Solution Synthesis, Growth Mechanism, And Property Investigation Of Multinary Oxygen Group Semiconductors In Nanoscale

Comparing with binary compounds, multinary oxygen-group compounds exhibit useful physical and chemical properties such as optical, electronic, magnetic, mechanical, and piezoelectricity properties. Therefore, the synthesis of multinary oxygen-group compounds is becoming an active area of solid state chemistry. Solvothermal reaction is motivated by their potential to provide an access to multinary oxygen-group compounds in nanoscale with obvious quantum confinement effect and size- and/or shape-dependent properties. However, the synthesis such of multiple component nanocrystals has been limited by the reactivities of the precursors and the ease of phase separation of the alloyed constituents. In other words, if the reaction activities of two metal precursors differ from each other, a separated nucleus will be generated and grow into heterostructures or even two compounds, especially to form the less solubility of transition metal oxide, sulfide or selenide, which make the number of known synthetic multinary oxygen-group compounds with metal ions is limited. Thus, structure and/or shape controlled synthesis of multinary oxygen-group semiconductor nanomaterials will not bring the theoretically meanings, but also the application significance which extended the semiconductor materials. In this thesis, we have attempted and extended to synthesis multinary oxygen-group semiconductor nanomaterials with new chemical synthetic method and thought, which gathered experience for controlled synthesis of multinary oxygen-group semiconductor nanomaterials. Detailed rerearch contents are summarized as following:(1) Controlled synthesis and synthesis mechanism of ZnGa2O4 nanocrystals and their research of optical properties. Truncated cubic shape of ZnGa2O4 nanocrystals with 20 nm have been synthesized via a simple anisole solvothermal method. The as-prepared ZnGa2O4 nanocrystals emitted strong blue light at 435 nm. By adjusting zinc quantum of precursors, solid solutions serial nanocrystals of cubicγ-Ga2O3 and cubic ZnGa2O4 that also be expressed to ZnχGa2O3+χ(0≤χ≤1) could be obtained. The lattice parameters and band gap Eg of ZnχGa2O3+χ(0≤χ≤1) serial nanocrystals changed linearly which consistent with Vegard's law basically. The Eg of ZnχGa2O3+χ(0≤χ≤1) serial nanocrystals ranged from 4.43 to 3.70 eV and could be tuned their emission spectra from 395 to 435nm. The formation of ZnχGa2O3+χ(0<χ<1) and ZnGa2O4 resulted from Zn2+ (came from dissociated amorphous ZnO) diffusing into theγ-Ga2O3 nanocrystal lattice structure. In the process of Zn2+ diffusing into nanocrystal lattice, the oxygen vacancies were gradually extinguished making distorted Ga-O octahedron transforming to regular one which is the self-activated blue emission site. In the hydrothermal reaction system, ZnGa2O4 and ZnAl2O4 nanocrystals with regular octahedron were obtained. With the blue fluorescent material ZnGa2O4 regular octahedrona nanocrystals as basilar material doped with Mn2+ and Cr3+, we successfully gained green and red fluorescent respectively and achieved the three primary colors.(2) Shape-Controlled synthesis of AgGaS2 nanocrystals and their research of optical properties. Nearly monodispersed AgGaS2 nanocrystals with flower-like or colloidal shape were synthesized in a simple solution system, in which a mixture of 1-octyl alcohol and cyclohexane was used as reactive medium and oleylamine as surfactant. The shape and size of these as-prepared nanocrystals could be tuned effectively by controlling the reaction conditions, such as the ratio of octanol to cyclohexane, the length of carbon chain of fatty alcohol and the concentration of oleylamine. The results showed that fatty alcohol play key factor for the shape and size transformation of AgGaS2 from 3D nanoflowers (50 nm) to colloids (10-20 nm), and a plausible shape evolution and crystal growth mechanism have been suggested for the formation of 3D nanoflowers and colloids. The simple reaction system might provide a new approach to controlled synthesis ternary nanomaterials and understood the reaction mechanism along with the growth kinetics of nanocrystals. Oleylamine combined with alcohol to absorb the AgGaS2 nanocrystals which could reduce the total surface energy and protect the nanocrystals. From the HRTRM and crystal structure analysis, monodispersed AgGaS2 nanoflowers were built by primary spherical nanoparticles with 5nm which prefer to grow along<112> direction. There were no obvious difference in UV-vis spectra between AgGaS2 nanoflower-like particles and colloids and the room temperature photoluminescence spectra of AgGaS2 colloids red-shifted 12 nm compared to that of AgGaS2 nanoflowers. The surface photovoltage (SPV) properties of AgGaS2 nanoflower powders were consistent with their UV absorption and their photovoltage response became stronger when an extra electric field increased which implies that AgGaS2 can absorb photons and separate electron- hole pairs in the built-in electric field. In the same reaction system, we can also obtained orthorhombic AgInS2 nanocrystals and AgInχGa1-χS2 (O≤x≤1) quaternary solid state serial nanocrystals.(3) Solution-controlled synthesis of CulnSe2, CuGaSe2, CuInxGa1-χSe2 hexangular nanoplatelets. We first applied two-step and DMF solvothermal method to synthesize ternary or quaternary selenide hexangular nanoplatelets, which provided a new strategy to resolve selenic source with Vc as reduce regent. CulnSe2 hexangular nanoplatelets with two dimensions were tetragonal chalcopyrite structure and their size was about 200 nm. From the HRTEM and crystal structure analysis, it was proved that CulnSe2 hexangular nanoplatelets with monocrystalline structure originated the preferentially growth along<112> and<001> two directions and the growth of <101> direction was limited. Moreover, the formation and/or crystal phase of monodisperse CulnSe2 hexangular nanoplatelets were strongly influenced by many external factors, e.g., pre-treating time, PVP quantum, Vc quantum, temperature, reaction time, etc. The 7days stability analysis of CulnSe2 hexangular nanoplatelets dispersed in alcohol proved that there was no change from transmission light and backscattering light. In other words, there was no phenomenon such as precipitate, emulsification, flocculation, condense, phase seperation, edc. in the 7days and could be a good "ink" for screen painting that was applied to make soft film solar cell. In the same reaction system, we can also obtained CuGaSe2 hexangular nanoplatelets. By adjusting the proportion of In/Ga, CuInχGa1-χSe2 quaternary selenide hexangular nanoplatelets also could be obtained. UV-vis absorption spectra of CuInχGa1-χSe2 (0≤x≤1) serial nanocrystals ranged 900～1300 nm and their Eg value ranged 0.95-1.46. The two-step method was widespread application for synthesis of multinary chalcogenidometalates. Spherical CuInSe2 in nano scale was obtained in the reaction system of CH3CH2OH-HOCH2CH2NH2. Using of CuInχGa1-χSe2 as absorption material, Ag/CdS/CuInχGa1-χSe2/FTO solar cell has been completed.