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- Switch to the new reference foil or compound. Reference foils are in the small wooden box of foils at the beam line.
- Low-energy configuration (E < 5 keV, using low-Z box with bellows or cryostream bag)
- Move CALVERT to out position (CALVERT = 4).
- Open feedthrough for motorized vertical CALVERT holder by loosening and removing C-clamp.
- Pull feedthrough out completely.
- Remove sample holder plate for old reference foil or compound and press new reference onto double stick tape on mount. Align holes on plate to holes on mount.
- Re-insert CALVERT holder and replace and tighten C-clamp.
- Attach I2 cable to BNC connector below motorized vertical CALVERT holder.
- High energy configuration (E > 4.9 keV, not using low-Z box with bellows or cryostream bag)
- For samples which will transmit beam through them, place foil in holder in front of I2 ion chamber. Attach I2 signal cable to I2 ion chamber.
- For thick or non-transmitting samples, insert foil in the scatter holder before on top of I0 ion chamber. Attach I2 signal cable to photodiode cable on scatter holder.
- Low-energy configuration (E < 5 keV, using low-Z box with bellows or cryostream bag)
- Make sure there are no samples or holders blocking the beam path through to I2.
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- Move MONO to the energy corresponding to the end of your desired XAS scan energy range.
- This number can be found by going to the Regions window and selecting the scan region you will use. Look towards the bottom of the window for the "stop energy" value.
- Alternatively, if the scan region is not yet defined, set energy to (edge energy + 1000 eV) if you plan to run EXAFS, or (edge energy +200 eV) if you plan to run only XANES.
- In XASUTILS window, select the “Mono Tuning” tab. Move the tuning in one direction or the other while monitoring I0 signal, until you reach a maximum in I0.
- If one click of the "Mono Tuning" seems too large or doesn't seem to move the I0 value at all, you can decrease or increase the Mono Tuning step size.
- If detuning is needed (see below), you will want to "Detune" with the UP arrow in the "Mono Tuning" interface.
- BL 4-3 runs with a harmonic rejection mirror, with energy cutoff at either 4 keV, 6 keV, or 10 keV, depending on what the beam line engineer has set it to.
- Because the mirror is bare Si and not coated with a metal, the cutoff is more gradual than other beam lines.
- If your harmonic energy (equal to 3x the MONO energy) is less than 4 keV above the cutoff energy, at least 25% detuning is recommended. Otherwise you can run fully tuned (maximize I0 to 100%).
- You may also want to detune some if you are looking at a dilute sample at lower energy edge (E < 4 keV) and sample matrix has a lot of a heavier element in it (e.g. Fe, Ti, Cr, etc.)
- Example 1: S edge (~2.5 keV), 4 keV cutoff. Harmonic energy is 7.5 keV, which is only 3.5 keV above the 4 keV cutoff. Detune 25% (reduce I0 to 75% of maximum)
- Example 2: S edge (~2.5 keV), 6 keV cutoff. Harmonic energy is 7.5 keV, which is only 1.5 keV above the 6 keV cutoff. Detune 35% (reduce I0 to 65% of maximum)
- Example 2: S edge (~2.5 keV), 10 keV cutoff. Harmonic energy is 7.5 keV, which is below the 10 keV cutoff. Detune 50% (reduce I0 to 50% of maximum)
- Example 4: Ti edge (~4.9 keV), 6 keV cutoff. Harmonic energy is 14.7 keV, which is 9 keV above the 6 keV cutoff. Run fully tuned (maximize I0 to 100%)
- Example 4: Ti edge (~4.9 keV), 10 keV cutoff. Harmonic energy is 14.7 keV, which is 4.7 keV above the 10 keV cutoff. Run fully tuned (maximize I0 to 100%)
- Example 5: Fe edge (~7.1 keV), 10 keV cutoff. Harmonic energy is 21.3 keV, which is 11 keV above the 10 keV cutoff. Run fully tuned (maximize I0 to 100%)
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- Move MONO to the energy corresponding to the middle of your desired XAS scan energy range.
