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3. EXAFS Data Analysis using Athena
2012 2 2913:30 14:20
IFEFFIT package
FEFFIT
Fit (k) data to the theoretical calculations of FEFF, and assess the errors in
the fitting parameters. The fitting is done in R-space, which allows spatial
selection of the interesting and accessible contributions to the XAFS. The
program allows the user to modify the FEFF calculations in a variety of ways
so that the user can model many different types of systems.
ATOMS
Interpret space group configuration and write an input file for FEFF. Several
experimental absorption corrections to XAFS data are also calculated.
AUTOBK
Evaluate and remove the background of raw absorption data, converting
absorption, (E), to XAFS, (k). The algorithm chooses the background that
minimizes the low-R components of (R), the Fourier Transform of (k).
These softwares have been further developed by Matt and Bruce, and now,
are called ifeffit and horae. Horae includes Athena, Artemis, Hephaestus
software, including example Projects.
IFEFFIT Installation
IFEFFIT installation for windows
1) Get ifeffit-1.2.11.exe or the latest version from
http://cars9.uchicago.edu/ifeffit/
2) Run the executable file.
This distribution includes the following programs:
athena GUI for Data Processing with Ifeffit
artemis GUI for XAFS Fitting with Ifeffit
hephaestus GUI for general x-ray properties of the elements
sixpack GUI for XAFS Processing and Fitting with Ifeffit
feff6 Stand-alone program for ab inito EXAFS calculations
atoms Stand-alone Crystallography -> feff.inp
autobk Stand-alone background removal program
feffit Stand-alone FEFF fitting program
ifeffit command-line version of Ifeffit
Athena
If you successfully installed the IFEFFIT package,
you will see several icons including Artemis,
Athena, Hephaestus, and SixPack, on the screen.
Athena is the software to prepare raw XAFS data
for further analysis. With Athena, one can generate
various data files, including xmu (E), chi(k), and
Fourier transformed chi(r).
Athena
Usage of Athena
Transmission raw data from ZnO powder measured at APS
Usage of Athena1 column: Energy
4 column: I05 column: Total x-ray absorption from ZnO powder near Zn K-edge.
x = ln(I0/I)
Atomic Background of Transmission Data
Energy space
)(26.0
/)(2
0
0
EE
EEmk
m
kE
m
mvE
mvEKEEE
2
)(
2
)(
2
1
2
0
2
0
2
00
E0
EXAFS in k-space
EXAFS data in k- and r-spaces
Usage of AthenaFluorescence raw data from ZnO film at Zn K-edge
Usage of Athena1 column: Energy
2 column: I07 column: Total intensity of fluorescence from a ZnO film.
Atomic Background of Fluorescence Data
AUTOBK Parameters
Determination of E0
Determination of E0
E0 = 9659.2 eV
Theory E0 = 9659 eV
E0 determined by derivative = 9660.272 eV
Pre-Edge range
-200 -50
Normalization Range
Absorption edge step to be 1
150 450
Spline Range (Kmin and Kmax)
)(26.0
/)(2
0
0
EE
EEmk
m
kE
m
mvE
mvEKEEE
2
)(
2
)(
2
1
2
0
2
0
2
00
Atomic Background Change with Kmin and Kmax
Rbkg
For Rbkg = 0.2
No good
For Rbkg = 1.2
good
Determination of Rbkg
Rbkg = 0.2 Rbkg = 1.2
1. The atomic background should be a smooth function.
2. No extra peak exists near the probe atom in the r-space.
acceptable acceptable
k weight
No k-weight k-weight = 1
k-weight = 2 k-weight = 3
k weight
No k-weight k-weight = 1
k-weight = 2 k-weight = 3
In general. K-weight = 2 or 3 is used.
k range
Affected by XANES:
chemical properties
and energy band
structure
r = /2k, EXAFS cannot detect smaller than 0.001 (XRD
can determine 0.0001 ).
Special resolution is inversely proportional to the k range.
Kmin may not be smaller than 2.0 because of the XANES
contribution.
Kmax can be determined by checking the reproducibility among
scans.
In general for T < 100 K,
Kmin = 3.0, Kmax = 15.0
Fourier Transform
Likr
ikr
drerL
k
dkekr
0
1
2
1
)()(
)()(
dkkrikrkdkekr ikr )}sin()){cos(()()(
2
1
2
1
Fourier Transform
r0 = 2.5 )sin()(
,)()(
0
2
1
krk
dkekr ikr
Fourier Transform
Real part Imaginary part
30
300
2
1dkkrikrkrr )}sin()){cos(sin()(
Fourier Transform
Magnitude of Fourier transformed function
FT(EXAFS) from ZnO Powder
k rage in FT
The amplitude and FWHM of the peak are contributed by k-
range of the FT, coordination number and Debye-Waller factor.
-30 < k < 30
-10 < k < 10
0< k < 10
The small oscillations are due to the signal in a
finite range.
FT Windows
To eliminate the data truncation effect at the edges, a FT window is used.
Sin windowHanning window
dk
Window effect
Hanning window
dk
Backward FT
Back FT of the data in specific range in r-space to k-space
The end of the third session