利用X光光電子能譜儀進行氬原子團簇游離能的研究

Studying of Ar Cluster Ionization Levels by X-Ray Laser Photoelectron Spectroscopy

翁士傑(Shih-Jie Wong)

指導教授 ： 朱旭新

國立中央大學/理學院/物理學系/碩士(2008年)

摘要

原子團簇在化學反應與催化作用中扮演重要角色，許多表面的物理與化學反應，從微觀來看，都是原子團簇的動態行為。本研究的目的，就在於利用X光光電子能譜學（x-ray photoelectron spectroscopy, XPS）技術，來研究氬原子團簇的游離能與團簇大小的關係。
我們使用本實驗室過去發展的氪氣X光雷射脈衝做為光電子能譜儀的游離光源，其輸出波長為32.8 nm，偏振方向經過實驗測量，確定為無特定偏振方向（random polarized）。同時，我們建造一套飛行時間能譜儀（time-of-flight spectrometer, TOF） 作為測量X光光電子能譜的工具，並引入磁瓶 (magnetic bottle) 技術以提高光電子的收集效率，設計估算光電子的收集範圍可以達到2π立體角。實驗上我們驗證了磁瓶技術的效果，光電子收集效率確實大幅提高，不過尚未達到預期的效率，未來我們將持續改善磁瓶裝置，達成收集效率的最佳化。最後，利用此氪氣X光雷射與飛行時間能譜儀，測量氬原子團簇被32.8-nm X光脈衝游離的光電子能量，就可以推得原子團簇的游離能。
我們藉由改變氬氣噴流的氣壓，可以控制形成氬原子團簇的大小，因此，我們研究了氬原子團簇的游離能與團簇粒徑的關係。實驗結果顯示原子團簇粒徑愈大，其游離能越低，這個現象與之前其他團隊研究原子團簇所得到的結果相符。其原因可能來自於所謂極化屏蔽效應。
藉由這次實驗的結果，我們可以改良目前的實驗設計，使XPS 可以有更好的解析度與精確度。未來期望能延伸這項技術到更廣泛的下游應用，如電子躍遷或表面原子與分子物理行為的研究。

關鍵字

氬 ； 原子團簇 ； X光 ； 游離能 ； 能譜儀

並列摘要

Cluster plays an important role in chemical reaction and catalysis. Many physical and chemical phenomenon of surface are the dynamics of clusters. The purpose of this thesis is to study the relations between cluster size and ionization potential by x-ray photoelectron spectroscopy, XPS.
We use an x-ray laser pulse which is produced from krypton as the source for ionizing clusters. The wavelength of x-ray laser pulse is 32.8 nm. The polarization is random polarized. In the meantime, we build time-of-flight spectrometer as a tool for measuring energy spectrum of x-ray photoelectrons. Furthermore, we use magnetic bottle device to increase the collection efficiency of photoelectron. According to our estimation, the solid angle for detecting electrons is about 2π. The experimental results show that the magnetic bottle does improve the collection efficiency.
We control the size of argon cluster by changing the backing pressure of cluster jet. Then we study the relations between the cluster size and ionization potential of argon cluster. The results show that the ionization potential decreases as the cluster size increases. The experimental results agree with other group’s studying. This is due to polarization screening.
By the results of the experiment, we can improve the design of experiment to get better resolution and accuracy in using XPS. We expect the technique will apply to more widely research.

並列關鍵字

Ar ； argon ； x-ray ； ionization potential ； photoelectron spectroscopy

參考文獻

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