| The studies of material processing and chemistryof the colloidal semiconductor nanocrstals(quantum dots)are advancing at an amazing rate,which also brings in some novel and exciting pespects in commercialized applications.In recent years,narrow bandgap nanocrystals have attracted more and more attentions.Some applications and perspects have been recently demonstrated,such as in infrared optoelectronics(e.g.optical modulators,lasers,photoimaging devices and photodetectors),solar cells,low cost/large format microelectronics,biosensors and biological imaging systems.All the nanocrystal materials have their own advantages and disadvartanges,Therefore,for special applications of quantum dots.How to assemble these materials "quantum dots solid film" and keeping its original excellent performance is based on the key scientific problems of the application of quantum dot devices In this thesis we studied the synthesis of near infrared nano-materials including PbS quantum dots,PbS/CdS Core/shell quantum dots and the thin film of silica-coated PbSe self-assembly nano-particles,and their application on near infrared light emitting diodes and electrical bistable devices.In recent years,aiming at colloidal lead chalcogenide quantum dots,such as PbS,PbSe,PbTe quantum dots,have been widely studied in terms of near-infrared light emitting diodes,infravision,such as biological markers and optoelectronic devices.Compared with ultraviolet and visible light emissions,lead chalcogenide semiconductors can get high quality quantum dots,which makes its become excellent candidate materials for the near-infrared(NIR)emission in the telecommunication wavelengths of 1.3-1.6?m.Because their small bulk band gaps,that PbS and PbSe have bulk band gaps of 0.41 and 0.28 respectively,large exciton Bohr radii and relatively large nanocrystal size while still maintaining quantum confinement.In these two materials,PbSe NCs are more broadly studied.PdS is considered more eco-friendly because of the decrease toxicity level of sulfur compared to selenium.Hines and Scholes first reported that colloidal organometallic synthetic routes for hydrophobic PbS NCs.Electroluminescent diode based on PbS quantum dots has become the field of near infrared light emitting device is a hot research field.However,the efficiency of PbS or PbS/CdS core-shell structure quantum dot near-infrared light emitting diode is not high.The problems include low fluorescent efficiency of the quantum dots,inappropriate surface ligand and unoptimized device structure.To,In the second chapter of this thesis,we tried to solve these problems by optimizing the stoichiometric ratio,reaction temperature,growning time of the shell and ligand exchange to improve near infrared photoelectric properties.In lead chalcogenide quantum dots synthesis and applications such as:PbSe quantum dots,ever since Murrray reported the first hot injection method for synthesis of monodisperse PbSe quantum dots.In the following researchse,various geometric shapes of PbSe NCs were reported,including spherical,square,strip,octahedron,linear and circular by organometallic synthesis in different organic solvent.The main growth mechanism of different geometric shapes appeared to be the self assbleming growth of more PbSe materials along one orientation of smaller PbSe NC seeds.The electoptical properties of self-assembled structures strongly depending on the different growth orientation that needs to be further explored,espcially the application of optical and electrical for PbSe three-dimensional octahedral NCs.Encapsulation of single NCs with silica shells favorates their applications such as storages and biomarkers.The silica itself is a good insulation material and dielectric material,it can protects the surface of the nanoparticles from oxidization,thus improving the stability of the nanoparticles.The thickness of silica shell can be adjusted by changing the manage rate and concentration of precursor.A wide variety of silica-coating methods have been developed for different nanoparticles in the past few decades.In the third chapter,we synthsis PbSe self-assembly NCs with silica-coating by the method of inverse microemulsion and then studied the carrier transmission mechanism based on PbSe self-assembly NCs with silica-coatin in bistable device applications.Organic materials have been attracted a lot of attentions for large-area,flexible and nonvolatile bistable memory devices.In electrical bistable devices two different resistance states are observed under opposite voltage-scanning directions.With the progress of synthesis and properties of semiconductor nanoparticles,nanoparticles have been widely used in organic bistable devices.So far,a lot of studies were reported about the application of nanoparticles in the organic bistable devices with different device structures,such as polymer-metal nanoparticles blender structures and organic/nanocrystals/organic sandwich structure.Recently,semiconductor nanoparticles such as ZnO,CdSe-InP,ZrO2 were embedded in an organic films and were used to make electrical bistable devices byspin-coating method.Here in the third chapter of the thesis,we reported electrical bistable devices with this newly synthized self-assembly PbSe nanoparticles with silica shell using the structure of ITO/PEDOT:PSS/PbSe self-assembly NCs@SiO2/Al.In this structure,self-assembly PbSe NCs with silica shell serves the porpose similar to the mix of nanoparticles and organic materials.We made three-dimensional octahedral PbSe QD through adjust and control the interaction between quantum dots and surface ligands including trioctylphine(TOPO)and oleic acid(OA),and then coated them with silicon dioxide.Utilizing this material to make the electrical bistable devices have better performance.We also studied the carrier transporting mechanism of the bistable devices by the current-voltage results.In general,the memory effect observed in these electrical bistable devices is related to its charge trapping,separation,and transfer properties. |
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