| With a wide direct band gap of 2.67 eV at room temperature, zinc selenide (ZnSe) has been widely investigated for its potential applications in short-wavelength optoelectronic devices, such as light emitting diodes, laser diodes. In this essay, ZnSe nanowires were fabricated by the method of pulsed laser deposition (PLD). And the characterization, growth mechanism and application in polymer/inorganic of the as-growth ZnSe nanowires were studied.There are three sections in this thesis:In the first part, the synthesis and characterization of the ZnSe nanowires were introduced. The ZnSe nanowires were deposited on the Si (100) substrate by the method of PLD.The sample preparation involves two steps. In the first step, catalyst (Ni or Au) intermediate layers of about 20-30nm were deposited on Si (100) substrate by the PLD with a laser repetition of 5HZ without background gas and substrate-heating. In the next step, the ZnSe nano-crystals were grown on the heated Ni/Au-catalyst coated substrates by the PLD. The morphologies of the as-grown ZnSe nano-crystals were examined by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), and their crystalline structures and compositions were characterized by selected-area electron diffraction (SAED) and energy dispersive spectroscopy (EDS) fitted on the TEM. From the result of SEM, there are a large number of nano-needles densely covering and randomly oriented on a Si (100) substrate. The average length of the as-grown nano-needles is about 200nm, and their distributive density is about 8 x 109 cm-2. The XRD result shows polycrystallinity of the ZnSe nanowire cluster. There are several peaks appear at 27.1°,45.2°, and 53.6°that are attributed to ZnSe (111), (110), and (112) peaks, respectively. ZnSe (111) peak, much higher than the other ZnSe peaks, is the preferred growth orientation of the ZnSe nanowires. Both the HRTEM image and SAED pattern demonstrate that the as-grown ZnSe nanowire was well crystalline.The results of Ultraviolet-visible absorption spectrum andphotoluminescence of ZnSe nanowires showed that compared with bulk ZnSe materials, ZnSe nanowires absorption peaks and band emission peak has significant blue shift. These results indicate that the band gap of ZnSe increased because of quantum effect.In the second section, the effects of experiment conditions on the growth of ZnSe nanowires were researched including substrate material, catalyst layer, substrate temperature and deposition duration. Two models for the growth of the ZnSe nano-needles and sphere-leading nano-wires under different substrate temperatures are proposed and verified experimentally. It is indicated that the substrate materials have great effects on the ZnSe nano-structures grown on them. There are a large number of nanowires densely covering and randomly oriented on a Si (100) substrate. And ZnSe nano-particles other than nanowires were grown on a sapphire (0001) substrate. While a number of ZnSe nano-rods were grown on a fused silica substrate. The lengths, diameters and distributive densities of the as-grown ZnSe nano-needles increase with the increment of the deposition duration. The ZnSe nano-needles could be grown on Ni-coated substrates with temperatures of 300-400℃and Au-coated substrates with a temperature of 300℃, while the winding nano-wires with catalyst sphere on the tops were grown on Ni-coated substrates with a temperature of 450℃and Au-coated substrates with a temperature of 400℃. There are no nano-needles or nano-wires grown on the substrate with a temperature of 200 or 500℃due to unmeltedness of catalyst layers or extreme instability of catalyst islands.In the third part, the potential application of ZnSe nanowires in organic/inorganic compound solar cell was studied. Organic solar cells have attracted considerable attention due to their potential advantages such as low production cost, processing at room temperature, and mechanical flexibility. However, exciton separation efficiency is very low in organic polymer, resulting in low efficiency of polymer solar cells. To improve the solar cell performance, inorganic nanostructures were employed in the photovoltaic devices. In this research, based on the ZnSe nanowires cathode, a five-layer composite structure of polymer/inorganic hybrid solar cell has been designed. The ultraviolet-visible absorption spectrum andⅠ-Ⅴcharacter results indicate that the existence of ZnSe nanowires benefits the light absorption of the polymer/inorganic hybrid solar cell. ZnSe nanowires have a great potential in improving efficiency of polymer/inorganic solar cell. |
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