Module DELIA (Dispersive Exafs caLIbration and Analysis)
Module characteristics
- Goal: To perform operations over a bunch of spectra.
Operations: calibration the spectra, extraction of the
XAFS signal and Fourier (and back-Fourier) filtering.
This applications has been designed for the particular needs of
the
ESRF/ID24 beamline. The Dispersive XAFS
and Turbo-XAS techniques generate a huge amount of XAFS spectra
in few seconds or minutes. This module allows the user to
visualize the spectra, calibrate them, extract the XAFS signal and
perform Fourier and back-Fourier transforms simultaneously over all
the spectra by simply point-and-click.
- Input: a file with raw data. The standard input file contains
three columns with X,Mu and Index, all floats, written in binary
format by a big endian system. The file size is then
number_of_points*3*8 bits. Note that you can run DELIA in both
little or big endian systems, but the file must be written by a
big endian system (or also by a little endian system but swapping
the byte ordering). To load a standard raw data file use
the Browser... buttin in the "Raw" control panel.
DELIA also accepts other ASCII input files (using the
File menu:
- ASCII RAW data: a multicolumn file containing at least
three columns (more columns also accepted) with X,Mu and index. The
index can be any value that identify the spectrum. Usually
indices are 0,1,2..., but can be, for example, a temperature
value, etc.
- Mu(E): a multicolumn file containing in the first
column the Energy values in eV, and then one additional column
for each spectrum (Mu(Energy)) value. When this kind of file is
used, the interpolation and calibration analyses are skipped.
- Mu(E): a multicolumn file containing in the first
column the Chi values in A, and then one additional column
for each spectrum (Chi(k)) value. When this kind of file is
used, the interpolation, calibration, and extraction analyses
are skipped.
- Output: The results of the operations performed with DELIA can
be saved in either multicolumn ASCII data files or in sequential
ASCII data files. They are usually saved from an XPlot window
using the menu File->Write ASCII file with current
set....
- Tricks:
- Better use binary raw input files: they are smaller and load
quicker.
Follow the steps
The DELIA analysis is done in four main steps, Each step is implemented
in a different panel in the main window: Raw, mu(E), chi(k) and
Fourier.
You should pass from one panel to the next one after completing the
operations in the current one. The names are self explanatory:
- Phase I [Raw]: allows to read raw data, visualize the
individual spectra, overplot them. The user must identify the
columns with X, Mu and indices. Using the ASCII raw sample file
f29 I obtained the sample
window 1.
- Phase II [mu(E)]: Interpolation and Calibration. It allows the
user to input the parameters. Default parameters for the
interpolation limits are presented. The minimum correspond to maximum
value between all the abscissas spectra minima, and the maximum
corresponds to the minimum between all abscissas maxima. They may
be changed by the user. The user should also supply the calibrating
coefficients a,b,c. By using the Get... button, the
XAID_CALIB application is started to
help in finding the coefficients. The coefficients found in this
way are automatically transferred to the DELIA window. Once all
parameters are filled, predd the RUN interpolate &
calibrate
button to make calculations over all spectra. The results appear in
the "Result:" text window and also in a newly created XPlot window.
The results can be visualized using the 2D and
3D
buttons.
If you want to create a file for further use with DELIA, press
the 2D button, and from the XPLot window, select
File->Write ASCII file with current set..., select then
Data to save: All columns
and Include header (SPEC type):
No. The resulting file can then be loaded using the DELIA
File->Load file with Mu(E)... menu.
Some example windows are in windows
2 and
3.
- Phase III [chi(k)]: extraction of the XAFS signal, i.e.,
calculate Chi(k) from Mu(Energy) over all the
spectra. For selecting the appropriate parameters for the extraction,
the user must perform interactively the extraction on a single spectrum
(select its index and then press the Go button to start
XAID_MU2CHI module (remember to
perform the extraction in k space). The parameters of the
extraction are copied automatically to their respective boxes. The
results can be visualized in 2D or 3D and saved to a file for further
use in DELIA as shown in Phase II. See examples in windows
4 and
5.
- Phase IV [Fourier]: Fourier transform and filtering. As in
the previous phase, the user must first perform the Fourier
Filtering on a single Chi(k) spectrum, by using the
XAID_FF module. The parameters are
copied automatically.
A sample can be found in
window 6 and
FAQs
- What to do if the programs crashes?
Restart from scratch.
Window examples
Window 1. Main panel after loading the ASCII raw data file
f29.
Window 2. Main panel after interpolation and calibration (Phase II).
Window 3. XPlot window after interpolation and calibration (Phase II).
(Click on the image for full resolution.)
Window 4. Main DELIA window during XAFS extraction (Phase III).
Window 5. XPlot window after XAFS extraction (Phase III).
(Click on the image for full resolution.)
Window 5. Main DELIA window during Fourier Filtering (Phase IV).
Acknowledgement
Thanks to the ID24 staff for providing me with the example data.
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