Chamorro Research Group

The group standard for powder diffraction. Every measurement uses the same holder, the same fixed optics and one of the shared programs below. Do not change a slit, a mask or a program. If something here does not fit your sample, ask Juan first.

Which instrument and program

Sample preparation

1. Use a group MTI zero background plate (32 mm Si, 10 mm by 0.2 mm cavity) in a group Malvern Panalytical 32 mm spring holder. Do not use MCF holders.
2. Grind the powder fine. Fill the cavity level with the plate surface using the edge of a glass slide. No mound and no dip: a surface above or below the plate shifts every peak.
3. Air sensitive: fill the plate in the glovebox and seal the whole plate with Kapton tape, always the same tape. The tape adds a broad hump at low angle. It is not airtight, so scan with Cham-Quick as soon as you can after mounting.
4. Precise lattice parameters: mix about 10 to 20 wt% of the group Si powder into a separate portion of the sample. Never into the whole product.
5. Spin the sample on the Aeris and the X'Pert (both have spinner stages). The Empyrean stage does not spin, so grind especially fine for it.

Shared programs

Stored on each instrument PC in Programs\Chamorro Group\. Never run a personal program.

Program	Aeris and Empyrean (Cu)	X'Pert (Co)	Use
Cham-Quick	10 to 80°, step 0.02°, 20 to 30 min	12 to 100°, step 0.02°, about 30 min	The default for everything
Cham-Long	10 to 120°, step 0.01°, 2 to 3 h	12 to 140°, step 0.013°, about 3 h	Only for paper quality data
Cham-Si	10 to 140°, step 0.01°, about 2 h	12 to 150°, step 0.013°, about 2 h	Instrument calibration only

The Co ranges cover the same d-spacings as the Cu ranges. MCF time costs $35 per hour.

Fixed optics

Check these before every scan. If anything differs, stop and tell Juan or Nicholas.

	Aeris (Cu)	Empyrean (Cu)	X'Pert "Elvis" (Co)
Divergence slit	1/4°	1/4°	Programmable, fixed at 1/4°
Mask	Narrowest, 10 mm or less	5 mm	5 mm
Incident anti-scatter	As installed	1/2°	1°
Soller slits	0.04 rad	0.04 rad	0.04 rad
Filter	Ni	Ni	Fe
Diffracted anti-scatter	As installed	6 mm	Programmable, fixed at 1/4°
Tube	40 kV, 15 mA	45 kV, 40 mA	45 kV, 32 mA

What the optics do

• Divergence slit (tube side): sets how far the beam fans out, so how long a strip of sample it lights. With 1/4° the strip fits inside the 10 mm cavity above about 14° on the MCF instruments and above about 9° on the Aeris. You can still scan lower: below that angle part of the beam lands on the blank plate around the cavity, which adds no peaks but makes the lowest-angle peaks weaker than they should be. Peak positions and phase ID are unaffected. In a Rietveld fit, treat the intensities of peaks below that angle with care.
• Mask: sets the beam width across the sample.
• Anti-scatter slits: block X-rays scattered by air, which lowers the background.
• Soller slits: stacks of thin foils that limit the peak asymmetry at low angle.
• Filter: removes most of the Kβ line of the tube.
• Fluorescence: a Cu tube makes Fe, Co, Mn, Cr, V, Ti and the lighter rare earths glow with their own X-rays, which raises the background. A Co tube does not excite Fe or Co. The Empyrean detector window is narrow enough to reject most of this light.

Refinement

• Start every TOPAS file with the instrument file for the instrument you used: #include "Cham_Empyrean.inc", Cham_XPert.inc or Cham_Aeris.inc, in Data/General/XRD-Standards/. These hold everything about the instrument, fitted from the Si standard.
• Refine only sample terms: background, scale, lattice parameters, sample displacement, crystallite size, strain, then atoms. Never refine the zero error; it is fixed in the instrument file. Zero and displacement both shift peaks, so refining both gives two meaningless numbers.
• Show fits in group meeting as exported plots (observed, calculated, difference, tick marks), not TOPAS screenshots.

Draft, October 2026. The instrument files do not exist yet; they come from the Si calibration.

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