Stresses in Cu Thin Films and Ag/Ni Multilayers - Harvard School of ...

Chapter 1: Background 15
assumed.
Appendix A provides some details on how x-ray strain measurements work. For more
information, the classic text for stress determination by x-rays is the book by Noyan and
Cohen [176]; there are several errors in this book that are corrected in Appendix B. Noyan
et al. [177] have also written a review on x-ray measurements of thin film stresses, and
Hauk et al. [95] have recently completed a comprehensive review of techniques used to
measure residual stresses.
A schematic of the diffractometer used at Harvard is shown in Figure 1.5. It consists
of a four-circle Huber diffractometer (a Huber 424 two-circle with a 511.1 Eulerian cra-
dle) equipped with a Model 20/20 linear position sensitive detector (PSD) from Reflection
Imaging (www.reflectionimaging.com). The system was put together with the
help of Molecular Metrology (www.molmet.com). Since the pinhole collimator has a
diameter of 0.3 mm, the samples are rocked ±2 ◦ in the diffractometer plane to achieve
adequate sampling statistics [111] (Appendix B).
Beamline X22C at the National Synchrotron Light Source at Brookhaven National Lab-
oratory was used for reflectivity [194], θ − 2θ, and grazing incidence diffraction (GID)
[148] measurements. The diffractometer is a six-circle Frank and Heydrich, and the inci-
dent beam is conditioned with a Pt focusing mirror and a two-crystal Si(111) monochro-
mator.
A schematic of the different scattering geometries is presented in Figure 1.6. Figure
1.6 (a) shows the symmetric θ − 2θ geometry used for x-ray reflectivity or powder scans.
As indicated by the arrow on the left, χ-scans are performed by rotating the sample normal
into or out of the plane of the page while maintaining the diffraction condition. Figure