AN ENHANCED TECHNIQUE FOR THE MODEL-INDEPENDENT RECONSTRUCTION OF STRAIN DISTRIBUTIONS IN CRYSTALS WITH NANOMETRE SPATIAL RESOLUTION. Andrei Nikulin, School of Physics, University of Melbourne, Parkville, Vic. 3052, Australia.

A new method for unique reconstruction of crystal-lattice strains in epitaxially grown layers from high-resolution x-ray diffraction data is discussed. The technique is based on the analysis of diffraction intensity profiles collected for two different radiation wavelengths.

The model-independent method for recovering one- (1D) and two-dimensional (2D) strain profiles in near-surface region of crystals has been recently developed [1-3]. The method relies on the high-resolution x-ray diffractometry. Spatial resolution is determined by the range of angles over which the data is collected. A logarithmic-dispersive relation is applied to retrieve the phases corresponding to the crystal truncation rod profiles. The method has been successfully applied to silicon crystals with ions implanted through a periodic oxide mask pattern and to SiGe/Si superlattices. However, the method did not give a unique solution because the measured intensity does not carry information about the phase of the scattered wave.

Present work reports the enhancement of the theory and recent experimental results in the practical implementation of the method:- a unique solution for the phase-retrieval technique [4];- a practical procedure for the numerical regularisation of a displacement profile directly reconstructed from the x-ray diffraction data to improve the method precision [5].

The technique is applied to determine thicknesses and alloy composition in SiGe/Si superstructures. The recent x-ray high-resolution diffraction experiments which had been performed at the Photon Factory and ESRF synchrotron sources demonstrate a 1-2 nm depth resolution in the structures under analysis.

1. Nikulin, A. Yu. et al., J. Appl. Cryst. 27, 338 (1994).

2. Nikulin, A. Yu. et al., J. Appl. Cryst. 28, 803 (1995).

3. Nikulin, A. Yu. et al., Phys. Rev. B. 53, (1996) (in press).

4. Nikulin, A. Yu. et al., Acta Cryst. (1996) (submitted).

5. Nikulin, A. Yu. & Zaumseil, P., Acta Cryst. (1996) (submitted).