Observation of intrinsic surface gratings on GaAs by lowangle xray diffractionThe sequential, layering techniques used to prepare multilayer materials result in signitlcant structural incoherence due to deviations from the intended thicknesses within an elemental layer and local deviations from the average due to islanding of the depositing elements during deposition. We demonstrate that if the domain size of the structural incoherence is large compared with the wavelength of the scattering radiation, the structural incoherence manifests itself in the low-angle diffraction pattern by attenuating the intensity of the subsidiary maxima relative to the Bragg maxima. We also show that the subsidiary maxima in the low-angle diffraction pattern of a multilayer result from incomplete destructive interference from all of the interfaces, not just from the top and bottom surface of the film. A technique for incorporating structural incoherence when modeling the diffraction pattern of a multilayer structure is presented. The ability of this model to simulate the experimental diffraction pattern of an iron-silicon multilayer is demonstrated. 905

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We report a simple and nondestructive method to determine directly the spatial profiles of the constituent elements in a synthetic multilayered material with a resolution of 10–20 Å. This has been accomplished by measuring the x-ray diffraction Bragg peak intensities over a large range of energies, and interpreting these data using a dynamical theory to deduce the first few Fourier coefficients of the relevant spatial profiles. We present initial results for Ti-Si multilayer samples grown by thermal deposition. These results demonstrate extensive interdiffusion of the silicon into the titanium layers, even without annealing.

We have developed a method to separate coherent interfacial interdiffusion from incoherent interfacial roughness by extending an electromagnetic dynamical theory to calculate the reflectivity of a multilayer having an arbitrary interfacial profile with a variable degree of randomness in the repeating layer thicknesses. We find that the intensity of the subsidiary maxima are extremely sensitive to incoherent roughness while the intensity of the Bragg maxima are largely determined by the interfacial electron density profiles. Experimental data are modeled in a manner similar to that used by Warren and Averback to determine domain size of crystallites. We divide the multilayer into coherent domains differing from one another by small deviations from the average layer thicknesses. The diffraction intensity from each of these domains is then added to obtain the experimental pattern. The diffraction spectra of a set of Pt/Co multilayers with similar layer thicknesses but prepared with different sputtering gases illustrates the ability to separate the effects of coherent interdiffusion from incoherent roughness. The extent of incoherent roughness obtained using this model to analyze the diffraction data of these Pt-Co multilayers is in good agreement with TEM and STM results from the same samples. The diffraction patterns could not be simulated with abrupt concentration profiles and the extent of interdiffusion was found to be correlated with the energy of reflected neutrals present during the synthesis of the multilayers.