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An Electrochemical and STM Study of Fluorosurfactant FSN Self-assembly on Gold Single Crystal Surfaces

Author: TangYongAn
Tutor: YanJiaWei；MaoBingWei
School: Xiamen University
Course: Physical and chemical
Keywords: Fluorosurfactant Self-assembly Single crystal Electrochemistry Scanning tunneling microscopy
CLC: O647.2
Type: Master's thesis
Year: 2009
Downloads: 126
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Abstract

Surface self-assembly of organic molecules is an attractive way to functionalize solid surfaces. Scanning Tunneling microscopy is a powerful tool and has been wildly used in the investigation of SAMs. By designing and choosing different self-assembled molecules, surface with different properties such as wettability, adhesion, and lubricity can be obtained. In recent years, SAMs based on physically natured surface-molecule interaction have attracted increasing attention, motivated by their potential applications in lubrication, thin film-based electronic devices, and novel molecular devices. Preparing SAMs with different molecules is highly desirable, which would benefit wider applications of the SAMs. However, because of weakness of SAMs, such as the weak interaction of physical adsorbed SAMs and the defects in chemical adsorbed SAMs, the applications of SAMs are insufficient.In view of the current research status and the problems encountered in the SAMs, we used Electrochemistry and STM to study the structure of FSN on Au single crystal. The main research contents and conclusions are listed as follows:1、Using STM, AFM and Contact angle and XPS to characterize the structure of Nonionic Fluorosurfactant Zonyl FSN SAMs on Au(111). The results revealed that the FSN forms SAMs on Au(111) with very large domain size and almost no defects. A (√3×√3)R30°arrangement of the FSN SAM on Au(111) is observed, which hydrophobic tails out to the air. The SAMs show excellent chemical stability and last for at least a month in atmospheric conditions. This kind of SAMs provides a comprehensive application. Furthermore, The experiment of AFM、Contact Angle、XPS demonstrated that the formation of FSN molecules is hydrophilic tails molecules toward the Au(111) substrate and the hydrophobic tails toward air. In addition, the rigid nature of FSN molecular performed an important role in the process of SAMs. The suitable force between FSN and the movement characteristic of FSN are the key factors for forming highly order FSN SAMs. 2、Using STM, AFM and Contact angle to characterize the SAMs on Au(100). The results revealed that the FSN forms SAMs on Au(100) are unique and different with the formation on Au(111). A (?) arrangement of the FSN SAM on Au(100) is observed. Because of the short distance of [0(?)1] direction in Au(100) surface, the structure of the FSN SAMs on Au(100) existed more defects when compared it with FSN on Au(111). And we also found the movement of Au atoms in the Au(100) surface. Furthermore, the length of SAMs molecule can affect the formation of SAMs. The SAMs of FSO, which less length than FSN, can form a SAMs content more defect, which present as molecules missing. The experiment of AFM、Contact Angle、XPS demonstrated that the formation of FSN molecules is hydrophilic tails molecules toward the Au(100) substrate and the hydrophobic tails toward air.3、By employing cyclic voltammetric and ECSTM measurements, we study the behaviors and properties of FSN on Au(111) and Au(100). And try the primary experiment of deposited Cu metal layer on the SAMs. The results revealed that FSN formed a same formation as it did in air at double layer range, a (√3×√3)R30°arrangement of the FSN SAM on Au(111) is observed. The SAMs was deoxidized and desorbed at -0.3V, oxidized and desorbed at 1.2V, and the adsorption of FSN can delay the oxidation of Au(111) surface. On Au(100) substrate, the FSN SAMs has an formation change in order to form a more denseness formation at double layer range, which ascribed to the congregation of negative charge. The SAMs was deoxidized and desorbed at -0.35V, oxidized and desorbed at 1.2V, and the adsorption of FSN can delay the oxidation of Au(100) surface.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > The physical chemistry of surface phenomena > Surfactant chemical
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