芳香基鹵化物在鍺(100)表面上之吸附與熱分解反應

Adsorption and Thermal Decomposition of Halo Aromatic Compounds on Ge(100) Surface

翁瑋君(Wei-Chun Weng)

指導教授 ： 洪偉修

國立臺灣師範大學/理學院/化學系/碩士(2010年)

摘要

利用程溫脫附質譜與X光光電子能譜來研究苯環(C6H6)與芳香基鹵化物(C6H5Cl、C6H5Br、C6H5I、C7H7I以及C8H9I)於鍺(100)表面的吸附與熱分解反應。
芳香基碘化物在鍺(100)表面上具有較高的反應性。在105K時，苯、氯苯及溴苯皆以分子形態吸附於鍺(100)表面，當升溫至220K~270K後以完整的分子形態脫附。碘苯除了以分子形態吸附外，並會斷C-I鍵進行分解，所有化學吸附的碘苯分子在525K時即全數分解為表面苯基與碘基。而當溫度高於620K，此時會有兩競爭反應─苯環的再結合脫附與表面苯基的分解。根據TPD質譜 ，我們認為苯基在鍺(100)表面上存在兩種不同能量的吸附形態─傾斜站立構形與平躺構形。
為了得到更多關於此兩種吸附形態的資訊，我們進一步研究了其它的芳香基碘化物(C7H7I和C8H9I)。在105K時，2-甲基苯和1,3-二甲基-2-碘苯皆是以分子形態吸附於表面上，並在升溫至420K後，斷C-I鍵分解。結果發現兩化合物較低溫的吸附態僅於高曝露量時出現，且1,3-二甲基-2-碘苯不同於其它的芳香基碘化物，於高溫未發現有芳香基重結合脫附的現象。這篇論文並針對前述所有化合物在鍺(100)表面的反應機制加以討論。

關鍵字

鍺 ； 芳香基鹵化物

並列摘要

The adsorption and thermal reactions of benzene (C6H6) and halo aromatic compounds (C6H5Cl, C6H5Br, C6H5I, C7H7I, and C8H9I) on Ge(100) were studied with temperature-programmed desorption (TPD) and X-ray photoelectron spectra (XPS) using synchrotron radiation.
Iodo aromatic compounds are more reactive and undergo the breakage of the C-I bond on Ge(100), compared to other halo aromatic compounds. Benzene, chlorobenzene, and bromobenzene adsorb molecularly on Ge(100) surface at 105K and desorb intact after raising the sample temperature to 220K~270K. Iodobenzene adsorbs molecularly and dissociatively at 105K. All chemisorbed iodobenzene molecules dissociate to form the surface benzyl groups and iodo groups at 525K. Upon to 620K, there are two competitive reactions - recombinative desorption of benzene and decomposition of surface benzyl groups. According to the TPD spectra, we propose that there are two adsorption states─the lifted structure and the parallel structure─for the benzyl groups on Ge(100).
Other iodo aromatic compounds, C7H7I and C8H9I, are also studied to provide more information about the two adsorption states. At 105K, both 2-iodotoluene and 1,3-dimethyl-2-iodobenzene adsorb molecularly and dissociate via scissoring the C-I bond by raising the sample temperature to 420K. A molecular desorption state appears only at large coverages and however, the recombination reaction is absent for thermal reaction of 1,3-dimethyl-2-iodobenzene. The corresponding reaction mechanisms of the iodo aromatic molecules on Ge(100) are proposed and discussed in this dissertation.

並列關鍵字

Ge ； Halo Aromatic Compounds

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