introduction

The well-known STOE STADI P diffractometer received a major upgrade to stay the ultimate platform for powder diffraction in transmission geometry: The ADAMAnT (Automated Diffractometer And Monochromator Alignment Tool), focusing on the absolute best data quality and ease of use. With its four software-controlled degrees of freedom (monochromator, slit width, collimator and goniometer position) this highly sophisticated platform makes it easy to assure perfect beam alignment, using the same or a different wavelength. Even less experienced users can now handle the automatic routines to align the beam via WinX^POW. Using the detector (Direct Photon Counting) for observation, fluorescent screens are now a thing of the past.

Like all STOE innovations it stays completely compatible with all accessories and with our modular concept even older instruments can be upgraded to this new milestone in powder diffraction.

Theoretical background

Merging the concepts of the Debye-Scherrer and the Guinier camera, the STOE Transmission Geometry possesses a surpassing advantage to the widely spread Bragg-Brentano setups: a constant sample volume in the beam yielding reliable intensities in the full 2θ­ range without having to worry about perfect sample height or who prepares the sample and how (possibly introducing preferred orientation). The core in the beam optics of every STOE STADI P is the curved 111-cut Ge monochromator (Johann type). Using the line focus of a sealed tube, it provides pure Ka₁-radiation focused on the detector circle for the highest angular resolution (FWHM < 0.03° for a LaB₆ 110 reflection and Mo Ka₁-radiation).

High precision motors now make it easy to align the monochromator crystal to the perfect angle, align the slits to their corresponding positions and finally drive the whole goniometer to center it in the aligned beam. Thus, the goniometer can be adapted to naturally aging tubes (moving spot on the anode) as well as changing to a completely different wavelength (exchanging tube/monochromator).

tales from the lab

A thorough series of tests were performed using the common anode materials Co, Cu, Mo and Ag in combination with new tubes, very old tubes and multiple slits and collimator inserts of various sizes. The outcome was always a perfectly aligned  STADI P in a matter of minutes.
Shown to the right are the individual steps of monochromator-, slit-, collimator- and goniometer-alignment.
Either the primary beam (using an attenuator) or the reflection of a mounted standard can be used as a feedback. To align the goniometer position, the eclipse of the primary beams’ intensity is used.

The final result of the positional deviation towards theoretical standard positions measurement (always using NIST standards) was always in the range of a few thousands of a degree.

Figure 4 impressively demonstrates that the ADAMAnT precisely controls the goniometer positioning, achieving a maximum deviation ≤ 0.005 featuring a new Cu X-ray source and using a silicon standard (NIST 640e, 0.3 mm capillary), which is less than one-third of the detector’s internal point increment.

Conclusion

The STOE STADI P builds on its well known performance with the ADAMAnT as a major upgrade, making it simpler than ever to keep the instrument in perfect shape. It also impressively lowers the less experienced user’s barrier to quickly change to a different wavelength, as the whole alignment-process can now be automated through the software. This gives always the perfect, pure Ka₁-radiation with the highest resolution, leading to the maximum data quality a powder diffractometer can achieve.