Synthesis And Property Modifications Of ZnSe 2D Nanomaterials And Nanoclusters

The synthesis of semiconductor nanoparticles has experienced more than 30 years of development,and corresponding integrations into routine applications has started to surface.Recently,one of the most important developments in the field of II-VI semiconductor nanocrystals(NC)is the synthesis of two-dimensional semiconductor nanocrystals,which adds the nanocrystals from zero dimensional quantum dots(QD)to one-dimensional nanowires(NW)or nanorods(NR),and then to nanoplate(NP),bringing one-dimensional quantum confinement into the family of II-VI semiconductor nanoparticles.It is worth noting that,because the thickness of these nanosheets can be controlled with atomic precision,line broadening related with particle size distributions was not observed,with corresponding demonstrations in their absorption and emission spectra.These II-VI particles have unique spectral characteristics,such as fast fluorescence lifetime and extremely high color purity(its photoluminescence full width at half maximum is very narrow)and wide absorption range.Another interesting results of nanocrystalline research is the discovery of so-called magic size nanoclusters(MSC).MSC has special properties different from normal NC:the characteristic of MSC is that the absorption peak is narrow,with the reaction going on,the growth-related red shift moves in discontinuous steps.Researchers predict that MSCs have a closed shell configuration and accurate stoichiometry,size,and shape,but the exact structure of these MSCs are still elusive.The particularity of MSCs are not only due to the discovery of new species,but also due to the intermediate role of MSCs in the formation of semiconductor nanocrystals.Although a lot of work has been done in the past few years,the scientific community has not reached a consensus on the exact composition,structure,and formation mechanism of MSC.Many have described MSC as an intermediate for the formation of conventional NC.Further applications of MSC and more effective investigations need to be explored by the peers in the field.In this paper,the synthesis and properties of a series of ZnSe nanoclusters,as well as the mutual transformation of ZnSe magic size nanoclusters were studied.The specific research contents are as follows:(1)In Chapter 2,a series of two-dimensional hexagonal wurtzite ZnSe NPs were synthesized by hot injection using the mixture of oleylamine(OLA)and octylamine(OTA)as the solution and zinc halide and selenium powder as the reaction precursor.They were named NP292,NP324 and NP347 according to their first exciton peak.The temperature has the greatest influence in the reaction process.The aforementioned three kinds of NPs can be obtained at 110?,135?,and 175?,respectively.The three kinds of NPs have high thermal stability,different shapes,and different properties.The initial temperature is too low to make NP292 fragments into a whole platelet,in addition,NP324 can hardly get rid of the interference of by-products.We improved the defect of NP292 by adding reaction fluid continuously and obtained single product of NP324 by changing the reaction precursor.(2)In Chapter 3,we obtained four MSCs,named MSC298-oleylamine,MSC298-mixed amine,MSC292 and MSC314 according to corresponding optical absorption.The peaks of all MSCs were very narrow and separated.We discussed the role of amines in the growth of MSC and found that it played a very crucial role.First of all,MSC298 was induced to be synthesized by amines.This process has great specificity that is not affected by the type of amines and the proportion of mixed amines or whether they are mixed or not.MSC298 is unstable and will decompose if further heated.Then two identical MSC298 with different solutions will generate MSC314 and MSC292 under the templates of oleylamine and mixed amine,respectively.Finally,four molecular formulas of MSC were proposed based upon corresponding characterizations and calculations.The molecular formulas of two MSC298 are Zn₆Se₈-(5OLA)and Zn₆Se₈-(2OLA+3OTA),MSC314 and MSC292 are Zn₆Se₆-(1OLA+3OTA)and Zn₁₃Se₁₃-(8OLA)respectively.