Application of a multifiber collimating lens to thin film structure analysis

A multifiber collimating lens designed to collect divergent Cu-K(alpha) x-rays over an 8.6 degree angle has been tested in a standard diffraction geometry. The lens was first characterized with a small (0.30 mm diameter) spot source and found to have transmission efficiency of 27%, output divergence of 0.22 degrees, and input focal spot size in the transverse and axial directions of 0.71 mm and 14.7 mm (FWHM), respectively. The lens was then tested with a standard rotating anode diffraction system for a variety of thin film structure and stress analyses. The measured data are compared to thoses obtained from a fixed tube parafocusing Bragg-Brentano geometry system. The effect of the lens on measurement efficiency was found to depend on the specific application, ranging from no benefit for small area (1.5 cm diameter) films to as much as 8.4 X computed gain in efficiency for highly textured films with finite-size broadened reflections. Typical efficiency gains for the same power and angular resolution were about 3.2 X. In general, the parallel beam geometry provided by the lens was more convenient then the Bragg-Brentano geometry because of reduced sample displacement and general defocusing errors. Since the lens was simply incorporated into systems optimized for non-lens measurements, it is felt that further diameter exceeded that of the soller slit, monochromator crystal, and detector. The geometric gain of the lens with respect to a pinhole with the same resolution is 74 for a line source in the point focus geometry and 159 for a point source. Incorporating straight capillary bundles as soller slits could provide a better match than traditional soller slits to diffraction system using a capillary lens and they may also be beneficial in reducing x-ray diffraction background. Optimization and other aspects of the use of the capillary lens in 'real world' analysis applications will be discussed.