X-ray Lab Technique

Medium-Resolution (MR) mode is well suited for textured epitaxial and textured polycrystalline thin films. It also can be used to analyze nearly perfect epitaxial layers. This mode can be used for w/2q scans and reflectivity measurements. Rocking curve (w-scan) in this mode is reasonable only if layer peak FWHM is lower than the instrumental resolution.

Note:
It is good idea to check instrumental resolution by measuring FWHM of high quality single crystal diffraction peak.

The reciprocal space mapping can be done in this mode. Again, it is only feasible for layers that exhibit relatively wide diffraction peaks or sufficient peak separation.

In X-ray Lab MR measurements can be done on both X'Pert 1 and X'Pert 2 diffractometers using the following optics:

Incident Beam:

PreFIX X-ray Mirror - X'Pert 1 and X'Pert 2

Polycapillary X-ray Lens - X-Pert 1

Diffracted Beam:

Parallel Plate Collimator (PPC) + Flat Graphite Monochromator - X'Pert 1

Parallel Plate Collimator (PPC) - X'Pert 2

Triple Axis/Rocking Curve (TA/RC) attachment's RC part - X'Pert 1

Programmable Receiving Slit - X'Pert 2

X-ray mirror focuses the divergent x-ray beam from a line focus tube to an intense quasi-parallel beam. The x-ray mirror provided with X'Pert diffractometer is designed for Ka radiation. The Kb radiation is suppressed to a level < 0.5%.

Note:
For very high intensity diffraction peaks (e.g. (004) peak from (001) oriented Si wafer) Kb peak can still be visible in this mode.

When using the x-ray mirror in combination with parallel beam optics on the diffracted beam side, the w/2q and rocking curve measurements are not sensitive to the exact height position of the sample. This geometry is also suitable for irregularly shaped samples.

A parallel plate collimator in place of receiving slit optics enables the use of asymmetric diffraction geometries. Properties such as twinning, texture and stress may be studied.

Medium Resolution applications and the required equipment

Application	Incident Beam Optics	Diffracted Beam Optics	Remarks	Notes
w-2q scan, phase analysis	X-ray Mirror	Parallel Plate Collimator	Line focus, high intensity.	Parallel Plate Collimator attachment is equipped with a flat graphite monochromator. This setup allows to significantly reduce background radiation as well as to filter Kb radiation.
w-2q scan, phase analysis	X-ray Mirror	RC part of TA/RC attachment	Line focus, highest intensity.	Higher background, sometimes visible peak from Kb radiation.
w-stress analysis	X-ray Mirror	Parallel Plate Collimator	Low background, high intensity.	The parallel beam geometry makes peak positions in the measurements insensitive to misalignment of the sample height. No defocusing effects occur over wide range of omega-tilts.
Reflectivity	X-ray Mirror	Parallel Plate Collimator + PPC Slit	Low background, high intensity.	Very narrow beam. Requires special care during sample alignment.