Controllable Synthesis And Optoelectronic Applications Of Two-dimensional CdS Nanostructures And Junctions

Owing to the ultrathin thickness,large surface area,excellent flexibility and novel physical properties,two-dimensional(2D)nanomaterials have attracted extensive attention and research.However,current research on 2D nanomaterials is usually limited to layered materials,and research on 2D non-layered nanomaterials is relatively few.This is mainly due to the fact that for layered materials,the in-plane atoms are closely connected by strong chemical bonds in each layer,while these layers stack together though the weak van der Waals interaction,so it is relatively easy to synthesize their 2D structures by mechanical exfoliation or chemical vapor deposition.However,for non-layered materials,bulk caystals are formed through covalent bonds in three-dimensional space.Therefore,it is quite difficult to realize controllable synthesis of 2D non-layered nanostructures and their heterojunctions,which greatly limits the optoelectronic applications of 2D non-layered nanomaterials.In addition,2D non-layered nanomaterials have many advantages such as surface dangling bonds,which show novel properties and enrich types and functions of 2D nanomaterials.Therefore,it is of great significance to realize controllable preparation of two-dimensional non-layered nanomaterials.This research focuses on controllable synthesis and optoelectronic applications of CdS 2D nanostructures and junctions.The main research contents are as follows:1.Controllable synthesis of 2D non-layered CdS nanosheets.2D CdS nanosheets were synthesized via the van der Waals epitaxy method.It is demonstrated that CdS nanosteets appear as hexagon geometry and are of high-quality structure by optical microscope,Raman spectrum and high resolution transmission electron microscope.In addition,morphologies and structures of CdS nanosheets were controlled by adjusting the parameters such as pressure,growth temperature and reaction time,and the growth mechanism of CdS nanosheets was clarified.Photoconductive photodetectors were constructed based on CdS nanosheets to study the ophotoelectric properties.The device exhibits exhibit excellent optoelectronic performance with a responsivity of 400 A/W and a detectivity of 5×1011 Jones.2.2D Cu2S/CdS vertical heterojunctions constructed by cation exchange reaction.CdS nanosheets were immersed in CuCl solution for cation exchange reaction,and Cu2S/CdS vertical heterojunctions and Cu2S nanosheets were prepared by controlling reaction time.The time evolution process of the reaction was studied.It was found that the reaction proceeded from top facets of nanosheets in a layer-bylayer fashion along the c-axis orientation,clarifying reaction mechanism of vertical heterojunctions.High-performance photovoltaic devices were built based on Cu2S/CdS vertical heterojunctions to study the ophotoelectric properties.The device efficiency was of 2.1%.3.2D CdS/C8-BTBT heterojunctions constructed by vapor deposition.Individual organic material or inorganic material have some shortcomings that cannot be overcomed by themselves,so it is disadvantageous for the development of new multifunctional materials.Organic-inorganic heterojunctions have unique properties.CdS/C8-BTBT heterojunctions were constructed by vapor deposition.The island growth model of C8-BTBT was elucidated and growth mechanism of CdS/C8-BTBT heterojunctions was studied.It was found that the heterojunctions show response ranging ultraviolet to visible light.The wide spectrum photodetectors based on CdS/c8-btbt heterojunctions were constructed.