Chemical Reactions of Downstream Microwave Plasma to the AlkanethiolateSelf-Assembled Monolayers on Gold Surface

• Main Authors: Chih-Chiang Weng, 翁志強
• Other Authors: Jiunn-Der Liao
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/94961550175992712769

碩士 === 中原大學 === 醫學工程研究所 === 89 === Low-temperature plasma processing has been greatly considered as a vital technique for polymer surface modification. According to the characteristic of plasma generation, the applied processing parameters and the type of gas plasma, the organic substrate may arise some effects such as polymerization, superficial chemical reactions and cross-linking and create specific, applicable and functionalized surfaces. This study utilizes self-assembled monolayers of the octadecanethiol (C18H37SH, or ODT) on Au(111) surface to simulate an organic structure with well-packed and long carbon chains. In this experiment, downstream N2 microwave plasma is generated by 80W under 1 torr; plasma-induced chemistries on the ODT/Au surface are studied. Using Langmuir probe, the state of electron temperature and the electron (or ionization) density are statically measured; they provide valuable information to adjust changing condition in practical plasma applications. The effect of UV generated in plasma, for the wavelengths higher than 200nm, to ODT/Au is also evaluated. Water contact angle and X-ray Photoemission Spectroscopy (XPS) measurements are applied for verifying structural modification at surface. Experimental result has indicated that current downstream plasma provides plasma density of ca. or electron temperature of ca. 0.46eV; it is regarded as low-density plasma. Surface analyses by XPS have revealed that after N2 plasma treatment, new chemical bonds such as C-N, C-O, C=O and O=C-OH are formed on the modified ODT/Au surface. These polarizable groups arise a hydrophilic characteristic at surface and decrease water contact angle from 120o to 18o. Analytical result also implies that N2 plasma takes O2 and reacts with ODT/Au within 10sec. After 30sec of plasma treatment, the C/Au ratio decreases, which is correlated with etching effect on the ODT/Au surface. After 60sec of plasma projection onto the ODT/Au surface, all N, O and C elements are decreased, however, relatively small decrease ratio of C is found, which may be directed to the formation of cross-linked structure at surface. Moreover, for introducing UV generated in plasma, wavelengths longer than 200nm and up to 120sec, the ODT/Au structure is insignificantly affected. This consequence has confirmed that UV produced in low-density plasma does not have the capability to provoke chemical reactions with the ODT/Au surface.