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XPS (X- ray photoelectron spectroscopy ) or ESCA ( Electron Spectroscopy for Chemical Analysis)

Advanced Nano -technology and Applied Optoelectronics Lab. Southern Taiwan University of Science Technology. XPS (X- ray photoelectron spectroscopy ) or ESCA ( Electron Spectroscopy for Chemical Analysis). Student:Chang-Yu Shih Advisor : 吳坤憲. Outline. History Introduction

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XPS (X- ray photoelectron spectroscopy ) or ESCA ( Electron Spectroscopy for Chemical Analysis)

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  1. Advanced Nano-technology and Applied Optoelectronics Lab. Southern Taiwan University of Science Technology XPS(X-rayphotoelectronspectroscopy)or ESCA (Electron Spectroscopy for Chemical Analysis) Student:Chang-YuShih Advisor:吳坤憲

  2. Outline History Introduction Measurement Results and Discussion Conclusions

  3. Outline History Introduction Measurement Results and Discussion Conclusions

  4. Outline History Introduction Measurement Results and Discussion Conclusions

  5. Introduction • XPS is also known as ESCA (Electron Spectroscopy for Chemical Analysis)。 X-ray photoelectron spectroscopy (XPS) is a surface-sensitive quantitative spectroscopic technique. that measures the elemental composition at the parts per thousand range, empirical formula, chemical state and electronic state of the elements that exist within a material. XPS requires ultra-high vacuum (UHV) conditions.

  6. Measurement XPS is used to measure: • elemental composition of the surface (top 1–10 nm usually). • empirical formula of pure materials. • elements that contaminate a surface. • chemical or electronic state of each element in the surface. • uniformity of elemental composition across the top surface (or line profiling or mapping). • uniformity of elemental composition as a function of ion beam etching (or depth profiling). 最簡式

  7. Components of a commercial XPS system The main components of a commercially made XPS system include: • A source of X-rays • An ultra-high vacuum (UHV) stainless steel chamber with UHV pumps • An electron collection lens • An electron energy analyzer • Mu-metal magnetic field shielding • An electron detector system • A moderate vacuum sample introduction chamber • Sample mounts • A sample stage • A set of stage manipulators

  8. Electric energy analyzer Foucs beam of X-ray source Chamber software

  9. BE = hν −KE −φ • BE = (binding energy of photoelectron) • h = Plank constant (6.63×10-34joule-second) • ν = frequency • KE =(kinetics energy of photoelectron) • φ = (work function of analyzer)

  10. BE = hν −KE −φ hν KE φ

  11. A source of X-rays

  12. Components of a commercial XPS system 1.目前的商業化系統中， XPS的靶材一般採用Al/Mg雙陽極靶，這樣可以根據分析需要來進行選擇，由Al靶產生的Al K射線光子的能量為1486.6 eV譜寬為0.85eV，Mg K為1253.6 eV譜寬為0.7eV。另外，也有選用Ti的K射線作為光源，其光子能量為2040 eV； 2.作為XPS的光源，要求需有光度強、單色性好的特點。X射線的單色性越高，能譜儀的能量解析度也越高，因此，一般說來，高解析度XPS系統中會自帶一套單色光源，Ex:單色Al K光源。 3. 選取何種X射線作為激發光源取決於具體的分析物件，因此，不存在哪種光源好或不好的問題，實際操作中，經常會為了提高讀取能譜的準確性，而連續採用兩種或兩種以上光源的情況。

  13. Quantitatively analyzed • 利用能譜的面積來進行元素定量分析。一個均勻分布在分析容積得樣品，每秒產生某一特定能量的光電子數目為: I=nfσθyλAT………(1) n: 樣品內每單位體積(cm3) 中所含的原子數目 f: X-ray 光子通量(Unit:photo/cm2-sec ) σ:原子軌域的光電截面積(Unit:cm2 ) y:形成光電子之效率 θ: 光子行徑與測得的電子之間的儀器裝置所建立的角度有效係數 A: 樣品上可測得光電子面積大小 T: 樣品激發出電子偵測係數 由(1)式可得到: n=I/fσθyλAT，式中分母可由S代表，稱為原子感受系數(Atomic sensitivity factor)，我們可以依照所使用光源訂出所有元素的S相對值。 材料若由兩個元素組成，兩個元素特徵能譜線，可由(2)式算出材料中元素比例: n1/n2=(I1/S1)/(I2/S2)…………(2),其中I1、I2為不同元素之能譜積分面積。 樣品若是多種成分所組成，則某一成份x的原子百分比(Cx) ，可由(3)式推導出 Cx= nx/Σn1 =(Ix/Sx)/ ΣI1/S1………(3)

  14. Precautions(注意) Sample size limits Older instruments accept samples: 1×1 to 3×3 cm. Present systems can accept samples up to 30×30 cm.

  15. Precautions(注意) 一.由於XPS對樣品表面非常靈敏的儀器，保持樣片表面的潔淨和原狀， 對分析結果的準確度非常重要。Ex:手指頭碰觸到樣片表面，可能會檢測出Cl、C、Na、O等外來的污染元素。 二.樣品不得具有磁性，毒性．輻射性。 三.偵測元素: H, He 以外的所有元素。 四.可與濺鍍槍搭配，亦可將表面打薄進行縱深分析。

  16. Outline History Introduction Measurement Results and Discussion Conclusion

  17. Application

  18. Application 自旋軌道分裂

  19. Application 面積比

  20. Outline Introduction Experimental Results and Discussion Conclusions

  21. Conclusions • 利用XPS系統可以準確得知樣品之化學元素組成，對於材料薄膜分析是值得參考的工具，但由於量測價格昂貴，建議研究人員可以深思並把試片依照不同需求而選用不同分析量測即能省錢也能把研究成本降低。

  22. Thanks for your attention

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