PDF measurements with GaliPIX3D

Approaching synchrotron quality PDF data in your lab

Introduction

Recent years have shown an increased interest in the study of nanocrystalline materials due to their specific properties for application in e.g. semiconductors,  pharmaceuticals and polymers. Structural information about these materials is present as broad, not well-defined features in a diffractogram. Analysis of nanomaterials and amorphous phases therefore requires a total scattering approach, including both Bragg peaks and diffuse scattering.

One of the most promising analytical methods used is atomic pair distribution function (PDF) analysis. Since the method requires short wavelengths to obtain high resolution in real space (well defined interatomic distances), often the measurements are performed at synchrotron facilities, making use of both the high photon energies and the high photon flux that these facilities offer.

Malvern Panalytical has been pioneering the implementation of PDF measurements on laboratory systems [1]. Now, by adding the high efficiency of the new GaliPIX3D detector we have managed to obtain data approaching synchrotron quality.

Experimental

X-ray diffraction experiments were performed on a Malvern Panalytical Empyrean diffractometer equipped with an X-ray source with a molybdenum anode, delivering Kα radiation with a wavelength of 0.0709 nm, a focusing mirror, a capillary spinner, and the new GaliPIX3D detector. This detector has an efficiency of ~100% for Mo radiation, thanks to the CdTe sensor used to detect the X-ray photons. The sample used for the investigation is nano-spinel ZnAl2O4 of 2-3 nm size. Data on the same sample were also collected at the ID31 and at ID11 beam lines at the ESRF in Grenoble, France.

Figure 1. The experimental setup for the PDF measurements on an Empyrean diffractometer 

Results/explanation

The data obtained at ID31, ID11 and using the Empyrean diffractometer are shown in Figure 2. The limitation in Q range to ~17 Å-1 with the Empyrean is due to the chosen radiation. It is possible to extend the range to ~22 Å-1 by using a silver anode instead and the efficiency of the detector would still be ~100%. Data collection time for the dedicated PDF beamline ID11 is only 45 seconds. Data collection times for ID31 and the Empyrean, however, are quite comparable with 5 hours against 7.5 hours respectively. In Figure 3 the comparison between the PDF data is made. Most of the features are the same; the main difference is indicated with arrows, where a slightly better atomic resolution from the data measured at the synchrotron is visible. In Table 1 the refined structural values obtained from the PDF data are compared. The comparison shows that the results are in good agreement within the standard deviations.

The great advantages of being able to collect excellent data using a laboratory diffractometer are multiple, for example, slow processes can be studied (i.e. over days), there is higher stability of the X-ray source over time and, in practice, there is no need for proposal approvals or lengthy trips to large facilities.

Figure 2. Structure function S(Q) comparison between two synchrotron beam lines and the Empyrean with GaliPIX3D [2].

Table 1. Parameters obtained from the fit of PDF data obtained using the synchrotron beam lines and the Empyrean diffractometer [2]

Figure 3. Comparison of the PDF obtained with data from the beam lines and the Empyrean diffractometer [2]. 

Conclusion

Thanks to the high efficiency of the new detector, the GaliPIX3D, from Malvern Panalytical, it is possible on a laboratory diffractometer to collect data of quality approaching that obtained at a synchrotron source and with data collection times comparable to those from non-dedicated PDF beam lines.