3. EXAFS Data Analysis using Athena 2012 년 2 월 29 일 13:30 14:20

Transcription

1 3. EXAFS Data Analysis using Athena 2012 년 2 월 29 일 13:30 14:20

2 IFEFFIT package FEFFIT Fit χ(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, μ(e), to XAFS, χ(k). The algorithm chooses the background that minimizes the low-r components of χ(r), the Fourier Transform of χ(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.

3 IFEFFIT Installation IFEFFIT installation for windows 1) Get ifeffit exe or the latest version from 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

4 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).

5 Athena

6 Usage of Athena Transmission raw data from ZnO powder measured at APS

7 Usage of Athena 1 column: Energy 4 column: I 0 5 column: Total x-ray absorption from ZnO powder near Zn K-edge. x = ln(i 0 /I)

8 Atomic Background of Transmission Data Energy space

9 ) ( 0.26 / ) ( E E E E m k m k E m mv E mv E KE E E 2 ) ( 2 ) ( E 0 EXAFS in k-space

10 EXAFS data in k- and r-spaces

11 Usage of Athena Fluorescence raw data from ZnO film at Zn K-edge

12 Usage of Athena 1 column: Energy 2 column: I 0 7 column: Total intensity of fluorescence from a ZnO film.

13 Atomic Background of Fluorescence Data

14 AUTOBK Parameters

15 Determination of E0

16 Determination of E 0 E 0 = ev Theory E 0 = 9659 ev E 0 determined by derivative = ev

17 Pre-Edge range

18 Normalization Range Absorption edge step to be 1

19 Spline Range (Kmin and Kmax) ) ( 0.26 / ) ( E E E E m k m k E m mv E mv E KE E E 2 ) ( 2 ) (

20 Atomic Background Change with Kmin and Kmax

21 Rbkg For Rbkg = 0.2 No good

22 For Rbkg = 1.2 good

23 Determination of Rbkg Rbkg = 0.2 Rbkg = 1.2 acceptable acceptable 1. The atomic background should be a smooth function. 2. No extra peak exists near the probe atom in the r-space.

24 k weight No k-weight k-weight = 1 k-weight = 2 k-weight = 3

25 k weight No k-weight k-weight = 1 k-weight = 2 k-weight = 3 In general. K-weight = 2 or 3 is used.

26 k range In general for T < 100 K, Kmin = 3.0, Kmax = 15.0 Affected by XANES: chemical properties and energy band structure Δr = π/2δk, EXAFS cannot detect smaller than 0.001Å (XRD can determine Å ). 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.

27 Fourier Transform L ikr ikr dr e r L k dk e k r ) ( ) ( ) ( ) ( dk kr i kr k dk e k r ikr )} sin( ) ){cos( ( ) ( ) (

28 Fourier Transform ( r) ( k) 1 2 sin( kr 0 ) ( k) e ikr dk, r 0 = 2.5 Å

29 Fourier Transform 1 30 ( r ) sin( kr 30 0){cos( kr) isin( kr)} dk 2 Real part Imaginary part

30 Fourier Transform Magnitude of Fourier transformed function

31 FT(EXAFS) from ZnO Powder

32 k rage in FT -30 < k < < k < 10 0< k < 10 The small oscillations are due to the signal in a finite range. The amplitude and FWHM of the peak are contributed by k- range of the FT, coordination number and Debye-Waller factor.

33 FT Windows To eliminate the data truncation effect at the edges, a FT window is used. Hanning window Sin window dk

34 Window effect Hanning window dk

35 Backward FT Back FT of the data in specific range in r-space to k-space

36 The end of the third session