  The measurement of the Si lattice parameter by x-ray interferometry assumes
the use of strain-free crystals, which might not be true because of intrinsic
stresses due to surface relaxation, reconstruction, and oxidation. We used
x-ray phase-contrast topography to investigate the strain sensitivity to the
finishing, annealing, and coating of the interferometer crystals.We assessed
the topography capabilities by measuring the lattice strain due to films of
copper deposited on the interferometer mirror-crystal. A byproduct has been the
measurement of the surface stresses after complete relaxation of the coatings.
