THE STOE TRANSMISSION GEOMETRY
The STOE Transmission geometry is a hybrid of the Scherrer (left) and the Guinier camera (right) using the sample position centered in the detector circle from the first and the focusing optic from the latter.
A (111)-cut Ge monochromator (Johanntype) provides pure Ka1-radiation. It focuses primary and diffracted beam on the detector circle yielding highest resolution in 2q (FWHM<0.03° for a LaB6 (110) reflection and Mo Kα1-radiation).
CONSTANT SAMPLE VOLUME
With a constant sample volume in the beam, the Transmission-/Debye-Scherrer geometry provides reliable intensities over the full 2q scale (appr. 0.3 to 140°) while the variable amount of unaffected beam as a function of the q-value in a reflection setup yields false intensities up to at least 10° 2q if not corrected by variable slits!
NO HEIGHT DISPLACEMENT
Reflection data often yields a zero shift in 2q if the sample thickness varies and cannot be corrected by an automated ztranslation. An aligned capillary is always in the center of the goniometer.
NO LINE BROADENING FOR WEAK ABSORBERS
In reflection geometry the difference in the depth penetration as a function of the absorption factor yields a remarkable peak broadening for weak absorbers. Powder diffraction in Transmission-/ Debye-Scherrer geometry avoids this phenomenon.
LESS EFFECTED BY PREFERED ORIENTATION
The statistical distribution of the particles in a capillary yields a pattern less effected by the effects of preferred orientation than the periodic stacking sequence of the planes in reflection mode.