Controlled Synthesis Of Copper Chalcogenide Nanomaterials And Their Localized Surface Plasmon Resonance Absorption Properties

Localized surface plasmon resonance（LSPR）absorption property,which is a novel optical phenomenon of nanomaterials,is one of the most active research directions in nano-optics filed.Localized surface plasmon（LSP）can be described as the collective oscillation of free carrier in nanocrystals（NCs）under the drive of incoming light wave.LSPR arises from the resonance between the collective oscillation of free carrier and incoming light wave at a certain frequency.These LSPR NCs can be widely applied in photothermal therapy,photoacoustic imaging,and other application fields.Generally,the traditional LSPR NCs are mainly noble metal nanocrystals,such as Au and Ag.With the in-depth study of the LSPR in NCs and the development of the synthesis technology of NCs,it is also found that some nonstoichiometric semiconductor NCs can also display LSPR behaviors.Recently,the LSPR properties of nonstoichiometric copper chalcogenide NCs have attracted wide research attention.These NCs are self-doped p-type semiconductor NCs,which have free holes due to the presence of the copper vacancies in the lattice.As a result,they usually have obvious LSPR absorbption properties in near-infrared region.Compared with noble metal NCs,the LSPR properties of copper chalcogenide NCs can be controlled in a larger spectral region.The thesis is mainly focused on the binary Cu_2-xS NCs,binary Cu_2-xSe NCs,ternary alloyed Cu_2-xS_ySe_1-y NCs and Cu_2-xS and Cu_2-xSe NCs induced by diffusion of Zn ions,and studies the tunable LSPR properties by changing sulfur source,surface ligand,size,shape,phase and so on.These strategies lead to wide tunable LSPR in the near-infrared（NIR）region.The main research results are summarized as follows:1.Cu_2-xS NCs were synthesized by using 1-dodecanethiol（DDT）and sulfur powder as sulfur sources,respectively,which exhibited obvious LSPR absorption properties in the NIR region.Firstly,monoclinic Cu_1.94S NCs were synthesized by using DDT as sulfur sources,which exhibited size-and shape-related LSPR absorption properties.The Cu_1.94S NCs with similar size and shape were selected as research objects,the effects of the surface ligands on the LSPR behavior were studied,and these NCs exhibited surface-ligand-dependent LSPR wavelength shift.Secondly,by using sulfur powder,Cu_2-xS NCs with different phases(hexagonal Cu S,monoclinic Cu₇S₄ and monoclinic Cu_1.94S)were obtained by changing the Cu/S precusor feeding ratios,and the LSPR absorption properties of Cu_2-xS NCs with different phase were explored.On the basis,the effects of surface ligands on the phase of Cu_2-xS NCs and their LSPR absorption properties were studied in detail.2.Cubic Cu_2-xSe NCs were synthesized by using selenium power as Se source via a hot-injection method,and the Cu_2-xSe NCs exhibited obvious LSPR absorption behaviors in the NIR region.Firstly,we explored the effects of size and the feeding ratios of copper/selenium precursor on the LSPR absorption properties of Cu_2-xSe NCs.With an increase of the Cu:Se ratios,a small red-shift of the LSPR absoption peak was observed.In contrast,the change of size had less effect on the LSPR behavior.Then,we explored the effects of surface ligands on the LSPR properties.With an increase of the oleic acid（OA）dosage,the LSPR absorption peak of the as-obtained Cu_2-xSe NCs showed an obvious red-shift,which mainly arised from the strong electron-donating ability of OA,and the OA decreased the amount of free holes.3.Ternary alloyed Cu_2-xS_ySe_1-y NCs were synthesized by using DDT and sulfur powder as sulfur sources respectively,which showed obvious LSPR absorption properties in the NIR region.With an increase of sulfur dosage,the phase transformed from cubic to monoclinic（djurleite）,accordingly,the NIR LSPR absorption peak exhibited obvious red-shift.By comparison,it is found that the LSPR absorption properties of Cu_2-xS_ySe_1-y NCs synthesized by using DDT as sulfur source can be controlled in a larger spectral region.As surface ligands,the electron-donating effects of the DDT played an important role in the tuning of LSPR behaviors.4.Owing the Cu ions show high mobilities at high temperature,it is explored that the effects of the LSPR absorption properties by introducing Zn ions to Cu_2-xS and Cu_2-xSe nanocrystals.By using sulfur powder as sulfur source,Cu_2-xS NCs were obtained in the presence of Zn ions.With the Zn ions feeding dosage increasing,the phase of as-obtained NCs tuned from monoclinic Cu_1.94S to monoclinic Cu₇S₄,and the LSPR showed a degree of blue-shift.In contrast,with an increase of Zn ions feeding dosage,there was no phase change in cubic Cu_2-xSe NCs obtained in the presence of Zn ions,while the LSPR absorption peak of as-obtained NCs showed a red-shift.Above results reflect that the effects of inducing foreign ions to the LSPR properties of Cu_2-xS and Cu_2-xSe NCs are different.