Synthesis And Microstructure And Surface Photovoltage Characteristics Research Of CdSe Nanocrystals

In this thesis, a series of CdSe nanocrystals was synthesized respective by the usingof TGA, MPA, L-Cys, ME and TG as the modifier agent in aqueous solution. The reactionconditions were optimized according to the orthogonal method and some single factors,such as pH, the mole ratio of Cd:ligand, refluence reaction time and the mole ratio ofCd:Se were investigated in detail.The crystal structure and size of CdSe nanocrystals were characterized by XRD. Theresult showed that TGA, MPA, ME and TG capped CdSe nanocrystals were zinc blendestructure, and L-Cys capped CdSe nanocrystals was wurtzite structure. The averagediameter was about2nm. The shape and microstructure of the sample were analyzed byTEM, HRTEM and selected area electron diffraction (SAED) pattern. Simultaneity, theanalyzing component and bond structure of the EDS and FI-IR indicated the sample weresimilar to CdSe/CdS/ligand core/shell structure. The surface electronic structure wascharacterized by UV-Vis and SPS. The transition energy of the fine structure of the lowest(1S3/2,1se) electron-hole pair state of core-CdSe, spin-orbit splitting valence-band statesSS-Oof core-Cdse and the lowest ground state of the CdS layer, and charge transitions ofthe ligand were located at about470nm (2.638ev), about399nm (3.108eV), and about375nm (3.303eV), which has been identified for CdSe nanocrystals stabilized by ligandsuch as TGA, MPA and L-Cys. At the same time, the fine structure of (2S3/2,1se)(3S3/2,1se)(1S1/2,1se)(2S1/2,1se) of excited-state transitions of core-CdSe has also beenidentified. The peaks of SPV response of the ME and TG capped CdSe nanocrystals had alowest (1S3/2,1se) electron-hole pair state transition at about396nm (3.131eV) and aligand charge transfer transitions at about373nm (3.324eV). The energy complementaryrelationship between SPS, PL and SPAS for the photoexcited carrier was investigated.Through analysis of EFISPS, the CdSe nanocrystals was thought to has a n-typesemiconductor properties, but the transposition of p-type photoelectric property wasobserved in the positive or negative electric field induced with different functional groupsin the ligand capped CdSe nanocrystals. The band structure, partial density of states and optical properties were calculatedabout the (111) plane and (220) plane of the CdSe crystal with adsorption N2, O2, H2O,C2H6O and CdSe crystal with S dopped by CASTEP module of Materials Studio software.Compare with experimental result, we analyse the nucleation structure of the CdSenanocrystals and correlation transition state of SPV response.