Controllable Preparation, Field Electron Emission And Photoelectric Detection Of Selenide And Selenide/graphene Nanocomposites

In recent years,selenide semiconductor nanomaterials have become the hot spot in the field of solar cells,photodetectors,field effect transistors and field emission display,especially more and more widely used in vacuum microelectronic devices and photoelectric devices due to their unique physical and chemical properties.Therefore,it is very important to study and develop more simple,green and general synthesis system to prepare selenide semiconductor nanomaterials with superior properties for further study on their related applications.Meanwhile,the controllable synthesis of selenide nanomaterials with different size,morphology and composition is also of great significance for exploring their new properties.Based on the above,combined the large specific surface area,high electron mobility and good electrical conductivity of graphene with the outstanding performance of selenide nanomaterials,researchers assemble and develop different selenide nanomaterials onto graphene to further broaden the range of applications for selenium/graphene nanocomposites.These novel nano electric materials have been demonstrated exciting and promising applications in photoelectric conversion device,energy storage system,sensors,photocatalysis,and field emission display.In this article,we used ZnSe,CdSe and Cu_2-xSe as the main research object.ZnSe nanowalls,CdSe nanograss/graphene oxide nanocomposites,CdSe nanosphere/graphene oxide nanocomposites and Cu_2-xSe nanograsses/graphene oxide nanocomposites have been successfully prepared via the hydrothermal process.The field electron emission properties of ZnSe nanowalls with different morphologies,CdSe nanograss with different morphologies on graphene oxide substrates and Cu_2-xSe nanograss with different morphologies on graphene oxide substrates have been studied.The photoelectric properties of CdSe nanospheres grown on graphene oxide substrates has also been investigated.These findings provide a solid foundation for the controllable synthesis of selenide nanomaterials and selenide/graphene composites and study on their physicochemical properties,as well as their applications in optoelectronic devices,vacuum microelectronic devices,solar cells and photocatalysis.The main contents and results of this research can be summarized as follows:（1）ZnSe nanowalls are prepared on Zn substrates hydrothermally at 180°C for 12h.The structure,morphology,and chemical composition of the ZnSe nanowalls are determined by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,energy-dispersive X-ray analysis（EDS）,X-ray photoelectron spectroscopy（XPS）and Raman scattering.The concentration of hydrazine hydrate（N₂H₄·H₂O）plays an important role in the formation and morphology of the ZnSe nanowalls and XRD reveals that all the ZnSe nanocrystals have a cubic zinc blende structure.The ZnSe nanowalls with the optimal morphology delivers good field electron emission performance with a turn-on field of 1.51 Vμm^-1and enhancement factor of 4797.The formation mechanism is discussed.The simple and controlled preparation procedures and good properties of the ZnSe nanowalls bode well for application to electronics and optoelectronics devices.（2）Four different morphologies of the CdSe semiconductor nanograss have been successfully grown on graphene oxide（GO）sheets via hydrothermal method at 220°C for 12h.The morphologies,structures,chemical compositions and optoelectronic properties of the as-obtained CdSe/GO nanocomposites were characterized by XRD,SEM,TEM,EDS,XPS and Raman spectra.It was found that the EDTA/Cd²⁺molar ratio is important for the formation of morphology of CdSe/GO nanocomposites.The results of XRD revealed that all the as-obtained CdSe/GO nanocomposites have zinc blend structure.Room temperature photoluminescence（PL）showed that the sample emits red light under different excitation wavelengths.The results of Raman spectra,EDS and XPS showed that the CdSe nanograss is grown on GO sheets.The results showed that CdSe/GO nanocomposites composed of nanorods have best field electron emission properties with a low turn-on electric field of 4.14 Vμm^-1 and a high field enhancement factor of 3315 among all the samples.（3）The morphology-selective synthesis of Cu_2-xSe nanograss grown on graphene oxide（GO）substrate has been achieved by a simple hydrothermal method at 100°C for 10 h.The structure,morphology,and chemical composition of the Cu_2-xSe/GO nanocomposites were determined by X-ray diffraction（XRD）,energy-dispersive X-ray analysis（EDS）,scanning electron microscopy（SEM）and Raman scattering.The concentration of hydrazine hydrate（N₂H₄·H₂O）has been found to be a crucial parameter for the controllable growth of the Cu_2-xSe nanostructures.The results of XRD reveal that the as-prepared Cu_2-xSe nanograss has zinc blend structure.The results of Raman spectra and EDS show that the Cu_2-xSe nanograss is grown on GO sheets.The field electron emission properties of the Cu_2-xSe/GO nanocomposites were investigated.The Cu_2-xSe nanograss with optimal morphology on GO delivers good field electron emission performance,indicating that the Cu_2-xSe/GO nanocomposites may have a number of promising applications in the vacuum microelectronics industry.（4）Different morphologies of CdSe microspheres have been synthesized on reduced graphene oxide（GO）sheets by a simple hydrothermal process using Cadmium nitrate and Se powder as the raw materials.The hybrid CdSe/GO samples were intensively investigated by XRD,EDS,SEM and UV-vis absorption spectrum.It was found that the EDTA/Cd²⁺molar ratio is crucial for the formation of morphology of CdSe grown on GO sheets.The results of XRD reveal that the as-prepared CdSe microspheres have zinc blende structure.The results of Raman spectra,EDS and SEM show that the CdSe microspheres are grown on GO sheets.In addition,UV-vis absorption spectrum indicates that the CdSe/GO nanocomposites are believed to serve as photoelectric devices to extend the absorption spectrum to visible light region.Superior optoelectronic properties of urchin-like CdSe microspheres grown on GO sheets relative to those of other CdSe/GO nanocomposites was observed under visible light irradiation.The photocatalytic mechanism of CdSe microspheres/GO nanocomposites was also described.