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题名: 功能有机分子在石墨表面自组装结构的STM研究
作者: 王亚敏
答辩日期: 2014-05-26
导师: 袁群惠
专业: 材料工程
授予单位: 中国科学院大学
授予地点: 北京
学位: 硕士
关键词: 自组装 ; 扫描隧道显微镜 ( STM ) ; 高定向裂解石墨(HOPG) ; 温度 ; 溶剂 ; 荧光
摘要:
具有特殊物理化学性质的功能有机分子由于其可以在基质表面形成结构多样的分子自组装膜而具有良好的应用前景。因此,研究基于功能有机分子的表界面分子自组 装膜结构已成为成为分子传感器领域的研究热点之一。分子自组装膜中分子的排列结构是影响分子传感器性能的重要因素之一,因此研究功能有机分子在表面的自组 装结构是很有必要的。 有机分子在表面的自组装结构的影响因素有温度、溶剂、基底、浓度、光照和电磁场等,通过选择合适的条件,将有可能得到目标的分子组装结构。本论文利用扫描 隧道显微术(STM)研究了三种功能有机分子在非共价键相互作用驱动下的分子自组装,探讨了温度、溶剂等对分子在石墨表面的自组装结构和形态的影响,并分 析了基于同源分子的不同的分子组装结构对组装膜性能的影响。本论文的研究内容和结果如下: 1.利用STM研究了CuPcOC8分子在HOPG表面的自组装结构并分析了温度对组装结构的影响。室温下CuPcOC8分子在HOPG表面可以同时形成 分子密度较低的四次对称结构和分子密度较高的六次对称结构。通过提高分子自组装时的温度或对室温下组装好的分子层进行退火处理,观察到了四次对称结构向六 次对称结构转化的现象。通过对在不同条件下获得的分子组装层的STM图像中四次对称和六次对称结构所占比例的统计分析,揭示了CuPcOC8分子在 HOPG表面的两种组装结构的形成机制和大气环境下这种铜酞菁分子组装结构的可调性。四次对称结构和六次对称结构之间存在着一个能垒,六次对称结构是热力 学稳定的结构,而四次对称结构是热力学不稳定但是在动力学上有利的结构。因此通过选择合适的温度或给予充足的组装时间就可以获得组装结构均为六次对称的大 范围均匀一致的分子自组装膜。 2.利用STM研究了PTB分子和PTB-C18分子在HOPG表面的自组装结构。在乙醇、辛醇和辛酸三种溶剂条件下PTB-C18分子自组装结构不同。 同时对比分析了由于组装结构的不同导致的PTB分子和PTB-C18分子在石墨表面形成的自组装层的荧光性能的不同。实验表明PTB分子组装层仍然具有荧 光性能且可以实现对水中Hg2+的荧光响应;而PTB-C18分子组装层则没有荧光性能且对水中Hg2+没有荧光响应性。
英文摘要: Functional organic molecules bearing unique physical and chemical properties make them to be promising in the application of molecular devices owing to the various self-assembled structures they formed on diversified substrates. Therefore, the investigation of the self-assembled structures on surfaces or at interfaces has become one of the hotspot in the field of molecular sensing devices. It is known that the performance of molecular devices would be strongly relied on the spatial arrangement of every molecular building blocks in the self-assembled films, thus the investigation of self-assemblies of functional organic molecules on solid substrates is an important perquisite. Environmental factors such as temperature, solvent, substrate, concentration, light and electric/magnetic fields are all important controlling factors for the self-assemblies of organic molecules on substrates. With proper selection of environmental conditions, the target assembling structures of the functional organic molecules can be obtained. In this thesis, we investigated the morphologies of three kinds of functional molecules self-assembled monolayers driven by non-covalent interactions, and explored the effects of temperature as well as various solvents on the assembling structures on highly oriented pyrolytic graphite (HOPG) by scanning tunneling microscopy (STM). Besides, the effect of different self-assembled structures with homologous molecules on the performance of the films was also studied. Our research contents and main conclusions have been summarized as follows: 1. The self-assemblies of CuPcOC8 molecules on HOPG surface and the temperature dependent structural transition have been investigated by STM. It is shown that copper(II) 2, 3, 9, 10, 16, 17, 23, 24-octakis(octyloxy)-29H, 31H-phthalocyanine (CuPcOC8) molecules can self-organize on highly oriented pyrolytic graphite and form both quartic symmetry structures with relatively low molecular packing density and hexagonal symmetry structures with high packing density at room temperature. Besides, by increasing the temperature during the self-assembly process, or applying an annealing treatment to the self-assembled film, the transition of the self-assembled structure from quartic to hexagonal symmetry was observed. With images obtained with scanning tunnelling microscopy under different conditions and statistical analysis of the ratios of the quartic to hexagonal domain areas, the mechanism of the formation of the two types of molecular adlayers, and the tunability of this metal phthalocyanine film in ambient atmosphere has been revealed. That is, there is an energy barrier between the quartic and the hexagonal structures. The hexagonal phase corresponds to a thermodynamically stable state while the quartic phase is kinetically favorable but thermodynamically metastable. Therefore, with a proper selection of temperature or given enough time, uniform ordered 6-fold symmetry assembly motifs of CuPcOC8 molecules in large scale can be obtained. 2. Self-assembly structures of PTB and PTB-C18 on HOPG was also investigated by STM. Ethanol, 1-octanol and octanoic were used as solvents and different kinds of self-assembling arrangements of PTB-C18 on HOPG was obtained. As comparison, the different fluorescence properties of the films on HOPG caused by the difference of assembled structures were analyzed. We found that films of PTB were still keeping fluorescence properties on HOPG and would be able to detect Hg2+ in water solution due to the changes of the fluorescent signals, while the films of PTB-C18 shown restricted fluorescence properties on HOPG and thus was incapable of detecting Hg2+ in water.
内容类型: 学位论文
URI标识: http://ir.xjipc.cas.cn/handle/365002/3405
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作者单位: 中国科学院新疆理化技术研究所

Recommended Citation:
王亚敏. 功能有机分子在石墨表面自组装结构的STM研究[D]. 北京. 中国科学院大学. 2014.
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