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I. General Introduction to SpectroscopyII. Absorption Spectroscopies --- UV-Vis, IR, RamanIII. Photon Electron Spectroscopy --- XPS, UPSIV. X-ray Absorption Spectroscopy --- XANES, EXAFSV. X-ray CrystallographyVI. 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.
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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)
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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)
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Shell K L M
n 12
LI LII LIII
3MI MII MIII MIV MV
l 002s
12p
03s
13p
23d
j
m
Number of
Electrons2 2 2 4 2 2 4 4 6
Table 6-3 Allowed combinations of quantum numbers
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
3
2
3
2
3
2
5
2
3
2
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3
2
3
2
5
2
1
2
12
1
2
12
1
Fig. 6-20 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 K2.)
l 1 ； j 0 or 1
Ag
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The photoionization process
Transmitted x-ray photons
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X-ray absorption / Emission spectroscopy
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CharacterizationCharacterization
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
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X-ray Absorption SpectroscopyX-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, 1986.
Abs
orpt
ion
Photon Energy
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Fig. 1. X-ray absorption spectrum of metallic platinum at 100 K in the region of the L-absorption edges.
K 78.395
LI 13.88
LII 13.273
LIII 11.564
MI 3.296
MII 3.027
MIII 2.551
MIV 2.202
MV 2.122
NI 0.725
NII 0.609
NIII 0.519
Pt
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XAS
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X-ray absorption from a local structure
XANES/ EXAFS
EXAFS 現象與物理機制
Probability of X-ray Absorption:
ffs EMmc
eP
2
2
222 spfM fs
where
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Fig. 1 K-edge x-ray absorption spectra of iron in K3Fe(CN)6 and K4Fe(CN)6. The relative absorption with respect to the high-energy continuum background,αA is plotted.
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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
Abs
orpt
ion
coef
fici
ent
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………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)
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Ti4+ 在各類鈦化合物之 XANES
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11560 11565 11570 11575 11580 11585 11590 11595 116000.0
0.2
0.4
0.6
0.8
1.0
1.2
Nor
mal
ized
abs
orpt
ion
coef
ficie
nt
Energy, eV
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)X-Ray Absorption Near Edge Spectroscopy (XANES)
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_
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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
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EXAFS APPARATUS
FLUORESCENCE EXAFS
