1 I. General Introduction to Spectroscopy II. Absorption Spectroscopies --- UV-Vis, IR, Raman III. Photon Electron Spectroscopy --- XPS, UPS IV. X-ray Absorption Spectroscopy --- XANES, EXAFS V. X-ray Crystallography VI. Magnetic Properties VII. Magnetic Resonance Spectroscopies Ph.D. students need to turn in Final written reports on a topic concerning a series of researches using one of the mentioned instruments. The topic and the titles of the main papers should be turned in before April 26.

2 X-Ray Absorption X-Ray Emission Photoelectron Emission Auger Electron Emission Fig.3 (a) Contributions to x-ray absorption. (After Henery, N.F.M., Lipson, H., and Weoster, W.A., “The Interpretation of X-ray Diffraction Photographs”. Macmillan, London, 1951.) (b) Various emission processes which give rise to spectroscopic analytical tools. Energy levels are shown schematically for atoms bound in a solid. (Adapted from Jenkins, R., “An Introduction to X-ray Spectroscopy”. Heyden, New York, 1974)

3 Interaction Between X-ray and material Incident beam (x-ray) absorbing substance Fluorescent x-rays heat Transmitted beam electrons scattered x-rays Compton recoil pohotoelectrons Unmodified electrons (coherent) Compton modified Auger electrons (incoherent)

4 ShellKLM n1 2 L I L II L III 3 M I M II M III M IV M V l0 02s02s 12p12p 03s03s 13p13p 23d23d j m Number of Electrons Table 6-3 Allowed combinations of quantum numbers Fig Energy-level diagram of a silver atom with the allowed transitions indicated by arrows. (The line are labeled after a convention proposed by Siegbahn, except that K  is used in place of K  2.)  l  1 ；  j  0 or 1 Ag

5 The photoionization process Transmitted x-ray photons

6 X-ray absorption / Emission spectroscopy

7 Characterization X-ray Absorption Spectroscopy  X-ray Absorption Near Edge Spectroscopy (XANES) Provides information on chemical states – Oxidation state – Density of states  Extended X-ray Absorption Fine Structure (EXAFS) Provides local (~10 Å) structural parameters – Nearest Neighbors (coordination numbers) – Bond distances – Disorder

8 X-ray Absorption Spectroscopy Absorption coefficient (  ) vs. incident photon energy The photoelectric absorption decreases with increasing energy “Jumps” correspond to excitation of core electrons Adapted from Teo, B. K. EXAFS: Basic Principles and Data Analysis; Springer-Verlag: New York, Absorption Photon Energy

9 Fig. 1. X-ray absorption spectrum of metallic platinum at 100 K in the region of the L-absorption edges. K L I L II L III M I M II M III M IV M V N I N II N III Pt

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11 XAS

12 X-ray absorption from a local structure XANES/ EXAFS EXAFS 現象與物理機制 Probability of X-ray Absorption:

13 Fig. 1 K-edge x-ray absorption spectra of iron in K 3 Fe(CN )6 and K 4 Fe(CN) 6. The relative absorption with respect to the high-energy continuum background,α A is plotted.

14 XANES 譜峰例：鉻與銅化合物 XANES 包含電子信息（化學鍵）（ a ）中心原子價化 (b) 中心原子配位幾何 EXAFS 含中心原子結構 Absorption coefficient

15 ………post-edge background 定法是用一直線適配吸收邊緣前端約 200eV 至 50eV 之區間內吸收係數的變化趨勢，再將此適配的背景外插至吸收光譜終點 ………pre-edge background 定法是用多段式的三次多項式加以近似之，在各段 的相接點處需滿足含數值及一階微分值皆為連續的要求 (A)Cr (bpb) 粉末樣品在 Cr K- 邊緣處之 X 光吸收全譜圖 (B) 經過背景扣除及正規化處理後所得之 XANES Cr(bpb)N

16 各種氧化態之錳金屬粉樣品在 Mn K- 邊緣處之 XANES Energy (eV)

17 Ti 4+ 在各類鈦化合物之 XANES

18 XANES measurements for reduced 10%, 40%, 60% Pt/C, and Pt foil at 200, 300, 473 and 673 K. A total of 16 measurements are shown. All overlay well with bulk Pt (Pt foil); therefore, the samples are reduced to their metallic state. X-Ray Absorption Near Edge Spectroscopy (XANES)

19 _

20 銅 K 吸收邊緣之吸收能譜受單光解析度之影響情況， 實線之解析度為 2eV ，虛線為 5eV ，折線為 9eV

21 EXAFS APPARATUS FLUORESCENCE EXAFS