I. General Introduction to Spectroscopy
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Transcript of I. General Introduction to Spectroscopy
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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 materialIncident 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 0 02s
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
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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
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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 structureXANES/ 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
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coef
ficie
nt
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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
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ized
abs
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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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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