An EXAFS Scan
This is an example for an EXAFS scan.
Four counters are used.
It is demonstrated how
different steps widths are used in
different energy regions.
The scan is called by:
ONLINE
scan/exafs
Table 15.13:
Example: EXAFS Scan Menu
--- EXAFS Scan ---
SPECTRA>
EXAFS: 8888.016 [eV] A-Move: [eV]
-------------------------------------------------------------------------------
Scan_Name: ak_0016
Generic Scan Name: ak
Comment:
Start: 8630 [eV] Stop: 9900 [eV]
Delta: 10 [eV] Sample_time: 0.5 [Seconds]
Range: NP:
Scan_par: 1 Wait_time 0.
Maximum x 0 [eV] SSA: No
Auto-return: (1) YES Repeats: 1
-------------------------------------------------------------------------------
Edit com-files
<~.prog>before_fast_scan.gra NO
<~.prog>during_fast_scan.gra NO
<~.prog>after_fast_scan.gra NO
-------------------------------------------------------------------------------
PF1 - Start Scan, PF2 - Continue Scan, PF4 - Exit, <Space bar> - Stop Scan
KP7 - Cursor scan_name, Z - Toggle Zoom, D - Display, ^W - Refresh Screen
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After pressing KP0 the 'Prepare' menu appears. Note that one
region (8920 - 9900) has a non-zero edge position. It is called a k-region.
In k-regions the step width is scaled to be constant in k and the
sample time is scaled by s_time = s_time
kn
. Kn is the
normalized momentum. It is 1 at the start of the region.
Table 15.14:
Example: Prepare EXAFS Scan Menu
Prepare an EXAFS Scan
Region Limit Delta Sample Time Edge Pos. Power Delta K Total Time NP
[eV] [eV] [s] [eV] [1/A] [s]
8630 10 0.5 0 0 0 11 22
8850 0.5 0.5 0 0 0 70 140
8920 0.5 0.5 8888 1 0.04402288 980.9201 593
9900 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
Sample + Wait Time 1061 Total 1061 755
-------------------------------------------------------------------------------
KP8 - Move up | KP2 - Move down | KP4 - Move left | KP6 - Move right
KP7 - Insert E. | KP9 - Delete Edge | KP1 - Load Regns | KP3 - Store Rgns
<ret> - Update | PF2 - Help | PF4 - Exit |
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The file before_exafs_scan.gra is listed in table
15.9.
Table 15.15:
Example: Before_exafs_scan.gra
!
! before_exafs_scan.gra
! ---------------------
!
scan_c1 = c1
descr_c1 = "Ioni0"
scan_c2 = c2
scan_c3 = c3
scan_c4 = c4
scan_ref = c3
scan_min_c1 = 1000
scan_timer = t1
!
! get_offsets() uses scan_timer and scan_ci to
! measure the offsets
!
if !search_symbol( scan_offset_c1)
s1 = get_offsets(10)
endif
! deactivate scan_name
end
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It is almost identical to
before_fast_scan.gra and most of the
explanations (![[*]](crossref.png)
) apply here
as well. The differences are:
scan_ref = c3
An optional counter for the reference sample.
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Counter assignment
During EXAFS scans absorption signals are monitored. This is
possible only, if there is a strict assignment of the counters.
Scan_c1 is behind the monochromator,
scan_c2 is behind the sample and scan_ref is
behind the reference sample. The reference signal is optional.
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! deactivate scan_name
Scan_name is no longer deactivated because it contains
the sample absorption signal.
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The file during_exafs_scan.gra is empty.
Table 15.9 shows the
file after_exafs_scan.gra.
Table 15.16:
Example: After_exafs_scan.gra
!
! after_exafs_scan.gra
! --------------------
!
if yesno( "Write to disk")
write/fio/scan/exafs ds_name
endif
if yesno( "Postscript")
post/nocon/print/dina4
endif
Cleanup
end
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The is one difference compared to after_fast_scan.gra:
The qualifier /exafs directs write/fio
to write the exafs regions into the output file.
Figure 15.3 shows the online display of an EXAFS scan.
The upper half of the screen contains the counter readings, the lower half
shows the absorption of the sample which is compared with a reference
signal.
Figure 15.3:
The Online Display of EXAFS Scans
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