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