Dramatically Enhanced Oxygen Uptake and Ionization Yield of Positive Secondary Ions with C60+ Sputtering

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• 作者：Hua-Yang Liao ; Meng-Hung Tsai ; Yun-Wen You ; Hsun-Yun Chang ; Chih-Chieh Huang ; Jing-Jong Shyue
• 刊名：Analytical Chemistry
• 出版年：2012
• 出版时间：April 3, 2012
• 年：2012
• 卷：84
• 期：7
• 页码：3355-3361
• 全文大小：391K
• 年卷期：v.84,no.7(April 3, 2012)
• ISSN：1520-6882

文摘

To explore C₆₀⁺ sputtering beyond low-damage depth profiling of organic materials, X-ray photoelectron spectrometry (XPS) and secondary ion mass spectrometry (SIMS) were used to examine metallic surfaces during and after C₆₀⁺ sputtering. During C₆₀⁺ sputtering, XPS spectra indicated that the degrees of carbon deposition were different for different metallic surfaces. Moreover, for some metals (e.g., Al, W, Ta, Ti, and Mo), the intensity of the O 1s photoelectron increased significantly during C₆₀⁺ sputtering, even though the instrument was under ultrahigh vacuum (<5 脳 10^鈥? Pa). This result indicated that the rate of oxygen uptake was greater than the rate of C₆₀⁺ sputtering. This behavior was not observed with the commonly used Ar⁺ sputtering. To measure the oxygen uptake kinetics, pure oxygen was leaked into the chamber to maintain a 5 脳 10^鈥? Pa oxygen environment. The C₆₀⁺-sputtered surface had a clearly increased rate of oxygen uptake than the Ar⁺-sputtered surface, even for moderately reactive metals such as Fe and Ni. For relatively nonreactive metals such as Cu and Au, a small amount of carbon was implanted and no oxygen uptake was observed. High-resolution XPS spectra revealed the formation of metal carbides on these reactive metals, and the carbon deposition and enhanced uptake of oxygen correlated to the carbide formation. Because oxygen enhances the secondary ion yield through surface passivation, the enhanced oxygen uptake due to C₆₀⁺ sputtering could be beneficial for SIMS analysis. To examine this hypothesis, C₆₀⁺ and Ar⁺ were used as primary ions, and it was found that the intensity enhancement (because of the oxygen flooding at 5 脳 10^鈥? Pa) was much higher with C₆₀⁺ than with Ar⁺. Therefore, oxygen flooding during C₆₀⁺ sputtering has a great potential for enhancing the detection limit due to the enhanced oxygen uptake.