氯化氫與氯氣在Ge(100)表面的吸附與熱分解反應
No Thumbnail Available
Date
2013
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
我們利用程溫脫附質譜(TPD)及X光光電子能譜(XPS)研究氯化氫(HCl)及氯氣(Cl2)在鍺(100)表面的吸附及熱分解反應。
於105 K，曝露氯化氫於鍺表面，最初只出現分解吸附(Ge-H、Ge-Cl)；當曝露量增大，伴隨有未分解吸附，依照曝露量多寡，在275 K未分解的氯化氫會分解並持續以分解吸附的型態吸附於表面；當溫度升至675 K時較弱的Ge-H鍵先斷，經由再結合形成H2、HCl脫附，而殘餘分解吸附的Cl則於700 K時Ge-Cl鍵斷裂，形成GeCl2脫附。因此氯化氫在鍺(100)表面熱分解的產物為H2、HCl、GeCl2。
為了更進一步了解氯在鍺(100)表面吸附的情形，將HCl的H置換成Cl，探討分子組成均為氯在鍺表面的吸附情形，並與氯化氫比較。發現兩者在鍺(100)表面於曝露量大時，均有未分解吸附的吸附態，但結構不同，氯氣之分子吸附態於225 K開始形成GeCl4脫附。兩者相似的是，室溫後均為分解吸附情形，故有相似的反應路徑，不同的是氯氣均為Ge-Cl吸附情形，無H存在，故於700 K時Ge-Cl鍵斷裂，形成GeCl2及微量Cl2脫附。因此氯氣在鍺(100)表面熱分解的產物為GeCl4、GeCl2、Cl2。
The adsorption and thermal reactions of hydrogen chloride (HCl) and chlorine (Cl2) on Ge(100) surface were studied with temperature- programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). The desorption products of thermal reactions were monitored with TPD and the reaction intermediates were identified with XPS using synchrotron radiation. At 105 K, HCl molecules adsorb dissociatively at the initial exposure. The molecular adsorption of HCl appears at high exposures and chemisorbed HCl molecules become dissociated at 275 K. On annealing to 675 K, surface Ge-H bonds break and desorb as H2 and HCl with recombination of H(ad)+H(ad) and H(ad)+Cl(ad). At 700 K, The Ge monochloride (GeCl) cleaves the Ge-Cl bonds to release Cl which further reacts with another Ge-Cl to desorb GeCl2. The desorption products during thermal reaction of hydrogen chloride on Ge(100) include H2, HCl, and GeCl2. We also investigated the thermal reaction of chlorine (Cl2) on Ge(100). Similar to HCl, molecular chlorine undergoes dissociative adsorption at initial exposures, and can molecularly adsorb at high exposures. On annealing to 225 K, adsorbed Cl2 scissors the Cl-Cl bonds, resulting the formation and desorption of GeCl4. At 300 K, only Ge monochloride (GeCl) is present on the surface upon annealing to 300 K. At 700 K, the Ge-Cl further reacts and desorbs as GeCl2 as observed on the case of HCl. In addition, a trace amount of Cl2 is observed as one of the desorption products due to recombination of surface Cl(ad). According to the TPD and XPS data, the detailed mechanisms of thermal reactions of HCl and Cl2 on Ge(100) are proposed in this dissertation.
The adsorption and thermal reactions of hydrogen chloride (HCl) and chlorine (Cl2) on Ge(100) surface were studied with temperature- programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). The desorption products of thermal reactions were monitored with TPD and the reaction intermediates were identified with XPS using synchrotron radiation. At 105 K, HCl molecules adsorb dissociatively at the initial exposure. The molecular adsorption of HCl appears at high exposures and chemisorbed HCl molecules become dissociated at 275 K. On annealing to 675 K, surface Ge-H bonds break and desorb as H2 and HCl with recombination of H(ad)+H(ad) and H(ad)+Cl(ad). At 700 K, The Ge monochloride (GeCl) cleaves the Ge-Cl bonds to release Cl which further reacts with another Ge-Cl to desorb GeCl2. The desorption products during thermal reaction of hydrogen chloride on Ge(100) include H2, HCl, and GeCl2. We also investigated the thermal reaction of chlorine (Cl2) on Ge(100). Similar to HCl, molecular chlorine undergoes dissociative adsorption at initial exposures, and can molecularly adsorb at high exposures. On annealing to 225 K, adsorbed Cl2 scissors the Cl-Cl bonds, resulting the formation and desorption of GeCl4. At 300 K, only Ge monochloride (GeCl) is present on the surface upon annealing to 300 K. At 700 K, the Ge-Cl further reacts and desorbs as GeCl2 as observed on the case of HCl. In addition, a trace amount of Cl2 is observed as one of the desorption products due to recombination of surface Cl(ad). According to the TPD and XPS data, the detailed mechanisms of thermal reactions of HCl and Cl2 on Ge(100) are proposed in this dissertation.
Description
Keywords
氯化氫, 氯氣, 吸附, 熱分解, hydrogen chloride, chlorine, adsorption, thermal decomposition