Fabrication Of Semiconductor ZnO Micro/nano Structures And Study Of Their Properties

In this paper, ZnO micro/nanostructures with various morphologies, such as stepped nanocombs, nanorods, nanowires, nanobelts, nanorods with ～30nm pinheads, nanonunchakus, brush pen-like nanostructures, nanoflowers made up of nanorods, nanodisks and nanoflowers composed of nanoplates and so on, have been synthesized using different methods, including thermal evaporation, treatment through chemical solution and hydrothermal. Growth mechanisms of some samples were discussed, such as nanocombs, nanobelts, nanorods with ～30nm pinheads and nanonunchakus. We analyzed and discussed the photoluminescence and field emission properties of some products. Main works and innovations in this paper are as follows:1. Stepped ZnO nanocombs and nanorods were fabricated by the conventional thermal evaporation in the early experiments. Meanwhile, unorderly nanowires, nanocombs with different morphologies were obtained by changing the growth temperature. The morphology and structure of the as-grown samples were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The crystal property of the stepped nanocombs was characterized using selected area electron diffraction (SAED). According to the experimental results, the stepped ZnO comb-like structures could be formed by the following steps: the first is a faster growth along [01-10] direction forming the nanobelt stems, and they were enclosed by the ±(0001) side facets and ±(21|-1|-0) top/bottom facets; the second step is the nucleation and growth of the nanorod branches along [0001] direction synchronously, which may be related to the structure characteristic of wurtzite family.2. ZnO nanorods with ～30nm diameter ultra-thin pinheads and ultra-thin nanobelts were synthesized using thiourea solution to etch nanorods and nancombs, which were obtained by conventional thermal evaporation method. EDX measurement was performed in order to determine the components of the nanorods with ～30nm diameter ultra-thin pinheads and ultra-thin nanobelts. The possible formation of the nanorods with ～30nm diameter ultra-thin pinheads and ultra-thin nanobelts were proposed. Finally, the photoluminescence and field emission properties of the sample before and after treatment through Tu solution., indicating that H⁺ ions in the Tu solution not only determine the formation of nanorods with ～30nm diameter ultra-thinpinheads and ultra-thin nanobelts but also play an important role in the improving the physical properties of the obtained samples treated through Tu solution.3. Only (Zn(NO₃)₂·6H₂O) and (C₆H₁₂N₄) were used to successfully synthesize ZnO micro/nanostructures with various morphologies, such as flower-like structures, brush-like structures, nanodisks and nanonunchakus, by a low-temperature hydrothermal route. Parallel experiments were performed by changing growth conditions, such as solution concentration, substrates and "temperature change". The formation processes of the brush pen-like nanostructures which ultimately lead to the formation of ZnO nanonunchakus have been proposed according to the experimental data. Room photoluminescence of the flower- and brush pen-like structures were studied.4. ZnO micro/nano flower-like structures have been synthesized in the high yield using only (ZnCl₂) and (NH₃·H₂O) by a low-temperature hydrothermal route. This chemical solution route has become another promising option for large-scale production of micro-/ nano-scale materials because of its simple, fast, less expensive, low-temperature growth and no pollution to the ambient environment virtues. Compared with other chemical solution methods, only two chemical reagents were used in this route without any other additive, so the fabrication cost was low and the obtained samples have high purity. These ZnO flower-like structures are made up of hexagon plates. Becausing of their high ratio of aspect to volume, they have potential application in chemical sensors, photocatalysts and optical storages and so on. And some as-synthesized samples were charactered using SEM, XRD, EDX and PL. Parallel experiments were performed by changing the solution centration, reaction time, substrates, and pH values. Room photoluminescence of the rose-like structures was investigated and the mechanism of blue and green bands was discussed in brief.