandgap of 1.07 eV,and indirect bandgap is 0.93e V.(2)SnS/SiOx core/shell NWs were synthesized by CVD technique without catalyst.The morphology and microstructure of the as-prepared samples were characterized.It was found that the synthesized NWs contain partially hollow core/shell structures.The shell was amorphous Si Ox,and the core was orthorhombic SnS.The growth of the novel NWs is thought to be a self-confined one-dimensional growth process that involves the decomposition of SnS and the formation of Sn-Si alloying droplets.Si comes from the substrate and O origins from the remained oxygen in the growth system.XPS analysis revealed that the sample is composed of Si with+2 valences,O with-2 valences,Sn with 0or+2 valences,S with-2 valences,which suggests the decomposition of SnS involved in the growth of the core/shell NWs.In summary,SnSe ultra-long single-crystalline NWs and novel SnS/SiOx core/shell NWs have been synthesized here,which presents some new growth behaviors the materials,and is helpful to enrich and expand the research of other one-dimensional layered materials.