Effect of surface structure on crystal-truncation-rod scattering under the Bragg condition

Theoretical and experimental studies have been made on crystal-truncation-rod (CTR) scattering when x rays satisfy the Bragg condition. Calculations were made on the basis of a dynamical theory in Darwin’s approach extended to a multibeam case. Calculated results indicated that the profile of intensity changes of CTR scattering as a function of incident angle under the Bragg condition is sensitive to surface structures. It was made clear by kinematical treatment that the profile reflects x-ray intensity changes of the standing-wave field at an atomic layer on a substrate crystal when x-ray scattering amplitude by the surface layer is larger than CTR scattering amplitude by the substrate, particularly in the case of intensity measurements on fractional-order rods of superstructures formed on the substrate crystal. The experimental result obtained for a Si (001) crystal was in good agreement with the theoretical calculation. Detailed analysis suggested that a strain field caused by the native oxide layer spreads from the surface of the substrate crystal to a depth of hundreds of Å.