Solution Synthesis, Growth Mechanism, And Property Investigations Of Chalcogenide Semiconductors In Nanoscale With Ploynary Structrure And Shapes

Colloidal monodisperse semiconductor sulfides often exhibit some novel optical, electronic, magnetic, mechanical, and piezoelectricity properties which cannot be obtained in their bulk counterparts due to the obvious quantum confinement effect and size- and/or shape-dependent properties. Therefore, these semiconductor nanocrystals have been widely applied in many technological fields,e.g., electroluminescent devices, photovoltaic solar cell, catalyst, magnetic recording materials, biological labeling and diagnostics, light-emitting diodes, gas-sensors, lasers, and single-electron transistors, etc. Moreover, research indicates the material performance and application are not only decided by its phase, composition, and structure, but also the size and shape. Thus, structure and/or shape controlled synthesis of colloidal monodisperse semiconducting nanomaterials will not only bring the theoretically progresses, but also extend the corresponding application field. Binary or ternary semiconductor chalcogenides, e.g. CuS, In2S3, NiSe2, CuInS2 and AgInS2 are several very important functional materials and have been widely used in solar cell, catalysis, luminescence, piezoelectricity, magnetic materials, and linear or nonlinear optic devices, etc. Therefore, they have attracted increasing research interests from many applied areas. In this thesis, we have synthesized quasi-2D hexagonal CuS nanoplatelets with the self-assembling tendency by virtue of a simple moderate toluene solvothermal method. Changing different solvent, we also successfully synthesizedβ-In2S3 nanobelts with the 1D and 2D properties for the first time. Optical and photo-catalytic performances of the as-synthesized nanobelts were investigated. Subsequently, monodisperse ternary chalcogenide CuInS2 and orthorhombic AgInS2 nanocrystals were synthesized in higher efficiency by a facile, inexpensive anisole solvothermal method. Finally, NiSe2 nanostars with six symmetrical horns were firstly prepared by solvothermally reducing Se method. Detailed research contents are summarized as following:(1) Shape-Controlled synthesis and self-assembly mechanism of hexagonal CuS nanoplatelets. Hexagonal CuS nanoplatelets have been synthesized via a simple toluene solvothermal method. Adjusting experimental parameters, they could self-assemble into columnar, raft-like and layered nanostructures. It has been proven that hexagonal plate-like shape originated from the growth limit along <001> direction and the accelerating growth along six equivalent <110> directions. From further researches, it was found that the special crystal structure, surfactants, van der Waals action and packing entropy mechanism result in the formation of hexagonal CuS nanoplatelets and the multilevel self-assembling forms.(2) Shape-controlled synthesis, optical and catalytic properties ofβ-In2S3 nanobelts. Cubicβ-In2S3 nanobelts were prepared for the first time by pyridine solvothermal route which were resulted from the preferential growth along <220> direction and enclosed by {202} and {02-2} crystallographic facets. The strong quantum confinement effect in Uv-vis spectra and the blue emission in PL spectra implied it as a promising candidate for phosphor in display devices. The well photo-catalytic effects indicatedβ-In2S3 nanobelts were likely applied as a new kind of photocatalyst in the future.(3) Solution-controlled synthesis of colloidal, monodisperse ternary chalcogenide nanocrystals. Highly crystallized, monodisperse, single-crystalline CuInS2 in truncated pyramidal shape and orthorhombic AgInS2 in rectangular shape nanocrystals with the uniform shape and narrow size-distribution were successfully synthesized via a convenient, surfactant-modified, anisole solvothermal process. From the HRTEM and crystal structure analysis, it was proved that pyramidal shape of CuInS2 originated the preferentially growth along positive polar face and retarded growth along negative polar face,and the rectangular shape of AgInS2 originated the similar growing speed along [100], [010] and [001] three directions. Moreover, the formation and/or crystal phase of monodisperse CuInS2 and AgInS2 colloids were strongly influenced by many external factors, e.g., temperature, time, capping regents, and solvent, etc. The well absorption in the range of visible wavelength at room-temperature means that the obtained CuInS2 colloids may favor its application as solar absorber. Additionally, because the donor defect Cui occupies the two different interstitial positions within the chalcopyrite lattice and the acceptor defect VIn resides at a cation site next to it, the combination of donor-acceptor defect pairs in different distance resulted in the two subbands in CuInS2 PL spectra. This inexpensive anisole solvothermal method extended the field of organic solution phase pyrolysis or the area of the traditional solvothermal process, and paves a new way for the synthesis of other important pure or doping ternary functional materials.(4) Solution synthesis and growth mechanism of symmetrical six-horn nickel diselenide nanostars. Symmetrical six-horn nickel diselenide nanostars were firstly synthesized with selenium powder as precursor but without any external reducing agents. Each nanostar consisted of a central core and six symmetrical nanohorns. The formation of six-horn star-like nickel diselenide was controlled by the oriented attachment mechanism and secondary crystallizing process: i.e., primary building particles oriented attaching along six {100} faces, the formed mesocrystals secondarily crystallizing and finally resulting in six-horn nanostars. This method without any external reducing agents also provided a facile, convenient synthetic route for other selenium compounds.