- This number The ending energy of your XAS scan energy range can be found by going to the Regions window and selecting the scan region you will use. Look towards the bottom of the window for the "stop energy" value.
- Set MONO to the midpoint between your edge energy and the "stop energy" value
- Alternatively, if the scan region is not yet defined, set energy to (edge energy + 500 eV) if you plan to run EXAFS, or (edge energy + 100 eV) if you plan to run only XANES.
- Close S1VGAP to 1.0 mm and S1HGAP to 10.0 mm.
- Scan TABLEVERT motor while looking at I0 signal.
- TABLEVERT scan parameters and apperance depend on mirror cutoff selected
- If at 4 keV cutoff:
- Scan +/- 3.5 mm, with 0.35 mm point spacing (Or use "rel3_5" align region from drop down).
- Select peak slightly to left of center of plateau. Hit "Accept position" Do NOT select peaks at either right or left side of plateau.
- If at 6 keV cutoff:
- Scan +/- 2.5 mm, with 0.25 mm point spacing (Or use "rel2_5" align region from drop down).
- Select peak on right side of scan. Hit "Accept position".
- If at 10 keV cutoff:
- Scan +/- 2.0 mm, with 0.2 mm point spacing (Or use "rel2" align region from drop down).
- Select peak value of I0. Hit "Accept position".
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- Move the edge energy about 20 eV above the nominal edge energy. At this point,
- I1 transmission through sample should be minimized
- I2 transmission through foil (on back ion chamber or on scatter reference) should be minimized
- I2 fluorescence from foil or compound on CALVERT holder should be near a maximum
- I3 fluorescence from your sample (if using PIPS/Lytle) should be near a maximum
- Make sure that the signal you read on I0 through I3 is > 0.5 and < 4
- Move the MONO 20-50 eV below the edge energy. At this point,
- I1 transmission through sample should be maximized
- I2 transmission through foil (on back ion chamber or on scatter reference) should be maximized
- I2 fluorescence from foil or compound on CALVERT holder should be at a minimum
- I3 fluorescence from your sample (if using PIPS/Lytle) should be near a minimum
- Make sure that the signal you read on I0 through I3 is > 0.5 and < 4
- Check I0 through I3 signal gains while you are at "stop energy" (highest energy) of your XAS scan energy region. This number can be found by going to the Regions window and selecting the scan region you will use. Look towards the bottom of the window for the "stop energy" value. At this point,
- I0 through I3 may be larger than their values when MONO is at or below the edge
- Make sure that the signal you read on I0 through I3 is > 0.5 and < 4
- Make sure that the signal you read on I0 through I3 is > 0.5 and < 4
- Move the MONO below the edge energy where I2 signal will reach its max. Check again that the signal you read on the ion chambers is > 0.5 and < 4.
- After changing gains, check offsets by closing beam shutter. You want the ion chamber signal to be a positive number which is as close to zero as possible. Adjust the offsets in the Ion Chambers tab.
- After changing offsets, collect offsets on the detector file you plan to use.
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- Run the default queue with a region made for calibration scan at that edge. If you do not have one, you can use the "Region Wizard" to create a "Foil" region.
- If running at low energy with calibration foil or compound on the motorized CALVERT holder, set CALVERT to its IN value (about 37.5)
- Open plotter
- Plot different quantities depending on calibration detection technique:
- If foil in front of I2 back ion chamber, plot log(I1/I2)
- If foil in scatter reference in front of I0 ion chamber, plot log(I0/I2)
- If foil or compound on CALVERT holder, plot I2/I0 or DIODE/I0
- When the sweep is complete, while still in the plotter window- click “Modify” and then “Derivative”
- Copy the highlighted value for the energy of the first large peak in the derivative (autoselected by the plotter in the list of energies)
- In the Mono controls:
- Send the Mono to the copied value from the derivative
- In the Calibrate tab: Set to the known/book value.
- If CALVERT has been moved to its IN value, move it back to its OUT value of CALVERT = 4 !!
Now you are able to move on with loading and aligning samples, windowing the detector (if using the 30 Element Ge 7-element Vortex detector), and running measurements!
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