Energy-dispersive diffraction of thin ceramic films

Date: 6-9 January 2011
Beamline: Eddi at Bessy
Team on site: Rudi Winter (Aber)
Manuela Klaus, Christoph Genzel (Eddi)
Instrument: Diffraction angle (2θ): 5o
Tilt angle (ψ) range: 0...88o in 4o steps
Sample env.: Sample freestanding on wax support
Samples: Various sintered ceramic coatings on Si
Fig.: Refractory sample during laser pulse.

This experiment is a post mortem study of the samples we studied earlier by in-situ GISAXS on the neighbouring beamline. In the previous experiment, ceramic thin films were formed from sol-gel precursor coatings by sintering, and the structural evolution of the film from polymer to ceramic was traced.

The objective of this experiment was to detect strain in these layers by analysing the variation of the peak positions and widths as a function of tilt angle with respect to the beam (the sin2ψ method). The advantage of doing this on an energy-dispersive rather than a conventional angle-dispersive instrument lies in the fact that buried layers are more easily accessible.

The image shows the sample stage inside the diffractometer. The sample is mounted on supporting bars on the square metal block at the centre. The block is attached to a cradle allowing to rotate the sample around the beam after carefully aligning the sample surface to match the beam height. The x-ray beam travels from left to right in this picture. The long flight distance in open air is acceptable due to the high x-ray energies used in the data analysis, ranging from 18keV (just above the zirconium fluorescence) to 80keV.

The difficulty and novelty of the experiment results from the thin nature of the layers (about 100nm for fully calcined films according to ellipsometry experiments). This means that for each individual layer, the scattering volume is very small and exposures of several minutes are needed, in particular at larger ψ angles, to improve statistics.